PENTAZOCINE

Absorption

Well absorbed from the gastro-intestinal tract.

Chemical properties

Crystalline Solid

Originator

Pentazocine,Mallinckrodt Inc.

The Uses of PENTAZOCINE

Mixed opioid agonist-antagonist. Controlled substance. Analgesic (narcotic).

The Uses of PENTAZOCINE

(?)-Pentazocine is a benzomorphan-type opiate with analgesic properties. It binds to opioid receptors (Ki values = 7.2, 31, and 5.7 nM for κ-, δ-, μ-opioid receptors, respectively) and to the type 1 σ-receptor (Kd = 12 nM). (?)-Pentazocine is abused with methylphenidate and other drugs. It is regulated as a Schedule IV compound in the United States. This product is intended for forensic and research applications.

Indications

For the relief of moderate to severe pain.

Background

The first mixed agonist-antagonist analgesic to be marketed. It is an agonist at the kappa and sigma opioid receptors and has a weak antagonist action at the mu receptor. (From AMA Drug Evaluations Annual, 1991, p97)

Definition

ChEBI: Pentazocine is a benzazocine.

Manufacturing Process

A solution of 3,4-dimethylpyridine was added to a methyliodid. Then to the resulting solution containing 1,3,4-trimethylpyridinium iodide the 4methoxybenzylmagnesium chloride was added. After reaction process the 1,3,4-trimethyl-2-(4-methoxy-benzyl)-pyridine was obtained.
To the solution of 1,3,4-trimethyl-2-(4-methoxy-benzyl)-pyridine was reduced by hydrogen over 10% palladium-on-charcoal, and when reduction was complete, the catalyst was removed by filtration and the filtrate taken to dryness. The residue was recrystallized to give 2-(4-methoxybenzyl)-1,3,4trimethyl-1,2,5,6-tetrahydropyridine.
To the 2-(4-methoxybenzyl)-1,3,4-trimethyl-1,2,5,6-tetrahydropyridine the solution of hydrobromic acid was added and heated under reflux.The product obtained was recrystallized and yield N-methyl-1,2,3,4,5,6-hexahydro-6,11dimethyl-8-hydroxy-2,6-methano-3-benzazocine (2'-hydroxy-2,5,9trimethylbenzo-6-morphen), which then was demethylated by bromcyan (BrCN). As a result the racemic cis-1,2,3,4,5,6-hexahydro-6,11-dimethyl-8hydroxy-2,6-methano-3-benzazocine was obtained (that is a. 2'-hydroxy-5,9dimethyl-6,7-benzomorphen).
A mixture of 8.7 g racemic cis-1,2,3,4,5,6-hexahydro-6,11-dimethyl-8hydroxy-2,6-methano-3-benzazocine, 6.0 g of 1-bromo-3-methyl-2-butene, 5.0 g of sodium bicarbonate, and 125 ml of N,N-dimethylformamide was stirred and refluxed for approximately 4.5 hours. The reaction mixture was then filtered, and the solid on the filter was washed with ethanol. The filtrate and the wash liquor were combined, concentrated under reduced pressure, and then extracted with chloroform. The chloroform extract was concentrated under reduced pressure to yield a syrup which weighed 15.8 g. This syrup was dissolved in 120 ml of diethyl ether and the resulting solution was filtered to remove approximately 0.5 g of a brown amorphous solid. The filtrate was extracted with a mixture of 5 ml of concentrated hydrochloric acid and 20 ml of water. To the extract there was added 5 ml of concentrated ammonium hydroxide solution and ice. A pale tan syrup separated from solution and after stirring, this syrup solidified. The resulting pale tan solid was collected and dried; it weighed 10.6 g. After two recrystallizations from a mixture of methyl alcohol and water, with charcoaling, the 1,2,3,4,5,6-hexahydro-3-(3-methyl-2butenyl)-6,11-dimethyl-8-hydroxy-2,6-methano-3-benzazocine weighed 8.2 g and melted at 145°-147°C.
The1,2,3,4,5,6-hexahydro-3-(3-methyl-2-butenyl)-6,11-dimethyl-8-hydroxy2,6-methano-3-benzazocinewas soluble in a mixture of 0.35 ml of 2 N hydrochloric acid and 0.15 ml of water to the extent of 10%, the pH of the 1% solution being 2.80; and when the pH of the 1% solution was gradually raised by addition of 10 N sodium hydroxide solution, a precipitate formed at pH 5.4. The 1,2,3,4,5,6-hexahydro-3-(3-methyl-2-butenyl)-6,11-dimethyl-8hydroxy-2,6-methano-3-benzazocine hydrochloride melted at 245°-247°C, dec.

brand name

Talwin (Sanofi Aventis);Fortagesic;Fortalgesic;Fortralin;Fortwin;Pentafen;Pentalgina;Talacen;Talwin nx.

Therapeutic Function

Analgesic

World Health Organization (WHO)

Pentazocine, which has both agonist and weak opioid antagonist activity, was introduced in 1967 for the treatment of moderate and severe pain. The risk of drug dependence is lower with pentazocine than with morphine-like drugs and pentazocine has been controlled under Section III of the 1971 Convention on Psychotropic Substances since 1984. The risk of dependence is now widely acknowledged to exist in vulnerable individuals and at least one country has applied controls analogous to those of Schedule I of the 1961 Single Convention on Narcotic Drugs. (Reference: (UNCPS3) United Nations Convention on Psychotropic Substances (III), , , 1971)

General Description

The benzomorphans are prepared synthetically and thus resultin several stereoisomers. The active benzomorphans arethose that have the equivalent bridgehead carbons in thesame absolute configuration of morphine (carbons 9, 13,and 14 of morphine). The only benzomorphan in clinical useis pentazocine, which is prepared as the 2(R), 6(R), 11(R)enantiomer (Chemical Abstracts numbering). Pentazocineis a mixed agonist/antagonist displaying differing intrinsicactivity at the opioid receptor subtypes. At the κ-receptor,pentazocine is a partial agonist and a weak antagonist.
According to the manufacturer, a 50-mg dose of pentazocinehas about the same analgesic potency as 60 mg of codeineand about 1/50th the antagonistic activity of nalorphine.74Pentazocine is also an agonist at the κ-receptor, and thismay be responsible for the higher percentage of patients thatexperience dysphoria with pentazocine versus morphine.75Some evidence also exists that women respond better to κ-agonists than men. Pentazocine is available in a 50-mgtablet along with a low dose of the antagonist naloxone 0.5mg (Talwin NX). Naloxone 0.5 mg orally is expected tohave no pharmacological effect but is included to dissuadeIV drug abusers from dissolving and injecting Talwin NX.

Pharmacokinetics

Pentazocine is a potent analgesic which when administered orally in a 50 mg dose appears equivalent in analgesic effect to 60 mg (1 grain) of codeine. Onset of significant analgesia usually occurs between 15 and 30 minutes after oral administration, and duration of action is usually three hours or longer. Onset and duration of action and the degree of pain relief are related both to dose and the severity of pretreatment pain. Pentazocine weakly antagonizes the analgesic effects of morphine and meperidine; in addition, it produces incomplete reversal of cardiovascular, respiratory, and behavioral depression induced by morphine and meperidine. Pentazocine has about 1/50 the antagonistic activity of nalorphine. It also has sedative activity.

Safety Profile

Poison by ingestion, subcutaneous, intramuscular, intraperitoneal, and intravenous routes. Experimental reproductive effects. Human systemic effects by intramuscular and intravenous routes: wakefulness, euphoria, hallucinations or distorted perceptions, tremors, convulsions, excitement, motor activity changes, muscle weakness, analgesia, withdrawal, parasympathomimetic effects, nausea or vomiting, and dernlititis. Can cause drug dependency and other central nervous system effects, An analgesic. When heated to decomposition it emits toxic fumes of NOx. See also ALLIT COMPOUNDS.

Metabolism

Hepatic