J Clin Pharmacol
HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS
QUICK SEARCH:   [advanced]


     

This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowRequest Permissions
Right arrow Request Reprints
Citing Articles
Right arrow Citing Articles via ISI Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by O'Connell, M. B.
Right arrow Articles by LaValleur, J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by O'Connell, M. B.
Right arrow Articles by LaValleur, J.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati  
What's this?

DRUG METABOLISM

Effect of Conjugated Equine Estrogens on Oxidative Metabolism in Middle-aged and Elderly Postmenopausal Women

Mary Beth O'Connell, PharmD, Reginald F. Frye, PharmD, PhD, Gary R. Matzke, PharmD, John V. St. Peter, PharmD, Laurie A. Willhite, PharmD, Margaret R. Welch, PharmD, Paul Kowal, PharmD, MS and June LaValleur, MD

From the Pharmacy Practice Department Eugene Applebaum College of Pharmacy and Health Sciences, Wayne State University, Detroit, Michigan (Dr O'Connell); College of Pharmacy, University of Florida, Gainesville, Florida (Dr Frye); College of Pharmacy, Virginia Commonwealth University, Richmond, Virginia (Dr Matzke); Department of Experimental and Clinical Pharmacology, College of Pharmacy, University of Minnesota, Minneapolis, Minnesota (Dr St. Peter); Fairview University Medical Center, Minneapolis, Minnesota (Dr Willhite); formally at the University of Minnesota, College of Pharmacy (Dr Welch, Dr Kowal), and Obstetrics and Gynecology Department, School of Medicine, University of Minnesota, Minneapolis, Minnesota (Dr LaValleur).

Address for reprints: Mary Beth O'Connell, PharmD, Wayne State University, Eugene Applebaum College of Pharmacy and Health Sciences, 259 Mack Avenue, Suite 2190, Detroit, MI 48201-2427; e-mail: mboconnell{at}wayne.edu.


   ABSTRACT
TOP
 ABSTRACT
METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGEMENTS
 REFERENCES
 
The effects of conjugated equine estrogens (CEE) 0.625 mg daily on cytochrome P450 (CYP) were quantified in 12 middle-aged and 13 elderly postmenopausal women at baseline and 6 months later. CYP phenotype was characterized by caffeine (CYP1A2), chlorzoxazone (CYP2E1), dapsone (CYP, N-acetyltransferase 2), dextromethorphan (CYP2D6), and mephenytoin (CYP2C19) metabolism. CEE significantly decreased CYP1A2 (caffeine metabolic ratio: 0.57 ± 0.20 before, 0.40 ± 0.20 after, P = .001) and significantly increased CYP2D6 (dextromethorphan/dextrorphan ratio: 0.0116 ± 0.0143 before, 0.0084 ± 0.0135 after, P = .022) metabolism. CEE had no overall effect on CYP2C19, CYP2E1, CYP-mediated dapsone metabolism, and N-acetyltransferase 2. The dextromethorphan metabolic ratio decreased only in the seniors. The dapsone recovery ratio decreased in the middle-aged group and increased in the seniors. CEE significantly influenced CYP1A2, CYP2D6, and CYP-mediated dapsone oxidative metabolism but not CYP2C19, CYP2E1, or N-acetyltransferase 2 metabolism in postmenopausal women. Age influenced CYP2D6 metabolism and dapsone hydroxylation.

Key Words: Estrogen • metabolism • cytochrome P450 enzyme system • caffeine • chlorzoxazone • dapsone • dextromethorphan • mephenytoin • drug interactions • aged • postmenopause

Estrogens are considered the drug of choice for menopausal symptom control.1,2 In fact, 10 million women were estimated to be using postmenopausal hormone therapy in 2003, one year after the Women's Health Initiative (WHI) study results were reported.3 Reanalyzing the WHI studies by age revealed less harm to potentially a protective effect of postmenopausal hormone therapy in women 50 to 59 years of age versus women 70 to 79 years of age.4,5

Many medications are eliminated by oxidative metabolism via cytochrome P450 (CYP) enzymes. Oral contraceptives have been associated with both increased and decreased metabolism of concomitant medications.6-14 Oral contraceptives seem to enhance conjugation of medications via glucuronidation6,7 while inhibiting,8-14 increasing,10 or having no effect10,15 on metabolism by specific CYP enzymes and N-acetyltransferase (NAT2). Although traditional postmenopausal hormone therapy contains smaller amounts of estrogen and different estrogen and progestin chemical entities than oral contraceptives, its use might still alter hepatic drug metabolism. Therefore, efficacy could be altered or adverse effects develop if significant drug-hormone interactions existed with postmenopausal hormone therapy. However, a paucity of information about the impact of postmenopausal hormone therapy on human hepatic oxidative and conjugative drug-metabolizing enzyme systems exists.16-19

Age is a potential factor that could confound estrogens' effect on oxidative metabolism. Normal adult aging is associated with minor decreases (CYP1A2, 2C9, 2C19) to no effect on phase I oxidative metabolism.20-22 Other aspects of aging, such as reduced liver blood flow, smaller hepatic mass, dehydration, increased fat mass, and lower lean body mass, can also lead to changes in drug clearance.20-22 Seniors are equally at risk for drug-drug interactions due to metabolism inhibition and induction, as are younger adults. Thus, the impact of estrogen therapy on drug metabolism might vary according to a woman's age. Therefore, the purpose of this study was to characterize the effect of postmenopausal estrogen therapy using conjugated equine estrogens on multiple oxidative drug-metabolizing enzymes (CYP and NAT2) in middle-aged and elderly postmenopausal women.


   METHODS
TOP
 ABSTRACT
 METHODS
RESULTS
 DISCUSSION
 ACKNOWLEDGEMENTS
 REFERENCES
 
Subjects
All subjects underwent a screening evaluation that was based on a complete medical history, physical examination, and biochemical and urinalysis tests. Eligibility criteria included normal hepatic function defined as normal serum liver function tests (bilirubin, alanine transaminase, aspartate transaminase, alkaline phosphatase, lactic dehydrogenase, and albumin), stable renal function defined as a measured creatinine clearance of 30 mL/min or greater, and body weight within 30% of ideal weight for height and body frame size according to the 1983 Metropolitan Life Insurance Company weight tables. All subjects were postmenopausal, defined as time since last menses of at least 1 year prior to evaluation or a follicle-stimulating hormone concentration of 50 units/L or higher. Each woman had a negative mammogram result within 1 year, a negative pap smear result within 1 month, and a negative progestin challenge test result (no bleeding for 5 days after 12 days of medroxyprogesterone acetate 10 mg (Provera, Upjohn, Kalamazoo, Mich). If any woman had uterine bleeding after the medroxyprogesterone, an endometrial biopsy was performed to rule out uterine abnormalities. Subjects with a normal endometrial biopsy result were eligible to participate. Three subjects were recruited into 1 of 8 age strata as follows: 45 to 50, 51 to 55, 56 to 60, 61 to 65, 66 to 70, 71 to 75, 76 to 80, 81 to 85, 86 to 90 years. This was done to ensure inclusion of subjects with a wide age distribution. Recruitment and study procedures were done before the Heart and Estrogen/Progestin Replacement Study (HERS) and WHI results were presented.

Subjects taking drugs known to interfere with the metabolism of any of the CYP probe drugs or with a known allergy or sensitivity were excluded. Smokers, individuals who received postmenopausal hormone therapy within the last 2 years, those with current or past breast cancer or thromboembolic disease, or those with current medical conditions that could alter drug metabolism or probe use (congestive heart failure, G6PD deficiency) were excluded from study participation. If during the study a woman began a medication or developed a disease that could alter hepatic metabolism or any of the probe study drug clearances, she would have been dropped from the study. The Institutional Review Boards at the University of Minnesota and Hennepin County Medical Center approved this study. All subjects granted written informed consent.

Study Design
A prospective, open-label, 2-phase study was performed. Drug-metabolizing enzyme activity/phenotyping, as described below, was conducted prior to and after 6 months of conjugated equine estrogen therapy 0.625 mg once daily (Premarin, Wyeth Ayerst Pharmaceuticals, Collegeville, Pa). A morning blood sample for estrone and estradiol concentrations was obtained before and after 6 months of estrogen therapy. The second sample for estrone and estradiol concentrations was drawn somewhere between 2 hours before or after conjugated equine estrogen ingestion, reflecting a value between a trough or peak concentration. Samples were processed and the resultant plasma frozen at -70°C until analysis. Women were evaluated for adverse reactions and medication adherence 3 and 6 months after starting estrogen therapy. Adverse reactions occurring between visits could be discussed via telephone. Adherence was determined from self-completed calendars listing time of ingestion and pill bottle counts by an investigator.

Phenotyping Procedures
All participants were instructed to abstain from alcohol and caffeine-containing products for at least 24 hours prior to and during each 3-day CYP study period. On the first night of each phenotyping procedure, subjects fasted from 8 PM, emptied their bladder at 10 PM, and saved an aliquot. They then ingested dextromethorphan 30 mg (15 mL Benylin DM, Parke-Davis, Ann Arbor, Michigan) with 240 mL water. They were instructed to collect all urine from 10 PM until 6 AM and bring it to the clinic in the morning. Two days later after an overnight fast, a modified version of the "Pittsburgh cocktail" study was conducted.23 One of the investigators administered single oral doses of caffeine 100 mg, chlorzoxazone 250 mg, mephenytoin 100 mg, and dapsone 100 mg with 240 mL water to each subject. Subjects fasted for 4 hours after administration of the 4-drug cocktail. Blood samples were collected at 0, 4, and 8 hours after drug ingestion. Urine was collected from 0 to 8 hours after drug administration into a container with 5 g ascorbic acid, which was kept on ice or refrigerated until processed. Samples were processed and the resultant plasma and urine specimens were frozen at -70°C until analysis.

Analytical Techniques
The following drugs and metabolites were measured by high-performance liquid chromatographic techniques previously described: caffeine and paraxanthine in plasma,24 chlorzoxazone and 6-hydroxychlorzoxazone in plasma,25 dapsone and dapsone hydroxylamine in urine and dapsone and monoacetyldapsone in plasma,26 and 4'-hydroxymephenytoin in urine.23 Dextromethorphan and dextrorphan in urine were measured by the method of Chen et al.27 No known interferences with concomitant medications were identified. The within- and between-day coefficients of variation for each of these assays were less than 10%. These samples were analyzed at the School of Pharmacy, University of Pittsburgh. The estradiol samples were analyzed at the University of Minnesota Hospital and Clinics laboratory, Minneapolis, Minnesota, and the estrone samples were sent to Endocrine Sciences, Tarzana, California, for analysis.

Determination of Drug-Metabolizing Enzyme Activities
Previously validated phenotypic trait measures were calculated for each probe drug. The caffeine metabolic ratio, which is the concentration of paraxanthine divided by the concentration of caffeine in the 8-hour plasma sample, was used as an index of CYP1A2 activity.28,29 The total urinary recovery of 4'-hydroxymephenytoin (µmoles) was used to estimate CYP2C19 activity.30 The activity of CYP2D6 was estimated using the dextromethorphan metabolic ratio, calculated as the molar concentration ratio of dextromethorphan to dextrorphan in the 8-hour urine collection.31 The ratio of 6-hydroxychlorzoxazone to chlorzoxazone concentrations in the 4-hour plasma sample was used to estimate CYP2E1 activity.32 The ability to N-hydroxylate dapsone (CYP-mediated) was estimated by the urinary recovery ratio, which is calculated as the amount of dapsone hydroxylamine recovered in an 8-hour urine sample divided by the sum of dapsone hydroxylamine and dapsone recovered in 8 hours.26 NAT2 phenotype was characterized by the ratio of monoacetyldapsone to dapsone concentrations in the 8-hour plasma sample.33

Statistical Analysis
Data are presented as mean ± standard deviation for the total sample and for each age group: middle-aged (45 to <65 years of age) and elderly (≥65 years of age). The demographic characteristics of the 2 study groups were compared with the independent samples t test, except for measured creatinine clearance, which was compared with the Mann-Whitney test. Phenotypic poor metabolizers were removed from analyses. When an outlier existed, the analysis was done with and without the outlier. Wilcoxon signed rank test was used to compare CYP and NAT2 activity before and after postmenopausal estrogen therapy. Differences between age groups were compared with the Mann-Whitney test. Relationships between CYP and NAT2 activity versus age, estrone concentration, and estradiol concentration were assessed using linear regression. Baseline and 6-month data were combined for the estrogen concentration and specific CYP or NAT2 activity analysis. P ≤ .05 was considered significant. SPSS versions 11 and 13 (SPSS Science Inc, Chicago, Ill) were used for the analysis.


   RESULTS
TOP
 ABSTRACT
 METHODS
 RESULTS
DISCUSSION
 ACKNOWLEDGEMENTS
 REFERENCES
 
Twenty-six women granted informed consent, and 25 completed the study without complications. One woman was dropped from the study within 1 month because of starting sertraline, a study exclusion. The demographics, estrone and estradiol concentrations, and estrogen therapy adherence of the study subjects are shown in Table I. The age and creatinine clearances of the 2 groups were the only baseline demographics that significantly differed. Estrone concentrations prior to beginning estrogen therapy were consistent with previously reported values in postmenopausal women; however, the estradiol concentrations were higher (usual menopausal concentrations, 5-20 pg/mL).34,35 The estrone and estradiol plasma concentrations measured after 6 months of therapy ranged from 21 to 680 pg/mL and 33 to 168 pg/mL, respectively, for the middle-aged women and 54 to 420 pg/mL and 42 to 201 pg/mL, respectively, for the elderly women.


View this table:
[in this window]
[in a new window]
  		Table I Subject Demographics

 

Table II and Figures 1 through 3 summarize the drug-metabolizing enzyme activities determined before and after 6 months of exposure to conjugated equine estrogens in the total group and the 2 age subgroups. No significant difference in CYP activity at baseline was apparent between the 3 age groups (Table II). The effects of estrogen therapy on the activity of individual CYPs and NAT2 activity are summarized below.


View this table:
[in this window]
[in a new window]
  		Table II Oxidative Metabolism Before and After 6 Months of Daily Conjugated Equine Estrogens 0.625 mg

 

Figure 1
View larger version (12K):
[in this window]
[in a new window]
  		Figure 1. Caffeine metabolic ratios. Caffeine metabolic ratio before and after 6 months of daily conjugated equine estrogens 0.625 mg in middle-aged and elderly postmenopausal women combined. In the box-and-whisker plots, the central box represents the values from the lower to upper quartile (25th to 75th percentile), the middle line represents the median, and the whiskers extend to the lowest and highest data points.

 

Figure 3
View larger version (13K):
[in this window]
[in a new window]
  		Figure 3. Dapsone metabolic ratios. Dapsone metabolic ratio before and after 6 months of daily conjugated equine estrogens 0.625 mg in middle-aged (circles) and elderly (triangles) postmenopausal women. In the box-and-whisker plots, the central box represents the values from the lower to upper quartile (25th to 75th percentile), the middle line represents the median, and the whiskers extend to the lowest and highest data points for the 2 groups combined.

 

CYP1A2
Postmenopausal estrogen therapy was associated with a significant decrease in the caffeine metabolic ratio (Table II, Figure 1) in the total group and each age subgroup. Because the magnitude of changes was similar in both age groups, age did not correlate with the change in caffeine metabolism rate. The mean percentage of decrease in the middle-aged group (26.7% ± 36.1%; range, -67% to 65%) was not statistically different from the elderly group (24.1% ± 35.8%; range, -77% to 62%). Estradiol (y = -0.36x + -0.002; P = .01) but not estrone concentrations correlated with the caffeine metabolic ratio; however, this parameter accounted for very little of the caffeine metabolic ratio variability (r2 = .13).

CYP2D6
The dextromethorphan/dextrorphan metabolic ratio was significantly smaller, indicating greater metabolism during concomitant postmenopausal estrogen therapy in the total group (Table II and Figure 2). Age did not correlate with the metabolic ratio; however, an age effect was detected during age subgroup analysis. The elderly group but not the middle-aged group showed statistically different metabolic ratios after therapy. However, the magnitude of change measured as percentage of change from baseline to end of the study was not statistically different between the 2 age groups (middle-aged group: -101% ± 330%; range, -828% to 86%; elderly group: 39% ± 44%, range, -70% to 92%). The results were not different after removing the 2 outliers. No relationships existed between either hormone concentration and dextromethorphan metabolic ratio.


Figure 2
View larger version (12K):
[in this window]
[in a new window]
  		Figure 2. Dextromethorphan metabolic ratios. Dextromethorphan metabolic ratio before and after 6 months of daily conjugated equine estrogens 0.625 mg in middle-aged and elderly postmenopausal women combined. In the box-and-whisker plots, the central box represents the values from the lower to upper quartile (25th to 75th percentile), the middle line represents the median, and the whiskers extend to the lowest and highest data points.

 
Dapsone Hydroxylation (CYP-mediated)
The dapsone recovery ratio was not altered in the total age group after postmenopausal estrogen therapy; however, different effects occurred in the age subgroups (Table II). The dapsone recovery ratio was significantly decreased in the middle-aged group (Figure 3, circles) and significantly increased in the elderly group (Figure 3, triangles). Age did not correlate with the dapsone recovery ratio before or after postmenopausal estrogen therapy but did correlate with the change and percentage of change after 6 months of estrogen therapy. The percentage of change from baseline to end of the study (magnitude of change) was statistically different between the 2 age groups (middle-aged group: 23% ± 24%; range, -8% to 61%, elderly group: -40% ± 65%; range, -224% to 22%). Analysis without the outlier did not influence the results. Neither hormone concentration was significantly correlated with the dapsone recovery ratio.

CYP2C19, CYP2E1, and N-acetyltransferase 2
Mephenytoin recovery (CYP2C19), chlorzoxazone metabolic ratio (CYP2E1), and dapsone acetylation ratio (NAT2) were not significantly altered after 6 months of conjugated equine estrogens (Table II). Analyzing with and without the senior woman who was an outlier for the chlorzoxazone metabolic ratio did not influence the results. Neither estrogen concentration data nor age was correlated with CYP2C19, CYP2E1, or NAT2 activities.


   DISCUSSION
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
ACKNOWLEDGEMENTS
 REFERENCES
 
Traditional postmenopausal estrogen therapy altered hepatic drug metabolism in this study. Postmenopausal estrogen therapy with conjugated equine estrogens significantly decreased CYP1A2 activity, as measured by the caffeine metabolic ratio, in postmenopausal women, regardless of age. CYP2D6 activity, as measured by the dextromethorphan metabolic ratio, was higher in the total and elderly group after postmenopausal estrogen therapy but was not different in the middle-aged group. CYP-mediated dapsone hydroxylation was decreased in the middle-aged postmenopausal women and increased in the elderly postmenopausal women, resulting in no change for the total group. CYP2C19, CYP2E1, and NAT2 activities were not altered by estrogen therapy at the doses used in this study. Thus, the results of this study show that administration of conjugated equine estrogens can alter drug-metabolizing enzyme activity in both younger and older postmenopausal women.

Traditional postmenopausal estrogen therapy contains smaller amounts of estrogen and different estrogen and progestin chemical entities than oral contraceptives, which are known to cause drug-metabolism interactions. Estradiol and estrone concentrations from oral postmenopausal estrogen therapy have been previously reported to be 34 to 50 pg/mL and 125 to 190 pg/mL, respectively.34,35 These estradiol concentrations are similar to the early follicular phase of the menstrual cycle, which represents the lowest estrogen values throughout the normal cycle. The estrogen concentrations in this study were somewhat higher, which can be related to lab-to-lab variation and timing of the sample in relationship to ingestion.

Exogenous estrogen therapy has been shown to decrease CYP1A2 metabolism. Postmenopausal estrogen therapy with oral estradiol (Estrace) 1 to 1.5 mg daily, adjusted to achieve estradiol concentrations of 50 to 150 pg/mL, decreased the caffeine metabolic ratio (paraxanthine/caffeine) by 29% ± 25% compared to placebo in a crossover study with 12 postmenopausal women (52-80 years of age).16 Our findings of a 24%-to-26% decrease during conjugated equine estrogens (Premarin) 0.625 mg daily are similar to the changes observed by Pollock et al16 and suggest that when similar estradiol concentrations are achieved, the decrement in CYP1A2 activity will be consistent, regardless of the pharmaceutical preparation that was administered. Using tacrine as a probe for CYP1A2 activity, postmenopausal estrogen therapy with estradiol valerate and levonorgestrel for 10 days decreased the CYP1A2-mediated metabolism of tacrine to 1-hydroxytacrine compared to baseline and thus the overall clearance in 10 premenopausal women.17 No estrogen concentrations were measured. In a crossover study, oral contraceptives containing 30 µg ethinyl estradiol with gestodene or levonorgestrel decreased caffeine metabolism by 54% to 55% compared to no estrogen therapy in premenopausal women who achieved mean ethinyl estradiol peak concentrations of 148 ± 59 pg/mL and 103 ± 35 pg/mL, respectively, after the oral contraceptive.9

Endogenous estrogen concentrations have variable effects on caffeine metabolism. As estrogen concentrations increase throughout pregnancy, caffeine clearance continues to decrease. Caffeine clearance decreased from 70 mL/kg·h during week 11 of pregnancy to 24 mL/kg/h during pregnancy week 38.36 In another study, postpartum caffeine clearance returned to 65 to 79 mL/kg·h. Salivary caffeine clearance continued to significantly decrease with each trimester of pregnancy; first (-33%), second (-48%), and third (-65%) trimester of pregnancy as compared to 6 to 8 weeks after delivery.37 However, the lower and higher estrogen concentrations achieved during the midfollicular and midluteal menstrual cycle phases in premenopausal women were not associated with differences in the caffeine metabolic ratio (AFMU + 1U + 1X/17U)38 or caffeine clearance.39,40 One study did measure intraindividual caffeine clearances during each menstrual cycle and found it varied by 11% to 39%, with direction of changes inconsistent with days after menstrual cycle.40 Thus, the increasing estrogen changes during pregnancy had a greater effect on caffeine metabolism than did the changes seen during menstrual cycles.

In this study, CYP2D6 metabolism measured by the dextromethorphan/dextrorphan molar ratio was increased in the total and elderly groups. Previous studies did not find altered dextromethorphan metabolism during oral contraceptive therapy11,13,15 or varying endogenous estrogen concentrations during the menstrual cycle15,41,42 but did find metabolism to be altered with increasing estrogen concentrations during pregnancy37,43 in premenopausal women. The previous clinical trials did not use a crossover study design, which might explain the lack of interaction due to significant within- and between-group variability. Dextromethorphan metabolism was shown to be increased in late pregnancy,37,43 which was consistent with findings for another CYP2D6 substrate metoprolol during pregnancy.43 Because significant intersubject variability of the dextromethorphan/dextrorphan molar ratio (12%-137%) has been measured in menstruating women,41,42 a type II error for the elderly group in this study cannot be ruled out. The discrepancy between the age subgroups could be explained by large intragroup variability, too small of a sample for the middle-aged group, or an age versus drug effect. Future studies will need to determine if the changes are real and the cause.

Metabolism via CYP2C19 activity, measured as 4'-hydroxymephenytoin recovery, was not altered by postmenopausal estrogen therapy in this study with postmenopausal women. Although this is the first evaluation in postmenopausal women, some research has been conducted in premenopausal women with exogenous estrogen therapy. In 2 studies comparing women with and without oral contraceptive therapy, the mephenytoin S/R ratio was increased, indicating decreased CYP2C19 activity.11,12 The combination of ethinyl estradiol and levonorgestrel decreased the 5'-hydroxylation of omeprazole, another CYP2C19 metabolized medication, but levonorgestrel alone had no effect.44 Variations in hormone concentrations between the midfollicular and midluteal phases of the menstrual cycle did not change the metabolic ratio of omeprazole.45 Possible explanations for the different effects between the premenopausal and postmenopausal women could be differences in the estradiol concentrations that were achieved, concomitant progestin therapy with oral contraceptives, and/or the study design (crossover vs different samples).10,46,47

CYP2E1 metabolism, measured as the 6-hydroxychlorzoxazone/chlorzoxazone ratio, and N-acetylation, measured as the dapsone acetylation ratio, were not altered by conjugated equine estrogen therapy in this study. No other information related to the effect of hormone therapy on these metabolic pathways was found.

A limitation of the current study is that we did not assess the effect of estrogen on CYP3A activity alone. In vitro, 17ß estradiol has been found to competitively inhibit 17{alpha}-ethinyl estradiol 2-hydroxylase (CYP3A) activity.48 A previous study found no effect of conjugated equine estrogen 0.625 mg given with (n = 6) or without (n = 4) medroxyprogesterone 5 mg on intravenous or oral midazolam metabolism in 10 elderly women (71 ± 6 years).19 An oral contraceptive containing ethinyl estradiol 30 µg and gestodene 75 µg decreased the midazolam metabolic ratio by 36% in 9 women 20 to 25 years of age during a crossover study, supporting a decrease in CYP3A4 metabolism by estrogen therapy in young women.14 However, in another sequential series study, 10 days of ethinyl estradiol 50 µg and norgestrel 500 µg did not change midazolam metabolism in 9 women 24 to 39 years of age.49 CYP3A4 activity did not significantly vary between the 4 phases of Triphasil in 12 women 21 to 27 years of age using the dextromethorphan/3-methoxymorphinan ratio as the probe.15 In this study, dapsone was included as a potential CYP3A probe. Although the dapsone recovery ratio was originally proposed as an index of CYP3A activity, it is now known that dapsone is metabolized by multiple enzymes including CYP3A, CYP2C8, CYP2C9, and CYP2E1, making it difficult to interpret changes in this index. In this study, the reasons for postmenopausal estrogen therapy to have different effects in the middle-aged group (decreased dapsone metabolic ratio) and the elderly group (increased dapsone metabolic ratio) cannot be explained. Furthermore, additional issues such as intestinal versus hepatic CYP3A susceptibilities50,51 that were not assessed in this study could be operating.

In this study, age differences in postmenopausal estrogen therapy's influence on metabolic clearance existed for CYP2D6 and dapsone hydroxylation (CYP-mediated metabolism) but not for the other drug-metabolizing probes (CYP1A2, CYP2C19, CYP2E1, and NAT2). In previous literature, an age influence on estrogen effects on metabolism was seen for CYP2C19,13 but not for CYP1A2,52 CYP2D6,13 or NAT2.53 Age in general has been associated to varying extents with changes in metabolism of substrates for CYP1A2, CYP2C9, CYP2C19, CYP2E1, and CYP3A3/4 metabolism.20-22,54 Further research on the interaction between age and the influence of estrogen on CYP activity is warranted. Larger samples will be required because of the wide interpatient variability in liver metabolism and age-associated changes.

In summary, conjugated equine estrogens altered CYP1A2 and CYP2D6 metabolism, suggesting that the use of postmenopausal estrogen therapy in women might alter the efficacy or increase adverse events of medications that are metabolized by these CYPs. Postmenopausal estrogen therapy's effect on CYP2D6 and CYP-mediated dapsone hydroxylation was influenced by age, thus differing effects on concurrent drug metabolism might occur in middle-aged and elderly postmenopausal women exposed to postmenopausal estrogen therapy. The influence of concomitant progestin with postmenopausal estrogen therapy on drug metabolism will also need to be quantified in young and older postmenopausal women.


   ACKNOWLEDGEMENTS
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGEMENTS
REFERENCES
 
The authors acknowledge the assistance of Ajayi Thomas-Ogunji, PharmD, and the staff of the Drug Evaluation Unit for their contributions to patient recruitment and care and data collection.

Financial disclosure: Supported in part by the National Institute of Aging 1RO1AG09566-01. Wyeth Ayerst Pharmaceuticals provided the Premarin, and Upjohn provided the Provera.

DOI: 10.1177/0091270006292249


   REFERENCES
TOP
 ABSTRACT
 METHODS
 RESULTS
 DISCUSSION
 ACKNOWLEDGEMENTS
 REFERENCES
 

1. North American Menopause Society. Recommendations for estrogen and progestogen use in peri- and postmenopausal women: October 2004 position statement of the North American Menopause Society. Menopause. 2004;11: 589-600.[CrossRef][Medline] [Order article via Infotrieve]

2. North American Menopause Society. Treatment of menopause-associated vasomotor symptoms: position statement of the North American Menopause Society. Menopause. 2004;11: 11-33.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

3. Hersh AL, Stefanick ML, Stafford RS. National use of postmenopausal hormone therapy: annual trends and response to recent evidence. JAMA. 2004;291: 47-53.[Abstract/Free Full Text]

4. Hsia J, Langer RD, Manson JE, et al. Conjugated equine estrogens and coronary heart disease: The Women's Health Initiative. Arch Intern Med. 2006;166: 357-365.[Abstract/Free Full Text]

5. Klaiber EL, Vogel W, Rako S. A critique of the Women's Health Initiative hormone therapy study. Fertil Steril. 2005;84: 1589-1601.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

6. Miners JO, Attwood J, Birkett DJ. Influence of sex and oral contraceptive steroids on paracetamol metabolism. Br J Clin Pharmacol. 1983;16: 503-509.[Web of Science][Medline] [Order article via Infotrieve]

7. Teichmann AT. Influence of oral contraceptives on drug therapy. Am J Obstet Gynecol. 1990;163: 2208-2213.[Web of Science][Medline] [Order article via Infotrieve]

8. Abernethy DR, Greenblatt DJ. Impairment of antipyrine metabolism by low-dose oral contraceptive steroids. Clin Pharmacol Ther. 1981;29: 106-110.[Web of Science][Medline] [Order article via Infotrieve]

9. Balogh A, Klinger G, Henschel L, Borner A, Vollanth R, Kuhnz W. Influence of ethinylestradiol-containing combination oral contraceptives with gestodene or levonorgestrel on caffeine elimination. Eur J Clin Pharmacol. 1995;48: 161-166.[Web of Science][Medline] [Order article via Infotrieve]

10. Shelepova T, Nafziger AN, Victory J, et al. Effect of a triphasic oral contraceptive on drug-metabolizing enzyme activity as measured by the validated Cooperstown 5+1 cocktail. J Clin Pharmacol. 2005;45: 1413-1421.[Abstract/Free Full Text]

11. Hagg S, Spigset O, Dahlqvist R. Influence of gender and oral contraceptives on CYP2D6 and CYP2C19 activity in healthy volunteers. Br J Clin Pharmacol. 2001;51: 169-173.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

12. Laine K, Tybring G, Bertilsson L. No sex-related differences but significant inhibition by oral contraceptives of CYP2C19 activity as measured by the probe drugs mephenytoin and omeprazole in healthy Swedish white subjects. Clin Pharmacol Ther. 2000;68: 151-159.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

13. Tamminga WJ, Wemer J, Oosterhuis B, et al. CYP2D6 and CYP2C19 activity in a large population of Dutch healthy volunteers: indications for oral contraceptive-related gender differences. Eur J Clin Pharmacol. 1999;55: 177-184.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

14. Palovaara S, Kivisto KT, Tapanainen P, Manninen P, Neuvonen PJ, Laine K. Effect of an oral contraceptive preparation containing ethinylestradiol and gestodene on CYP3A4 activity as measured by midazolam 1'-hydroxylation. Br J Clin Pharmacol. 2000; 50: 333-337.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

15. McCune JS, Lindley C, Decker JL, et al. Lack of gender differences and large intrasubject variability in cytochrome P450 activity measured by phenotyping with dextromethorphan. J Clin Pharmacol. 2001;41: 723-731.[Abstract]

16. Pollock BG, Wylie M, Stack JA, et al. Inhibition of caffeine metabolism by estrogen replacement therapy in postmenopausal women. J Clin Pharmacol. 1999;39: 936-940.[Abstract]

17. Laine K, Palovaara S, Tapanainen P, Manninen P. Plasma tacrine concentrations are significantly increased by concomitant hormone replacement therapy. Clin Pharmacol Ther. 1999;66: 602-608.[Web of Science][Medline] [Order article via Infotrieve]

18. Palovaara S, Pelkonen O, Uusitalo J, Lundgren S, Laine K. Inhibition of cytochrome P450 2B6 activity by hormone replacement therapy and oral contraceptive as measured by bupropion hydroxylation. Clin Pharmacol Ther. 2003;74: 326-333.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

19. Gorski JC, Wang Z, Haehner-Daniels BD, Wrighton SA, Hall SD. The effect of hormone replacement therapy on CYP3A activity. Clin Pharmacol Ther. 2000;68: 412-417.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

20. McLean AJ, Le Couteur DG. Aging biology and geriatric clinical pharmacology. Pharmacol Rev. 2004;56: 163-184.[Abstract/Free Full Text]

21. Cusack BJ. Pharmacokinetics in older persons. Am J Geriatr Pharmacother. 2004;2: 274-302.[CrossRef][Medline] [Order article via Infotrieve]

22. Herrlinger C, Klotz U. Drug metabolism and drug interactions in the elderly. Best Pract Res Clin Gastroenterol. 2001;15: 897-918.[CrossRef][Medline] [Order article via Infotrieve]

23. Frye RF, Matzke GR, Adedoyin A, Porter JA, Branch RA. Validation of the five-drug "Pittsburgh Cocktail" approach for assessment of selective regulation of drug-metabolizing enzymes. Clin Pharmacol Ther. 1997;62: 365-376.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

24. Frye RF, Stiff DD, Branch RA. A sensitive method for the simultaneous determination of caffeine and its dimethylxanthine metabolites in human plasma: application to CYP1A2 phenotyping. J Liq Chromatogr Rel Tech. 1998;21: 1161-1171.

25. Frye RF, Stiff DD. Determination of chlorzoxazone and 6-hydroxychlorzoxazone in human plasma and urine by high-performance liquid chromatography. J Chromatogr B Biomed Appl. 1996;686: 291-296.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

26. May DG, Porter JA, Uetrecht JP, Wilkinson GR, Branch RA. The contribution of N-hydroxylation and acetylation to dapsone pharmacokinetics in normal subjects. Clin Pharmacol Ther. 1990;48: 619-627.[Web of Science][Medline] [Order article via Infotrieve]

27. Chen ZR, Somogyi AA, Bochner F. Simultaneous determination of dextromethorphan and three metabolites in plasma and urine using high-performance liquid chromatography with application to their disposition in man. Ther Drug Monit. 1990;12: 97-104.[Web of Science][Medline] [Order article via Infotrieve]

28. Fuhr U, Rost KL. Simple and reliable CYP1A2 phenotyping by the paraxanthine/caffeine ratio in plasma and saliva. Pharmacogenetics. 1994;4: 109-116.[Web of Science][Medline] [Order article via Infotrieve]

29. Tanaka E, Ishikawa A, Yamamoto Y, et al. A simple useful method for the determination of hepatic function in patients with liver cirrhosis using caffeine and its three major dimethylmetabolites. Int J Clin Pharmacol Ther Toxicol. 1992;30: 336-341.[Medline] [Order article via Infotrieve]

30. Wedlund PJ, Aslanian WS, McAllister CB, Wilkinson GR, Branch RA. Mephenytoin hydroxylation deficiency in Caucasians: frequency of a new oxidative drug metabolism polymorphism. Clin Pharmacol Ther. 1984;36: 773-780.[Web of Science][Medline] [Order article via Infotrieve]

31. Schmid B, Bircher J, Preisig R, Kupfer A. Polymorphic dextromethorphan metabolism: co-segregation of oxidative Odemethylation with debrisoquine hydroxylation. Clin Pharmacol Ther. 1985;38: 618-624.[Web of Science][Medline] [Order article via Infotrieve]

32. Frye RF, Adedoyin A, Mauro K, Matzke GR, Branch RA. Use of chlorzoxazone as an in vivo probe of cytochrome P450 2E1: choice of dose and phenotypic trait measure. J Clin Pharmacol. 1998;38: 82-89.[Abstract]

33. May DG, Arns PA, Richards WO, et al. The disposition of dapsone in cirrhosis. Clin Pharmacol Ther. 1992;51: 689-700.[Web of Science][Medline] [Order article via Infotrieve]

34. Lobo RA. Menopause. In: Goldman L, Bennett JC, eds. Cecil Textbook of Medicine. Philadelphia, Pa: WB Saunders; 2000: 1360-1366.

35. O'Connell MB. Pharmacokinetic and pharmacologic variation between different estrogen products. J Clin Pharmacol. 1995; 35: 18S-24S.[Abstract]

36. Aldridge A, Bailey J, Neims AH. The disposition of caffeine during and after pregnancy. Semin Perinatol. 1981;5: 310-314.[Web of Science][Medline] [Order article via Infotrieve]

37. Tracy TS, Venkataramanan R, Glover DD, Caritis SN. Temporal changes in drug metabolism (CYP1A2, CYP2D6 and CYP3A activity) during pregnancy. Am J Obstet Gynecol. 2005;192: 633-639.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

38. Kashuba AD, Bertino JS Jr, Kearns GL, et al. Quantitation of three-month intraindividual variability and influence of sex and menstrual cycle phase on CYP1A2, N-acetyltransferase-2, and xanthine oxidase activity determined with caffeine phenotyping. Clin Pharmacol Ther. 1998;63: 540-551.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

39. Kamimori GH, Joubert A, Otterstetter R, Santaromana M, Eddington ND. The effect of the menstrual cycle on the pharmacokinetics of caffeine in normal, healthy eumenorrheic females. Eur J Clin Pharmacol. 1999;55: 445-449.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

40. Zaigler M, Rietbrock S, Szymanski J, Dericks-Tan JS, Staib AH, Fuhr U. Variation of CYP1A2-dependent caffeine metabolism during menstrual cycle in healthy women. Int J Clin Pharmacol Ther. 2000;38: 235-244.[Web of Science][Medline] [Order article via Infotrieve]

41. Labbe L, Sirois C, Pilote S, et al. Effect of gender, sex hormones, time variables and physiological urinary pH on apparent CYP2D6 activity as assessed by metabolic ratios of marker substrates. Pharmacogenetics. 2000;10: 425-438.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

42. Kashuba AD, Nafziger AN, Kearns GL, et al. Quantification of intraindividual variability and the influence of menstrual cycle phase on CYP2D6 activity as measured by dextromethorphan phenotyping. Pharmacogenetics. 1998;8: 403-410.[Web of Science][Medline] [Order article via Infotrieve]

43. Wadelius M, Darj E, Frenne G, Rane A. Induction of CYP2D6 in pregnancy. Clin Pharmacol Ther. 1997;62: 400-407.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

44. Palovaara S, Tybring G, Laine K. The effect of ethinyloestradiol and levonorgestrel on the CYP2C19-mediated metabolism of omeprazole in healthy female subjects. Br J Clin Pharmacol. 2003; 56: 232-237.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

45. Kim MJ, Bertino JS Jr, Gaedigk A, Zhang Y, Sellers EM, Nafziger AN. Effect of sex and menstrual cycle phase on cytochrome P450 2C19 activity with omeprazole used as a biomarker. Clin Pharmacol Ther. 2002;72: 192-199.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

46. Eugster HP, Probst M, Wurgler FE, Sengstag C. Caffeine, estradiol, and progesterone interact with human CYP1A1 and CYP1A2. Evidence from cDNA-directed expression in Saccharomyces cerevisiae. Drug Metab Dispos. 1993;21: 43-49.[Abstract]

47. Back DJ, Houlgrave R, Tjia JF, Ward S, Orme ML. Effect of the progestogens, gestodene, 3-keto desogestrel, levonorgestrel, norethisterone and norgestimate on the oxidation of ethinyloestradiol and other substrates by human liver microsomes. J Steroid Biochem Mol Biol. 1991;38: 219-225.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

48. Guengerich FP. Inhibition of oral contraceptive steroidmetabolizing enzymes by steroids and drugs. Am J Obstet Gynecol. 1990;163: 2159-2163.[Web of Science][Medline] [Order article via Infotrieve]

49. Belle DJ, Callaghan JT, Gorski JC, et al. The effects of an oral contraceptive containing ethinyloestradiol and norgestrel on CYP3A activity. Br J Clin Pharmacol. 2002;53: 67-74.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

50. Gorski JC, Vannaprasaht S, Hamman MA, et al. The effect of age, sex, and rifampin administration on intestinal and hepatic cytochrome P450 3A activity. Clin Pharmacol Ther. 2003;74: 275-287.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

51. Gorski JC, Jones DR, Haehner-Daniels BD, Hamman MA, O'Mara EM Jr, Hall SD. The contribution of intestinal and hepatic CYP3A to the interaction between midazolam and clarithromycin. Clin Pharmacol Ther. 1998;64: 133-143.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

52. Chung WG, Kang JH, Park CS, Cho MH, Cha YN. Effect of age and smoking on in vivo CYP1A2, flavin-containing monooxygenase, and xanthine oxidase activities in Koreans: determination by caffeine metabolism. Clin Pharmacol Ther. 2000;67: 258-266.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]

53. Korrapati MR, Sorkin JD, Andres R, Muller DC, Loi CM, Vesell ES, Vestal RE. Acetylator phenotype in relation to age and gender in the Baltimore Longitudinal Study of Aging. J Clin Pharmacol. 1997;37: 83-91.[Abstract]

54. Tanaka E. In vivo age-related changes in hepatic drug-oxidizing capacity in humans. J Clin Pharm Ther. 1998;23: 247-255.[CrossRef][Web of Science][Medline] [Order article via Infotrieve]
Add to CiteULike CiteULike   Add to Connotea Connotea   Add to Del.icio.us Del.icio.us   Add to Digg Digg   Add to Reddit Reddit   Add to Technorati Technorati    What's this?



This Article
Right arrow Abstract Freely available
Right arrow Full Text (PDF)
Right arrow Alert me when this article is cited
Right arrow Alert me if a correction is posted
Right arrow Citation Map
Services
Right arrow Email this article to a friend
Right arrow Similar articles in this journal
Right arrow Similar articles in ISI Web of Science
Right arrow Similar articles in PubMed
Right arrow Alert me to new issues of the journal
Right arrow Download to citation manager
Right arrowRequest Permissions
Right arrow Request Reprints
Citing Articles
Right arrow Citing Articles via ISI Web of Science (2)
Right arrow Citing Articles via Google Scholar
Google Scholar
Right arrow Articles by O'Connell, M. B.
Right arrow Articles by LaValleur, J.
Right arrow Search for Related Content
PubMed
Right arrow PubMed Citation
Right arrow Articles by O'Connell, M. B.
Right arrow Articles by LaValleur, J.
Social Bookmarking
Add to CiteULike   Add to Connotea   Add to Del.icio.us   Add to Digg   Add to Reddit   Add to Technorati  
What's this?

HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS