Pharmacological properties : תכונות פרמקולוגיות

Pharmacodynamic Properties

14.2      Pharmacodynamics

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 2nd SUBLOCADE injection [see Clinical Studies (16.1)].
Figure 10 illustrates 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, O2 saturation, 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 O2 saturation 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 single 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 to assess a potential impact of 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.

Pharmacokinetic Properties

14.3    Pharmacokinetics

Absorption
The pharmacokinetics (PK) of buprenorphine following subcutaneous injection of SUBLOCADE was evaluated in subjects with opioid use disorder after single doses (50 mg to 200 mg) and repeated doses (50 to 300 mg) separated by 28 days for up to 12 injections.
After SUBLOCADE injection, an initial buprenorphine peak was observed and the median Tmax occurred at 24 hours after injection. After the initial buprenorphine peak, the plasma buprenorphine concentrations decreased slowly to a plateau. Steady-state was achieved at 4-6 months.
Distribution
Buprenorphine is approximately 96% protein bound, primarily to alpha and beta globulin.
Elimination
Buprenorphine is metabolized and eliminated in urine and feces. The apparent terminal plasma half-life of buprenorphine following subcutaneous injection of SUBLOCADE ranged between 43 to 60 days as a result of the slow release of buprenorphine from the subcutaneous depot.
A study assessing buprenorphine exposure 22 to 38 months following the last SUBLOCADE injection indicated that buprenorphine could potentially be detected in plasma and urine over that time period. Concentrations in urine were more variable than in plasma and generally higher depending on the test used. Hence, it is expected that buprenorphine will be detected in patients for a longer time in urine than in plasma.


Metabolism
Buprenorphine is metabolized to its major metabolite, norbuprenorphine, primarily by CYP3A4.
Norbuprenorphine can further undergo glucuronidation. Norbuprenorphine has been found to bind opioid receptors in vitro; however, it has not been studied clinically for opioid-like activity.
Norbuprenorphine steady-state plasma concentrations in humans after subcutaneous injection of SUBLOCADE are low compared to buprenorphine (AUC norbuprenorphine/buprenorphine ratio of 0.20 to 0.40).
Excretion
A mass balance study of buprenorphine administered by IV infusion in humans showed complete recovery of radiolabel in urine (30%) and feces (69%) collected up to 11 days after dosing. Almost all of the dose was accounted for in terms of buprenorphine, norbuprenorphine, and two unidentified buprenorphine metabolites. In urine, most of buprenorphine and norbuprenorphine were conjugated (buprenorphine: 1% free and 9.4% conjugated; norbuprenorphine: 2.7% free and 11% conjugated). In feces, almost all of the buprenorphine and norbuprenorphine were free (buprenorphine: 33% free and 5% conjugated; norbuprenorphine: 21% free and 2% conjugated).
Drug Interaction Studies
CYP3A4 Inhibitors and Inducers
The effects of co-administered CYP3A4 inhibitors and inducers on buprenorphine exposure in subjects treated with SUBLOCADE have not been studied; however, such interactions have been established in studies using transmucosal buprenorphine. The effects of buprenorphine may be dependent on the route of administration.
Buprenorphine is metabolized to norbuprenorphine primarily by cytochrome CYP3A4; therefore, potential interactions may occur when SUBLOCADE is given concurrently with agents that affect CYP3A4 activity. The effects of co-administered CYP3A4 inducers or inhibitors have been established in studies using transmucosal buprenorphine. Patients who transfer to SUBLOCADE treatment from a regimen of transmucosal buprenorphine used concomitantly with CYP3A4 inhibitors (e.g., ketoconazole), macrolide antibiotics (e.g., erythromycin), or HIV protease inhibitors, or CYP3A4 inducer (e.g., phenobarbital, carbamazepine, phenytoin, rifampicin) should be monitored to ensure that the plasma buprenorphine level provided by SUBLOCADE is adequate and not excessive [see Drug Interactions (9)].
Buprenorphine has been found to be a CYP2D6 and CYP3A4 inhibitor and its major metabolite, norbuprenorphine, has been found to be a moderate CYP2D6 inhibitor in in vitro studies employing human liver microsomes. However, the plasma concentrations of buprenorphine and norbuprenorphine resulting from therapeutic SUBLOCADE doses are not expected to significantly affect metabolism of other co-medications.
Specific Populations
Based on population pharmacokinetic analyses, age, sex and race do not have a clinically meaningful effect on PK of SUBLOCADE.
Hepatic Impairment
Severe hepatic impairment is a contraindication to the use of SUBLOCADE [see Contraindications (6)].

The effect of hepatic impairment on the pharmacokinetics of SUBLOCADE has not been studied.
However, the effect of hepatic impairment on the PK of buprenorphine has been evaluated in a study using 2 mg/0.5 mg buprenorphine/naloxone sublingual tablet in subjects with various degrees of hepatic impairment as indicated by Child-Pugh criteria. While no clinically relevant changes were observed in subjects with mild hepatic impairment, buprenorphine plasma exposure was increased by 64% and 181% in subjects with moderate and severe hepatic impairment, respectively, compared to healthy subjects [see Use in Specific Populations (10.6)].
Renal Impairment
The effect of renal impairment on the pharmacokinetics of SUBLOCADE has not been studied. Clinical studies of SUBLOCADE did not include subjects with severe renal impairment.
Less than 1% is excreted as unchanged buprenorphine in urine following IV buprenorphine administration. No differences in buprenorphine pharmacokinetics were observed between 9 dialysis- dependent and 6 normal patients following IV administration of 0.3 mg buprenorphine [see Use in Specific Populations (10.7)].
Population PK analyses indicated no notable relationship between creatinine clearance and steady-state buprenorphine plasma concentrations.
HCV infection
In subjects with HCV infection but no sign of hepatic impairment, the changes in the mean Cmax, AUC0-last, and half-life values of buprenorphine were not clinically significant in comparison to healthy subjects without HCV infection. No dose adjustment is needed in patients with HCV infection.