SUBUTEX
Clinical safety rating: caution
Comprehensive clinical and safety monograph for SUBUTEX (SUBUTEX).
Partial agonist at mu-opioid receptors; antagonist at kappa-opioid receptors. High affinity binding reduces withdrawal symptoms and blocks effects of full agonists.
| Metabolism | N-dealkylation by CYP3A4 (major pathway) to norbuprenorphine; also undergoes glucuronidation. CYP2C8 and CYP2C9 minor contributions. |
| Excretion | Renal: approximately 30% of administered dose excreted unchanged in urine. Fecal: about 70% eliminated via feces, predominantly as conjugated metabolites. Biliary excretion contributes to fecal elimination. |
| Half-life | Terminal elimination half-life of buprenorphine ranges from 24 to 60 hours (mean ~37 hours). Clinical context: Long half-life allows for alternate-day dosing in maintenance therapy but requires careful monitoring for accumulation in renal impairment. |
| Protein binding | Approximately 96% bound to plasma proteins, primarily alpha- and beta-globulins, with minimal binding to albumin. |
| Volume of Distribution | Volume of distribution is approximately 2.5 L/kg (range 1.0-4.0 L/kg). This large Vd indicates extensive tissue distribution, including into the brain and adipose tissue. |
| Bioavailability | Sublingual: 40-90% (mean 50-60%) due to first-pass metabolism; oral bioavailability is <10% due to extensive hepatic extraction. |
| Onset of Action | Sublingual: onset of analgesic effect within 15-30 minutes; peak effect at 1-2 hours. Sublingual administration for opioid dependence: onset of withdrawal suppression within 30-60 minutes. |
| Duration of Action | Analgesic effect: 6-8 hours due to high affinity and slow dissociation from mu-opioid receptors. For opioid dependence: suppression of withdrawal for 24-72 hours depending on dose and tolerance. |
| Molecular Weight | 467.64 |
Sublingual tablet: initial 2-4 mg, titrated to 8-16 mg daily as a single dose; maximum 24 mg per day.
| Dosage form | TABLET |
| Renal impairment | No dose adjustment required for mild to moderate renal impairment; caution in severe impairment (CrCl <30 mL/min) with extended dosing intervals. |
| Liver impairment | Child-Pugh Class A: no adjustment; Class B: reduce dose by 50%; Class C: avoid use or use with extreme caution at reduced doses. |
| Pediatric use | Not approved for patients <16 years; safety and efficacy not established. |
| Geriatric use | No specific dose adjustment recommended; monitor for increased sensitivity and adverse effects; consider lower starting doses and slower titration. |
| 1st trimester | Use only if potential benefit justifies risk; associated with neonatal abstinence syndrome and congenital anomalies in some studies. |
| 2nd trimester | Use only if potential benefit justifies risk; monitor for withdrawal and preterm labor. |
| 3rd trimester | Use only if potential benefit justifies risk; prolonged use may cause neonatal opioid withdrawal syndrome (NOWS). |
Clinical note
Comprehensive clinical and safety monograph for SUBUTEX (SUBUTEX).
| Placental transfer | Buprenorphine crosses the placenta; fetal concentrations are approximately 50-70% of maternal levels. |
| Breastfeeding | Subutex (buprenorphine) is excreted into breast milk in low concentrations. The American Academy of Pediatrics considers it compatible with breastfeeding in mothers on stable doses. Infant sedation and withdrawal upon abrupt discontinuation may occur; monitor infant for drowsiness and respiratory depression. |
■ FDA Black Box Warning
Risk of serious injury or death if administered intravenously; only prescribe for sublingual or buccal use. Risk of respiratory depression, especially in opioid-naive patients or if used with CNS depressants. Risk of neonatal opioid withdrawal syndrome with prolonged use during pregnancy. Concomitant use with benzodiazepines or other CNS depressants may cause severe respiratory depression, coma, and death.
| Serious Effects |
Hypersensitivity to buprenorphine or any component of the formulationSevere respiratory insufficiencyAcute alcoholism or delirium tremensConcurrent use of opioid antagonists (naltrexone, nalmefene)Severe hepatic impairment
| Precautions | Respiratory depression; risk of drug interactions with CNS depressants; impairment of cognitive/motor function; adrenal insufficiency; QT prolongation; hepatic impairment; neonatal withdrawal; misuse/abuse potential; abrupt discontinuation leads to withdrawal; individuals with compromised respiratory function; elevated CSF pressure; head injury. |
| Food/Dietary | No specific food interactions. Avoid grapefruit juice as it may increase buprenorphine levels. Alcohol should be avoided due to additive CNS depression. |
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| Lactation Rating | L3 (Moderately Safe) |
| Teratogenic Risk | Buprenorphine is classified as Pregnancy Category C. First trimester: Limited human data; animal studies show increased risk of neural tube defects at high doses. Second and third trimesters: Chronic use may lead to neonatal abstinence syndrome (NAS). No increased risk of major malformations in human studies. |
| Fetal Monitoring | Maternal: Liver function tests (LFTs) baseline and periodically; urine drug screens; assessment of withdrawal symptoms. Fetal: Ultrasound for growth; non-stress test or biophysical profile in third trimester if indicated; neonatal monitoring for NAS after delivery. |
| Fertility Effects | Buprenorphine may cause menstrual irregularities and anovulation. In males, may reduce libido and impair spermatogenesis. Effects are reversible upon discontinuation. |
| Clinical Pearls | Use SUBUTEX (buprenorphine) for opioid dependence treatment under the DATA 2000 waiver. Induce only when objective signs of withdrawal are present (COWS >12). Low ceiling effect on respiratory depression reduces overdose risk vs full agonists. Monitor for precipitated withdrawal if given too soon after last opioid. Buprenorphine can cause prolonged QT interval; consider ECG in at-risk patients. |
| Patient Advice | Take SUBUTEX once daily placed under the tongue until completely dissolved; do not chew or swallow. · Do not use alcohol or benzodiazepines while on SUBUTEX as it increases risk of severe respiratory depression. · Do not stop suddenly; withdrawal may occur; taper under medical supervision. · Keep out of reach of children; accidental ingestion can cause severe harm or death. · Report any signs of liver problems (yellowing skin/eyes, dark urine) right away. |