Pethidine

Introduction

Pethidine, is a synthetic opioid analgesic that acts mainly as a -opioid agonist. Pethidine is used for the relief of most types of moderate to severe acute pain including the pain of labour. It is more lipid soluble than morphine and has a less potent and shorter lasting analgesic effect; analgesia usually lasts for 2 to 4 hours. Its short duration of action and accumulation of its neurotoxic metabolite make it unsuitable for the management of chronic pain.

Generic Name 藥名	HA Code 藥物代碼	Classification藥物分類
Pethidine 1ml injection	PETH02	DD

Equivalent doses of opioid analgesics

Analgesic/Route	Dose
Codeine: PO	100 mg
Diamorphine: IM, IV, SC	3 mg
Dihydrocodeine: PO	100 mg
Morphine: PO	10 mg
Morphine: IM, IV, SC	5 mg
Oxycodone: PO	6.6 mg
Tramadol: PO	100 mg

Route of Adminstration	SC
	IV

Dosage

For moderate to severe acute pain:

Oral	50-150 mg every 4 hours if necessary
Subcutaneous or intramuscular	25-100 mg, then 25-100 mg after 4 hours
Intravenous	25-50 mg, then, 25-50mg repeated after 4 hours

In obstetric analgesia 50 to 100 mg may be given by intramuscular or subcutaneous injection as soon as contractions occur at regular intervals. This dose may be repeated after 1 to 3 hours if necessary up to a maxmum of 400 mg in 24 hours.

Doses in children

Oral or intramuscular	0.5 to 2mg/kg, repeated after 4 hours if necessary

Side Effects

As for Opioid Analgesic in general

The commonest adverse effects are nausea, vomiting, constipation, drowsiness and confusion.

Large doses of opioids produce respiratory depression and hypotension, with circulatory failure and deepening coma. Death may occur from respiratory failure.

Treatment of Adverse Effects

1.Constipation can be treated with laxatives such as senna tables and lactulose.

2.Nausea and vomiting can be alleviated by metoclopramide.

3.Intensive supportive therapy may be required to correct respiratory failure and shock. Naloxone is used for rapid reversal of the severe respiratory depression and coma.

Euphoria, nausea and vomiting, respiratory depression, constipation and cough suppression.

Pharmacokinetics

bioavailability	Pethidine hydrochloride is absorbed from the gastrointestinal tract, but only about 50% of the drug reaches the systemic circulation because of first-pass metabolism. Absorption after intramuscular injection is variable.
Onset of action	Peak plasma concentrations have been reported 1 to 2 hours after oral doses. It is about 60 to 80% bound to plasma proteins.
Elimination half-life	It has a plasma elimination half-life of about 3 to 6 hours.
Metabolism	Pethidine is metabolized in the liver. Drug Management Efficiency pain control Safety mental status, blood pressure, respiratory drive, and misuse/overuse. Caution Not suitable for severe chronic pain In patients with a history of convulsive disorders or supraventricular tachycardias. Tolerance and dependence