|Oral, IV, IM|
|Onset of action||15 min|
|Biological half-life||2 to 3 hours|
|Chemical and physical data|
|Molar mass||285.424 g/mol|
|3D model (Jmol)|
Pentazocine is a synthetically-prepared prototypical mixed agonist–antagonist narcotic (opioid analgesic) drug of the benzomorphan class of opioids used to treat moderate to moderately severe pain. Pentazocine is sold under several brand names, such as Fortral, Sosegon, Talwin NX (with the μ-antagonist naloxone, will cause withdrawal in opioid dependent persons on injection), Talwin, Talwin PX (without naloxone), Fortwin (Lactate injectable form) and Talacen (with acetaminophen). This compound may exist as one of two enantiomers, named (+)-pentazocine and (−)-pentazocine. (−)-pentazocine is a κ-opioid receptor agonist, while (+)-pentazocine is not, instead displaying a ten-fold greater affinity for the σ receptor. Usually, in its oral formulations, it is combined with naloxone so as to prevent people from crushing the tablets, dissolving them in a solvent (like water) and injecting them for a high (as naloxone is not orally bioavailable it produces no effect when the formulation is used orally, but it blocks the opioid effects of pentazocine if injected intravenously for a high). Related drugs include phenazocine, dezocine, cyclazocine and several chemicals used in research on the central nervous system.
Pentazocine is used primarily to treat pain, although its analgesic effects are subject to a ceiling effect. It has been discontinued by its corporate sponsor in Australia, although it may be available through the special access scheme.
In the 1970s, recreational drug users discovered that combining pentazocine with tripelennamine (a first-generation ethylenediamine antihistamine most commonly dispensed under the brand names Pelamine and Pyribenzamine) produced a euphoric sensation. Since tripelennamine tablets are typically blue in color and brand-name Pentazocine is known as Talwin (hence "Ts"), the pentazocine/tripelennamine combination acquired the slang name Ts and blues. After health-care professionals and drug-enforcement officials became aware of this scenario, the mu-opioid-antagonist naloxone was added to oral preparations containing pentazocine to prevent injection misuse, and the reported incidence of its misuse has declined precipitously since.
In an open-label, add-on, single-day, acute-dose small clinical study, pentazocine was found to rapidly and substantially reduce symptoms of mania in individuals with bipolar disorder that were in the manic phase of the condition. It was postulated that the efficacy observed was due to κ-opioid receptor activation-mediated amelioration of hyperdopaminergia in the reward pathways. Minimal sedation and no side effects including psychotomimetic effects or worsening of psychosis were observed at the dose administered.
Side effects are similar to those of morphine, but pentazocine, due to its action at the kappa opioid receptor is more likely to invoke psychotomimetic effects. High dose may cause high blood pressure or high heart rate. It may also increase cardiac work after myocardial infarction when given intravenously and hence this use should be avoided where possible. Respiratory depression is a common side effect, but is subject to a ceiling effect, such that at a certain dose the degree of respiratory depression will no longer increase with dose increases. Likewise rarely it has been associated with agranulocytosis, erythema multiforme and toxic epidermal necrolysis.
Tissue damage at injection sites
Severe injection site necrosis and sepsis has occurred (sometime requiring amputation of limb) with multiple injection of pentazocine lactate. In addition, animal studies have demonstrated that Pentazocine is tolerated less well subcutaneously than intramuscularly.
Pentazocine was developed by the Sterling Drug Company, Sterling-Winthrop Research Institute, of Rensselaer, New York. It was approved by the Food and Drug Administration in June 1967 after being favorably reviewed following testing on 12,000 patients in the United States. The analgesic compound was first made at Sterling in 1958. U.S. testing was conducted between 1961 and 1967. By mid 1967 Pentazocine was already being sold in Mexico, England, and Argentina, under different trade names.
Pentazocine was originally classified in Schedule V under the Controlled Substances Act but a petition was filed with the D.E.A. on October 1, 1971, to shift it to Schedule III. The petition was filed by Joseph L. Fink III, a pharmacist and law student at Georgetown University Law Center as part of the course Lawyering in the Public Interest. That petition was accepted for review on November 10, 1971 D.E.A. published a Final Rule transferring it to schedule IV on January 10, 1979, with an effective date of February 9, 1979 This is understood to be the first instance of a successful petition to reclassify a substance under the relatively recently enacted Controlled Substances Act. Pentazocine is still classified in Schedule IV under the Controlled Substances Act in the United States, even with the addition of Naloxone. although some states classify it in Schedule III. Internationally, pentazocine is a Schedule III drug under the Convention on Psychotropic Substances. Pentazocine has a DEA ACSCN of 9720; being a Schedule IV substance, the DEA does not assign an annual manufacturing quota for pentazocine for the United States.
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- Pain-Killing Drug Approved By F.D.A., New York Times, June 27, 1967, pg. 41.
- 36 Fed.Reg. 217
- 44 Fed. Reg. 2169
- "List of psychotropic substances under international control" (PDF). Green List - Annex to the annual statistical report on psychotropic substances (form P) (23rd ed.). International Narcotics Control Board. August 2003.