BUPRENORPHINE

Absorption

Bioavailablity of buprenorphine/naloxone is very high following intravenous or subcutaneous administration, lower by the sublingual or buccal route, and very low when administered by the oral route. It is therefore provided as a sublingual tablet that is absorbed from the oral mucosa directly into systemic circulation.
Clinical pharmacokinetic studies found that there was wide inter-patient variability in the sublingual absorption of buprenorphine and naloxone, but within subjects the variability was low. Both Cmax and AUC of buprenorphine increased in a linear fashion with the increase in dose (in the range of 4 to 16 mg), although the increase was not directly dose-proportional. Buprenorphine combination with naloxone (2mg/0.5mg) provided in sublingual tablets demonstrated a Cmax of 0.780 ng/mL with a Tmax of 1.50 hr and AUC of 7.651 ng.hr/mL.
Coadministration with naloxone does not effect the pharmacokinetics of buprenorphine.

Toxicity

Manifestations of acute overdose include pinpoint pupils, sedation, hypotension, respiratory depression and death.

Chemical properties

White Solid

The Uses of BUPRENORPHINE

Controllled substance (narcotic). Analgesic that demonstrates narcotic agonist-antagonist properties.

Background

Buprenorphine is a weak partial mu-opioid receptor agonist and a weak kappa-opioid receptor antagonist used for the treatment of severe pain. It is also commonly used as an alternative to methadone for the treatment of severe opioid addiction. Buprenorphine is commercially available as the brand name product Suboxone which is formulated in a 4:1 fixed-dose combination product along with naloxone, a non-selective competitive opioid receptor antagonist. Combination with naloxone is intended to reduce the abuse potential of Suboxone, as naloxone is poorly absorbed by the oral route (and has no effect when taken orally), but would reverse the opioid agonist effects of buprenorphine if injected intravenously. Buprenorphine has poor gastrointestinal absorption and is therefore formulated as a sublingual tablet.
Buprenorphine has a number of unique pharmacokinetic and pharmacodynamic properties that make it a preferred agent for the treatment of conditions requiring high doses of strong opioids. For example, buprenorphine dissociates from opioid receptors very slowly, resulting in a long duration of action and relief from pain or withdrawal symptoms for upwards of 24-36 hours. Use of once-daily buprenorphine may benefit individuals who have developed tolerance to other potent opioids and who require larger and more frequent doses. Buprenorphine may also be a preferred agent over methadone (which is also commonly used to treat severe pain and opioid use disorder), as it has less effect on Qtc interval prolongation, fewer drug interactions, reduced risk of sexual side effects, and an improved safety profile with a lower risk of overdose and respiratory depression.
Buprenorphine acts as a partial mu-opioid receptor agonist with a high affinity for the receptor, but lower intrinsic activity compared to other full mu-opioid agonists such as heroin, oxycodone, or methadone. This means that buprenorphine preferentially binds the opioid receptor and displaces lower affinity opioids without activating the receptor to a comparable degree. Clinically, this results in a slow onset of action and a clinical phenomenon known as the "ceiling effect" where once a certain dose is reached, buprenorphine's effects plateau. This effect can be beneficial, however, as dose-related side effects such as respiratory depression, sedation, and intoxication also plateau at around 32mg, resulting in a lower risk of overdose compared to methadone and other full agonist opioids. It also means that opioid-dependent patients do not experience sedation or euphoria at the same rate that they might experience with more potent opioids, improving quality of life for patients with severe pain and reducing the reinforcing effects of opioids which can lead to drug-seeking behaviours.
Treatment of opioid addiction with buprenorphine, methadone, or slow-release oral morphine (SROM) is termed Opioid Agonist Treatment (OAT) or Opioid Substitution Therapy (OST). The intention of substitution of illicit opioids with the long-acting opioids used in OAT is to prevent withdrawal symptomns for 24-36 hours following dosing to ultimately reduce cravings and drug-seeking behaviours. Use of OAT is also intended to improved social stabilization including a reduction in crime rates, marginalization, incarceration, and use of illicit substances such as heroin or fentanyl. Illegally purchased opioids can often be injected and may be laced with other substances that increase the risk of harm or overdose. Provision of OAT is often combined with education about harm reduction including use of clean needles and injection supplies in an effort to reduce the risks associated with injection drug use which includes contraction of HIV and Hepatitis C and other complications including skin infections, abscesses, or endocarditis.

Indications

Buprenorphine is available in different formulations, such as sublingual tablets, buccal films, transdermal films, and injections, alone or in combination with naloxone.
The buccal film, intramuscular or intravenous injection, and transdermal formulation are indicated for the management of pain severe enough to require an opioid analgesic and for which alternate treatments are inadequate.
The extended-release subcutaneous injections of buprenorphine are indicated for the treatment of moderate to severe opioid use disorder in patients who have initiated treatment with a single dose of a transmucosal buprenorphine product or who are already being treated with buprenorphine. Injections are part of a complete treatment plan that includes counselling and psychosocial support.
Sublingual tablets and buccal films, in combination with naloxone, are indicated for the maintenance treatment of opioid dependence as part of a complete treatment plan that includes counselling and psychosocial support.

Definition

ChEBI: A morphinane alkaloid that is 7,8-dihydromorphine 6-O-methyl ether in which positions 6 and 14 are joined by a -CH2CH2- bridge, one of the hydrogens of the N-methyl group is su stituted by cyclopropyl, and a hydrogen at position 7 is substituted by a 2-hydroxy-3,3-dimethylbutan-2-yl group.

brand name

Buprenex (Reckitt Benckiser); Subutex (Reckitt Benckiser);Buprex;Buprx;Finibron;Prefin;Temagesic.

World Health Organization (WHO)

Buprenorphine, an opioid analgesic with both morphine agonist and antagonist activity, was introduced in 1978. It was originally considered to possess low dependence potential. However, it has latterly been identified as causing a socially significant abuse problem in several countries which have consequently subjected it to control in 1989 under Schedule III of the 1971 Convention of Psychotropic Substances. (Reference: (UNCPS3) United Nations Convention on Psychotropic Substances (III), , , 1971)

Biological Functions

Buprenorphine (Temgesic) is a mixed agonist–antagonist and a derivative of the naturally occurring opioid thebaine. Buprenorphine is highly lipophilic and is 25 to 50 times more potent than morphine as an analgesic. The sedation and respiratory depression it causes are more intense and longer lasting than those produced by morphine. Its respiratory depressant effects are not readily reversed by naloxone. It binds to the -receptor with high affinity and only slowly dissociates from the receptor, which may explain the lack of naloxone reversal of respiratory depression.
Buprenorphine has more agonist than antagonist effects and is often considered a partial agonist rather than a mixed agonist–antagonist, although it precipitates withdrawal in opioid-dependent patients. Its pharmacological effects are similar to those produced by both morphine and pentazocine. Indications for its use are similar to those of pentazocine, that is, for moderate to severe pain. Sublingual preparations are available, but have a slow onset and erratic absorption. The abuse potential of buprenorphine is low.While high doses of the drug are perceived by addicts as being morphinelike, it does reduce the craving for morphine and for the stimulant cocaine. Thus, buprenorphine is a potential new therapy for the treatment of addiction to both classes of drugs.
Drug interactions and contraindications are similar to those described for pentazocine and morphine.

General Description

Buprenorphine is a semisynthetic, highly lipophilic opiate derivedfrom thebaine. Pharmacologically, it is classified as amixed μ-agonist/antagonist (a partial agonist) and a weak κ-antagonist. It has a high affinity for the μ-receptors(1,000 times greater than morphine) and a slow dissociationrate leading to its long duration of action (6–8 hours). Atrecommended doses, it acts as an agonist at the μ-receptorwith approximately 0.3 mg IV equianalgesic to 10 mg of IVmorphine. One study in humans found that buprenorphine displaysa ceiling effect to the respiratory depression, but not theanalgesic effect over a dose range of 0.05 to 0.6 mg.In practice,this makes buprenorphine a safer opiate (when usedalone) than pure μ-agonists. Relatively few deaths frombuprenorphine overdose (when used alone) have been reported.113 The tight binding of the drug to the receptor also hasled to mixed reports on the effectiveness of using naloxone toreverse the respiratory depression. In animal studies, normaldoses of the pure antagonist naloxone were unable to removebuprenorphine from the receptor site and precipitate withdrawal.In a human study designed to precipitate withdrawalfrom buprenorphine, a naloxone dose (mean=35 mg) 100times the dose usually needed to precipitate withdrawal inmethadone-dependent subjects was used. For comparison, approximately0.3 mg, 4 mg, 4 mg, and 10 mg of naloxonewould be required to precipitate withdrawal from heroin, butorphanol,nalbuphine, or pentazocine respectively.

Contact allergens

This semisynthetic opioid analgesic drug is derived fromwith transdermal systems (TDS). In case of localized or generalized allergic contact dermatitis due to buprenorphine in TDS, TDS containing fentanyl can be safely used thebaine. It can be used parenterally, orally, and topically

Pharmacology

Buprenorphine is the only partial agonist in common use. It binds to the MOP receptor and dissociates from it very slowly. Consequently, although significant respiratory depression is less likely compared with morphine, it may be more difficult to reverse. It has poor oral bioavailability, and parenteral, sublingual or transdermal formulations are used. In addition to partial agonism at the MOP receptor, it is also a partial agonist at the NOP receptor and an antagonist at the KOP receptor. This may contribute to some of its analgesic effects. Increasingly it is also used instead of methadone for the management of opioid abuse (usually in relatively large doses up to 24 mg day?1).

Clinical Use

Opioid analgesic

Drug interactions

Potentially hazardous interactions with other drugs
Analgesics: possible opiate withdrawal with other opioids.
Antidepressants: possible CNS excitation or depression (hypotension or hypertension) if administered with MAOIs or moclobemide - avoid; sedative effects possibly increased when given with tricyclics.
Antifungals: metabolism inhibited by ketoconazole - reduce buprenorphine dose.
Antihistamines: sedative effects possibly increased with sedating antihistamines.
Antipsychotics: enhanced hypotensive and sedative effects.
Antivirals: concentration possibly increased by ritonavir; possibly reduced tipranavir concentration.
Dopaminergics: avoid with selegiline.
Sodium oxybate: avoid concomitant use.

Metabolism

Buprenorphine is metabolized to norbuprenorphine via Cytochrome P450 3A4/3A5-mediated N-dealkylation. Buprenorphine and norbuprenorphine both also undergo glucuronidation to the inactive metabolites buprenorphine-3-glucuronide and norbuprenorphine-3-glucuronide, respectively.
While norbuprenorphine has been found to bind to opioid receptors in-vitro, brain concentrations are very low which suggests that it does not contribute to the clinical effects of buprenorphine.
Naloxone undergoes direct glucuronidation to naloxone-3-glucuronide as well as N-dealkylation, and reduction of the 6-oxo group.

Metabolism

Elimination of buprenorphine is bi- or triphasic; metabolism takes place in the liver by oxidation via the cytochrome P450 isoenzyme CYP3A4 to the pharmacologically active metabolite N-dealkylbuprenorphine (norbuprenorphine), and by conjugation to glucuronide metabolites. Buprenorphine is subject to considerable first-pass metabolism after oral doses. However, when given by the usual routes buprenorphine is excreted mainly unchanged in the faeces; there is some evidence for enterohepatic recirculation. Metabolites are excreted in the urine, but very little unchanged drug is excreted in this way.