Mu-Opioid Receptor Occupancy and Association With Opioid Blockade

In a Positron Emission Tomography (PET) study with SUBLOCADE in 2 subjects (one subject receiving 200 mg subcutaneous injections and one subject receiving 300 mg subcutaneous injections) with opioid use disorder, 75 to 92% occupancy of the mu-opioid receptors in the brain was maintained for 28 days following the last dose under steady-state conditions.

The opioid blockade study evaluated the blockade of subjective opioid effects, pharmacokinetics (PK) and safety of subcutaneous injections of SUBLOCADE. Stabilization doses of SL buprenorphine prior to injection of SUBLOCADE failed to provide full blockade of subjective effects of hydromorphone 18 mg IM. After SUBLOCADE injections at Weeks 0 and 4, on average, subjective effects of both 6 mg and 18 mg doses of hydromorphone were blocked; however, wide variability was seen across subjects. Complete blockade continued throughout the 8 weeks of observation that followed the 2 ndSUBLOCADE injection [see Clinical Studies ( 14.1)] . 

Figure 10illustrates the relationship between buprenorphine plasma level and drug liking after 18 mg hydromorphone IM. 

Figure 10 Drug Liking VAS vs. Plasma Buprenorphine Concentration Following 18 mg Hydromorphone Challenges

Exposure-response relationships were assessed for illicit opioid use, based on urine samples negative for illicit opioids combined with self-reports negative for illicit opioid use, and withdrawal symptoms using data obtained from 489 opioid dependent patients in the double-blind Phase 3 Study (13-0001).

The observed plateau for maximal response was reached at buprenorphine plasma concentrations of approximately 2-3 ng/mL for illicit opioid use and 4 ng/mL for opioid withdrawal symptoms.

Population PK/PD modeling indicated that patients using opioids by the injectable route at baseline may require higher buprenorphine exposure compared to patients not using opioids by the injectable route at baseline.

Cardiac Electrophysiology

Serial ECGs were collected following a single dose and at steady-state to evaluate the effect of SUBLOCADE on the QT interval in five clinical studies including the Phase 3 study. In a Phase 3 study, seven patients had an increase from baseline QTc greater than 60 msec at any time [2/203 patients (1.0%) in the 300 mg/100 mg group and 5/201 patients (2.0%) in the 300 mg/300 mg group] and one patient in the 300 mg/300 mg group was found to have a QTc greater than 500 msec. These QTc findings were all sporadic and transient and none led to aberrant ventricular rhythm. Review of ECG and adverse event data provided no evidence for syncope, seizure, or ventricular tachycardia or fibrillation.

Physiological Effects

Buprenorphine in IV (2, 4, 8, 12 and 16 mg) and sublingual (12 mg) doses have been administered to opioid-experienced subjects who were not physically dependent to examine cardiovascular, respiratory, and subjective effects at doses comparable to those used for treatment of opioid dependence. Compared to placebo, there were no statistically significant differences among any of the treatment conditions for blood pressure, heart rate, respiratory rate, O 2saturation, or skin temperature across time. Systolic BP was higher in the 8 mg group than placebo (3 hour AUC values). Minimum and maximum effects were similar across all treatments. Subjects remained responsive to low voice and responded to computer prompts. Some subjects showed irritability, but no other changes were observed. The respiratory effects of sublingual buprenorphine were compared with the effects of methadone in a double-blind, parallel group, dose ranging comparison of single doses of buprenorphine sublingual solution (1, 2, 4, 8, 16, or 32 mg) and oral methadone (15, 30, 45, or 60 mg) in non-dependent, opioid-experienced volunteers. In this study, hypoventilation not requiring medical intervention was reported more frequently after buprenorphine doses of 4 mg and higher than after methadone. Both drugs decreased O 2saturation to the same degree. 

In clinical studies conducted with SUBLOCADE at doses ranging from 50 to 300 mg, no incidences of temperature elevations, or clinically significant lowering of oxygen saturation were observed.

Androgen Deficiency 

Chronic use of opioids may influence the hypothalamic-pituitary-gonadal axis, leading to androgen deficiency that may manifest as low libido, impotence, erectile dysfunction, amenorrhea, or infertility. The causal role of opioids in the clinical syndrome of hypogonadism is unknown because the various medical, physical, lifestyle, and psychological stressors that may influence gonadal hormone levels have not been adequately controlled for in studies conducted to date. Patients presenting with symptoms of androgen deficiency should undergo laboratory evaluation.

Pharmacodynamic Interaction with Fentanyl

An open-label, cross-over study was conducted in 8 opioid-tolerant subjects to assess the ability of intravenous buprenorphine to prevent respiratory depression associated with high doses of fentanyl administered in a clinical setting. Opioid-tolerant subjects were medically stable and taking oral morphine equivalents of ≥ 90 mg daily with no other CNS depressant use. Buprenorphine infusions at three dose levels and placebo infusions were administered, followed by up to four doses of fentanyl. The three intravenous buprenorphine dose levels were designated as low (0.25 mg/70kg bolus + 0.1 mg/70kg/hr), mid (0.5 mg/70kg bolus + 0.2 mg/70kg/hr), and high (1.25 mg/70kg bolus + 0.5 mg/70kg/hr). The low, mid, and high buprenorphine dose levels produced average plasma concentrations (from 2 hours to 6 hours after infusion onset) of 1.06 ng/mL, 2.26 ng/mL, and 6.04 ng/mL, respectively.

Escalating intravenous fentanyl boluses of 0.25, 0.35, 0.50 and 0.70 mg/70 kg (up to a maximum cumulative dose of 1.8 mg/70 kg) were administered over 90 seconds at + 2hr, + 3hr, + 4hr and + 5hr after the start of intravenous infusion of buprenorphine or placebo. Apnea events after each fentanyl bolus are shown in Figure 11. Four of the 8 subjects in the placebo infusion groups discontinued prior to the fourth fentanyl bolus because of apnea (2 after the second bolus and 2 after the third bolus); 3 of the remaining 4 subjects experienced apnea after the fourth fentanyl dose. All 8 subjects in the buprenorphine infusion groups completed the fentanyl boluses and 2 of the 8 experienced apnea. 

Figure 11 Occurrence of Apnea Events After Fentanyl Doses in a Pharmacodynamic Interaction Study

There were 2 opioid-tolerant subjects in the low intravenous buprenorphine (BUP) group (Arm A), 3 in the mid BUP group (Arm B), and 3 in the high BUP group (Arm C). The numbers in parentheses represent the geometric mean of buprenorphine plasma concentrations in each group from 2 hours to 6 hours after infusion onset. The escalating fentanyl doses 1 to 4 were 0.25, 0.35, 0.50 and 0.70 mg/70 kg body weight. The same subject in the low BUP group had apnea after the third and fourth fentanyl boluses.