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PHARMACOKINETICS |
From California Clinical Trials, Glendale, California (Dr Jhee, Dr Zarotsky, Ms Moran, Dr Rosenthal, Mr Kim, Dr Ereshefsky), and Eli Lilly and Company, Indianapolis, Indiana (Dr Chappell, Dr Chalon, Dr Toublanc, Dr Brandt, Dr Coutant).
Address for reprints: S. S. Jhee, PharmD, California Clinical Trials Medical Group, Inc, 1509 Wilson Terrace, 55 Wing Main Floor, Glendale, CA 91206-4007.
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ABSTRACT |
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 TOP ABSTRACT METHODSRESULTSDISCUSSIONREFERENCES |
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Key Words: AMPA receptor potentiators • pharmacokinetics • cerebrospinal fluid • clinical trials • phase I
LY450108 and LY451395 are AMPA receptor potentiators with possible use in
cognitive disorders such as Alzheimer's disease, schizophrenia, depression,
and Parkinson's disease. LY450108 and LY451395 have been evaluated in phase I
studies in healthy young male subjects in doses up to 20 mg for both compounds
and in patients with Alzheimer's disease in doses upto 30 mg twice daily and
18 mg twice daily, respectively. However, preclinical evidence suggests that
lower doses of LY450108 and LY451395 may be effective, based on the fact that
plasma levels in animals were low at efficacious doses in the radial arm maze
(data on file). The objective of this study was to determine whether doses of
1 mg and 5 mg LY450108 and LY451395 have central penetration by measuring the
steady-state cerebrospinal fluid (CSF) concentrations. Secondary objectives
were to evaluate the safety, pharmacokinetics, and the steady-state ratio of
plasma:CSF concentration for LY450108 and LY451395. Based on plasma half-life
(t
) information, the postulation can be made that CSF
concentrations were at steady state. This study was approved by the California
Institutional Review Board. Informed consent was obtained from all
participants before study initiation.
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METHODS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONREFERENCES |
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Study Design
This study was a phase I, single-center, open-label, multiple-dose
pharmacokinetic study in healthy subjects.
LY450108. Six subjects were divided into 2 groups of 3 to receive 1 mg or 5 mg LY450108. Both dosing groups were conducted concurrently. Subjects meeting all inclusion criteria were admitted to the research unit 1 day before dosing (day 0). Subjects received study medication once on day 1 and then twice daily on days 2 through 5 and once on day 6. Blood samples measuring LY450108 in plasma were taken before dosing on day 1 and at various time points during a 24-hour period and then again on day 6 at various time points spanning 48 hours after dosing. A CSF sample was taken via lumbar puncture approximately 1.5 hours postdose on day 6. Subjects were discharged on day 7 and required to come in for a follow-up assessment in 7 ± 3 days after discharge.
LY451395. Six healthy subjects were divided into 2 groups of 3 to receive 1 mg or 5 mg LY451395. Subjects meeting all inclusion criteria were admitted to the research unit 1 day before dosing (day 0). Subjects received study medication once on day 1 and then twice daily on days 3 through 7 and once on day 8. Blood samples measuring LY451395 in plasma were taken before dosing on day 1 and at various time points during a 48-hour period and then again on day 8 at various time points spanning 60 hours postdose. A CSF sample was taken via lumbar puncture approximately 1 hour after dosing on day 8. Subjects were required to come in for a follow-up assessment in 7 ± 3 days after discharge.
Pharmacokinetic Assessment
LY450108. Sequential venous blood samples (3 mL) were obtained for
the measurement of LY450108 at the following times:
On day 5, urine was collected during a 24-hour period for exploratory metabolite profiling. On day 6, 2 aliquots of CSF (2.5-3 mL) were collected, one aliquot to be used for the determination of cell count, protein, and glucose, and the other aliquot to be used for the measurement of LY450108. Analysis of LY450108 was conducted using validated liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI/MS/MS) methods for this compound in sodium heparinized plasma or CSF.
LY451395. Sequential venous blood samples (3 mL) were obtained for the measurement of LY451395 at the following times:
On day 7, urine was collected during a 24-hour period for exploratory metabolite profiling. On day 8, 2 aliquots of CSF (2.5-3 mL) were collected at 1 hour postdose similarly to LY450108. Analysis of LY451395 was conducted using validated LC/ESI/MS/MS methods for this compound in sodium heparinized plasma or CSF.
Safety Assessment
Safety data included vital signs, electrocardiograms (ECG), neurologic
examination, physical examination, laboratory tests, and reporting of adverse
events. Vital signs, which included blood pressure and heart rate, were
measured at screening, on each morning prior to dosing, at discharge, and at
the follow-up visit. Twelve-lead ECGs were performed at screening and after
the final dose on day 6 for LY450108 or day 8 for LY451395 or at other times
if judged clinically necessary. A neurologic examination, which included the
following assessments: finger to nose, heel to shin, heel-to-toe walking,
rapid alternating movements and the Romberg test, was performed at screening,
twice daily during inpatient days, prior to discharge, and at follow-up. A
physical examination and routine laboratory tests (hematology, clinical
biochemistry, and urinalysis) were performed at screening, at admission, and
prior to discharge. All adverse events were documented as to their nature,
time of onset, duration, and severity.
Statistical Methodology
Pharmacokinetic parameters of LY450108 and LY451395 were computed by
noncompartmental methods of analysis using the actual sampling times for all
parameter estimations. The CSF concentrations of LY450108 and LY451395 were
plotted versus plasma concentrations, and the plasma:CSF concentration ratios
at both the 1-mg and 5-mg doses were calculated. Pharmacokinetic parameters
determined for both compounds included t, maximum
concentration (Cmax, and time to maximum concentration
(tmax). Sample size determination was not based on a statistical
power calculation but was intended to provide sufficient data to evaluate the
pharmacokinetics of the 2 compounds.
LC/MS/MS Procedures for the Determination of LY451395 in Human Plasma or Human Cerebrospinal Fluid
The methods for the determination of LY451395 in human CSF and human plasma
were each validated over 2 calibration ranges: 0.05 to 5 ng/mL and 5 to 500
ng/mL. In outline, the methods involved a liquid/liquid extraction with a
mixture of hexane/ethyl acetate (85/15, volume/volume [v/v]), followed by
reversed-phase LC analysis of the extract. Chromatographic separations were
achieved using a Prodigy column (ODS3, 5 µm, 100Å, 1 x 50 mm)
at ambient temperature and using an isocratic mobile phase of
MeOH/H2O containing 20 mM pH 3 ammonium formate (85/15, v/v).
Detection was achieved using tandem MS with positive ion electrospray
ionization. The stable-labeled [2H8]-LY451395 was used
as the internal standard. The transitions monitored for detection were
m/z 456.2
m/z 316.2 for LY451395 and m/z
464.3m/z 324.3 for [2H8]-LY451395.
For the determination of LY451395 in human CSF, all intrabatch and interbatch imprecisions and inaccuracies were less than 14%. For the determination of LY451395 in human plasma, the intrabatch and interbatch imprecisions and inaccuracies were less than 20% of theoretical concentration at the lower limit of quantification (LLOQ, 0.05 ng/mL) and less than 12% at the other validation quality control (QC) levels assayed. The specificities of the methods were verified against endogenous human CSF components or human plasma components, respectively.
LC/MS/MS Procedures for the Determination of LY450108 in Human Plasma or Human Cerebrospinal Fluid
The methods for the determination of LY450108 in human CSF and human plasma
were each validated over 2 calibration ranges: 0.05 to 5 ng/mL and 5 to 500
ng/mL. A 10-fold dilution was also validated for each calibration range in the
analysis of human plasma. In outline, the methods involved a liquid/liquid
extraction with a mixture of hexane/ethyl acetate (85/15, v/v), followed by
reversed phase LC analysis of the extract. Chromatographic separations were
achieved using a Prodigy column (ODS3, 5 µm, 100Å, 1 x 50 mm)
column at ambient temperature and using an isocratic mobile phase of
MeOH/H2O containing 20 mM pH 3 ammonium formate (80/20, v/v).
Detection was achieved using tandem MS with positive ion electrospray
ionization. The stable-labeled [13C6]-LY450108 was used
as the internal standard. The transitions monitored for detection were
m/z 397.2m/z 274.2 for LY4510108 and m/z
403.3m/z 279.9 for [13C6]-LY450108.
For the determination of LY450108 in human CSF, the intrabatch and interbatch imprecisions were less than 9%. Intrabatch and interbatch inaccuracies were less than 18% of theoretical concentration at the LLOQ (0.05 ng/mL) and within 9% of theoretical concentrations at the other validation QC levels assayed. For the determination of LY450108 in human plasma, the intrabatch and interbatch inaccuracies were within 18% of theoretical concentration at the LLOQ (0.05 ng/mL) and within 11% of theoretical concentrations at the other validation QC levels assayed. The specificities of the methods were verified against endogenous human CSF components or human plasma components, respectively.
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RESULTS |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONREFERENCES |
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LY451395. Six healthy male subjects completed the study. For the 1-mg group, 1 subject was Hispanic and 2 were African American between the ages of 22 and 28 years (mean, 26.0 years). For the 5-mg group, 1 subject was white, 1 was Hispanic, and 1 was African American between the ages of 26 to 29 years (mean, 27.7 years). The mean age and body mass index were similar for both the 1-mg and the 5-mg LY451395 treatment groups (Table II).
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Pharmacokinetic Evaluation
LY450108. Individual LY450108 plasma versus CSF concentration
after multiple administrations of 1 mg and 5 mg are presented in
Figure 1. Cerebrospinal fluid
concentrations were quantifiable in all subjects after 1-mg dose
administration. At the 5-mg dose, the CSF concentration was 5 times higher
than that observed in subjects receiving 1 mg LY450108. Because of technical
difficulties, the CSF sample for 1 subject in the 1-mg dose group was taken at
3.48 hours rather than at 1.5 hours postdose, and the 1.5-hour value was
determined via interpolation. Mean plasma:CSF ratios for 1 mg and 5 mg are
presented in Table III. The
ratio remained the same for the 1-mg dose and the 5-mg dose.
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Individual LY450108 plasma concentration versus time profiles after single
and multiple oral administration of 1 mg and 5 mg are presented in
Figure 2. There was a fairly
rapid increase in LY450108 plasma concentration until the tmax.
Absorption after multiple doses at 1 mg and 5 mg appeared to be prolonged, as
illustrated by a plateau or double peak. After the Cmax, LY450108
plasma concentration declined in a mono- or biphasic manner. Plasma
concentrations were quantifiable until the last sampling time for all of the
subjects. Pharmacokinetic parameters presented in
Table IV confirmed these
observations. Absorption of LY450108 was rapid for the majority of subjects
who exhibited a tmax that was less than or equal to 1.5 hours on
both days at both doses. One subject randomized to the 5-mg regimen had a
tmax of 2.0 and 3.2 hours on days 1 and 6, respectively. Mean
Cmax after the administration of 1 mg on days 1 and 6 was 46.7 and
50.2 ng/mL, respectively, and after the administration of 5 mg on days 1 and 6
was 154 and 208 ng/mL, respectively. The mean t after the
1-mg dose on days 1 and 6 was 4.58 and 6.25 hours, respectively, and after the
5-mg dose was 6.81 and 7.40 hours, respectively.
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LY451395. Individual LY451395 plasma versus CSF concentrations after multiple administrations of 1 mg and 5 mg are presented in Figure 3. Because of technical difficulties, the CSF sample for 1 subject in the 1-mg treatment group was not collected. Cerebrospinal fluid concentrations were quantifiable after 1 mg in both subjects analyzed. In subjects receiving the 5-mg dose, CSF concentration was approximately 5-fold higher than in those receiving the 1-mg dose. Mean Plasma:CSF rations for 1 mg and 5 mg are presented in Table V. The ratios were similar between the 1-mg and the 5-mg doses. At the 5-mg dose, the variability was low.
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Individual LY451395 plasma concentrations versus time profiles after single
and multiple oral administration of 1 mg and 5 mg are presented in
Figure 4. There appeared to be
a fairly rapid increase in LY451395 plasma concentration until
tmax. After Cmax, LY451395 plasma concentration declined
in a mono- or biphasic manner. Plasma concentrations were quantifiable until
the last sampling time for all subjects. The observations made from the plasma
concentration versus time profiles were confirmed by the pharmacokinetic
parameters presented in Table
VI. Absorption of LY451395 was quite rapid on days 1 and 8 for
both doses with the overall tmax values ranging between 1 and 3
hours postdose. After multiple administrations of 1 mg and 5 mg, there appears
to be a prolonged absorption, as illustrated by a plateau or a double peak for
2 of the 3 subjects. This prolonged absorption was also present after both
single-dose and multiple-dose administrations of 5 mg. There did not appear to
be any relationship between tmax and the dosing regimen (single vs
multiple dose) or the dose administered. Mean Cmax after the
administration of 1 mg on days 1 and 8 was 9.20 and 18.7 ng/mL, respectively,
and after the administration of 5 mg on days 1 and 8 was 44.0 and 78.4 ng/mL,
respectively. The mean t after the 1-mg dose on days 1 and
8 was 10.2 and 11.6 hours, respectively, and after the 5-mg dose was 9.19 and
9.92 hours, respectively.
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Adverse Events
LY450108. The overall incidence of adverse events was very low,
with all adverse events being mild in severity. There were no drug-related
adverse events at the 1-mg dose level and only one adverse event of facial
flushing was reported at the 5-mg dose, which was considered possibly related
to study medication. This episode occurred at approximately 6 hours after
dosing on day 1 and was brief and self-limited. In addition, 2 subjects showed
decreases in supine and standing blood pressure at the 5-mg dose level; none
of the subjects, however, reported dizziness at any time during the study.
There were no clinically significant changes in laboratory parameters, ECGs,
or neurologic and physical examinations.
LY451395. The overall incidence of adverse events was low, with no drug-related adverse events reported at the 5-mg dose level and 6 drug-related adverse events reported by 2 subjects at the 1-mg dose. All adverse events were mild in severity. The majority of the adverse events started at the end of the multiple-dosing period, between days 8 and 10, inclusive. The adverse events considered possibly drug related included increased alanine aminotransferase (ALT), aspartate aminotransferase (AST), and back gammaglutamyltransferase (GGT) in one subject. The increased AST and GGT lasted for approximately 4 days, and the ALT remained elevated for 34 days. The other subject had an increase in ALT, AST, and back pain. The ALT and AST resolved in approximately 6 days, and the back pain resolved in approximately 24 hours. For both the 1-mg and the 5-mg doses, there was a trend of a decrease in mean supine diastolic blood pressure, with the greatest change observed before dosing on day 4 (mean decreases of 9 and 11 mm Hg, respectively). These changes were not deemed clinically significant, and none of the subjects complained of dizziness during the study. There were no other clinically significant changes in laboratory parameters, ECGs, or neurologic and physical examinations.
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DISCUSSION |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONREFERENCES |
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Cerebrospinal fluid concentrations were quantifiable for both compounds at the 1-mg and 5-mg dose level. The CSF concentration appeared to be linearly correlated with plasma concentration for both compounds, with a plasma:CSF ratio of 44:1 and 82:1 for LY450108 and LY451395, respectively. The absorption for LY450108 and LY451395 was fairly rapid.
The extent of exposure of LY450108 as indicated by Cmax and area
under the curve from time zero to infinity (AUC0-
) after a
single 1-mg dose was comparable to that observed in a previous single oral
dose study in young healthy male
subjects.12 The
AUC0- after the single 5-mg dose administration was
approximately 5 times higher than after the single 1-mg dose administration.
There were 7% and 35% increases in Cmax after multiple 1-mg and
5-mg doses, respectively. The multiple-dose pharmacokinetic data point to some
accumulation of LY450108 as compared to the single-dose pharmacokinetics. The
mean terminal t of LY450108 after 1-mg single dose
administration was 4.58 hours and was comparable to that observed in the
previous single-dose study (mean t, 4.74
hours).12 The
accumulation expected based on the t would range between
19% (LY450108 1 mg) and 42% (LY450108 5 mg). However, based on
Cmax, the accumulation observed is less than expected. After 1-mg
multiple administration, mean t increased to 6.25 hours.
Similarly, with the multiple administrations of 1 mg and 5 mg, mean
t increased from 6.81 to 7.40 hours, respectively. These
increases in t are attributable to a decrease in clearance
after multiple administrations.
The Cmax after a single oral dose of 1 mg or 5 mg of LY451395
was approximately 30% lower than in a previous single oral dose study
conducted in young healthy male
subjects.13 The
AUC0- after single dose administration of 5 mg LY451395 was
approximately 5 times higher than that after the 1-mg single dose. There is
believed to be some accumulation occurring after the multiple dose regimen.
Similarly to LY450108, accumulation for LY451395 is expected to be 79% based
on 1 mg day 1 t and 68% based on 5 mg day 1. Based on
Cmax, accumulation was 103% for 1 mg (more than expected) and 78%
for 5 mg (around what was expected). The mean terminal t
for LY451395 after both the 1-mg and 5-mg single doses was comparable to those
determined in the previous single-dose
study13 in which a
mean t was 10.1 hours and 8.86 hours after 1.6 mg and 5 mg,
respectively. Further research will need to focus on the safety and
pharmacokinetics of LY450108 and LY451395 in patients with Alzheimer's
disease. These 2 compounds are comparable in profile, with demonstration of
penetration in the central compartment. Both are viable candidates for further
development.
Drug measurement in CSF is helpful in establishing the concentration
required for a desired pharmacologic effect. Investigation of drug
distribution in the CSF is of great importance for 2 main
reasons14: (1) Drug
and adverse effects on the central nervous system have unique clinical
relevance because of the severity of conditions that drugs are supposed to
either cure or cause; (2) the blood-brain barrier, which drugs must cross to
reach the specific site of action or toxicity, is characterized by particular
properties of permeability and transport. During the clinical development of a
well-known Alzheimer's disease medication, rivastigmine, a CSF study was
conducted evaluating the central activity of rivastigmine in patients with
Alzheimer's disease and its relationship to central and peripheral
pharmacokinetic parameters. Results from a continuous CSF sampling procedure
demonstrated significant dose-dependent inhibition of CSF acetylcholinesterase
(AChE) activity, allowing appropriate dose selection. This CSF study also
demonstrated the value of evaluating pharmacokinetic parameters in both the
central and peripheral compartments, as the t in CSF
appeared longer than that in plasma. In addition, the assessment of
pharmacokinetics and pharmacodynamics measures provided information relative
to the dosing interval; the CSF AChE inhibition in this study justified twice
daily dosing with
rivastigmine.15
Many novel drug development programs produce multiple candidates for clinical trials. Although preclinical models may be beneficial in narrowing down these candidates, there is no substitute for clinical data. The pharmaceutical industry has traditionally studied 1 compound at a time, with a significant lag time for a backup compound. In the development of LY451395 and LY450108, we employed a novel approach of studying both candidates simultaneously in early clinical development. These data will help in selecting the better candidate for further development. Only time and more data will tell if this approach saves time in the drug development process.
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REFERENCES |
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TOPABSTRACTMETHODSRESULTSDISCUSSIONREFERENCES |
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