Plasma Concentrations Of Buprenorphine Research Articles

A Single-Dose Study to Evaluate the Relative Bioavailability, Safety, and Tolerability of Monthly Extended-Release Buprenorphine at Alternative Injection Locations in Adult Participants with Opioid Use Disorder.

Buprenorphine extended-release monthly formulation (BUP-XR, SUBLOCADE®) is approved for treatment of moderate-to-severe opioid use disorder (OUD) following subcutaneous injection in the abdomen. This open-label pharmacokinetic study assessed three alternative injection locations (upper arm, thigh, buttocks) to offer additional flexibility considering the chronic nature of the disease and patient preferences. Following stabilization on 12/3 mg/day of sublingual buprenorphine/naloxone for ≥ 7 days, participants with moderate-to-severe OUD were randomized to receive a single 300-mg BUP-XR injection in the upper arm, thigh, buttocks, or abdomen (reference). Serial blood samples were taken to measure buprenorphine plasma concentrations over 28 days and assess buprenorphine relative bioavailability. Safety evaluations included treatment-emergent adverse events and assessments of injection site pain, tenderness, erythema, induration, and swelling. A total of 88 participants received a single subcutaneous injection of 300-mg BUP-XR in the upper arm (N = 21), thigh (N = 23), buttocks (N = 22), or abdomen (N = 22); 81/88 (92%) completed the study. Buprenorphine plasma exposure (area under the plasma concentration-time curve over 28 days) was comparable across injection site groups with mean buprenorphine plasma concentrations sustained at approximately 2 ng/mL (therapeutic target concentration) or above. Buprenorphine maximum plasma concentration (Cmax) was approximately 39% and 52% higher after injection in the upper arm and thigh, respectively, versus the abdomen, while comparable between buttocks and abdomen. Higher Cmax values were not associated with an increased incidence of adverse events. Safety and injection site tolerability were comparable across injection groups. These pharmacokinetic and safety findings support BUP-XR injection into the upper arm, thigh, and buttocks. Clinicaltrials.gov: NCT05704543.

Effect of buprenorphine delivered by target-controlled infusion on the minimum alveolar concentration of isoflurane in cats

ObjectiveTo characterize the effect of buprenorphine on the minimum alveolar concentration of isoflurane (MACiso) in cats. Study designRandomized, crossover experimental study. AnimalsA group of six healthy 2 to 8 years old male neutered cats, body mass 5.0 ± 0.3 kg. MethodsThe MACiso had been determined in each cat in a previous study. Cats were anesthetized with isoflurane in oxygen. Catheters were placed in a medial saphenous vein for drug and fluid administration and in a jugular vein for blood sampling. Buprenorphine was given intravenously using a target-controlled infusion system to reach and maintain plasma concentrations of 0.5, 1, 2, 4, 8, 16, 32 and 64 ng mL-1 and MACiso was determined in duplicate at each concentration using the tail clamp technique. Four target plasma buprenorphine concentrations were administered on each study day, with at least 2 weeks between experiments. Blood was sampled after the second MAC determination at each target for determination of plasma buprenorphine concentration. ResultsA significant effect of buprenorphine on MAC was found; however, pairwise comparisons to MACiso without buprenorphine did not reach statistical significance. Maximum reduction in MACiso in individual cats ranged from 2 to 34% at plasma buprenorphine concentrations ranging from 0.25 to 8.15 ng mL-1. Conclusions and clinical relevanceAlthough buprenorphine significantly affected MACiso in cats, the magnitude of the effect and the plasma concentration at which the largest effect occurred was highly variable among cats, limiting the clinical usefulness of buprenorphine as an agent to reduce MAC in cats.

A Pharmacologic Evaluation of Buprenorphine in Pregnancy and the Postpartum Period.

The dosing regimen in the package insert for sublingual buprenorphine is similar for pregnant and nonpregnant people despite the physiologic changes seen during pregnancy. To compare plasma buprenorphine pharmacokinetics during and after pregnancy and relate buprenorphine concentration to the pharmacodynamic endpoints of pupil diameter, Clinical Opioid Withdrawal Scale (COWS), and craving scores. Prospective cohort of 22 pregnant people undergoing 33 pharmacologic studies (6-8 hours each) during pregnancy or postpartum. Participants were on a stable daily dose of 2-8 mg sublingual buprenorphine every 6 or 8 hours. The dosing frequency was selected by the participant. On study day, baseline measurements of plasma buprenorphine, pupil diameter, COWS, and craving scores were obtained, then the usual morning dose was taken, and measurements were repeated several times over 1 dosing interval. The dose-normalized area under the plasma buprenorphine concentration time curve was significantly (P = 0.036) lower during pregnancy (155 ± 52 ng × min/mL) than postpartum (218 ± 113 ng × min/mL). Buprenorphine trough concentrations were similar at the start (1.1 ± 0.7 ng/mL) and end of a dosing cycle (1.2 ± 0.8 ng/mL) regardless of dosing frequency. Pupillary diameter, COWS, and craving scores returned to baseline as buprenorphine concentrations approached ~1 ng/mL. Pregnant people require a higher dose of buprenorphine to achieve concentrations comparable to nonpregnant people. There is a temporal relationship between the plasma buprenorphine concentration and the pharmacodynamic markers of pupillary diameter, COWS, and craving scores. An average plasma concentration of ~1 ng/mL was associated with the lowest level of COWS and craving scores.

Pharmacokinetics of Injectable Meloxicam and Buprenorphine in the Naked Mole-Rat (Heterocephalus glaber).

Unique characteristics of the naked mole-rat (NMR) have made it increasingly popular as a laboratory animal model. These rodents are used to study many fields of research including longevity and aging, cancer, circadian rhythm, pain, and metabolism. Currently, the analgesic dosing regimens used in the NMR mirror those used in other rodent species. However, there is no pharmacokinetic (PK) data supporting the use of injectable analgesics in the NMR. Therefore, we conducted 2 independent PK studies to evaluate 2 commonly used analgesics in the NMR: meloxicam (2 mg/kg SC) and buprenorphine (0.1 mg/kg SC). In each study, blood was collected at 8 time points after subcutaneous injection of meloxicam or buprenorphine (0 [predose], 0.25, 0.5, 1, 2, 4, 8, and 24 h). Three NMRs were used per time point for a total of 24 animals per PK study. Plasma concentrations of meloxicam were highest between 0.5 and 1 h postinjection. Levels remained above the extrapolated dog and cat therapeutic threshold levels (390 to 911 ng/mL) for at least 24 h. Plasma concentrations of buprenorphine were highest between 0.25 and 0.5 h postinjection. Levels remained above the human therapeutic threshold (1 ng/mL) for up to 21 h. No skin reactions were seen in association with injection of either drug. In summary, these data support dosing meloxicam (2 mg/kg SC) once every 24 h and buprenorphine (0.1 mg/kg SC) once every 8 to 12 h in the NMR. Further studies should be performed to evaluate the clinical efficacy of these drugs by correlating plasma concentrations with postoperative pain assessments.

Pharmacokinetic Evaluation of a Topical Extended-release Analgesic in Mice.

Mice often undergo painful procedures and surgeries as part of biomedical research protocols. Buprenorphine, a partial μ-opioid receptor agonist and κ receptor antagonist, is commonly used to alleviate the pain associated with such procedures. Due to its pharmacokinetic profile, buprenorphine requires frequent dosing, resulting in handling stress that can impact animal welfare and study data. A long-acting transdermal buprenorphine formulation (LA-bup) was recently approved for use in cats to provide up to 4 d of postoperative analgesia. In this study, we characterized the pharmacokinetics of a single topical dosing of LA-bup in male and female CD-1 mice administered a 0.36-mg or 18-μL topical dose at select time points. Plasma buprenorphine concentrations were evaluated at 0.25, 0.5, 1, 1.5, 2, 4, 8, 24, 48, and 72 h (n = 3 mice/time point) and remained above the purported therapeutic threshold (1 ng/mL) from 1 to 24 h postadministration. Repeated daily dosing at 24 and 48 h demonstrated plasma levels above 1 ng/mL for up to 72 h with minimal accumulation or changes in maximal concentrations over time. Inadvertent transfer of the topical drug to nondosed mice in the same cage was evaluated by measuring plasma buprenorphine concentrations in nondosed mice cohoused with a single-dosed mouse. Male mice did not demonstrate transfer of drug via grooming or interactions, yet 2 out of 26 nondosed female mice had detectable buprenorphine plasma levels indicating a relatively low incidence of cross-ingestion in cohoused female mice. This study demonstrates that LA-bup is a promising analgesic in mice that could be used for tailored analgesia strategies, depending on the surgical model or duration of analgesic therapy.

Plasma concentrations of buprenorphine administered via matrix-type transdermal patches applied at three different anatomical locations in healthy adult horses.

Anatomical location-dependent differences in transdermal opioid penetration are well described in human patients. Although this has been investigated in horses with fentanyl, there is no literature available on location-dependent plasma buprenorphine concentrations when administered as a transdermal matrix-type patch. This study aims to compare the plasma concentrations achieved from the matrix-type transdermal buprenorphine patches placed at different anatomical sites (metacarpus, gaskin, and ventral tail base) in healthy adult horses. This is a randomized experimental study with a Latin square design. Six adult horses were given each of three treatments with a minimum 10-day washout period. For each treatment, two 20 μg h-1 matrix-type buprenorphine patches were applied to the ventral aspect of the tail base (TailTDP), metacarpus region (MetacarpusTDP), or gaskin region (GaskinTDP). Whole blood samples (for determination of buprenorphine concentration) and physiological variables were collected before (0 h) and at 0.5, 2, 4, 6, 8, 10, 12, 16, 24, 32, 48, 56, 72, 96 and 120 h after patches were applied. The patches were removed 96 h following placement and were analyzed for residual buprenorphine content. Buprenorphine concentrations were measured in plasma by LC-MS/MS. A mixed-effects model was used to analyze the physiological variables. Between the three treatment groups, there was no change in physiological variables across timepoints as compared to baseline and when compared to each other in a single horse and between horses (p > 0.3). When comparing all three locations, the buprenorphine uptake was observed to be more consistent with respect to measurable plasma concentrations >0.1 ng ml-1 when applied to the ventral aspect of the tail base. In the TailTDP group, the mean plasma buprenorphine concentrations were >0.1 ng ml-1 from 2 to 32 h. The highest group mean was 0.25 ng ml-1 noted at 4 h. The metacarpal and gaskin regions presented more erratic and inconsistent buprenorphine uptake and plasma concentrations as compared to the ventral aspect of the tail base. Further research must be directed at investigating the optimal dose, achievable duration of analgesia, change in measurable plasma concentrations, and behavioral and systemic effects.

Pharmacokinetics, Fecal Output, and Grimace Scores in Rabbits Given Long-acting Buprenorphine or Fentanyl for Postsurgical Analgesia.

The New Zealand white rabbit (Oryctolagus cuniculus) is a frequently used surgical model. Pain management after surgery is a critical aspect of animal welfare. Recently, a long-acting buprenorphine formulation (Ethiqa XR; EXR) was approved for use in rats and mice but has not yet been investigated in rabbits. The current study aimed to determine whether a single subcutaneous dose of 0.15mg/kg of EXR could achieve and maintain therapeutic buprenorphine plasma concentrations (0.1ng/mL) for 72h in male and female rabbits. We also evaluated the safety profiles of EXR and the fentanyl patch (FP) by assessing fecal output after surgery, because opioids are known to decrease intestinal motility. Behavior and pain scores were compared for rabbits that received either EXR or the FP after undergoing an annulus puncture procedure to induce osteoarthritis. EXR at 0.15mg/kg SC provided a shorter time to onset and sustained analgesia for 72h in male and female rabbits, whereas the FP provided suboptimal analgesia after 48h. Both EXR and FP reduced fecal output after surgery. Output returned to baseline levels within 72h for the EXR group and remained slightly below baseline at 96h after surgery for the fentanyl group. Grimace pain scores revealed no significant difference between treatment groups. These results suggest that EXR is a safe and effective option for postoperative pain management in rabbits.

Evaluation of physical variables, thermal nociceptive threshold testing and pharmacokinetics during placement of transdermal buprenorphine matrix-type patch in healthy adult horses.

Matrix type transdermal buprenorphine patches have not been investigated in horses and may provide an effective means of providing continuous pain control for extended period and eliminating venous catheterization. Assessment of the physiological variables (heart rate, respiratory rate, body temperature) and thermal nociceptive threshold testing, and describing the pharmacokinetic profile of transdermal buprenorphine matrix-type patch (20 μg h-1 and 40 μg h-1 dosing) in healthy adult horses. Randomised experimental study with a Latin-square design. Six adult healthy horses received each of the three treatments with a minimum 10 day washout period. BUP0 horses did not receive a patch (control). BUP20 horses received one patch (20 μg h-1) applied on the ventral aspect of the tail base resulting in a dose of 0.03-0.04 μg kg-1 h-1. BUP40 horses received two patches placed alongside each other (40 μg h-1) on the tail base resulting in a dose of 0.07-0.09 μg kg-1 h-1. Whole blood samples (for determination of buprenorphine concentration), physiological variables and thermal threshold testing were performed before (0 h) and at 2, 4, 8, 12, 16, 24, 32, 40, 48, 56, 64, 72, and 96 h after patch application. The patches were removed 72 h following placement and were analyzed for residual buprenorphine content. Between the three groups, there was no change in physiological variables across timepoints as compared to baseline (p > 0.1). With the higher dose, there was a significant increase in thermal thresholds from baseline values from 2 h until 48 h and these values were significantly higher than the group receiving the lower patch dose for multiple timepoints up to 40 h. 40 μg h-1 patch led to consistent measurable plasma concentrations starting at 2 h up to 96 h, with the mean plasma concentrations of > 0.1 ng/ml from 4 h to 40 h. 20 μg h-1 and 40 μg h-1 patch doses were well tolerated by all horses. At higher dose, plasma buprenorphine concentrations were more consistently measurable and blunted thermal thresholds for 48 h vs. 32 h with 20 μg h-1 dosing as compared to control.

Salivary Therapeutic Monitoring of Buprenorphine in Neonates After Maternal Sublingual Dosing Guided by Physiologically Based Pharmacokinetic Modeling.

Opioid use disorder (OUD) during pregnancy is associated with high mortality rates and neonatal opioid withdrawal syndrome (NOWS). Buprenorphine, an opioid, is used to treat OUD and NOWS. Buprenorphine active metabolite (norbuprenorphine) can cross the placenta and cause neonatal respiratory depression (EC 50 = 35 ng/mL) at high brain extracellular fluid (bECF) levels. Neonatal therapeutic drug monitoring using saliva decreases the likelihood of distress and infections associated with frequent blood sampling. An adult physiologically based pharmacokinetic model for buprenorphine and norbuprenorphine after intravenous and sublingual administration was constructed, vetted, and scaled to newborn and pregnant populations. The pregnancy model predicted that buprenorphine and norbuprenorphine doses would be transplacentally transferred to the newborns. The newborn physiologically based pharmacokinetic model was used to estimate the buprenorphine and norbuprenorphine levels in newborn plasma, bECF, and saliva after these doses. After maternal sublingual administration of buprenorphine (4 mg/d), the estimated plasma concentrations of buprenorphine and norbuprenorphine in newborns exceeded the toxicity thresholds for 8 and 24 hours, respectively. However, the norbuprenorphine bECF levels were lower than the respiratory depression threshold. Furthermore, the salivary buprenorphine threshold levels in newborns for buprenorphine analgesia, norbuprenorphine analgesia, and norbuprenorphine hypoventilation were observed to be 22, 2, and 162 ng/mL. Using neonatal saliva for buprenorphine therapeutic drug monitoring can facilitate newborn safety during the maternal treatment of OUD using sublingual buprenorphine. Nevertheless, the suitability of using adult values of respiratory depression EC 50 for newborns must be confirmed.

Pharmacokinetic-pharmacodynamic analysis of drug liking blockade by buprenorphine subcutaneous depot (CAM2038) in participants with opioid use disorder

Buprenorphine is used to treat opioid use disorder (OUD). Weekly and monthly subcutaneous long-acting buprenorphine injections (CAM2038) provide more stable buprenorphine plasma levels and reduce the treatment burden, misuse, and diversion associated with sublingual transmucosal buprenorphine formulations. To characterize the pharmacokinetic/pharmacodynamic (PK/PD) relationship, a maximum inhibition (Imax) model was developed relating CAM2038 buprenorphine plasma concentration to drug liking maximum effect (Emax) visual analog scale (VAS; bipolar) score after intramuscular hydromorphone administration. Data included time-matched observations of buprenorphine plasma concentration and drug liking Emax VAS score after hydromorphone 18 mg administration in 47 non-treatment-seeking adults with moderate to severe OUD in a phase 2 study. Analysis used non-‍linear mixed-effects modeling (NONMEM®). The final Imax model adequately described the PK/PD relationship between buprenorphine plasma concentration and drug liking Emax VAS score. Simulations showed drug liking was effectively blocked at low buprenorphine plasma concentrations (0.4 ng/mL) where the upper 95% confidence interval of the drug liking Emax VAS score was below the pre-defined 11-point complete blockade threshold. The buprenorphine plasma concentration required to achieve 90% of the maximal effect (IC90) of drug liking was 0.675 ng/mL. Interindividual variability in responses to buprenorphine was observed; some participants experienced fluctuating responses, and a few did not achieve drug liking blockade even with higher buprenorphine plasma concentrations. This affirms the need to individualize treatment and titrate doses for optimal treatment outcomes. PK/PD models were also developed for desire to use VAS and Clinical Opiate Withdrawal Scale (COWS) scores, with results aligned to those for drug liking.

Examining the benefit of a higher maintenance dose of extended-release buprenorphine in opioid-injecting participants treated for opioid use disorder

BackgroundBUP-XR (SUBLOCADE®) is the first buprenorphine extended-release subcutaneous injection approved in the USA for monthly treatment of moderate-to-severe opioid use disorder (OUD). Among patients with OUD, those who inject or use high doses of opioids likely require higher doses of buprenorphine to maximize treatment efficacy. The objective of this analysis was to compare the efficacy and safety of 100-mg versus 300-mg maintenance doses of BUP-XR in OUD patients who inject opioids.MethodsThis was a secondary analysis of a randomized, double-blind, placebo-controlled study in which adults with moderate or severe OUD received monthly injections of BUP-XR (2 × 300-mg doses, then 4 × 100-mg or 300-mg maintenance doses) or placebo for 24 weeks. Abstinence was defined as opioid-negative urine drug screens combined with negative self-reports collected weekly. Each participant’s percentage abstinence was calculated after the first, second, and third maintenance doses in opioid-injecting and non-injecting participants. The proportion of participants achieving opioid abstinence in each group was also calculated weekly. Treatment retention rate following the first maintenance dose was estimated for opioid-injecting participants with Kaplan–Meier method. Risk-adjusted comparisons were made via inverse propensity weighting using propensity scores. Buprenorphine plasma concentration–time profiles were compared between injecting and non-injecting participants. The percentages of participants reporting treatment-emergent adverse events were compared between maintenance dose groups within injecting and non-injecting participants separately.ResultsBUP-XR 100-mg and 300-mg maintenance doses were equally effective in non-injecting participants. However, in opioid-injecting participants, the 300-mg maintenance dose delivered clinically meaningful improvements over the 100-mg maintenance dose for treatment retention and opioid abstinence. Exposure–response analyses confirmed that injecting participants would require higher buprenorphine plasma concentrations compared to non-injecting opioid participants to achieve similar efficacy in terms of opioid abstinence. Importantly, both 100- and 300-mg maintenance doses had comparable safety profiles, including hepatic safety events.ConclusionsThese analyses show clear benefits of the 300-mg maintenance dose in injecting participants, while no additional benefit was observed in non-injecting participants relative to the 100-mg maintenance dose. This is an important finding as opioid-injecting participants represent a high-risk and difficult-to-treat population. Optimal buprenorphine dosing in this population might facilitate harm reduction by improving abstinence and treatment retention.Trial registration: ClinicalTrials.gov, NCT02357901.

Buprenorphine plasma and cerebrospinal fluid concentrations in osteoarthritis patients during low-dose transdermal patch dosing

MethodsFifty-six (56) patients scheduled for arthroplasty, received 7-day extended-release buprenorphine transdermal patches (5 µg/h) for five consecutive weeks, starting two weeks prior to the surgery. Simultaneous plasma and cerebrospinal fluid (CSF) samples were collected during spinal anesthesia.ResultsMedian buprenorphine plasma and CSF concentrations at steady-state were 54 pg/mL (range 8.6 – 167 pg/mL) and 1.6 pg/mL (0.30 – 7.3 pg/mL), respectively. The median CSF/plasma -ratio was 3% (range 0.35 – 16%). Large between-subject variability was observed in the measured buprenorphine concentrations within the study population.

Population Pharmacokinetic Analysis Supports Initiation Treatment and Bridging from Sublingual Buprenorphine to Subcutaneous Administration of a Buprenorphine Depot (CAM2038) in the Treatment of Opioid Use Disorder.

In treating opioid use disorder (OUD), subcutaneous (SC) extended-release buprenorphine (BPN) depots, e.g.,CAM2038, have been shown to provide smaller and less frequent fluctuations in BPN plasma concentrations and pharmacodynamic responses, improve outcomes, reduce treatment burden, and lower risks of misuse and diversion compared to daily sublingual (SL) BPN. This analysis characterized the pharmacokinetics (PK) of BPN following intravenous and SL administration, and administration of SC CAM2038 weekly and monthly. Pharmacokinetic data from two Phase 1 and two Phase 2 trials in healthy participants and participants with OUD, respectively, were used to develop a population PK model using non-linear mixed effects modelling. The analysis included data from 252 participants and 10,658 BPN observations. The disposition of BPN was best described by a three-compartment model with first-order elimination, and absorption of SL BPN and SC CAM2038 weekly and monthly by dual parallel absorption pathways. Model diagnostics indicated good predictive performance of BPN concentrations. Buprenorphine plasma concentration-time profiles were simulated for treatment initiation, switching from SL BPN to CAM2038 weekly and monthly, and tapering after interrupting treatment with CAM2038. Simulations predicted CAM2038 weekly and monthly doses that provided BPN plasma maximum concentration (Cmax) and trough concentration (Ctrough) values at steady state within those observed following SL BPN administration. This population PK model supports the use of CAM2038 doses as individualized treatment for OUD across different treatment stages, including initiation, switching from SL BPN according to established dose conversion schedules, and tapering. ISRCTN41550730 (05/19/2014), ISRCTN24987553 (07/29/2014), NCT02611752 (11/23/2015), NCT02710526 (03/16/2016).

High-concentration buprenorphine exceeds target plasma concentrations for extended periods following subcutaneous administration in American flamingos (Phoenicopterus ruber).

To determine the pharmacokinetic parameters of a high-concentration buprenorphine formulation after a single SC dose in American flamingos (Phoenicopterus ruber). 6 healthy adult American flamingos (3 males and 3 females). A single dose of high-concentration buprenorphine (1.8 mg/kg) was administered SC to all birds. Blood samples were collected at 0.25, 0.5, 1, 2, 4, 8, 12, 24, 48, 72, and 96 hours after drug administration between October 14 and October 18, 2022. Plasma buprenorphine concentrations were determined by liquid chromatography-tandem mass spectrometry and a noncompartmental analysis was used to determine pharmacokinetic parameters. Mean ± SD peak plasma drug concentration (Cmax) was 195.1 ± 187.4 ng/mL, the mean time to peak plasma concentration (Tmax) was 0.32 ± 0.31 hours, the mean area under the concentration-vs-time curve from time 0 to the last measured concentration (AUC0-last) was 881.4 ± 205.4 ng/mL, and mean terminal half-life (t1/2) was 12.6 ± 3.86 hours. Mean plasma buprenorphine concentrations were >1 ng/mL for at least 48 hours after drug administration. No clinically significant adverse effects were observed. High-concentration buprenorphine dosed at 1.8 mg/kg SC in American flamingos rapidly exceeded plasma drug concentrations reported to have analgesic effects in other avian species and maintained these levels for extended periods. Sedative effects were similar to those reported for other species. Additional studies are needed to evaluate the clinical efficacy of high-concentration buprenorphine at this dose in American flamingos.

Evaluation and comparison of pharmacokinetic profiles and safety of two extended-release buprenorphine formulations in common marmosets (Callithrix jacchus)

While sustained-release buprenorphine (BSR) is used as a long-lasting opioid analgesic in common marmosets (Callithrix jacchus), there are no published studies on pharmaceutical-grade extended-release buprenorphine options such as Ethiqa XR (EXR) for this species. However, BSR is a compounded product and has been reported to cause injection site reactions in multiple species, including marmosets. Additionally, now with the availability of EXR, a pharmaceutical-grade veterinary product, the use of BSR in laboratory animals is not compliant with the Guide for the Care and Use of Laboratory Animals (Guide) unless scientifically justified and approved by the IACUC. We compared pharmacokinetic and safety profiles of BSR (0.15 mg/kg) and EXR (0.1–0.2 mg/kg) administered subcutaneously to adult marmosets. Blood was collected by venipuncture of the saphenous vein at multiple time points (0.25–72 h) and analyzed by liquid chromatography-tandem mass spectrometry (LC–MS/MS). EXR between 0.1 and 0.2 mg/kg resulted in a dose-dependent increase in Cmax (1.43–2.51 ng/mL) and were not statistically different from BSR (1.82 ng/mL). Tmax, lambdaz, and t1/2 were not statistically different between formulations. Mean plasma buprenorphine concentrations for BSR and EXR exceeded the therapeutic threshold (0.1 ng/mL) within 0.25 h and lasted for > 72 h. Mild sedation, but neither respiratory depression nor ataxia, was observed for both formulations. BSR injection sites had significantly higher histopathological scores compared to EXR. Video recordings for monitoring drug-induced behavioral changes showed increased animal activity levels after BSR and EXR versus saline controls. Norbuprenorphine, a buprenorphine metabolite associated with respiratory depression, was detected in the plasma after BSR and EXR administration as well as by in vitro liver microsome assays. In conclusion, we recommend using EXR over BSR as a long-lasting buprenorphine analgesic in marmosets because EXR is a pharmaceutical-grade formulation that is compliant with FDA guidelines and the Guide as well as exhibits comparable PK and safety profiles as BSR.

Comparative Pharmacokinetics and Injection Site Histopathology in Nude Mice Treated with Long-acting Buprenorphine Formulations.

Two long-acting formulations of buprenorphine are commercially available as analgesics for rodents. However, these drugs have not yet been studied in nude mice. We sought to investigate whether the manufacturer-recommended or labeled mouse doses of either drug would provide and sustain the purported therapeutic plasma concentration of buprenorphine (1 ng/mL) over 72 h in nude mice and to characterize the injection site histopathology. NU/NU nude and NU/+ heterozygous mice were subcutaneously injected with extended-release buprenorphine polymeric formulation (ER; 1 mg/kg), extendedrelease buprenorphine suspension (XR; 3.25 mg/kg), or saline (2.5 mL/kg). Plasma concentrations of buprenorphine were measured 6, 24, 48, and 72 h after injection. The injection site was examined histologically at 96 h after administration. XR dosing yielded significantly higher plasma buprenorphine concentrations than did ER dosing at every time point in both nude and heterozygous mice. No significant difference in plasma buprenorphine concentrations were detected between nude and heterozygous mice. Both formulations yielded plasma levels of buprenorphine of over 1 ng/mL at 6 h; XR sustained buprenorphine plasma levels above 1 ng/mL for over 48 h, whereas ER sustained this level for over 6 h. Injections sites of both formulations were characterized by a cystic lesion with a fibrous/fibroblastic capsule. ER induced more inflammatory infiltrates than did XR. This study indicates that while both XR and ER are suitable for use in nude mice, XR has a longer duration of likely therapeutic plasma levels and induces less subcutaneous inflammation at the injection site.

Pharmacokinetics of Extended-release Buprenorphine in Mongolian Gerbils (Meriones unguiculatus).

Both the Guide for the Care and Use of Laboratory Animals and the Animal Welfare Act and Regulations require animals in research to receive adequate analgesia unless an exception can be scientifically justified and IACUC approved. Extended- release buprenorphine (BUP-XR) is a pharmaceutical-grade formulation that is FDA-indexed for use in mice and rats. However, this new formulation has not been evaluated in adult Mongolian gerbils (Meriones unguiculatus). Our goal was to determine whether the extrapolated dose (1 mg/kg SC) would achieve plasma buprenorphine concentrations above the murine therapeutic threshold (> 1.0 ng/mL) in male and female gerbils. We hypothesized that BUP-XR administered at 1 mg/kg would achieve the murine therapeutic threshold in both male and female gerbils until at least 48 h after injection. Gerbils received one injection of BUP-XR (1 mg/kg SC) and underwent 4 serial blood collections (0.5, 1, 2, and 4, or 0.5, 24, 48, and 72 h after injection). The average plasma buprenorphine concentrations were above 1 ng/mL within 30 min of administration for both males and females. Plasma buprenorphine concentrations remained above 1.0 ng/mL for 48 h after administration. In males, plasma buprenorphine concentrations were significantly higher at 1 h after injection as compared with females; no other significant differences were observed between sexes. Mild to moderate injection-site granulomas were observed in five of nine gerbils, presumably due to the lipid matrix of the BUP-XR formulation. Our findings demonstrate that a single BUP-XR dose (1 mg/kg SC) achieves plasma buprenorphine levels that remain above the murine therapeutic threshold of 1.0 ng/mL for up to 48 h in both sexes.

Buprenorphine exposure levels to optimize treatment outcomes in opioid use disorder.

The severity of the ongoing opioid crisis, recently exacerbated by the COVID-19 pandemic, emphasizes the importance for individuals suffering from opioid use disorder (OUD) to have access to and receive efficacious, evidence-based treatments. Optimal treatment of OUD should aim at blocking the effects of illicit opioids while controlling opioid craving and withdrawal to facilitate abstinence from opioid use and promote recovery. The present work analyses the relationship between buprenorphine plasma exposure and clinical efficacy in participants with moderate to severe OUD using data from two clinical studies (39 and 504 participants). Leveraging data from placebo-controlled measures assessing opioid blockade, craving, withdrawal and abstinence, we found that buprenorphine plasma concentrations sustained at 2-3ng/ml (corresponding to ≥70% brain mu-opioid receptor occupancy) optimized treatment outcomes in the majority of participants, while some individuals (e.g., injecting opioid users) needed higher concentrations. Our work also included non-linear mixed effects modeling and survival analysis, which identified a number of demographic, genetic and social factors modulating treatment response and retention. Altogether, these findings provide key information on buprenorphine plasma levels that optimize clinical outcomes and increase the likelihood of individual treatment success. NLM identifiers: NCT02044094, NCT02357901.

Pharmacokinetics of Sustained-release and Extended-release Buprenorphine in Mice after Surgical Catheterization.

The Guide for the Care and Use of Laboratory Animals strongly encourages the use of pharmaceutical-grade chemicals and analgesics. Sustained-release buprenorphine (SRB) is administered extralabel to rodents to mitigate moderate to severe pain. An FDA-indexed buprenorphine formulation-extended-release buprenorphine (XRB)-has recently become available and is currently the only pharmaceutical-grade slow-release buprenorphine formulation approved for use in mice and rats. However, no studies have directly compared the pharmacokinetic parameters of SRB and XRB in surgically catheterized mice. To this end, we compared the plasma buprenorphine concentrations and pharmacokinetic parameters of SRB and XRB in mice after surgical catheterization. We hypothesized that mice treated before surgery with SRB or XRB would have circulating buprenorphine concentrations that exceeded the therapeutic threshold for as long as 72 h after surgery. Male and female C57Bl/6J mice were anesthetized, treated with a single dose of either SRB (1 mg/kg SC) or XRB (3.25 mg/kg SC), and underwent surgical catheterization. Arterial blood samples were collected at 6, 24, 48, and 72 h after administration. Weight loss after surgery (mean ± SEM) was similar between groups (SRB: males, 12% ± 2%; females, 8% ± 2%; XRB: males, 12% ± 1%; females, 8% ± 1%). Both SRB and XRB maintained circulating buprenorphine concentrations above the therapeutic level of 1.0 ng/mL for 72 h after administration. Plasma buprenorphine concentrations at 6, 24, and 48 h were significantly greater (3- to 4-fold) with XRB than SRB, commensurate with XRB's higher dose. These results support the use of either SRB or XRB for the alleviation of postoperative pain in mice. The availability of FDA-indexed XRB increases options for safe and effective pharmaceutical-grade analgesia in rodents.

Single-dose pharmacokinetics and bioavailability of a novel extended duration transdermal buprenorphine solution in cats.

A novel transdermal buprenorphine solution (TBS) was developed for evaluation in order to make available an extended duration opioid analgesic for cats. Healthy adult cats were administered a single TBS dose of 10mg (1.57-4.35mg/kg), 30mg (4.72-13.0mg/kg), or 50mg (7.87-21.7mg/kg) (4 cats per group) applied topically to the unclipped dorsal cervical skin and plasma buprenorphine concentrations were evaluated through 7days. To determine the absolute bioavailability of TBS, healthy cats were administered single TBS dose of 20mg (3.33-4.76mg/kg) or 0.05mg (0.008-0.011mg/kg) IV buprenorphine (6 cats per group). The mean±standard deviation maximum plasma buprenorphine concentrations (Cmax ) were 10.5±6.28, 18.6±8.68, and 22.5±4.47ng/ml following 10, 30, and 50mg doses, respectively, with the time of Cmax occurrence (tmax ) typically occurring at 2-12h post-dosing. Mean plasma buprenorphine terminal half-lives ranged between 78.3 and 91.2h. Increasing the dose threefold and fivefold from the 10mg dose increased the exposure by 2.8- and 3.6-fold, respectively, indicating that plasma buprenorphine exposure increased in a less than proportional manner at doses >30mg. Transient sedation, mydriasis, and euphoria were observed within 4h post-dosing. Mean rectal temperatures were increased 0.6-0.9°C greater than baseline (37.4-37.8°C) through 168h post-dosing. The absolute bioavailability was 16.0% (90% CI: [11.8%-21.7%]). Flip-flop pharmacokinetics were observed with a terminal elimination half-life of 0.82±0.13 and 64.9±15.0h for IV buprenorphine and 20mg of TBS, respectively. A single administration of TBS over a range of doses resulted in extended plasma buprenorphine concentrations and opioid physiological and behavioral effects.