Belbuca - Pharmaceutical Information, Clinical Trials, Detailed Pharmacology, Toxicology
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Belbuca - Scientific Information

Manufacture: Endo Pharmaceuticals Inc.
Country: United States
Condition: Chronic Pain, Pain
Class: Narcotic analgesics
Form: Skin patch (transdermal), Powder
Ingredients: buprenorphine hydrochloride, carboxymethylcellulose sodium USP, citric acid anhydrous USP, hydroxyethylcellulose NF, hydroxypropylcellulose NF, methylparaben NF, monobasic sodium phosphate anhydrous USP, peppermint oil NF, polycarbophil USP, propylene glycol USP, propylparaben NF, sodium benzoate NF, sodium hydroxide NF, saccharin sodium NF, titanium dioxide USP, vitamin E acetate USP, yellow iron oxide, purified water USP, and TekPrint SW-9008 black ink (shellac NF, black iron oxide NF)

Description

BELBUCA is a buccal film providing transmucosal delivery of buprenorphine hydrochloride, a partial opioid agonist. BELBUCA is a rectangular bi-layer, peppermint-flavored, buccal film with rounded corners, consisting of a white to off-white backing layer with strength identifier printed in black ink and a light yellow to yellow active mucoadhesive layer containing buprenorphine hydrochloride. The yellow side of the buccal film is applied to the inside of the cheek where it adheres to the moist buccal mucosa to deliver the drug as the film dissolves. 

The chemical name of buprenorphine hydrochloride is 6,14-ethenomorphinan-7-methanol, 17-(cyclopropylmethyl)- α-(1,1-dimethylethyl)-4, 5-epoxy-18,19-dihydro-3-hydroxy-6-methoxy-α-methyl-, hydrochloride, [5α, 7α, (S)]. The structural formula is:

The molecular weight of buprenorphine hydrochloride is 504.10; the empirical formula is C29H41NO4∙HCl. Buprenorphine hydrochloride occurs as a white or off white crystalline powder. It is sparingly soluble in water, freely soluble in methanol, soluble in alcohol, and practically insoluble in cyclohexane. The pKa is 8.5 for the amine function and 10.0 for the phenol function.

BELBUCA is available as 75 mcg, 150 mcg, 300 mcg, 450 mcg, 600 mcg, 750 mcg, and 900 mcg buprenorphine per film. The strength of each film is dependent on the buprenorphine concentration in the formulation and the surface area of the film. Unique identifiers and film size for each strength are listed in Table 1.

Table 1: BELBUCA Identifier & Size
Buprenorphine Strength
(mcg)
BELBUCA
Identifier
Film Size
(cm2)
75E01.215
150E12.431
300E30.934
450E41.400
600E61.867
750E72.334
900E92.801

The active ingredient in BELBUCA is buprenorphine hydrochloride. Each buccal film also contains carboxymethylcellulose sodium USP, citric acid anhydrous USP, hydroxyethylcellulose NF, hydroxypropylcellulose NF, methylparaben NF, monobasic sodium phosphate anhydrous USP, peppermint oil NF, polycarbophil USP, propylene glycol USP, propylparaben NF, sodium benzoate NF, sodium hydroxide NF, saccharin sodium NF, titanium dioxide USP, vitamin E acetate USP, yellow iron oxide, purified water USP, and TekPrint SW-9008 black ink (shellac NF, black iron oxide NF).

Clinical Pharmacology

Mechanism of Action

Buprenorphine is a partial agonist at the mu-opioid receptor and an antagonist at the kappa-opioid receptor.

Pharmacodynamics

Effects on the Central Nervous System

The principal action of therapeutic value of buprenorphine is analgesia and is thought to be due to buprenorphine binding with high affinity to opioid receptors on neurons in the brain and spinal cord. Buprenorphine may also cause sedation or somnolence via an action in the brain.

Buprenorphine produces mu opioid receptor-mediated respiratory depression by direct action on brainstem respiratory centers by reducing sensitivity of the brainstem to increases in carbon dioxide tension and to electrical stimulation.

Buprenorphine causes miosis, even in total darkness, and little tolerance develops to this effect. Pinpoint pupils are a sign of opioid overdose but are not pathognomonic (e.g., pontine lesions of hemorrhagic or ischemic origins may produce similar findings). Marked mydriasis rather than miosis may be seen with worsening hypoxia in the setting of buprenorphine overdose.

Unlike other opioids, buprenorphine appears to exhibit a dose-ceiling effect. 

Effects on the Gastrointestinal Tract and Other Smooth Muscle

Gastric, biliary, and pancreatic secretions are decreased by buprenorphine. Buprenorphine causes a reduction in motility associated with an increase in tone in the stomach and duodenum. Digestion of food in the small intestine is delayed and propulsive contractions are decreased. Propulsive peristaltic waves in the colon are decreased while tone is increased to the point of spasm. The end result is constipation. Buprenorphine may cause an increase in biliary tract pressure as a result of spasm of the sphincter of Oddi.

Effects on the Cardiovascular System

Buprenorphine may cause a reduction in blood pressure. 

Effects on Cardiac Electrophysiology

QTc prolongation with BELBUCA has been observed. Of the 1590 patients that were treated with BELBUCA in controlled and open-label chronic pain trials at doses up to 900 mcg every 12 hours, 2% demonstrated a prolongation of QTcF to a post-baseline value between 450 - 480 msec during therapy.

Effects on the Endocrine System

Opioids inhibit the secretion of ACTH, cortisol, and luteinizing hormone (LH) in humans. They also stimulate prolactin, growth hormone (GH) secretion, and pancreatic secretion of insulin and glucagon.

Effects on the Immune System

Opioids have been shown to have a variety of effects on components of the immune system in in vitro and animal models. The clinical significance of these findings is unknown. Overall, the effects of opioids appear to be modestly immunosuppressive.

Pharmacokinetics

Absorption

Systemic plasma levels of buprenorphine increased in a linear manner (Cmax and AUC) over the single dose range of 75 to 1200 mcg as shown in Table 2. The absolute bioavailability of BELBUCA ranged from 46 to 65%.

Table 2: Mean (± SD) BELBUCA Pharmacokinetic Parameters
Regimen Dosage (mcg)Cmax
(ng/mL)
AUC0-t
(h∙ng/mL)
AUC0-∞
(h∙ng/mL)
Tmax*
(hr)
Single Dose750.17±0.300.46±0.220.63±0.243.00 (1.50-4.00)
3000.47±0.472.00±0.682.3±0.682.50 (0.50-4.00)
12001.43±0.459.6±2.910.5±3.323.00 (1.00-4.00)
 *  Tmax values reported as median and range

Following the multiple dose administration (60 to 240 mcg every 12 hours) of BELBUCA, apparent steady-state buprenorphine plasma concentrations were achieved prior to the 6th dose. Buprenorphine steady-state Cmax and AUC increased proportional to dose. 

Systemic exposure to buprenorphine from BELBUCA film was reduced by 23-27% by the ingestion of liquids (cold, hot and room temperature water) during film administration; additionally coadministration with low pH liquid, such as decaffeinated cola, decreased buprenorphine exposure from BELBUCA by approximately 37%. The consumption of liquids should be avoided until the buccal film has completely dissolved [see Dosage and Administration]. 

Distribution

Buprenorphine is approximately 96% protein bound, primarily to alpha and beta globulin.

Elimination

Metabolism

Buprenorphine undergoes both N-dealkylation to norbuprenorphine and glucuronidation. The N-dealkylation pathway is mediated primarily by CYP3A4. Norbuprenorphine, the major metabolite, 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

Excretion

A mass balance study of buprenorphine 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 was conjugated (buprenorphine, 1% free and 9.4% conjugated; norbuprenorphine, 2.7% free and 11% conjugated). In feces, almost all of the buprenorphine and norbuprenorphine was free (buprenorphine, 33% free and 5% conjugated; norbuprenorphine, 21% free and 2% conjugated).

Based on multiple dose studies performed with BELBUCA, the mean plasma elimination half-life of buprenorphine was 27.6±11.2 hours. 

Drug Interactions

CYP3A4 Inhibitors and Inducers: Buprenorphine undergoes N-dealkylation pathway mediated primarily by CYP3A4, so its metabolism can be inhibited by CYP3A4 inhibitors.  The interaction of buprenorphine with all CYP3A4 inducers has not been studied. [see Drug Interactions].

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 relatively low plasma concentrations of buprenorphine and norbuprenorphine resulting from therapeutic doses are not expected to raise significant drug-drug interaction concerns.

Specific Populations

Hepatic Impairment

BELBUCA has not been evaluated in patients with severe hepatic impairment. The pharmacokinetics of buprenorphine following an IV infusion of 0.3 mg of buprenorphine were compared in 8 patients with mild hepatic impairment (Child-Pugh A), 4 patients with moderate impairment (Child-Pugh B), and 12 subjects with normal hepatic function. Buprenorphine and norbuprenorphine plasma levels did not increase in mild or moderately impaired patient cohorts.

In another pharmacokinetic study, the disposition of buprenorphine was determined after administering a 2.0/0.5 mg buprenorphine/naloxone sublingual tablet in subjects with varied degrees of hepatic impairment as indicated by Child-Pugh criteria. The disposition of buprenorphine in patients with hepatic impairment was compared to disposition in subjects with normal hepatic function. In subjects with mild hepatic impairment, the changes in mean Cmax, AUC0-last, and half-life values of buprenorphine were not clinically significant. No dose adjustment is needed in patients with mild hepatic impairment.

For subjects with moderate and severe hepatic impairment, mean Cmax, AUC0-last, and half-life values of buprenorphine were increased. [see Dosage and Administration, Warnings and Precautions, and Use in Specific Populations].

Table 3. Changes in Pharmacokinetic Parameters in Subjects With Moderate and Severe Hepatic Impairment
Hepatic ImpairmentPK ParametersIncrease in buprenorphine compared to healthy subjects
ModerateCmax8%
AUC0-last64%
Half-life35%
SevereCmax72%
AUC0-last181%
Half-life57%
Oral Mucositis

In an open-label pharmacokinetic study in 6 cancer patients with Grade 3 mucositis, buprenorphine was absorbed more rapidly from BELBUCA resulting in a higher Cmax (~79%) and AUC (~56%) compared to age- and gender-matched healthy control patients [see Dosage and Administration, Warnings and Precautions].

Geriatric Patients

No notable differences in pharmacokinetics were observed from population PK analysis in subjects aged 65 compared to younger subjects. Other reported clinical experience with buprenorphine has not identified differences in responses between the elderly and younger patients. In general, dose selection for an elderly patient should be cautious, usually starting at the low end of the dosing range, reflecting the greater frequency of decreased hepatic, renal, or cardiac function, and of concomitant disease or other drug therapy. 

Pediatric Patients

BELBUCA has not been studied in children and is not recommended for pediatric use.

Sex

No notable sex differences in pharmacokinetics were observed from population PK analysis.

Renal Impairment

No studies in patients with renal impairment have been performed with BELBUCA. In an independent study, the effect of impaired renal function on buprenorphine pharmacokinetics after IV bolus and after continuous IV infusion administration was evaluated; and no notable differences in plasma buprenorphine concentrations were identified in patients with normal renal function compared to impaired renal function or renal failure.

Nonclinical Toxicology

Carcinogenesis, Mutagenesis, Impairment of Fertility

Carcinogenesis

Carcinogenicity studies of buprenorphine were conducted in Sprague-Dawley rats and CD-1 mice. Buprenorphine was administered in the diet to rats at doses of 0.6, 5.5, and 56 mg/kg/day for 27 months (estimated exposure was approximately 3, 29, and 299 times the maximum recommended human dose (MRHD) of  buccal Belbuca of 1.8 mg on a mg/m2 basis, respectively). Statistically significant dose-related increases in testicular interstitial (Leydig’s) cell tumors occurred. In an 86-week study in CD-1 mice, buprenorphine was not carcinogenic at dietary doses up to 100 mg/kg/day (estimated exposure was approximately 267 times the MRHD).

Mutagenesis

Buprenorphine was studied in a series of tests utilizing gene, chromosome, and DNA interactions in both prokaryotic and eukaryotic systems.  Results were negative in yeast (S. cerevisiae) for recombinant, gene convertant, or forward mutations; negative in Bacillus subtilis “rec” assay, negative for clastogenicity in CHO cells, Chinese hamster bone marrow and spermatogonia cells, and negative in the mouse lymphoma L5178Y assay. 

Results were equivocal in the Ames test: negative in studies in two laboratories, but positive for frame shift mutation at a high dose (5 mg/plate) in a third study.  Results were positive in the Green-Tweets (E. coli) survival test, positive in a DNA synthesis inhibition (DSI) test with testicular tissue from mice, for both in vivo and in vitro incorporation of [3H]thymidine, and positive in unscheduled DNA synthesis (UDS) test using testicular cells from mice.

Impairment of Fertility

Reproduction studies of buprenorphine in rats demonstrated no evidence of impaired fertility at daily oral doses up to 80 mg/kg/day (estimated exposure approximately 427 times the MRHD) or up to 5 mg/kg/day IM or SC (estimated exposure was approximately 27 times the MRHD).

Clinical Studies

The efficacy of BELBUCA has been evaluated in three 12-week double-blind, placebo-controlled clinical trials in opioid-naïve and opioid-experienced patients with moderate-to-severe chronic low back pain using pain scores as the primary efficacy variable. Two of these studies, described below, demonstrated efficacy in patients with low back pain. One study in low back pain did not show a statistically significant pain reduction for BELBUCA compared to placebo. 

12-Week Study in Opioid-Naïve Patients with Chronic Low Back Pain

A total of 749 patients with chronic low back pain entered an open-label, dose-titration period for up to eight weeks.  Potential subjects were excluded from participation for QTcF interval of 450 ms or more, hypokalemia, clinically unstable cardiac disease, a history of Long QT Syndrome or an immediate family member with this condition, or taking Class IA or Class III antiarrhythmic medications. Patients initiated therapy with a single 75 mcg dose of BELBUCA on Day 1 and continued taking BELBUCA 75 mcg either once daily or every 12 hours for 4-8 days as tolerated. The dose was then increased to 150 mcg every 12 hours, and patients could continue to dose escalate in 150 mcg dose increments every 4-8 days for up to 6 weeks if the adverse effects were tolerable and the analgesic effects were not adequate. Patients who achieved adequate analgesia and tolerable adverse effects on BELBUCA for at least 2 weeks were then randomized to continue their titrated dose of BELBUCA or matching placebo. Sixty-one percent (61%) of the patients who entered the open-label dose titration period were able to titrate to a tolerable and effective dose and were randomized into a 12-week, double-blind treatment period. Fifteen percent of patients discontinued due to an adverse event and 4% discontinued due to lack of a therapeutic effect. The remaining 20% of patients discontinued due to various non-drug related administrative reasons. 

During the first 2 weeks of double-blind treatment, patients were allowed up to 2 tablets per day of hydrocodone/acetaminophen 5/325 mg as supplemental analgesia to minimize opioid withdrawal symptoms in patients randomized to placebo. Thereafter, the supplemental analgesia was limited to 1 to 2 tablets of acetaminophen 500 mg per day. Seventy-six percent  of the patients treated with BELBUCA completed the 12-week treatment compared to 73% of the patients treated with placebo. Of the 209 patients randomized to BELBUCA, 4% discontinued due to lack of efficacy and 8% due to adverse events. Of the 211 patients randomized to placebo, 11% discontinued due to lack of efficacy and 4% due to adverse events. 

Of the patients who were randomized, the mean pain (SD) scores on a 0 to 10 numeric rating scale (NRS) were 7.1 (1.06) and 7.2 (1.05) prior to open-label titration and 2.8 (1.01) and 2.8 (1.12) at the beginning of the double-blind period for BELBUCA and placebo, respectively. The change from double-blind baseline to week 12 in mean pain (SD) NRS score was statistically significant favoring patients treated with BELBUCA, compared with patients treated with placebo. 

A higher proportion of BELBUCA patients (62%) had at least a 30% reduction in pain score from prior to open-label titration to study endpoint when compared to patients who received placebo buccal film (47%). A higher proportion of BELBUCA patients (41%) also had at least a 50% reduction in pain score from prior to open-label titration to study endpoint compared to patients who received placebo (33%). 

The proportion of patients with various degrees of improvement, from prior to open-label titration (Titration-Baseline) to study endpoint, is shown in Figure 1 below.

Figure 1: Percentage Improvement in Pain Intensity from Titration-Baseline to Week 12

12-Week Study in Opioid-Experienced Patients with Chronic Low Back Pain

Eight hundred and ten (810) patients on chronic opioid therapy (total daily dose 30-160 mg in oral morphine sulfate equivalents (MSE) for at least 4 weeks) entered an open-label, dose-titration period with BELBUCA for up to 8 weeks, following taper of their prior opioids to 30 mg oral MSE daily. Potential subjects were excluded from participation for QTcF interval of 450 ms or more, hypokalemia, clinically unstable cardiac disease, a history of Long QT Syndrome or an immediate family member with this condition, or taking Class IA or Class III antiarrhythmic medications.  Patients were initiated with BELBUCA 150 mcg every 12 hours if they were on 30 to 89 mg oral MSE daily and 300 mcg every 12 hours if they were on 90 to160 mg oral MSE daily prior to taper. If a patient tolerated the adverse events and the analgesic effects were not adequate, the dose was increased in increments of 150 mcg every 12 hours after 4 to 8 days for up to 6 weeks. Patients were permitted to take hydrocodone/acetaminophen 5/325 mg as analgesic rescue as needed up to a maximum of 4 doses per day during the open-label dose titration period. After a dose was reached with adequate analgesia and tolerable adverse effects for a period of 2 weeks, patients were randomized to continue their titrated dose of BELBUCA or matching placebo. Sixty-three percent (63%) of the patients who entered the open-label titration period were able to titrate to a tolerable and effective dose and were randomized into a 12-week double-blind treatment phase. Ten percent (10%) of patients discontinued due to an adverse event, 8% discontinued due to lack of a therapeutic effect, and 0.1% discontinued due to opioid withdrawal during the open-label titration period. The remaining 20% of patients discontinued due to various non drug related administrative reasons. 

During the double-blind period, patients were permitted to take up to 2 doses of 5/325 mg or 10/650 mg of hydrocodone/acetaminophen per day for the first 2 weeks to minimize opioid withdrawal symptoms in patients randomized to placebo. After the first 2 weeks, patients were permitted to take 1 dose of 5/325 mg or 10/650 mg per day. Eighty-three percent of patients treated with BELBUCA and 57% of patients treated with placebo buccal film completed the 12-week treatment period. Of the 243 patients randomized to BELBUCA, 8% discontinued due to lack of efficacy and 2% due to adverse events. Of the 248 patients randomized to placebo buccal film, 25% discontinued due to lack of efficacy and 5% due to adverse events.

Of the patients who were randomized into the double-blind period, the mean pain (SD) NRS scores were 6.8 (1.28) and 6.6 (1.32) prior to open-label titration and 2.9 (0.985) and 2.8 (1.05) at the beginning of the double-blind period for BELBUCA and placebo, respectively. The change from baseline to week 12 in mean pain (SD) NRS score was statistically significant in favor of patients treated with BELBUCA compared with patients treated with placebo.

A higher proportion of BELBUCA patients (64%) had at least a 30% reduction in pain score from prior to open-label titration to study endpoint when compared to patients who received placebo buccal film (31%). A higher proportion of BELBUCA patients (39%) also had at least a 50% reduction in pain score from prior to open-label titration to study endpoint compared to patients who received placebo (17%). 

The proportion of patients with various degrees of improvement from prior to open-label titration (Titration-Baseline) to study endpoint is shown in Figure 2 below.

Figure 2: Percentage Improvement in Pain Intensity from Titration-Baseline to Week 12