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`A Pharmacokinetic and Pharmacodynamic
`Drug Interaction Study of Acamprosate
`and Naltrexone
`
`Barbara J. Mason, Ph.D., Anita M. Goodman, M.D., Russell M. Dixon, M.D.,
`Magdy H. Abdel Hameed, Ph.D., Thierry Hulot, Pharm.D., Keith Wesnes, Ph.D.,
`John A. Hunter, M.S., and Michael G. Boyeson, Ph.D.
`
`Acamprosate and naltrexone have each demonstrated safety
`and efficacy for alcohol dependence in placebo-controlled
`clinical trials. There is scientific and clinical interest in
`evaluating these drugs in combination, given their high
`tolerability, moderate effect sizes, different pharmacological
`profiles and potentially different effects on drinking
`outcomes. Thus, this is the first human pharmacokinetic
`and pharmacodynamic drug interaction study of
`acamprosate and naltrexone. Twenty-four normal, healthy
`adult volunteers participated in a double-blind, multiple
`dose, within subjects, randomized, 3-way crossover drug
`interaction study of the standard therapeutic dose of
`acamprosate (2 g/d) and the standard therapeutic dose of
`naltrexone (50 mg/d), given alone and in combination, with
`seven days per treatment condition and seven days washout
`between treatments. Blood samples were collected on a
`standardized schedule for pharmacokinetic analysis of
`
`␤
`naltrexone, 6-
`-naltrexol, and acamprosate. A
`computerized assessment system evaluated potential drug
`effects on cognitive functioning. Coadministration of
`acamprosate with naltrexone significantly increased the
`rate and extent of absorption of acamprosate, as indicated by
`an average 33% increase in acamprosate maximum plasma
`concentration, 33% reduction in time to maximum plasma
`concentration, and 25% increase in area under the plasma
`concentration-time curve. Acamprosate did not affect the
`␤
`pharmacokinetic parameters of naltrexone or 6-
`-naltrexol.
`A complete absence of negative interactions on measures of
`safety and cognitive function supports the absence of a
`contraindication to co-administration of acamprosate and
`naltrexone in clinical practice.
`[Neuropsychopharmacology 27:596–606, 2002]
`© 2002 American College of Neuropsychopharmacology.
`Published by Elsevier Science Inc.
`
`
`:
`Pharmacodynamics; Pharmacokinetics;
`KEY
`WORDS
`Alcohol; Naltrexone; Acamprosate; Cognition
`
`From the Division of Substance Abuse, Department of Psychiatry
`and Behavioral Sciences, University of Miami School of Medicine,
`Miami, FL (BJM), Lipha Pharmaceuticals, Inc., New York, NY
`(AMG), Covance Clinical Research Unit, Madison, WI (RMD,
`MHAH, MGB, JAH), Lipha s.a., Lyon, France (TH), and Cognitive
`Drug Research Limited, Reading, UK (KW).
`Address correspondence to: Barbara Mason, Alcohol Disorders
`Research Unit, 1400 N.W. 10th Avenue, Suite 307A, Miami, FL
`33136. Tel.: (305) 243-4059; E-mail: bjmason246@aol.com
`Received February 12, 2002; revised April 18, 2002; accepted
`April 22, 2002.
`Online publication: 5/7/02 at www.acnp.org/citations/Npp
`050702298.
`
`Recent efforts to develop pharmacological interven-
`tions for relapse-prevention in newly abstinent alcohol-
`ics initially focused on acamprosate (Campral ®, Aotal ®)
`in Europe and naltrexone (ReVia ®) in the United States
`of America. Acamprosate and naltrexone have each
`demonstrated efficacy and safety in randomized, dou-
`ble-blind, placebo-controlled trials in alcohol-depen-
`dent outpatient volunteers (Garbutt et al. 1999; Litten
`and Allen 1998; Mason 2001; Mason and Ownby 2000;
`Swift 1999). Neither medication interacts with alcohol
`or has abuse potential or rebound effects when discon-
`tinued. Despite these similarities, acamprosate and nal-
`trexone induce their action via very different mecha-
`
`,
`.
`–
`N
`
`.
`4
`27
`2002
`NO
`VOL
`EUROPSYCHOPHARMACOLOGY
`© 2002 American College of Neuropsychopharmacology
`Published by Elsevier Science Inc.
`655 Avenue of the Americas, New York, NY 10010
`
`0893-133X/02/$–see front matter
` PII S0893-133X(02)00368-8
`
`AMN1068
`Amneal Pharmaceuticals LLC v. Alkermes Pharma Ireland Limited
`IPR2018-00943
`
`

`

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`N
`EUROPSYCHOPHARMACOLOGY
`
`
`–
`2002
`VOL
`
`.
`
`,
`27
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`NO
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`4
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`Interaction Study of Acamprosate and Naltrexone
`
`597
`
`nisms and may affect different behavioral aspects of
`alcohol dependence.
`Acamprosate is a centrally acting synthetic analog of
`the naturally occurring amino acid neuromediator tau-
`rine (Dahchour and de Witte 2000). Chronic alcohol ex-
`posure is associated with decreased GABAergic trans-
`mission and increased glutamate activity (Grant et al.
`1990; Hoffman and Tabakoff 1994). Although the pre-
`cise mechanism of action or cellular target of acampro-
`sate is not fully elucidated, acamprosate appears to
`methyl-
`-aspartate (NMDA) receptor ac-
`modulate
`N-
`D
`tivity in the glutamate system, and to inhibit the upreg-
`⫹
`2
` channels that is induced
`ulation of voltage-gated Ca
`by chronic alcohol ingestion and states of withdrawal
`(Allgaier et al. 2000; Popp and Lovinger 2000). Thus,
`acamprosate may act on neurobiological mechanisms
`that may persist for many months following alcohol
`withdrawal, and that may contribute to the vulnerabil-
`ity for drinking relapse (Borg 1988).
`The clinical safety and efficacy of acamprosate was
`evaluated in 16 placebo-controlled, double-blind trials
`of 3, 6, or 12 months duration conducted across 11 Eu-
`ropean countries and involving more than 4,500 male
`and female outpatients with alcohol dependence (Bar-
`rias et al. 1997; Besson et al. 1998; Chick et al. 2000a;
`Geerlings et al. 1997; Gual and Lehert 2001; Ladewig et
`al. 1993; Lhuintre et al. 1985, 1990; Paille et al. 1995; Pelc
`et al. 1992, 1997; Poldrugo 1997; Rousseaux et al. 1996;
`Sass et al. 1996; Tempesta et al. 2000; Whitworth et al.
`1996). Fourteen of 16 trials showed a significant advan-
`tage for acamprosate over placebo on abstinence mea-
`sures. There are no serious or rate-limiting adverse ef-
`fects associated with acamprosate. Mild and transient
`diarrhea is the only drug-related adverse event that dif-
`fered consistently from placebo across studies. Acamp-
`rosate is not metabolized. It is eliminated by the kid-
`neys and
`is contra-indicated
`in cases of renal
`insufficiency (Saivin et al. 1998). Oral acamprosate tab-
`lets are available by prescription in 39 countries, with
`about 1.5 million people treated with acamprosate
`worldwide. The Food and Drug Administration
`granted Investigational New Drug status for acampro-
`sate, and a 21-site, 6-month, double-blind placebo-con-
`trolled dose-ranging trial has recently been completed
`in 601 alcohol-dependent outpatients in support of USA
`regulatory approval (for methodology see Mason and
`Ownby 2000).
`Naltrexone is a highly selective opioid antagonist
`(Chang et al. 1979). A large body of pre-clinical studies
`suggests that endogenous opioids play a role in the re-
`inforcing effects of alcohol, and that blockade of these
`receptors with an antagonist decreases the positive re-
`inforcing effects of alcohol and reduces drinking (Koob
`et al. 1998). These findings suggest that an opioid antag-
`onist may not initially prevent sampling of alcohol (i.e.,
`promote abstinence), but may reduce risk of relapse to
`
`excessive drinking in subjects who sample alcohol
`while taking an opioid antagonist. Double-blind pla-
`cebo-controlled clinical trials with naltrexone and a
`structural analog, nalmefene, provide support for the
`use of opioid antagonists for reducing relapse severity
`in persons with alcohol dependence (Anton et al. 1999;
`Mason et al. 1999; O’Malley et al. 1992; Oslin et al. 1997;
`Volpicelli et al. 1992, 1997), although some recent trials
`have been inconclusive (Chick et al. 2000b; Kranzler et
`al. 2000; Krystal et al. 2001). A multicenter safety study
`found naltrexone to be well tolerated with patients
`complaining primarily of headache and nausea that
`tended to be transient in nature (Croop et al. 1997). Nal-
`trexone is metabolized by the hepatic cytosolic enzyme
`␤
`-naltrexol, a major pharmacologi-
`system to form 6-
`cally active metabolite (Porter et al. 2000). It is contra-
`indicated in cases of hepatic insufficiency (Sifton 1997).
`With drugs for a common indication where the over-
`all effect size is moderate and there are not overlapping
`toxicities, it is of interest to explore whether or not
`coadministration may enhance clinical outcome. There
`is considerable interest in evaluating the safety of com-
`bined administration of acamprosate and naltrexone
`given the high tolerability of each drug, their different
`pharmacological profiles (glutamate vs. opiate), poten-
`tially different effects on drinking outcomes (e.g., in-
`creased abstinence duration vs. decreased relapse se-
`verity), and the increasing world-wide availability of
`both compounds. The objectives of this study are to de-
`termine if there is a pharmacokinetic (PK) or pharmaco-
`dynamic (PD) drug interaction between acamprosate
`and naltrexone in normal, healthy adult subjects.
`Chronic heavy alcohol intake and some pharmacologi-
`cal agents selective for either opioid or NMDA recep-
`tors have been associated with changes in memory and
`cognition (Chaves et al. 1988; Cohen et al. 1983; Kath-
`mann et al. 1996; Malenka 1991; O’Mahony and Doherty
`1996; Parsons and Farr 1981; Schneider et al. 1999; Wil-
`letts et al. 1990). Therefore, evaluation of a pharmacody-
`namic drug interaction will focus on tests of cognitive
`functioning.
`
`METHODS
`
`Subjects
`
`Subjects were normal, healthy male and female paid
`volunteers. The study was conducted under appropri-
`ate guidelines for the protection of human subjects, in
`accordance with the Declaration of Helsinki. To be eli-
`gible, subjects had to be 18 to 40 years of age; weigh at
`least 110 pounds and be within 15% of their normal
`body weight for height; have negative results on hepati-
`tis panel, HIV antibody, urine drug and alcohol, and
`pregnancy (if female) tests; and provide written in-
`
`AMN1068
`Amneal Pharmaceuticals LLC v. Alkermes Pharma Ireland Limited
`IPR2018-00943
`
`

`

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`598
`
`B.J. Mason et al.
`
`N
`EUROPSYCHOPHARMACOLOGY
`
`
`
`–
`2002
`
`VOL
`
`.
`,
`27
`
`NO
`
`.
`
`4
`
`formed consent. Subjects were excluded if they met cur-
`rent Diagnostic and Statistical Manual Fourth Edition
`(American Psychiatric Association 1994) criteria for al-
`cohol or other drug use disorders, including nicotine
`and opiates; had clinically relevant medical or psychiat-
`ric disorders; used any prescribed medications within
`two weeks prior to study entry, except contraceptives;
`used over-the-counter preparations within one week
`prior to study entry, except vitamins which could be
`continued at the same dosage; used any alcohol, caf-
`feine or xanthine-containing products within 72 h prior
`to the first dose of study drug for each treatment pe-
`riod; were pregnant, lactating, or refused to use a reli-
`able method of contraception.
`
`Study Procedures
`
`This was a double-blind, multiple-dose, within subjects,
`randomized 3-way crossover interaction study of the
`standard therapeutic doses of acamprosate (2 g/d) and
`naltrexone (50 mg/d), given alone and in combination.
`All subjects received all three treatment conditions in
`an order determined by a computer-generated random-
`ization code. Subjects were admitted to the inpatient
`clinical research unit on the day prior to the first dose
`administration and were discharged after completion of
`study procedures on Day 11, for each treatment condi-
`tion. Steady state levels of acamprosate are achieved by
`the seventh day of dosing (Wilde and Wagstaff 1997).
`Therefore, in order to adequately test for drug interac-
`tions, all subjects were dosed with each study medica-
`tion for seven days and completed PK and PD studies
`through Day 11 (Hansten and Horn 1993). The 7-day
`treatment periods were separated with at least a 7-day
`washout period to avoid carryover drug effects from
`the previous treatment condition.
`
`Treatment Conditions
`
`Treatment conditions were: (1) acamprosate 1000-mg
`(two 500-mg tablets manufactured by Groupe Lipha)
`.
`., for
`administered orally every 12 h, starting at 7:00
`A
`M
`a total of 13 doses, plus one naltrexone placebo capsule
`.
`., for a total of
`administered orally once daily at 7:00
`A
`M
`seven doses; (2) two acamprosate placebo tablets ad-
`.
`., for a
`ministered orally every 12 h starting at 7:00
`A
`M
`total of 13 doses, plus one 50-mg naltrexone tablet (one
`50-mg ReVia ® tablet manufactured by DuPont
`Pharma, over-encapsulated to match naltrexone pla-
`.
`. for a
`cebo) administered orally once daily at 7:00
`A
`M
`total of seven doses; and (3) acamprosate 1000 mg (two
`500-mg tablets) administered orally every 12 h starting
`.
`., for a total of 13 doses, plus a 50-mg naltrex-
`at 7:00
`A
`M
`one tablet administered orally every 24 h starting at
`.
`., for a total of seven doses. A mouth check was
`7:00
`A
`M
`performed by Unit staff to verify that the dose was
`
`swallowed. All doses were taken with 240 mL of water
`thirty minutes prior to consumption of standardized
`meals, except for Day 7 (PK day) when subjects fasted
`for 4.5 h post dose. On Day 7, subjects also remained
`ambulatory, i.e., standing or seated, for 4 h post dose.
`Use of concomitant medication during the study was
`prohibited unless pre-approved or necessary in a medi-
`cal emergency. Any such use and the reason was docu-
`mented.
`
`Safety and Tolerability
`
`Clinical laboratory evaluations (hematology, clinical
`chemistry (fasting), and urinalysis) were performed at
`screening and during each treatment period at check-in,
`on Day 2 (24 h after first dose of study drug), on Day 8
`(24 h after last dose of study drug), and on Day 11
`␤
`-HCG) preg-
`(prior to each clinic discharge). A serum (
`nancy test was performed for females at screening, at
`each check-in day, and at study completion (Day 11 of
`Period 3). A urine screen for drugs of abuse (including
`alcohol, amphetamines, barbiturates, benzodiazepines,
`cannabinoids, cocaine, methadone, opiates, phencyclid-
`ine and propoxyphene) was performed at screening
`and repeated at each check-in. Complete physical and
`neurological examinations were performed at screen-
`ing, with follow-up exams at check-in and Days 7, 8,
`and 11 of each treatment period. A 12-lead ECG was ob-
`tained at screening, check-in of Period 1, and at study
`completion (Day 11 of Period 3). Vital signs were ob-
`tained at screening, at check-in, on Days 1 through 10,
`prior to and 3 and 6 h following the morning dose, and
`prior to inpatient discharge on Day 11. In conjunction
`with vital sign measurement at pre-dose on Days 1
`through 10 and on Day 11, subjects were asked “Have
`there been any changes in the way you feel since the
`last time you were asked?”
`Adverse events were recorded using the Coding
`Symbols for Thesaurus of Adverse Reaction Terms (De-
`partment of Health and Human Services 1995) termi-
`nology from check-in through study completion. All
`adverse events, whether spontaneously reported by the
`subject or observed by study personnel, were docu-
`mented along with any medical intervention, and eval-
`uated according to standardized criteria in terms of se-
`verity, frequency, duration and causal relationship to
`study medication.
`
`Pharmacokinetic Parameters
`
`Acamprosate has no biologically active metabolites. The
`␤
`-
`activity of naltrexone is due to both the parent and 6-
`naltrexol metabolite (Meyer et al. 1984). Separate blood
`samples for PK analysis of acamprosate and for PK anal-
`␤
`-naltrexol were collected dur-
`ysis of naltrexone and 6-
`ing each treatment period as follows: Day 1 prior to the
`
`AMN1068
`Amneal Pharmaceuticals LLC v. Alkermes Pharma Ireland Limited
`IPR2018-00943
`
`

`

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`N
`EUROPSYCHOPHARMACOLOGY
`
`
`
`–
`2002
`VOL
`
`.
`,
`27
`NO
`
`.
`4
`
`Interaction Study of Acamprosate and Naltrexone
`
`599
`
`first dose of study drug, i.e., baseline; Days 5 and 6, pre-
`morning dose, i.e, PK trough concentrations; Day 7 pre-
`morning dose and 0.5, 1.0, 1.5, 2, 3, 4, 6, 8, 10, 12, 24, 36,
`48, 72, and 96 h after the Day 7 morning dose.
`
`Bioanalytical Methods
`␤
`-naltrexol plasma concentrations
`Naltrexone and 6-
`were measured using a validated high performance liq-
`uid chromatographic mass spectrometric analytical
`method with a lower limit of quantification set at 0.25
`ng/mL (Beyerlein and Polywacz 1998). The variability
`of back-calculated concentrations of calibration stan-
`dards ranged from 4.0% to 9.4% for naltrexone. The be-
`tween-day precision was determined at levels of 0.750,
`⫽
` 36,
`7.50, 80.0 and 250 ng/mL in replicate analyses (n
`36, 60 and 12, respectively). The between-day variabil-
`ity did not exceed 14.3%. The relative standard devia-
`tion (RSD) for the back-calculated concentration for nal-
`⫺
`1.2% from the
`trexone was 5.4% with a deviation of
`␤
`-naltrexol, the RSD for
`theoretical concentration. For 6-
`the back-calculated concentration was 3.4% with a devi-
`ation of 0.5% from the theoretical concentration.
`Acamprosate plasma concentrations were measured
`by a validated gas chromatography/negative ion chem-
`ical ionization mass spectrometry method with a lower
`limit of quantification of 3.12 ng/mL (Girault et al.
`1990). At this level, the precision (% RSD) and accuracy
`(mean percentage of error), calculated from 10 replicate
`samples were equal to 4.36% and 0.87% respectively.
`The between-day precision was determined at levels of
`6.25, 50, and 400 ng/mL in replicate analyses. The RSD
`values were lower than 6.53% and the accuracy was be-
`⫺
`0.83% and 2.45%.
`tween
`For each subject, the following pharmacokinetic pa-
`␤
`-naltrexol,
`rameters were determined for naltrexone, 6-
`and acamprosate using plasma concentration-time pro-
`files on Day 7 according to the model independent ap-
`proach with Win Nonlin Professional Version 1.5 soft-
`ware (Scientific Consultant, Inc.): maximum observed
`); time to maximum concentra-
`(peak) concentration (C
`max
`); degree of fluctuation at steady state (DF); area
`tion (T
`max
`under the plasma concentration-time curve over one
`dosing interval, i.e., from hours 0 to 12 for acamprosate
`␤
`-naltrexol, esti-
`and hours 0 to 24 for naltrexone and 6-
`); and apparent
`mated by linear trapezoidal rule (AUC
`␶
`o-
`).
`plasma terminal phase elimination half-life (T
`1/2
`
`trolled, with stimuli presented on high-resolution mon-
`itors, and the responses recorded via two buttons, one
`marked ‘NO’ and the other ‘YES’.
`Tasks assessing reaction time (Simple Reaction Time,
`Choice Reaction Time) or speed of performance (Nu-
`meric Working Memory, Delayed Word Recognition)
`were measured in milliseconds. Tasks assessing the ac-
`curacy of performance (Immediate and Delayed Word
`Recall, Digit Vigilance) were scored as the percent of
`possible correct responses. Additionally, a Sensitivity
`Index was calculated for Numeric Working Memory
`and Delayed Word Recognition in which the ability to
`identify previously presented items was assessed rela-
`tive to the ability to correctly reject “distracter” items
`which were not previously presented. A score of 1 rep-
`resents perfect sensitivity to the task information: all
`previously presented items are correctly identified and
`all distracter items are rejected as novel. A score of zero
`represents chance performance or insensitivity to task
`information.
`Subjects completed four training sessions. Subjects
`were tested during each treatment period at check in,
`on Days 1, 3, and 7 at pre-dose, 4 and 7 h post-dose, and
`on Day 11 prior to discharge. Parallel forms of tests
`were presented in each testing session to control for
`practice effects. As a secondary endpoint, results from
`the 4-hour post-dose testing session were evaluated in
`relation to PK effects from the same timepoint.
`
`Sample Size Determination
`
`A primary objective of this study was to test for a phar-
`macokinetic drug interaction between oral doses of
`acamprosate and naltrexone. Sample size calculations for
`acamprosate were based on summarized data from a
`2-way crossover study of repeated doses of acamprosate
`using within-subject variability data (Lipha Pharmaceu-
`ticals, Inc. 1996). Naltrexone calculations were based on
`summarized data from a 4-way crossover study of vary-
`ing doses of naltrexone using between-subject variability
`data (Meyer et al. 1984). A sample size of 24 in a cross-
`over design which uses within-subject variance as com-
`pared with the between-subject variance of other designs
`␣
`⫽
`
` 0.05) to
`was estimated to have at least 90% power (
`detect mean percentage changes of 20% for acamprosate
`AUC and 20% for naltrexone AUC.
`
`Statistical Analyses
`
`Tests of Cognitive Functioning
`
`A pharmacodynamic drug interaction was evaluated
`with the Cognitive Drug Research computerized assess-
`ment system that assesses drug effects on various pa-
`rameters of cognitive functioning, e.g., word recall,
`word recognition, attention and reaction time (Wesnes
`et al. 1991, 1994, 2000). All tasks are computer-con-
`
`Statistical significance for selected pharmacokinetic pa-
`rameters was assessed using an analysis of variance
`(ANOVA) model with terms for sequence, subject
`within sequence, period, and treatment. In addition to
`ANOVAs on untransformed data, ANOVAs were done
` and AUC
` data.
`on natural log (ln) transformed C
`␶
`max
`o-
`The ln-transformed results were the pivotal criterion
`
`AMN1068
`Amneal Pharmaceuticals LLC v. Alkermes Pharma Ireland Limited
`IPR2018-00943
`
`

`

`600
`
`B.J. Mason et al.
`
`N
`EUROPSYCHOPHARMACOLOGY
`
`
`
`–
`2002
`VOL
`
`.
`,
`27
`NO
`
`.
`
`4
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`
`
`
`
`
`
`
`
`
`
`
`used to draw conclusions regarding drug interaction,
` AUC
` was the pri-
`and due to large variability in C
`␶
`max,
`o-
` data were not
`mary variable analyzed. Since the T
`max
`normally distributed, they were compared using the
`Friedman’s nonparametric test (Sokal and Rohlf 1995).
`␤
`-naltrexol had an effect
`To assess if naltrexone or 6-
`on acamprosate and if acamprosate had an effect on
`␤
`-naltrexol, per FDA recommendations,
`naltrexone or 6-
`90% confidence intervals (two 1-sided tests) were com-
`puted for the difference between the test (co-dosing)
`and reference (acamprosate or naltrexone alone) values
` and AUC
` (Steinijans et al. 1991). For C
` and
`for C
`␶
`max
`o-
`max
` , no drug interaction effect was assumed if the
`AUC
`␶
`o-
`90% confidence interval was between 80% and 120%.
` and AUC
` , no drug in-
`For the Ln-transformed C
`␶
`max
`o-
`teraction effect was assumed if the 90% confidence in-
`terval was between 80% and 125%.
`Steady state levels of acamprosate are achieved by the
`seventh day of dosing. Therefore, the trough concentra-
`) observed on Days 5, 6, and 7 were compared
`tions (C
`min
`by ANOVA to check the equilibrium achievement.
`To test for pharmacodynamic drug interactions be-
`tween acamprosate and naltrexone, the pre-dose cogni-
`tive assessment on Day 1 was used as a baseline, and
`subtracted from subsequent scores to derive difference
`from baseline scores. The post-dose difference scores
`were then subject to an ANOVA, terms being fitted for
`treatment, the repeated assessments, and the interac-
`tion between the treatment conditions and repeated as-
`sessments. Where the main effect or the interaction was
`significant, the least squares means procedure was used
`to make multiple comparisons between the conditions
`to identify where the differences lay.
`Fisher exact test probabilities were calculated for fre-
`quency analysis of adverse drug experiences between
`test and reference groups.
`All statistical tests were two-sided and had an
`of .05.
`
` level
`
`␣
`
`RESULTS
`
`Subjects
`
`Twenty-five subjects entered the study, and 24 com-
`pleted all three treatment periods. One subject became
`noncompliant with meal and daily task requirements in
`the first treatment period and was replaced with a sub-
`ject who completed the three treatments in the origi-
`nally assigned sequence. Data for the replaced subject
`were included in the demographic and safety analysis.
`The double-blind was maintained for all subjects across
`all treatment conditions. Subjects (19 males and six fe-
`⫾
`⫾
` 5.2) years, 175.3 (
`males) were a mean age of 31.8 (
`⫾
`8.9) cm tall, and 74.5 (
` 8.9) kg in weight. The sample
`consisted of 23 Caucasian, one Hispanic, and one Afri-
`can American subject.
`
`Acamprosate Pharmacokinetics
`
`Coadministration of naltrexone significantly enhanced
`the rate and extent of acamprosate bioavailability, re-
` and
`sulting in significantly shorter acamprosate T
`max
` values, in comparison with administration
`higher C
`max
`of acamprosate alone (Table 1). Acamprosate median
` values were 6.0 h following dosing alone and 4.0 h
`T
`max
`⬍
`
`following dosing in combination with naltrexone (
`p
`.01). The mean acamprosate C
` when administered in
`max
`combination with naltrexone (517 ng/mL) was approxi-
` when adminis-
`mately 33% higher than the mean C
`max
`⬍
`
` .01), and the 90% confidence
`tered alone (390 ng/mL,
`p
`interval for the test/reference ratio for the ln-transformed
` (120% to 156%) was not entirely contained within
`C
`max
`the 80% to 125% range, indicating that administration of
`acamprosate in combination with naltrexone signifi-
`cantly increased the rate of absorption of acamprosate.
` when administered
`The mean acamprosate AUC
`␶
`o-
`in combination with naltrexone (4,658 ng hr/mL) was
` when
`approximately 25% greater than the mean AUC
`␶
`o-
`acamprosate was administered alone (3,734 ng hr/mL).
`Likewise, the 90% confidence interval for the test/refer-
` (114% to 143%)
`ence ratio for the Ln-transformed AUC
`␶
`o-
`was not entirely contained within the 80% to 125%
`range, indicating that administration of acamprosate in
`combination with naltrexone significantly improved
`the absorption of acamprosate (Figure 1).
`Naltrexone did not significantly affect the elimina-
`tion half-life of acamprosate. Acamprosate was slowly
`eliminated following oral administration with mean T
`1/
` values of 18.5 and 17.9 h when administered alone or
`2
`in combination with naltrexone, respectively.
`Steady-state was verified
`for acamprosate by
`ANOVA of trough concentrations from Days 5, 6 and 7,
`⫽
`⫾
` 264
` 128.4
`both when administered alone (Day 5
`⫽
`⫾
`⫽
`⫾
` 271
` 123.7 ng/mL, Day 7
` 256
`ng/mL, Day 6
`⫽
`⫽
`120.9 ng/mL, F
`
` 0.48,
`
` .62) and in combination
`p
`2,23
`with naltrexone (Day 5 ⫽ 336 ⫾ 153.0 ng/mL, Day 6 ⫽
`332 ⫾ 148.5 ng/mL, Day 7 ⫽ 344 ⫾ 147.4 ng,mL F2,23 ⫽
`0.18, p ⫽ .83).
`
`Naltrexone and 6-␤-Naltrexol Pharmacokinetics
`Co-administration of acamprosate and naltrexone had
`no effect on the pharmacokinetics of naltrexone and its
`metabolite, 6-␤-naltrexol. The 90% confidence intervals
`for the Ln-transformed Cmax and AUC for naltrexone
`and 6-␤-naltrexol are entirely contained within the 80–
`125% range (Table 1, Figure 2). Acamprosate also had
`no effect on the elimination half life of naltrexone or 6-
`␤-naltrexol.
`Steady state analysis was only performed for 6-␤-
`naltrexol, as all the trough concentrations for naltrex-
`one, which has an elimination half life of about 4 h (Ta-
`ble 1), were below the limit of quantitation. Steady state
`
`AMN1068
`Amneal Pharmaceuticals LLC v. Alkermes Pharma Ireland Limited
`IPR2018-00943
`
`

`

`NEUROPSYCHOPHARMACOLOGY 2002–VOL. 27, NO. 4
`
`Interaction Study of Acamprosate and Naltrexone
`
`601
`
`Table 1. Pharmacokinetic (PK) Drug Interaction Analyses of Acamprosate, Naltrexone and 6-␤-Naltrexol Plasma Data
`Within Subjects (n⫽24)*
`
`PK Parameter
`
`Test
`
`Reference
`
`Percent
`Test/Reference
`
`90%
`Confidence
`Interval
`
`p value
`Treatment
`
`Acamprosate
`AUCo-␶ (ng hr/mL)
`lnAUCo-␶
`Cmax (ng/mL)
`ln Cmax
`Tmax (Hour)
`T1/2 (Hour)
`Naltrexone
`AUCo-␶ (ng hr/mL)
`lnAUCo-␶
`Cmax (ng/mL)
`ln Cmax
`Tmax (Hour)
`T1/2 (Hour)
`6-␤-Naltrexol
`AUCo-␶ (ng hr/mL)
`lnAUCo-␶
`Cmax (ng/mL)
`ln Cmax
`Tmax (Hour)
`T1/2 (Hour)
`
`4658⫾1778.2
`4277
`517⫾183.6
`482
`4.00 (0-12.0)
`17.9⫾8.81
`
`38.0⫾16.07
`35.1
`11.0⫾4.76
`10.0
`1.00 (0.5-3.01)
`3.58⫾1.63
`
`779⫾128.3
`769
`91.3⫾19.34
`89.4
`1.00 (0.5-3.0)
`15.1⫾4.18
`
`3734⫾1644.2
`3349
`390⫾160.0
`353
`6.00 (0-12.0)
`18.5⫾14.9
`
`38.6⫾16.53
`35.5
`11.8⫾6.55
`10.4
`1.00 (0.5-2.0)
`4.02⫾3.49
`
`788⫾134.8
`777
`96.1⫾21.05
`94
`1.00 (0.5-2.0)
`14.7⫾3.88
`
`125
`128
`133
`137
`NA
`119
`
`98.4
`98.9
`93.3
`96.2
`NA
`89.1
`
`98.8
`98.9
`95.0
`95.1
`NA
`103
`
`(112, 137)
`(114, 143)
`(118, 148)
`(120, 156)
`NA
`NA
`
`(90.1, 107)
`(92.0, 106)
`(79.6, 107)
`(85.0, 109)
`NA
`NA
`
`(95.0, 103)
`(95.4, 103)
`(87.2, 103)
`(88.1, 103)
`NA
`NA
`
`<.01
`<.01
`<.01
`<.01
`.03
`.09
`
`0.74
`0.79
`0.41
`0.60
`0.20
`0.57
`
`0.60
`0.61
`0.29
`0.27
`1.0
`0.51
`
`*Values given are means ⫾ standard deviations, except for Tmax values for which the median and range are given. P-value for difference between
`treatment means from ANOVA, except Tmax P-value is from Friedman’s nonparametric test.
`Test ⫽ combination treatment with acamprosate and naltrexone. Reference ⫽ naltrexone treatment for naltrexone and 6-␤-naltrexol PK parameters,
`and acamprosate treatment for acamprosate PK parameters. Cmax ⫽ maximum observed (peak) plasma concentration. Tmax ⫽ time to maximum
`plasma concentration.
`ln ⫽ Natural log transformed. AUCo-␶ ⫽ area under the plasma concentration-time curve during one dosing interval from pre-dose. T1/2 ⫽ terminal
`phase elimination half-life.
`
`was achieved for 6-␤-naltrexol, which has an elimina-
`tion half life of about 15 h (Table 1), when naltrexone
`was administered alone (Day 5 ⫽ 13.4 ⫾ 14.4 ng/mL,
`Day 6 ⫽ 14.4 ⫾ 4.2 ng/mL, Day 7 ⫽ 14.3 ⫾ 3.5 ng,mL,
`F2,23 ⫽ 2.49, p ⫽ .09). However, for the combination of
`acamprosate and naltrexone, steady state was not veri-
`fied (Day 5 ⫽ 13.8 ⫾ 3.7 ng/mL, Day 6 ⫽ 13.7 ⫾ 3.6 ng/
`mL, Day 7 ⫽ 14.5 ⫾ 3.9 ng,mL, F2,23 ⫽ 4.78, p ⫽ .01). The
`15-hour half life of 6-␤-naltrexol and seven days of veri-
`fied dosing were sufficient to achieve steady state.
`However, there were considerable within and between
`subject fluctuations in naltrexone plasma concentra-
`tions in both the single drug (DF ⫽ 702% ⫾ 156.9) and
`co-dosing conditions (DF ⫽ 721% ⫾ 190.6), as is typical
`in a drug that is subject to extensive first-pass metabo-
`lism (Meyer et al. 1984). Degree of fluctuation (DF) in 6-␤-
`naltrexol plasma concentrations was marked in both the
`single drug (DF ⫽ 251% ⫾ 55.8) and co-dosing conditions
`(DF ⫽ 240% ⫾ 51.6). In contrast, acamprosate DF was rela-
`tively small under both the single drug (DF ⫽ 48.5% ⫾
`37.8) and co-dosing conditions (DF ⫽ 38.9% ⫾ 21.9).
`Dissolution profiles were equivalent for the over en-
`capsulated naltrexone tablets compared with the stan-
`dard ReVia® naltrexone tablets.
`
`Cognitive Testing to Assess Pharmacodynamic
`Drug Interaction
`
`Naltrexone alone was associated with significantly slower
`performance speed than acamprosate alone or when
`dosed in combination with acamprosate on two atten-
`tional tasks: Choice Reaction Time (F2,23 ⫽ 5.04, p ⫽ .007)
`and Digit Vigilance Speed (F2,23 ⫽ 4.23, p ⫽ .015) (see
`Table 2 for pairwise comparisons). Naltrexone alone
`was also associated with significantly lower sensitivity
`on Delayed Word Recognition than acamprosate alone
`or when dosed in combination with acamprosate (F2,23 ⫽
`6.43, p ⫽ .002). Acamprosate alone was associated with
`a significant drop in Immediate Word Recall accuracy rel-
`ative to naltrexone alone (F2,23 ⫽ 3.70, p ⫽ .025). Con-
`versely, acamprosate alone was associated with signifi-
`cantly faster performance speed on Delayed Word
`Recognition than naltrexone alone or when dosed in com-
`bination with naltrexone (F2,23 ⫽ 4.46, p ⫽ .002). There
`were no performance deficits associated with the com-
`bined treatment condition relative to naltrexone alone or
`acamprosate alone on any cognitive assessments. Fur-
`thermore, there were no significant interactions between
`repeated cognitive assessments over time and treatment
`condition, i.e., there were differences between the treat-
`
`AMN1068
`Amneal Pharmaceuticals LLC v. Alkermes Pharma Ireland Limited
`IPR2018-00943
`
`

`

`602 B.J. Mason et al.
`
`NEUROPSYCHOPHARMACOLOGY 2002–VOL. 27, NO. 4
`
`Figure 1. Mean concentration (ng/mL) of
`acamprosate in human plasma (linear scale).
`
`ment conditions, but the differences did not depend on
`the duration of dosing.
`Relationships between drug plasma concentration
`levels and cognitive data were evaluated as secondary
`endpoints by subjecting the coinciding Day 7 Hour 4
`plasma concentrations and cognitive assessments to
`correlation analysis. A positive correlation was found
`with acamprosate alone on the Delayed Word Recogni-
`tion Sensitivity Index (r ⫽ 0.45, p ⫽ .03). No other rela-
`tionship between PK and PD variables was detected.
`
`due to side effect complaints.