Source: Medicines & Healthcare Products Regulatory Agency (GB) Revision Year: 2019 Publisher: Martindale Pharma, Bampton Road, Romford, RM3 8UG, England
Pharmacotherapeutic group: Phenylpiperidine derivatives
ATC code: N02AB02
Pethidine binds to opioid receptors and exerts its chief pharmacological action on the CNS and the neural elements of the bowel. The analgesic effects of pethidine are detectable about 15 minutes after oral administration, reaching a peak in about 2 hours and subsiding gradually over several hours. In equianalgesic doses pethidine depresses respiration to a similar extent to morphine. Pethidine has a spasmogenic effect on certain smooth muscles similar to that observed for other opioids.
Ambulatory patients given pethidine may experience syncope associated with hypotension but symptoms rapidly clear on lying down. Otherwise in therapeutic doses pethidine has no significant untoward effects on the cardiovascular systems, especially if patients are lying down. Pethidine combines analgesic and antispasmodic properties; it is relatively short acting and has little soporific effect. These properties make pethidine particularly useful for pain relief in labour and as an adjunct to nitrous oxide-oxygen anaesthesia.
Peak plasma concentrations are normally observed between 1 and 2 hours after oral administration. However, only about 50% of the drug escapes first pass metabolism to enter the circulation. About 60% is protein bound in plasma.
Heavy alcohol drinkers have an increased apparent volume of distribution with consequent initially lower pethidine plasma concentrations. Older Patients have higher plasma concentrations and reduced protein binding which may account for the increased response in therapeutic dosages. Pethidine is mainly metabolised in the liver by hydrolysis to pethidinic acid, or by N-demethylation to norpethidine, followed by hydrolysis to norpethidinic acid. Subsequent, partial conjugation with glucuronic acid may also occur.
None stated.
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