Rifampicin decreases exposure to sublingual buprenorphine in healthy subjects

Nanoparticle delivery systems for substance use disorder

Innovative breakthroughs in nanotechnology are having a substantial impact in healthcare, especially for brain diseases where effective therapeutic delivery systems are desperately needed. Nanoparticle delivery systems offer an unmatched ability of not only conveying a diverse array of diagnostic and therapeutic agents across complex biological barriers, but also possess the ability to transport payloads to targeted cell types over a sustained period. In substance use disorder (SUD), many therapeutic targets have been identified in preclinical studies, yet few of these findings have been translated to effective clinical treatments. The lack of success is, in part, due to the significant challenge of delivering novel therapies to the brain and specific brain cells. In this review, we evaluate the potential approaches and limitations of nanotherapeutic brain delivery systems. We also highlight the examples of promising strategies and future directions of nanocarrier-based treatments for SUD.

Evaluation of Drug-Drug Interaction Liability for Buprenorphine Extended-Release Monthly Injection Administered by Subcutaneous Route

Buprenorphine extended‐release (BUP‐XR) formulation is a once‐monthly subcutaneous injection for the treatment of opioid use disorder (OUD). Buprenorphine undergoes extensive cytochrome P450 (CYP) 3A4 metabolism, leading to potential drug‐drug interactions (DDIs) as reported for sublingual buprenorphine. Sublingual buprenorphine is subject to first‐pass extraction, as a significant proportion of the dose is swallowed. Because subcutaneous administration avoids first‐pass extraction, the DDI with CYP3A4 inhibitors is expected to be less than the 2‐fold increase reported for the sublingual route. The objective of this analysis was to predict the magnitude of DDI following coadministration of BUP‐XR with a strong CYP3A4 inhibitor or inducer using physiologically based pharmacokinetic (PBPK) modeling. Models were developed and verified by comparing predicted and observed data for buprenorphine following intravenous and sublingual dosing. Comparison of predicted and observed pharmacokinetic (PK) profiles and PK parameters demonstrated acceptable predictive performance of the models (within 1.5‐fold). Buprenorphine plasma concentrations following administration of a single dose of BUP‐XR (300 mg) were simulated using a series of intravenous infusions. Daily coadministration of strong CYP3A4 inhibitors with BUP‐XR predicted mild increases in buprenorphine exposures (AUC, 33%‐44%; C_max, 17‐28%). Daily coadministration of a strong CYP3A4 inducer was also associated with mild decreases in buprenorphine AUC (28%) and C_max (22%). In addition, the model predicted minimal increases in buprenorphine AUC (8%‐11%) under clinical conditions of 2 weeks’ treatment with CYP3A4 inhibitors administered after initiation of BUP‐XR. In conclusion, the PBPK predictions indicate that coadministration of BUP‐XR with strong CYP3A4 inhibitors or inducers would not result in clinically meaningful interactions.

Physiologically-Based Pharmacokinetic (PBPK) Modeling of Buprenorphine in Adults, Children and Preterm Neonates

Buprenorphine plays a crucial role in the therapeutic management of pain in adults, adolescents and pediatric subpopulations. However, only few pharmacokinetic studies of buprenorphine in children, particularly neonates, are available as conducting clinical trials in this population is especially challenging. Physiologically-based pharmacokinetic (PBPK) modeling allows the prediction of drug exposure in pediatrics based on age-related physiological differences. The aim of this study was to predict the pharmacokinetics of buprenorphine in pediatrics with PBPK modeling. Moreover, the drug-drug interaction (DDI) potential of buprenorphine with CYP3A4 and P-glycoprotein perpetrator drugs should be elucidated. A PBPK model of buprenorphine and norbuprenorphine in adults has been developed and scaled to children and preterm neonates, accounting for age-related changes. One-hundred-percent of the predicted AUC_last values in adults (geometric mean fold error (GMFE): 1.22), 90% of individual AUC_last predictions in children (GMFE: 1.54) and 75% in preterm neonates (GMFE: 1.57) met the 2-fold acceptance criterion. Moreover, the adult model was used to simulate DDI scenarios with clarithromycin, itraconazole and rifampicin. We demonstrate the applicability of scaling adult PBPK models to pediatrics for the prediction of individual plasma profiles. The novel PBPK models could be helpful to further investigate buprenorphine pharmacokinetics in various populations, particularly pediatric subgroups.

The optimization of methadone dosing whilst treating with rifampicin: A pharmacokinetic modeling study

BACKGROUND

The use of oral methadone in opioid substitution treatment (OST) for the management of opioid use disorder is established clinical practice. Confounding treatment is the increased risks of contracting Mycobacterium tuberculosis, the mainstay treatment of which incorporates the potent CYP 2B6 inducer rifampicin.

METHODS

This study applied pharmacokinetic modelling using virtual clinical trials, to pharmacokinetically quantify the extent and impact of rifampicin-mediated drug-drug interactions (DDI) on methadone plasma concentrations. An R-methadone model was developed and validated against 11 retrospective clinical studies prior to use in all subsequent studies. The aims were to investigate: (i) the impact of the DDI on daily methadone doses of 60 mg, 90 mg and 120 mg; (ii) dose escalation during rifampicin and (iii) dose reduction following rifampicin cessation.

RESULTS

A dose increase to 160 mg daily during rifampicin treatment phases was required to maintain peak methadone plasma concentrations within a derived therapeutic window of 80-700 ng/mL. Dose escalation prior to rifampicin initiation was not required and resulted in an increase in subjects with supra-therapeutic concentrations. However, during rifampicin cessation, a dose reduction of 10 mg every 2 days commencing prior to rifampicin cessation, ensured that most patients possessed a peak methadone plasma concentration within an optimal therapeutic window.

IMPLICATIONS

Rifampicin significantly alters methadone plasma concentrations and necessitates dose adjustments. Daily doses of almost double those used perhaps more commonly in clinical practice are required for optimal plasma concentration and careful consideration of dose reduction strategies would be required during the deinduction phase.

Unusual Route of Buprenorphine Administration: An Alternative Approach for Bypassing Adverse Drug Reactions

Tramadol abuse is a critical and growing health concern in Asia. In Iran, tramadol abuse arises most commonly as a result of self-medicating that leads to tramadol dependence. Buprenorphine, a partial agonist of mu opioid receptors approved for the treatment of tramadol dependence, is administered sublingually due to its extensive first-pass metabolism and resulting low oral bioavailability. A 50-year-old man presenting with tramadol dependence after self-medicating for chronic low back pain experienced adverse reactions to a minimal dosage (0.8 mg) of sublingual buprenorphine. He was treated successfully with a modified protocol composed of swallowing sublingual tablets (0.2 mg/day initially, which increased to 0.2 mg every 12 hours during maintenance therapy). This unusual case suggests that swallowing buprenorphine sublingual tablets may prevent adverse effects and reduce the rate of treatment dropout.

Voriconazole greatly increases the exposure to oral buprenorphine

PURPOSE

Buprenorphine has low oral bioavailability. Regardless of sublingual administration, a notable part of buprenorphine is exposed to extensive first-pass metabolism by the cytochrome P450 (CYP) 3A4. As drug interaction studies with buprenorphine are limited, we wanted to investigate the effect of voriconazole, a strong CYP3A4 inhibitor, on the pharmacokinetics and pharmacodynamics of oral buprenorphine.

METHODS

Twelve healthy volunteers were given either placebo or voriconazole (orally, 400 mg twice on day 1 and 200 mg twice on days 2-5) for 5 days in a randomized, cross-over study. On day 5, they ingested 0.2 mg (3.6 mg during placebo phase) oral buprenorphine. We measured plasma and urine concentrations of buprenorphine and norbuprenorphine and monitored their pharmacological effects. Pharmacokinetic parameters were normalized for a buprenorphine dose of 1.0 mg.

RESULTS

Voriconazole greatly increased the mean area under the plasma concentration-time curve (AUC_0-18) of buprenorphine (4.3-fold, P < 0.001), its peak concentration (C_max) (3.9-fold), half-life (P < 0.05), and excretion into urine (A_e; P < 0.001). Voriconazole also markedly enhanced the C_max (P < 0.001), AUC_0-18 (P < 0.001), and A_e (P < 0.05) of unconjugated norbuprenorphine but decreased its renal clearance (P < 0.001). Mild dizziness and nausea occurred during both study phases.

CONCLUSIONS

Voriconazole greatly increases exposure to oral buprenorphine, mainly by inhibiting intestinal and liver CYP3A4. Effect on some transporters may explain elevated norbuprenorphine concentrations. Although oral buprenorphine is not commonly used, this interaction may become relevant in patients receiving sublingual buprenorphine together with voriconazole or other CYP3A4 or transporter inhibitors.

Rifampicin decreases exposure to sublingual buprenorphine in healthy subjects

Buprenorphine is mainly metabolized by the cytochrome P450 (CYP) 3A4 enzyme. The aim of this study was to evaluate the role of first‐pass metabolism in the interaction of rifampicin and analgesic doses of buprenorphine. A four‐session paired cross‐over study design was used. Twelve subjects ingested either 600 mg oral rifampicin or placebo once daily in a randomized order for 7 days. In the first part of the study, subjects were given 0.6‐mg (placebo phase) or 0.8‐mg (rifampicin phase) buprenorphine sublingually on day 7. In the second part of the study, subjects received 0.4‐mg buprenorphine intravenously. Plasma concentrations of buprenorphine and urine concentrations of buprenorphine and its primary metabolite norbuprenorphine were measured over 18 h. Adverse effects were recorded. Rifampicin decreased the mean area under the dose‐corrected plasma concentration–time curve (AUC_0–18) of sublingual buprenorphine by 25% (geometric mean ratio (GMR): 0.75; 90% confidence interval (CI) of GMR: 0.60, 0.93) and tended to decrease the bioavailability of sublingual buprenorphine, from 22% to 16% (P = 0.31). Plasma concentrations of intravenously administered buprenorphine were not influenced by rifampicin. The amount of norbuprenorphine excreted in the urine was decreased by 65% (P < 0.001) and 52% (P < 0.001) after sublingual and intravenous administration, respectively, by rifampicin. Adverse effects were frequent. Rifampicin decreases the exposure to sublingual but not intravenous buprenorphine. This can be mainly explained by an enhancement of CYP3A‐mediated first‐pass metabolism, which sublingual buprenorphine only partially bypasses. Concomitant use of rifampicin and low‐dose sublingual buprenorphine may compromise the analgesic effect of buprenorphine.