Phenazocine

drugbox
IUPAC_name = 1,2,3,4,5,6-hexahydro-6,11-dimethyl-3-(2-phenylethyl)-
2,6-Methano-3-benzazocin-8-ol


width = 180
CAS_number = 127-35-5
synonyms = Fenazocina, Phenazocinum, DEA No. 9715
ATC_prefix =
ATC_suffix =
PubChem = 173449
DrugBank =
C = 22 | H = 27 | N = 1 | O = 1
molecular_weight = 321.45588 g/mol
bioavailability =
protein_bound =
metabolism =
elimination_half-life =
excretion =
pregnancy_AU =
pregnancy_US =
pregnancy_category =
legal_AU =
legal_CA =
legal_UK = Class A, Withdrawn
legal_US =
legal_status =
routes_of_administration = Oral

Phenazocine (brandnames Prinadol, Narphen) is an opioid analgesic drug, which is related to pentazocine and has a similar profile of effects.

Effects of phenazocine include analgesia and euphoria, also may include dysphoria and hallucinations at high doses, most likely due to action at κ-opioid and σ receptors.cite journal | author= Harris LS, Pierson AK | title=Some Narcotic Antagonists in the Benzomorphan Series | journal=Journal of Pharmacology and Experimental Therapeutics | month=February | year=1964 | pages=141–8 | volume= | issue=143 | pmid=14163985 | accessdate= 2008-01-11]

Phenazocine appears to be a much stronger analgesic with fewer side effects than pentazocine, probably due to a more favorable μ/κ binding ratio. Phenazocine is a much more potent analgesic than pentazocine and other drugs in the benzomorphan series, most probably due to the presence of an N-phenethyl substitution, which is known to boost μ-opioid activity in many classes of opioid analgesics.cite journal | author= Feinberg AP, Creese I, Snyder SH | title=The opiate receptor: a model explaining structure-activity relationships of opiate agonists and antagonists | journal=Proceedings of the National Academy of Sciences USA | month=November | year=1976 | pages=4215–9 | volume=73 | issue=11 | pmid=186791 | accessdate= 2008-01-11 | doi=10.1073/pnas.73.11.4215]

Consequently phenazocine is some 4x the potency of morphine as an analgesic. Also it does not cause spasm of the sphincter of Oddi, making it more suitable than morphine for the treatment of biliary or pancreatic pain.cite journal | author=Hopton D. | title=Double-blind clinical trial of the analgesic effects of phenazocine hydrobromide (Narphen) compared with morphine sulphate in patients with acute abdominal pain | journal=Gut | month=January | year=1971 | pages=51–4 | volume=12 | issue= 1 | pmid=4929685 | accessdate= 2008-01-11 | doi=10.1136/gut.12.1.51]

History

Phenazocine was invented in the 1950s. cite journal | author= Clarke EG | title=Identification of Phenazocine, a Potent New Analgesic | journal=Nature | date=August 8, 1959 | pages=451 | volume= | issue=184(Suppl 7) | pmid=13810504 | accessdate= 2008-01-11] cite journal | author= Eckenhoff JE | title=Phenazocine, a new benzomorphan narcotic analgesic | journal=Anesthesiology | date=May-June 1959 | pages=355–8 | volume=20 | issue=3 | pmid=13650222 | accessdate= 2008-01-11] It was one of a number of benzomorphan opioids (including pentazocine, dezocine, and cyclazocine) developed in the search for non-addictive strong analgesics.

Phenazocine was once widely used, and was mainly supplied as 5mg tablets of the hydrobromide salt for sublingual use (Narphen®, Prinadol® and other names), but its use was discontinued in the United Kingdom in 2001.cite web | month = February | year = 2001 | url = http://www.connectingforhealth.nhs.uk/systemsandservices/data/readcodes/docs/tandc0201.pdf | title = Monthly Release Terming and Coding Newsletter | format = PDF | publisher = NHS Information Authority | accessdate = 2008-01-11]

Phenazocine was briefly used in the United States but fell out of favour for the above-mentioned reasons; it remains a Schedule II substance under the Comprehensive Drug Abuse Control & Prevention Act (aka Controlled Substances Act) of 1970 (CSA) but is not manufactured; other Schedule II narcotics not in use in the United States include bezitramide and metopon.

References