BP

Cimetidine

Proprietary

Dyspamet^® (Goldshield Pharmaceuticals Ltd), Tagamet^® (SmithKline Beecham), cimetidine (non-proprietary, see BNF for details)

Group

Antacid, H₂ receptor antagonist

Uses/indications

To reduce gastric acidity, intrapartum or prior to caesarean section

Type of drug

POM

Presentation

Tablets – light green, also chewable and effervescent, IM injection, syrup

Dosage

Oral – 400 mg at start of labour repeated 4 hrly (max 2.4 g/day)
IM – 200 mg 4–6-hrly (max dosage 2.4 g daily), IV – slow injection 200 mg over at least 5 min 4–6-hrly, IV infusion – 50–100 mg/h over 24 h

Route of admin

Oral, IM, rarely IV slow injection or IV infusion

Contraindications

Hypersensitivity to cimetidine, avoid in clients stabilized on phenytoin and warfarin

Side effects

Rare but include dizziness, rash, in high doses reversible confusional states, headache

Interactions

Analgesics – inhibits the metabolism of opioid analgesics and increases their plasma concentration
Antibiotics – inhibits the metabolism of metronidazole and erythromycin
Anticoagulants – inhibits the metabolism of warfarin, and enhances its effects
Antiepileptics – inhibits the metabolism of phenytoin, sodium valproate and carbamazepine
Antihypertensives – inhibits the metabolism of labetalol

Pharmacodynamic properties

H₂ receptor antagonist that rapidly inhibits both basal and stimulated gastric secretion of acid. It also reduces pepsin output