Journal of Analytical Toxicology, Vol. 20, October ! 996 Human Pharmacokinetics of Intravenous, Sublingual, and Buccal Buprenorphine* James J. Kuhlman, Jr J, Shairose Lalani 1, Joseph Magluilo, Jr. 1, Barry Levine 1, William D. Darwin 2, Rolley E. Johnson 2,t, and Edward J. Cone 2 1Division of Forensic Toxicology, Armed Forces Institute of Pathology, Washington, DC and 2Division of Intramural Research, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland Abstract Buprenorphine is a potent opioid analgesic used in the treatment of moderate to severe pain. At higher doses, it has demonstrated potential for treating heroin dependence. This study was undertaken to investigate buprenorphine pharmacokinetics by different routes of administration at dosages approximating those used in opioid-dependence studies. Six healthy men who were nondependent but who had a history of heroin use were administered buprenorphine in a crossover design study by intravenous (1.2 rag), sublingual (4.0 rag), and buccal (4.0 rag) routes of administration. Plasma samples were collected up to 96 h and assayed for buprenorphine and norbuprenorphine by negative chemical ionization tandem mass spectrometry. Plasma concentrations of buprenorphine and norbuprenorphine were analyzed by nonlinear regression analysis with standard noncompartmental methods. Buprenorphine bioavailability by the sublingual and buccal routes was estimated as 51.4% and 27.8%, respectively, although there was considerable interindividual variability by both routes of administration. The terminal elimination half-lives were longer for the sublingual and buccal routes than for the intravenous route. The extended elimination half-lives may be due to a shallow depot effect involving sequestration of buprenorphine in the oral mucosa. Norbuprenorphine mean peak plasma concentrations were less than 1 ng/mL and were highly variable among different routes of administration and individuals. The terminal elimination half-life of norbuprenorphine was longer than buprenorphine. Introduction Buprenorphine is a semisynthetic opioid used for the treat- ment of moderate to severe pain in postoperative and cancer cases. Therapeutic doses administered by the intravenous and intramuscular routes range from 0.3 to 0.6 mg. Buprenor- * Disclaimer: The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of Defense or of the Army, Navy, or Air Force, Current address: Department of Psychiatry, Johns Hopkins School of Medicine, Behavioral Phar- macology Research Units, John Hopkins Bayview Medical Center, Baltimore, MD. phine produces effects similar to morphine but is 25-40 times more potent and has a large therapeutic index. At higher doses (4-16 rag), buprenorphine has been shown to be an effective treatment for suppressing heroin withdrawal (1). Buprenor- phine appears to display a ceiling effect at high doses and has been categorized as a partial agonist at the ]J receptor. Walsh et al. (2) found that buprenorphine produced less respiratory depression at a 32-mg sublingual dose than at a 16-rag dose. Buprenorphine also possesses an unusually long duration of action most likely due to its high affinity for opioid receptors. Jasinski et al. (3) suggested in 1978 that buprenorphine may be useful in the treatment of opioid-dependent individuals be- cause it produced morphine-like subjective effects, had a long duration of action, and produced limited withdrawal symp- toms. Mello and co-workers (4,5) demonstrated that buprenor- phine significantly suppressed heroin self-administration. A daily subcutaneous dose of 4-8 mg of buprenorphine reduced heroin self-administration of experienced heroin abusers by 69-98%. A nonparenteral dosage form of buprenorphine that could achieve and maintain blood levels that prevent opiate craving and withdrawal would be preferred for the treatment of opioid- dependent individuals. Buprenorphine, unlike methadone, is less effective by the oral route of administration and undergoes a significant first-pass effect. The bioavailability of an oral dose of buprenorphine was estimated as 15% (6). Consequently, oral buprenorphine treatment requires large relative doses, which increase the cost to a prohibitive level. The sublingual route exhibits greater bioavailability and has been used exten- sively in clinical efficacy studies (7-11). Other routes of administration, such as the buccal mute, could also be effective means of drug delivery of buprenorphine. An understanding of buprenorphine pharmacokinetics by different routes of administration is essential for determining the most efficient treatment of opioid dependence. A number of studies reported pharmacokinetic data for buprenorphine administered at lower analgesic doses by the intravenous (12-15), intramuscular (12), and sublingual (6,16,17) routes. Buprenorphine elimination half-lives ranged from 3 to 5 h, and sublingual bioavailability was estimated at 55%, although there Reproduction (photocopying) of editorial content of this journal is prohibited without publisher's permission, 369
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`Journal of Analytical Toxicology, Vol. 20, October ! 996 Human Pharmacokinetics of Intravenous, Sublingual, and Buccal Buprenorphine* James J. Kuhlman, Jr J, Shairose Lalani 1, Joseph Magluilo, Jr. 1, Barry Levine 1, William D. Darwin 2, Rolley E. Johnson 2,t, and Edward J. Cone 2 1Division of Forensic Toxicology, Armed Forces Institute of Pathology, Washington, DC and 2Division of Intramural Research, National Institute on Drug Abuse, National Institutes of Health, Baltimore, Maryland Abstract Buprenorphine is a potent opioid analgesic used in the treatment of moderate to severe pain. At higher doses, it has demonstrated potential for treating heroin dependence. This study was undertaken to investigate buprenorphine pharmacokinetics by different routes of administration at dosages approximating those used in opioid-dependence studies. Six healthy men who were nondependent but who had a history of heroin use were administered buprenorphine in a crossover design study by intravenous (1.2 rag), sublingual (4.0 rag), and buccal (4.0 rag) routes of administration. Plasma samples were collected up to 96 h and assayed for buprenorphine and norbuprenorphine by negative chemical ionization tandem mass spectrometry. Plasma concentrations of buprenorphine and norbuprenorphine were analyzed by nonlinear regression analysis with standard noncompartmental methods. Buprenorphine bioavailability by the sublingual and buccal routes was estimated as 51.4% and 27.8%, respectively, although there was considerable interindividual variability by both routes of administration. The terminal elimination half-lives were longer for the sublingual and buccal routes than for the intravenous route. The extended elimination half-lives may be due to a shallow depot effect involving sequestration of buprenorphine in the oral mucosa. Norbuprenorphine mean peak plasma concentrations were less than 1 ng/mL and were highly variable among different routes of administration and individuals. The terminal elimination half-life of norbuprenorphine was longer than buprenorphine. Introduction Buprenorphine is a semisynthetic opioid used for the treat- ment of moderate to severe pain in postoperative and cancer cases. Therapeutic doses administered by the intravenous and intramuscular routes range from 0.3 to 0.6 mg. Buprenor- * Disclaimer: The opinions or assertions contained herein are the private views of the authors and are not to be construed as official or as reflecting the views of the Department of Defense or of the Army, Navy, or Air Force, Current address: Department of Psychiatry, Johns Hopkins School of Medicine, Behavioral Phar- macology Research Units, John Hopkins Bayview Medical Center, Baltimore, MD. phine produces effects similar to morphine but is 25-40 times more potent and has a large therapeutic index. At higher doses (4-16 rag), buprenorphine has been shown to be an effective treatment for suppressing heroin withdrawal (1). Buprenor- phine appears to display a ceiling effect at high doses and has been categorized as a partial agonist at the ]J receptor. Walsh et al. (2) found that buprenorphine produced less respiratory depression at a 32-mg sublingual dose than at a 16-rag dose. Buprenorphine also possesses an unusually long duration of action most likely due to its high affinity for opioid receptors. Jasinski et al. (3) suggested in 1978 that buprenorphine may be useful in the treatment of opioid-dependent individuals be- cause it produced morphine-like subjective effects, had a long duration of action, and produced limited withdrawal symp- toms. Mello and co-workers (4,5) demonstrated that buprenor- phine significantly suppressed heroin self-administration. A daily subcutaneous dose of 4-8 mg of buprenorphine reduced heroin self-administration of experienced heroin abusers by 69-98%. A nonparenteral dosage form of buprenorphine that could achieve and maintain blood levels that prevent opiate craving and withdrawal would be preferred for the treatment of opioid- dependent individuals. Buprenorphine, unlike methadone, is less effective by the oral route of administration and undergoes a significant first-pass effect. The bioavailability of an oral dose of buprenorphine was estimated as 15% (6). Consequently, oral buprenorphine treatment requires large relative doses, which increase the cost to a prohibitive level. The sublingual route exhibits greater bioavailability and has been used exten- sively in clinical efficacy studies (7-11). Other routes of administration, such as the buccal mute, could also be effective means of drug delivery of buprenorphine. An understanding of buprenorphine pharmacokinetics by different routes of administration is essential for determining the most efficient treatment of opioid dependence. A number of studies reported pharmacokinetic data for buprenorphine administered at lower analgesic doses by the intravenous (12-15), intramuscular (12), and sublingual (6,16,17) routes. Buprenorphine elimination half-lives ranged from 3 to 5 h, and sublingual bioavailability was estimated at 55%, although there Reproduction (photocopying) of editorial content of this journal is prohibited without publisher's permission, 369
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`Journal of Analytical Toxicology, Vol. 20, October 1996 was considerable interindividual variability (6). No pharmacokinetic information is available for norbuprenorphine, the active metabolite of buprenorphine, in humans. Much of the buprenorphine pharmacoki- netic data has been obtained with radioim- munoassay. Unfortunately, cross-reactivity with buprenorphine glucuronide and nor- buprenorphine makes these data less reli- able. We developed a specific gas chromato- graphic-tandem mass spectrometric (GC-MS-MS) assay for buprenorphine and norbuprenorphine in biological fluids (18). The assay was used for the measurement of these analytes in the plasma of six individ- uals after intravenous, sublingual, and buccal administration. The buprenorphine doses administered approximated those used in opioid-dependence studies. Pharmacoki- netic parameters and estimates of bioavail- ability for the sublingual and buccal routes of administration are reported. Methods Chemicals and materials Buprenorphine HC1 and norcodeine were purchased from Sigma Chemical Co. (St. Louis, MO). Buprenorphine-d4 and bupre- norphine were purchased from Radian Corp. (Austin, TX). Buprenorphine from separate sources was used to prepare cali- brator and control samples. Norbupre- norphine was obtained from the Research Technology Branch, National Institute on Drug Abuse (Rockville, MD). Heptafluoro- butyric anhydride (HFBA) was purchased from Aldrich Chemical Co. (Milwaukee, WI). All solvents were obtained from Fisher Chemical (Fair Lawn, NJ) and were high- performance liquid chromatographic-grade. Clean Screen (ZCDAU020) solid-phase ex- traction columns were purchased from World Wide Monitoring (Bristol, PA). Argon and ammonia gases from MG Industries (Valley Forge, PA) were used in chemical ionization tandem mass spectrometry. Instrumentation Quantitative analyses were performed with a Finnigan MAT TSQ 700 tandem mass spectrometer equipped with a Varian 3400 gas chromatograph. Injections were made by a split-splitless injector onto a J&W DB-5 MS capillary column (15 m x 0.25-mm i.d., 0.25-1Jm film thickness). The tandem mass Table I. Plasma Concentrations of Buprenorphine and Norbuprenorphine after Buprenorphine Administration by the Intravenous, Sublingual, and Buccal Routes of Drug Administration Time Subject plasma concentrations (ng/mL) (h) A C D E G I Mean SEM 1.2-mg buprenorphine-intravenous -0.50 0 0 M * 0 0 0 0 0 0.04 37.83 43.93 M 25.60 24.40 55.83 37.52 5.88 0.08 16.71 26.21 M 13.43 12.40 28.24 19.40 3.29 0.13 12.85 15.81 M 11.10 11.10 18.07 13.79 1.37 0.17 9.53 18.92 M 7.71 7.03 13.64 11.37 2.21 0.25 6.92 10.82 M 5.00 5.25 M 7.00 1.34 0.33 5.52 11.01 M 3.75 4.19 7.84 6.46 1.34 0.50 4.27 7.81 M 3.00 3.07 6.44 4.92 0.95 0.75 3.64 6.37 M 2.03 2.76 5.97 4.15 0.86 1.00 2.69 4.90 M 1.05 2.16 4.67 3.09 0.74 1.50 1.71 3.90 M 0.88 1.79 4.07 2.47 0.64 2.00 0.87 2.46 M 2.05 1.32 2.50 1.84 0.32 3.00 1.04 1.92 M 1.22 0.77 1.76 1.34 0.22 4.00 0.43 1.06 M 0.90 0.56 1.05 0.80 0.13 5.00 0.33 0.61 M 0.54 0.22 0.57 0.45 0.08 6.00 0.28 0.87 M 0.55 0.18 0.49 0.47 0.12 7.00 0.25 0.67 M 1.01 0.21 0.51 0.53 0.15 10.00 0.26 0.21 M 0.38 M 0.43 0.32 0.05 13.00 0 0 M 0.40 0.17 0.26 0.17 0.08 23.75 0 0 M 0.18 0 0 0.04 0.04 28.00 0 0 M 0.19 0 0 0.04 0.04 36.00 0 0 M 0.21 0 0 0.04 0.04 48.00 0 0 M 0 0 0 0 0 60.00 0 0 M 0 0 0 0 0 72.00 0 0 M 0 0 0 0 0 96.00 0 0 M 0 0 0 0 0 1.2-m[4 norbupren~;rphine intraw,nous -0.50 0 0 0 0 0 0 0 0 0.04 0.18 0.18 0.25 0 0.10 0.81 0.25 0.12 0.08 0.13 0.68 0.45 0 0.21 0.96 0.41 0.15 0.13 0.18 0.86 0.48 0.20 0.44 1.04 0.53 0.14 0.17 0.19 0.72 0.55 0.25 0.41 1.06 0.53 0.13 0.25 0.15 0.69 0.36 0.15 0.51 M 0.37 0.10 0.33 0.17 0.61 0.33 0.06 0.48 0.38 0.34 0.08 0.50 0.12 0.55 (/.28 0.04 0.43 0,36 0.30 0.08 0.75 0,10 0.33 0.15 M 0.29 0.39 0.25 0.06 1.00 0.05 0.38 0.16 0.04 0.34 0,41 0.23 0.07 1.50 0.05 0.33 0.13 0 0.31 0.39 0.20 0.07 2.(/0 0.07 0.29 0.11 0 0.24 0.37 0.18 0.06 3.00 0.04 0.25 0.11 0 0.22 0.31 0.16 0.05 4.00 0.02 0.15 0.07 0 0.20 0.30 0.12 0.05 5.00 M 0,20 0.08 0 0.20 0.29 0.15 0.05 6.00 0.02 0.17 0.09 0 0.22 0.39 0.15 0.06 7.00 M 0.20 0.07 0 0.12 0.29 0.14 0.05 10,00 0 0.12 0.07 0 0.17 0.35 0.12 0.05 13.00 0 0.08 0.07 0 0.17 0.35 0.11 0.05 23.75 0 0.04 0.08 0 0.16 0.57 0.14 0.09 28.00 0 0.10 0.07 0 0.15 0.28 0.10 0.04 36.00 0 0.10 0.06 0 0.13 0.16 0.07 0.03 48.00 0 0.06 0.05 0 0.09 0.29 0.08 0.04 60.00 0 0.06 0.06 0 0.11 0.24 0.(/8 0.04 * SEM = Standard error of the mean. t M = Missing data or measure not taken. 370
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`Journal of Analytical Toxicology, Vol. 20, October 1996 Table I continued. Plasma Concentrations of Buprenorphine and Norbuprenorphine after Buprenorphine Administration by the Intravenous, Sublingual, and Buccal Routes of Drug Administration Time Subject plasma concentrations (ng/mt) (h) A C D E G I Mean SEM 1.2-mg norbuprenorphine-intravenous 72.00 0 0.03 0.03 0 0.12 0.20 0.06 0.03 96.00 0 0 0 0 0.05 0.08 0.02 0.01 4.0-mg buprenorphine-sublingual -0.50 0 0 0 0 0 0 0 0 0.04 0.59 0.45 0 0.21 0.75 1.13 0.52 0.16 0.08 1.03 0.65 0.20 0.64 1.19 1.72 0.91 0.22 0.13 1.19 1.15 0.34 0.89 1.35 2.42 1.22 0.28 0.17 1.45 0.12 0.74 0.93 1.72 2.84 1.30 0.38 0.25 1.39 0,85 0.74 1.58 2.35 4.48 1.90 0.57 0.33 2.17 1.49 1.20 1.85 3.26 5.01 2.50 0.58 0.50 2.52 1.12 1.32 2.76 2.95 5.98 2.78 0.71 0.75 M 1.74 2.06 2.09 3.38 7.19 3.29 1.01 1.00 2.06 1.93 2.01 2.50 2.76 5.55 2.80 0.57 1.50 1.33 1.90 1.48 2.03 1.56 3.71 2.00 0.36 2.00 1.38 1.52 1.09 1.58 1.14 3.40 1.69 0.35 3.00 0.86 0,98 0.63 1.00 0,62 2.07 1.03 0.22 4.00 0.37 0.62 0.38 0.41 0.44 1.29 0.59 0.15 5.00 0.49 0.48 0.27 0.64 0.35 1.04 0.55 0.11 6.00 0.35 0.34 0.23 0.41 M 0.73 0.41 0.08 7.00 0.35 0.32 0.19 0.33 0.33 0.88 0.40 0.10 10.00 0.35 0 0.16 0.35 0.34 M 0,24 0.07 13.00 0.33 0.17 0 0.41 M 0.52 0,29 0.09 23.75 0 0 0.17 0.30 0.28 0.43 0.20 0.07 28.00 0 0 0 0.22 0 0.28 0.08 0.05 36.00 0 0 0 0.21 0 0.35 0.09 0.06 48.00 0 0 0 0.19 0 0.17 0.06 0.04 60.00 0 0 0 0 0 0 0 0 72.00 0 0 0 0 0 0 0 0 96.00 0 0 0 0 0 0 0 0 4.0-mg norbuprenorphine-sublingual -0.50 0 0 0 0 0 0 0 0 0.04 0.07 0 0 0 0 0 0.01 0.01 0.08 0.09 0 0 0 0 0.04 0.02 0.02 0.13 0.10 0 0.02 0 0 0.06 0.03 0.02 0.17 0.11 0 0.07 0 0 0.06 0.04 0.02 0.25 0.10 0.13 0,10 0.03 0.04 0.10 0.08 0.02 0.33 0.14 M 0.15 0.05 0.12 0.11 0.11 0.02 0.50 0.16 M 0.16 0,15 0.16 0.12 0.15 0,01 0.75 0.14 0.06 0.26 0.17 0.32 0.23 0.20 0.04 1.00 0,24 0.09 0.25 0.40 0.36 0.34 0.28 0.05 1.50 0.22 0.09 0.15 0.38 0.29 0.59 0.29 0.07 2.00 0.22 0.13 0.12 0.41 0.20 M 0.22 0.05 3.00 0.29 0.12 0.08 0.35 0.14 0.59 0.26 0.08 4.00 0.37 0.16 0.05 0.61 0.17 0.47 0.31 0.09 5.00 0.30 0.14 0.05 0.38 0.14 0.64 0.28 0.09 6.00 0.38 0.11 0.04 0.30 M 0.44 0.25 0.08 7.00 0.42 0.09 0.04 0.21 0,12 0.56 0.24 0.08 10.00 0.40 M 0.04 0.22 0.11 0.16 0.19 0.06 13.00 0.36 0.05 0.02 0.23 M 0.33 0.20 0.07 23.75 0.36 0.05 0.06 0,26 0.04 0.48 0.21 0.08 ' SEM = Standard error of the mean. M = Missing data or measure not taken. spectrometer was operated in the negative chemical ionization mode. Ammonia was the reagent gas, and argon was the collision gas. Collision-induced dissociation spectra were collected in the selected reaction monitoring mode. Collision chamber con- ditions were as follows: argon cell pressure, 2.0 millitorr; buprenorphine and buprenor- phine-d4 collision energy, 24 eV; nor- buprenorphine collision energy, 20 eV; and norcodeine collision energy, 17 eV. Research protocol The research subjects were six men who provided written informed consent and were paid for their participation. The research protocol was approved by the Francis Scott Key Institutional Review Board. The subjects had a history of heroin use but were drug-free at the time of the study. On the basis of physical examination, history, routine laboratory chemistries, and chest x-rays, the participants were in good health and without significant psychiatric disturbances other than drug abuse. The subjects participated while residing on a secured clinical research ward. An initial intravenous dose-escalation study was performed to ensure that the sub- jects could tolerate the higher buprenor- phine doses given during the protocol. The physiologic and subjective effects on these subjects during the intravenous dose esca- lation were reported in a previous publica- tion (19). Buprenorphine was administered in a crossover design study in the following doses and routes of administration: 1.2 mg intravenous, 4.0 mg sublingual, and 4.0 mg buccal. Only one dose was administered to the subjects each week. Intravenous buprenorphine was administered via a catheter in the antecubital vein at a con- stant rate for 1 min. The sublingual prepa- ration, administered by a Ped-Pod (SoloPak Laboratories, Franklin Park, IL) oral dis- penser, consisted of a 30% alcoholic solu- tion that was placed under the tongue for 10 min. The buccal preparation delivery system consisted of a small plastic strip embedded with drug that was placed between the lip and gum for rapid absorp- tion for a period of 10 min. Timed blood samples were collected periodically for 3 days via a catheter in the antecubital vein of the opposite arm from the intravenous dose. 371
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`Journal of Analytical Toxicology, Vol. 20, October 1996 Table I continued. Plasma Concentrations of Buprenorphine and Norbuprenorphine after Buprenorphine Administration by the Intravenous, Sublingual, and Buccal Routes of Drug Administration Time Subject plasma concentrations (ng/mt) (h) A C D E G I Mean SEM 4.0-mg norbuprenorphine-sublingual 28.00 0.35 0.04 0.03 0.20 0.03 0.38 0.17 0.07 36.00 0.34 0 M 0.16 0.03 0.43 0.19 0.08 48.00 0.30 0 0.04 0.14 0 0.48 0.16 0.08 60.00 0.30 0 0.04 0.13 0 0.22 0.12 0.05 72.00 0.17 0 0.03 0.11 0 0.31 0.10 0.05 96.00 0.18 0 0 0.08 0 0.26 0.09 0.05 4.0-mg buprenorphine-buccal q~.50 0 0 0 0 0 0 0 0 0.04 0 0 0.20 0 0 0.79 0.17 0.13 0.08 0 0.18 0.20 0 0 1.31 0.28 0.21 0.13 0 0.34 0.40 0.19 0 2.11 0.51 0.33 0.17 0 0.59 0.75 0.21 0 2.81 0.74 0.43 0.25 0.22 1.02 1.96 0.71 0.17 3.30 1.23 0.49 0.33 0.33 1.62 2.37 0.83 0 3.75 1.48 0.57 0.50 0.42 M 2.32 1.24 0.18 3.90 1.61 0.68 0.75 0.62 2.56 2.24 2.15 0.17 3.67 1.90 0.53 1.00 0.63 2.20 2.18 1.94 0.20 2.68 1.64 0.40 1.50 0.48 1.69 1.51 1.43 0.25 2.32 1.28 0.32 2.00 0.38 1.39 1.04 1.13 M 1.64 1.12 0.21 3.00 0.22 0.78 0.57 0.76 M 0.99 0.66 0.13 4.00 0 0.50 0.37 0.59 M 0.71 0.43 0.12 5.00 0 0.34 0.25 0.43 M 0.63 0.33 0.10 6.00 0 0.29 0.17 0.36 0 0.72 0.26 0.11 7.00 0 0.27 0.15 0.31 0 0.55 0.21 0.09 10.00 0 0.24 0.18 0.25 0 0.46 0.19 0.07 13.00 0 0.27 0 0.27 0 0.33 0.15 0.07 23.75 0 0.19 0 0.24 0 0.21 0.11 0.05 28.00 0 0.22 0 0.20 0 0.28 0.12 0.05 36.00 0 0.18 0 0.25 0 0.24 0.I1 0.05 48.00 0 0 0 0.17 0 0.24 0.07 0.04 60.00 0 0 0 0.17 0 0 0.03 0.03 72.00 0 0 0 0.16 0 0 0.03 0.03 96.00 0 0 0 0 0 0 0 0 4.0-mg norbuprenorphine-buccal -0.50 0 0 0 0 0 0 0 0 0.04 0 0 0 0 0 0.04 0.01 0.01 0.08 0 0 0 0 0 0.18 0.03 0.03 0.13 0 0 0.02 0 0 0.33 0.06 0.05 0.17 0 0 0.03 M 0.02 0.59 0.13 0.12 0.25 0 0 0.11 0.13 0.05 0.81 0.18 0.13 0.33 0 0.02 0.14 0.16 0.03 0.94 0.22 0.15 0.50 0 0.15 0.17 0.28 0.05 0.77 0.24 0.11 0.75 0 0.23 0.20 0.69 0.06 1.26 0.41 0.2 1.00 0 0.23 0.21 0.96 0.09 0.99 0.41 0.18 1.50 0.03 0.24 0.21 0.90 0.17 0.78 0.39 0.15 2.00 0.03 0.37 0.18 0.76 0.10 0.63 0.35 0.12 3.00 0.03 0.24 0.14 0.66 0.08 0.48 0.27 0.1 4.00 0.02 0.20 0.15 0.33 0.08 0.37 0.19 0.06 5.00 0 0.14 0.12 0.34 0.05 0.43 0.18 0.07 6.00 0 0.14 0.11 0.30 0.09 0.31 0.16 0.05 * SEM = Standard error of the mean. t M = Missing data or measure not taken. Collection and analysis of blood specimens Blood samples (5 mL) were collected in heparinized Vacutainer tubes. The samples were centrifuged, and the plasma was trans- ferred to cryotubes and stored frozen until analysis. The plasma samples were analyzed for buprenorphine and norbuprenorphine by negative chemical ionization tandem mass spectrometry according to a previ- ously published procedure (18). Briefly, buprenorphine-d4 and norcodeine were added as internal standards to 1.5 mL of plasma plus 3 mL 100mM phosphate buffer (pH 6). The samples were mixed and cen- trifuged. The supernatant was added to a Clean Screen extraction column that was conditioned with 3 mL methanol, 3 mL water, and 1 mL 100mM phosphate buffer (pH 6). The columns were washed with 2 mL water, 2 mL acetate buffer (pH 4.5), and 3 mL methanol. The drugs were eluted from the column with 4 mL methylene chloride-isopropanol-ammonium hydrox- ide (78:20:2). The eluates were evaporated and derivatized at room temperature with toluene and HFBA. Excess derivatizing reagent was removed by evaporation, and the residue was reconstituted in 20 IAL ethyl acetate. An aliquot (4 IJL) was injected into the GC for MS-MS analysis. Six-point stan- dard curves and controls were analyzed in duplicate. Between-run percent coefficients of variation for a 0.5-ng/mL plasma control sample were as follows: buprenorphine, 12.8% (N = 52) and norbuprenorphine, 20.4% (N = 46). Pharmacokinetic analyses Buprenorphine and norbuprenorphine plasma data were analyzed by nonlinear regression analysis with standard noncom- partmental methods. The analysis was per- formed with PCNONLIN software (Scien- tific Consulting, Apex, NC). The area under the plasma concentration-time curve (AUC) was calculated by the trapezoidal rule. Extrapolation of the AUC to infinity was determined by dividing the last observed plasma concentration by the terminal elim- ination rate constant (ke). The ke was esti- mated via linear regression of the points in the linear portion of the time versus log concentration curve. The elimination half- life was derived from tl/2 (ke)= 0.693/ke. Plasma clearance (CL) after intravenous administration was calculated with the equation 372
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`Journal of Analytical Toxicology, Vol. 20, October 1996 CL - Dose Eq 1 AUC (0 - > oo) The area under the first moment of the plasma concentra- tion-time curve (AUMC) was extrapolated to infinity, and the mean residence time (MRT) was derived from MRT = AUMC/AUC. The intravenous volume of distribution at steady state (Vss) was derived from Vss = CL x MRT. The maximum plasma concentration (Cma~) and the time to maximum plasma concentration (Tm~) were obtained by visual inspection of the plasma concentration versus time curves. Bioavailability (F) was derived according to the equation F = AUC(route) x Dose(intravenous) Eq 2 AUC (intravenous) Dose(route) The average initial volume of distribution divided by the fraction of an absorbed sublingual and buccal dose was calcu- lated from Vd/F = Dose/(AUC x ke). The average total clearance divided by the fraction of an absorbed sublingual and buccal dose was calculated from CL/F = Dose/AUC. Statistics Differences among the three routes of administration were analyzed for statistical significance using a repeated measures single-factor analysis of variance (ANOVA). The ANOVA was used to test the null hypothesis of no significant difference at an alpha level of 0.05. A Newman-Keuls test was used to deter- mine significant differences among pharmacokinetic parame- ters at p < .05. Results Plasma concentrations of buprenorphine and norbuprenor- phine from six male subjects were measured by negative chem- ical ionization tandem mass spectrometry. The technique was Table I continued. Plasma Concentrations of Buprenorphine and Norbuprenorphine after Buprenorphine Administration by the Intravenous, Sublingual, and Buccal Routes of Drug Administration Time Subject plasma concentrations (ng/mt) (h) A C D E G I Mean Table II. Subject Ages and Weights Subject Age (yrs) Weight (Ibs/kg) 4.O-rag norbuprenorphine-buccal 7.00 0 0.16 0.10 0.27 0.06 0.33 10.00 0 0.10 0.10 0.23 0.06 0.22 13.00 0 0.25 0.20 0.26 0.05 0.21 23.75 0 0.21 0.11 0.27 0.03 0.18 28.00 0 0.13 0.10 0.28 0.05 0.21 36.00 0 0.12 0.09 0.29 0.07 0.42 48.00 0 0.07 0.09 0.19 0.08 0.16 60.00 0 0.04 0.09 0.22 0.05 0.17 72.00 0 0 0.11 0.16 0.04 0.09 96.00 0 0 0.05 0.14 0 0.02 * SEM = Standard error of the mean. M = Missing data or measure not taken. A 40 154/69.8 C 34 147/66.7 D* E 36 138/62.6 G 27 160/72.7 I 35 147/66.5 * Information was unavailable. developed to measure both parent drug and metabolite simul- taneously in biological fluids at subnanogram-per-milliliter concentrations. The limit of detection (LOD) for buprenor- phine was 0.15 ng/mL, and the limit of quantitation (LOQ) was 0.20 ng/mL. The LOD for norbuprenorphine was 0.016 ng/mL, and the LOQ was 0.031 ng/mL. Individual subject and mean plasma concentrations of buprenorphine and norbuprenorphine for intravenous, sub- lingual, and buccal routes of administration are presented in Table I. Plasma concentrations less than the LOQ but greater than the LOD were included in Table I. The inclusion of these plasma concentrations allowed better estimates of pharma- cokinetic parameters. Six subjects completed the entire study. Subject ages and weights are presented in Table II. Intravenous buprenorphine data from subject D were lost because of an analytical error, but norbuprenorphine measurements were unaffected. After a 1.2-mg intravenous buprenorphine dose, peak plasma concentrations ranged from 24.40 to 55.98 ng/mL (mean peak, 37.52 ng/mL; N - 5). Individual subject plasma concentrations declined below the assay's LOD between 13 and 48 h. After 4.0-mg buprenorphine doses by the sublin- gual and buccal routes of administration, peak sublingual buprenorphine plasma concentrations occurred at an average time of 0.71 h (range, 0.50-1.00 h; N = 6), and buccal buprenorphine plasma concentrations peaked at an average time of 0.81 h (range, 0.33-1.50 h; N = 6). The average maximum buprenorphine plasma concentration after sublingual ad- ministration was 3.31 ng/mL (range, 1.93-7.19 ng/mL), whereas the average maximum buprenorphine plasma concen- SEM tration after buccal administration was 1.98 ng/mL (range, 0.25-3.90 ng/mL). Both sub- o.15 o.o5 lingual and buccal buprenorphine plasma o.12 o.o4 concentrations were detected for a longer 0.16 o.o4 period of time than the intravenous o.13 o.04 buprenorphine plasma concentrations. The o.13 o.o4 subjects' sublingual buprenorphine plasma o.17 o.o6 concentrations declined below the LOD O.lO o.o3 from 23.75 to 60 h after dose administra- O.lO o.o3 tion, and the buccal plasma buprenorphine o.o7 o.o3 concentrations fell below the LOD from 4 to o.04 o.o2 96 h. Statistical analysis by ANOVA indicated that the buprenorphine peak times and 373
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`peak concentrations were significantly different among the three routes of administration. Intravenous peak times were significantly less (p < .01) and peak concentrations were sig- nificantly greater (p < .01) than sublingual and buccal routes of administration. The N-dealkyl metabolite, norbuprenorphine, appeared in the plasma immediately after intravenous administration in low concentrations and reached an average peak plasma con- centration at 0.18 h. Peak plasma concentrations after intra- venous administration ranged from 0.19 to 1.06 ng/mL (mean, 0.57 ng/mL; N = 6). Norbuprenorphine appeared initially in plasma after sublingual administration in one subject at 0.04 h and in all other subjects at 0.25 h. The average peak con- centration was 0.41 ng/mL (range, 0.16-0.64 ng/mL; N = 6), and the average peak time was 3.63 h. After buccal adminis- tration, norbuprenorphine appeared in one subject at 0.04 h and in all other subjects at 0.33 h, except for subject A. Nor- buprenorphine concentrations peaked after buccal adminis- tration at 1.29 h (range, 0.7-2.00 h; N = 6) at an average con- centration of 0.50 ng/mL (range, 0.03-1.26 ng/mL; N = 6). All three routes of administration had similar peak norbuprenor- phine plasma concentrations, but the peak concentrations occurred at different times. Norbuprenorphine continued to be detected in some subjects' plasma for 96 h. Norbuprenorphine peak concentrations were not signifi- cantly different among the three routes of administration, but Journal of Analytical Toxicology, Vol. 20, October 1996 the time to peak concentration was significantly different. Peak times for norbuprenorphine by the intravenous route were found to be significantly less (p < .01) than by the sublingual route, and the buccal route times were significantly less (p < .05) than by the sublingual route. Pharmacokinetic parameters for each subject after intra- venous, sublingual, and buccal routes of administration are presented in Tables III-V. Buprenorphine AUCs by the intra- venous, sublingual, and buccal routes of administration were not significantly different (p < .05). The elimination half-life by the intravenous route (mean, 3.21 h; range, 1.62-8.18 h) was significantly less (p < .05) than the sublingual elimination half-life, but it was not significantly different than the buccal elimination half-life (p < .05). Comparison of half-lives of buprenorphine by the sublingual (mean, 27.72 h; range, 5.21-49.09 h) and buccal (mean, 19.01 h; range, 1.32-48.63 h) routes indicated that they were not significantly different (p < .05). The average bioavailability for the sublingual route of administration (mean, 51.4%; range, 12.8-92.2%; N = 5) was not significantly different (p < .05) than that observed for the buccal route of administration (mean, 27.8%; range, 4.1-42.7%; N = 4). Estimated elimination half-lives for norbuprenorphine were longer than for buprenorphine. The mean half-lives for nor- buprenorphine were as follows: 35.56 h (range, 1.11-66.78 h) by the intravenous route; 83.0 h (range, 9.7-216.3 h) by the Table III. Pharmacokinetic Parameters* of Buprenorphine and Norbuprenorphine after a Single Intravenous Dose (1.2 rag) of Buprenorphine Parameters Tma ~ Cma x k e tl/2(k e) AUC AUMC MRT CL V~s Subjects (h) (ng/mL} (l/h) (h) (h.ng/mL) (h2.ng/mL) (h) (I/h) (L) No. Obs. AUC(N)/AUC(B) Buprenorphine A 0.04 37.83 0.39 1.77 11.81 29.24 2.48 101.6 251.5 17 C 0.04 43.93 0.43 1.62 21.58 48.39 2.24 55.6 124.6 17 D M* M M M M M M M M M E 0.04 25.60 0.08 8.18 21.36 293.1 13.72 56.2 770.8 21 G 0.04 24.40 0.32 2.17 ]0.41 32.52 3.12 115.3 360.2 17 I 0.04 55.83 0.30 2.31 21.72 65.81 3.03 55.2 167.3 17 Mean 0.04 37.52 0.30 3.21 17.38 93.8 4.92 76.8 334.9 - SEM* 0 5.88 0.06 1.25 2.57 50.24 2.21 13.1 116.2 - Norbuprenorphine A 0.17 0.19 0.26 2.71 0