Pethidine

Pethidine is a synthetic opioid analgesic of the phenylpiperidine class. Pethidine is the prototype of a large family of analgesics that also includes, for example, fentanyl. Pethidine is indicated for the treatment of moderate to severe pain and is administered as a hydrochloride salt in tablets, as a syrup or by intramuscular, subcutaneous or intravenous injection.

Pharmadynamics

Like morphine, pethidine exerts its analgesic effects by acting as an agonist at the μ-opioid receptor. Pethidine has structural similarities to atropine and other tropane alkaloids and may have some of their effects and side effects. In addition to these opioidergic and anticholinergic effects, it has a local anesthetic effect related to its interactions with sodium ion channels.

Pharmacokinetics

Pethidine is rapidly hydrolyzed in the liver to pethidic acid and also demethylated to norpethidine, which has half the analgesic activity of pethidine but a longer elimination half-life; it accumulates with regular administration or with decreased renal function. The metabolites of pethidine are further conjugated with glucuronic acid and excreted in the urine.

Side Effects

The adverse effects of pethidine are primarily those of opioids as a class: nausea, vomiting, dizziness, diaphoresis, urinary retention, and constipation. Because of the moderate stimulant effects mediated by dopamine and norepinephrine, sedation is less likely compared to other opioids. Unlike other opioids, it does not cause miosis due to its anticholinergic properties.

Overdose may cause muscle flaccidity, respiratory depression, obtundation, cold and clammy skin, hypotension, and coma.

Toxicological data

LD50 (rat, oral): 162 mg-kg-1