PETHIDINE

Pethidine may be given by intramuscular, subcutaneous or slow intravenous injection. For intravenous administration the contents of the ampoule can be diluted to 10ml with Water for Injections giving a strength of 5 mg/ml(1 ml ampoule) or 10 mg/ml (2ml ampoule).

Pre-anaesthetic medication Administered about one hour before the operation. Adults : 50mg-100mg by intramuscular injection. Elderly: 50mg-100mg by intramuscular injection. Elderly patients may be more sensitive to pethidine. 0mg/kg by intramuscular injection Obstetric analgesia 50-100mg may be given by intramuscular or subcutaneous injection as soon as contractions occur at regular intervals.

The dose may be repeated after one to three hours if necessary up to a maximum of 400mg in 24 hours. Management of severe pain, including post-operative pain Adults : 25 mg-100mg by intramuscular or subcutaneous injection every four hours By slow intravenous injection 25-50mg repeated every four hours.

Elderly: 25 mg-100mg by intramuscular or subcutaneous injection every four hours. By slow intravenous injection 25-50mg repeated every four hours. Elderly patients may be more sensitive to pethidine. The total daily dose may need to be reduced in elderly patients receiving repeated doses.

Initial doses should not exceed 25mg as this group of patients may be especially sensitive to the central depressant effect of the drug. 5 - 2mg/kg by intramuscular injection every four hours. Hepatic impairment The dose should be reduced.

Renal impairment The dose should be reduced in mild to moderate impairment. Severe renal impairment is a contraindication to use (see

The most serious hazard of therapy is respiratory depression (see also

3 Contraindications • Known hypersensitivity to pethidine. • Severe renal impairment. • Acute respiratory depression. • Concurrent use of monoamine oxidase inhibitors (including moclobemide and phenelzine) or use within two weeks of their discontinuation, as severe CNS excitation or depression (hypertension or hypotension) may occur.

• Concurrent use of ritonavir – risk of norpethidine toxicity. • Concurrent use of selegiline – risk of hyperpyrexia and CNS toxicity. • Phaeochromocytoma • Coma • Raised intracranial pressure or head injury, as there is an increased risk of respiratory depression that may lead to elevation of CSF pressure.

The sedation and pupillary changes produced may interfere with accurate monitoring of the patient. • Acute alcoholism. • Where there is a risk of paralytic ileus or in acute diarrhoeal conditions associated with antibiotic-induced pseudomembranous colitis or diarrhoea caused by poisoning (until the toxic material has been eliminated).

4 Special warnings and precautions for use Repeated administration of pethidine may lead to dependence and tolerance developing, but this should not deter its use in the control of pain in terminal illness. Abrupt withdrawal in patients who have developed tolerance may precipitate a withdrawal syndrome.

Caution should be exercised in patients with a known tendency or history of drug abuse. Babies born to opioid dependent mothers may suffer withdrawal symptoms. 3 Contraindications). Use with caution or in reduced doses in patients with biliary tract disorders, hypothyroidism, adreno-cortical insufficiency, hypotension, shock, prostatic hypertrophy, urethral stricture, inflammatory or obstructive bowel disorders, myasthenia gravis, supraventricular tachycardia, a history of convulsive disorders, and in debilitated patients.

Pethidine neurotoxicity may be seen in patients with renal failure, cancer or sickle cell anaemia, during concomitant administration of drugs that may increase the production of the metabolite norpethidine (see

). For concomitant illnesses/conditions where dose reduction may be appropriate see