Pentazocine
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Mechanism of action
The preponderance of evidence suggests that pentazocine antagonizes the opioid effects by competing for the same receptor sites, especially the opioid mu receptor.
/Pentazocine/ ... is an agonist at the kappa & sigma opioid receptors & has a weak antagonist action at the mu receptor. ... Pentazocine has a more rapid onset & a shorter duration of action than morphine ... /Pentazocine hydrochloride; pentazocine lactate/
The pattern of CNS effects produced by pentazocine is generally similar to that of the morphine-like opioids, including analgesia, sedation, and respiratory depression. The analgesic effects of pentazocine are due to agonistic actions at kappa1-opioid receptors. Higher doses of pentazocine (60 to 90 mg) elicit dysphoric and psychotomimetic effects similar to those of nalorphine.
Pharmacodynamics
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.
Pharmacokinetics
Half-life
2 to 3 hours
THE HALF-LIFE IN PLASMA IS 4-5 HR.
The elimination half-life is 203 +/- 71 min following iv admin & 177 +/- 34 min following oral admin. /Pentazocine hydrochloride; pentazocine lactate/
Absorption
Well absorbed from the gastro-intestinal tract.
TRACE AMT OF PENTAZOCINE AND ITS METABOLITES CAN BE DETECTED IN URINE FOR SEVERAL DAYS AFTER A SINGLE ADMIN OF THE DRUG. /PENTAZOCINE LACTATE/
... DOSE FOR DOSE, BLOOD CONCN & URINARY EXCRETION RATES OF PENTAZOCINE WERE LOWER AFTER ORAL & RECTAL DOSAGE THAN AFTER IV DOSAGE TO MAN. FECAL RECOVERY WAS LOW EVEN AFTER RECTAL DOSING, SUGGESTING THAT REDUCED AVAILABILITY MAY BE DUE TO INTESTINAL OR HEPATIC CLEARANCE DURING ABSORPTION.
PENTAZOCINE ENTERS THE CSF RAPIDLY FROM PLASMA AND CSF:PLASMA RATIOS, WHICH VARIED FROM 0.2 TO 0.6 BETWEEN 2 AND 3 HR AFTER IV DOSES, AGREED WELL WITH THE RATIO OF UNBOUND:TOTAL PENTAZOCINE IN PLASMA.
PENTAZOCINE IS WELL ABSORBED BY ALL ROUTES OF ADMIN, BUT THERE IS CONSIDERABLE INDIVIDUAL VARIATION. BIOAVAILABILITY AFTER ORAL ADMIN IS 18.4% +/- 7.8%; THE REDUCTION IS DUE TO FIRST-PASS METABOLISM.
For more Absorption, Distribution and Excretion (Complete) data for PENTAZOCINE (7 total), please visit the HSDB record page.
Metabolism
Hepatic
PENTAZOCINE YIELDS 1,2,3,4,5,6-HEXAHYDRO-8-HYDROXY- ALPHA,6(EQ),11(AX)-TRIMETHYL-2,6-METHANO-3-BENZAZOCINE-3-CIS-2-BUTEN-1-OL & 1,2,3,4,5,6-HEXAHYDRO-8-HYDROXY-ALPHA,6(EQ),11(AX)- TRIMETHYL-2,6-METHANO-3-BENZAZOCINE-3-TRANS-2-BUTEN-1-OL IN MONKEY & MOUSE. /FROM TABLE/
... RATE OF METABOLISM OF PENTAZOCINE HAS BEEN SHOWN TO DIFFER /BETWEEN/ SMOKERS & NON-SMOKERS.
IN THE RAT, AFTER ORAL ADMIN OF PENTAZOCINE, MAINLY PENTAZOCINE & ITS GLUCURONIDE CONJUGATES WERE FOUND IN URINE. ALTHOUGH EIGHT METABOLITES WERE EXTRACTED FROM URINE & CHARACTERIZED ... THE AMOUNTS WERE SMALL AND INDICATED HYDROXYLATION AND METHOXYLATION OF THE AROMATIC RING, WITH SOME OXIDN OF THE DIMETHYLALLYL SIDE-CHAIN.
Pentazocine is metabolized in the liver, mainly by oxidation of the terminal methyl groups of the dimethyl alkyl side chain to form alcoholic and carboxylic acid metabolites; glucuronide conjugation also occurs.
Hepatic
Half Life: 2 to 3 hours
External links
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