Determination of buprenorphine, naloxone and phase I and phase II metabolites in rat whole blood by LC-MS/MS.

Buprenorphine and buprenorphine/naloxone combination are maintenance treatments used worldwide. However, since their marketing, despite ceiling respiratory effects, poisonings and fatalities have been attributed to buprenorphine misuse and overdose. Therefore, to better understand the mechanisms of buprenorphine-related toxicity in vivo, experimental investigations have been conducted, mainly in the rat. We developed a liquid chromatographic-tandem mass spectrometric (LC-MS/MS) method with electrospray ionization for the simultaneous quantification of buprenorphine, naloxone and their metabolites (norbuprenorphine, buprenorphine glucuronide, norbuprenorphine glucuronide and naloxone glucuronide) in rat whole blood. Compounds were extracted from whole blood by protein precipitation and chromatographically separated using gradient elution of aqueous ammonium formate and methanol in a Raptor Biphenyl core-shell column (100 mm x 3,0 mm x 2,7 µm). Following electrospray ionization, quantification was carried out in the multiple reaction monitoring (MRM) mode by the tandem mass spectrometer API 3200 system. The LC-MS/MS method was validated according to the currently accepted criteria for bioanalytical method validation. The method required small sample volumes (50 µL) and was sensitive with limits of quantification of 6.9, 6.2, 3.6, 3.3, 1.3 and 57.7 ng/mL for buprenorphine, norbuprenorphine, buprenorphine glucuronide, norbuprenorphine glucuronide, naloxone and naloxone glucuronide respectively. The upper limit of quantification was 4000 ng/ml for all the studied compounds. Trueness (88-115 %), repeatability and intermediate precision (both <15%) were in accordance with the international recommendations. The procedure was successfully used to quantify these compounds in the whole blood sample from one rat 24 h after the intravenous administration of buprenorphine/naloxone (30.0/7.5 mg/kg).

Is the 3,4-methylendioxypyrovalerone/mephedrone combination responsible for enhanced stimulant effects? A rat study with investigation of the effect/concentration relationships.

RATIONALE: The use of synthetic cathinones as recreational drugs frequently sold in combination has been increasing exponentially. However, the consequences of combining cathinones on the resulting stimulant effects and the pharmacokinetics have been poorly investigated. OBJECTIVE AND METHODS: To study 3,4-methylenedioxypyrovalerone (MDPV; 3 mg/kg) and mephedrone (4-MMC; 30 mg/kg)-induced effects on rat locomotor activity and pharmacokinetics, administered alone or in combination by the intragastric route. The pharmacokinetic parameters were determined using non-compartmental analysis and the relationships between the locomotor activity and drug concentrations using sigmoidal Emax modeling. RESULTS: Locomotor activity significantly increased during the first hour post-administration with the MDPV/4-MMC combination in comparison to MDPV (p < 0.001) and 4-MMC (p < 0.01) alone. The pharmacokinetic profile of MDPV, but not 4-MMC, was significantly modified with the combination resulting in decreases in Cmax (16.4 ± 5.5 versus 62.2 ± 14.2 µg/L, p < 0.05) and AUC0 → ∞ (708 ± 91 versus 3316 ± 682 µg/L/min, p < 0.01) and increases in V/F (582.6 ± 136.8 versus 115.9 ± 42.7 L/kg, p < 0.05) and Cl/F (4.6 ± 0.7 versus 1.2 ± 0.4 L/kg/min, p < 0.01) in comparison to MDPV alone. The sigmoidal Emax model fitted the observed data well; MDPV being markedly more potent than 4-MMC (EC50, 0.043 versus 0.7 µmol/L). The enhancing factor representing the MDPV contribution to the alteration in the relationships between locomotor activity and 4-MMC concentrations was 0.3. CONCLUSION: An MDPV/4-MMC combination results in enhanced stimulant effects in the rat, despite significant reduction in MDPV bioavailability. Enhanced effects could be explained by increased MDPV distribution and/or possible complementation at the brain dopaminergic targets. However, the exact consequences of the MDPV/4-MMC combination in humans remain to be clarified.

Illicit Drugs in Oral Fluid: Evaluation of Two Collection Devices.

Driving after illicit drug use is a worldwide growing concern requiring rapid and sensitive screening at the roadside. It is noteworthy that the sampling method used to collect oral fluid (OF) may significantly influence drug concentrations in the collected sample and thus alter the accuracy of the measurement. We evaluated two OF collection devices, Quantisal® and Certus® collectors, for their suitability for collecting samples to allow laboratory confirmation of driving after illicit drug use. Four parameters were studied including (i) the collected OF volume; (ii) the recovery efficiency using OFs spiked with opiates, cannabinoids, amphetamines, cocaine and its metabolites; (iii) drug stability after storage for 1, 7 and 14 days at -20°C, +4°C and room temperature; and (iv) the impact of mouth cells present in the collected OF on drug stability. Drug concentrations were measured using gas and liquid chromatography-mass spectrometry. Certus® collector allowed the collection of significantly larger (0.94 ± 0.18 mL vs. 0.84 ± 0.06 mL, P = 0.08) but less reproducible OF volumes (19 vs. 6.7%) compared with Quantisal® collector. Drug recovery was significantly better with Quantisal® than with Certus® collector, especially when used to detect cannabinoids (0.94 vs. 0.54, P < 0.001 for ∆9-tetrahydrocannabinol (THC)). For both OF collectors, storage at 4°C was preferable except for methadone, the stability of which was altered by adherence to the collector device. In the presence of mouth cells in the OF sample, THC concentrations were significantly decreased at Day 7 in comparison with Day 1 with both collection devices (P = 0.001 with Quantisal® collector and P = 0.01 with Certus® collector). In conclusion, Quantisal® collector is more reliable than Certus® collector although the practicability of both devices remains to be determined at the roadside.

Editor's Highlight: Neurorespiratory Effects of Buprenorphine and Ethanol in Combination: A Mechanistic Study of Drug-Drug Interactions in the Rat.

Respiratory depression and fatalities have been attributed to ethanol/buprenorphine (BUP) combination in drug addicts maintained with BUP/naloxone or BUP alone. The exact mechanisms of the ethanol/BUP interaction and the contribution to the toxicity of norbuprenorphine (NBUP), the main BUP metabolite with respiratory depressant properties are unknown. We investigated the sedative and plethsymographic effects resulting from the co-administration of intragastric ethanol (3 g/kg) and intravenous BUP (30 mg/kg) in Sprague-Dawley rats. We determined the whole blood pharmacokinetics of ethanol (using gas chromatography coupled to mass spectrometry), BUP and its metabolites (using liquid chromatography coupled to tandem mass spectrometry) and investigated the mechanisms of drug-drug interactions in the presence or absence of naloxone (7.5 mg/kg). Ethanol/BUP and ethanol/BUP/naloxone combinations significantly deepened sedation in comparison to BUP alone (P < .01) and BUP/naloxone (P < .05), respectively. Ethanol/BUP combination significantly increased the inspiratory time and decreased the minute volume in comparison to BUP alone (P < .01 and P < .01, respectively) and ethanol/BUP/naloxone (P < .05 and P < .01, respectively). Neither naloxone nor flumazenil reversed ethanol/BUP-induced sedation and respiratory depression. In the presence of ethanol, the area under the BUP concentration-time curve was significantly decreased (P < .05), BUP volume of distribution increased (P < .05) and the metabolic ratios of NBUP and norbuprenorphine-3-glucuronide increased (P < .01). In conclusion, the ethanol/BUP combination results in marked sedation and respiratory depression in the rat, prevented but not reversed by naloxone. Ethanol/BUP interactions are mainly pharmacokinetic resulting in increased NBUP production. Despite the non-reversal by naloxone and flumazenil of the effects attributed to the ethanol/BUP combination, protection provided by naloxone suggests an additional pharmacodynamic interaction.

Respiratory effects of buprenorphine/naloxone alone and in combination with diazepam in naive and tolerant rats.

Respiratory depression has been attributed to buprenorphine (BUP) misuse or combination with benzodiazepines. BUP/naloxone (NLX) has been marketed as maintenance treatment, aiming at preventing opiate addicts from self-injecting crushed pills. However, to date, BUP/NLX benefits in comparison to BUP alone remain debated. We investigated the plethysmography effects of BUP/NLX in comparison to BUP/solvent administered by intravenous route in naive and BUP-tolerant Sprague-Dawley rats, and in combination with diazepam (DZP) or its solvent. In naive rats, BUP/NLX in comparison to BUP significantly increased respiratory frequency (f, P<0.05) without altering minute volume (VE). In combination to DZP, BUP/NLX significantly increased expiratory time (P<0.01) and decreased f (P<0.01), tidal volume (VT, P<0.001), and VE (P<0.001) while BUP only decreased VT (P<0.5). In BUP-tolerant rats, no significant differences in respiratory effects were observed between BUP/NLX and BUP. In contrast, in combination to DZP, BUP/NLX did not significantly alter the plethysmography parameters, while BUP increased inspiratory time (P<0.001) and decreased f (P<0.01) and VE (P<0.001). In conclusion, differences in respiratory effects between BUP/NLX and BUP are only significant in combination with DZP, with increased depression in naive rats but reduced depression in BUP-tolerant rats. However, BUP/NLX benefits in humans remain to be determined.