cimetidine: clinical use

Prescribing considerations

• Review the full medication list because cimetidine affects CYP-mediated metabolism, renal tubular secretion and pH-dependent absorption.
• Assess renal function; systemic exposure rises in renal impairment.
• Exclude gastric malignancy where appropriate because symptom improvement and superficial healing can delay diagnosis.
• Assess new or changing dyspepsia, weight loss and other alarm features.
• Periodically reassess prolonged treatment.
• Consider excipients including propylene glycol, sorbitol, preservatives, colouring, ethanol and sodium.

Contraindications and cautions

• Hypersensitivity to cimetidine or any ingredient of the selected product.
• Liquid products containing sorbitol or maltitol are unsuitable in hereditary fructose intolerance.

Monitoring

• Renal function and clinical response, particularly in older people or renal impairment.
• Prothrombin time or INR with coumarin anticoagulants.
• Clinical effects or concentrations of narrow-therapeutic-index medicines such as phenytoin and theophylline.
• Blood counts when concurrent illness or treatment can suppress bone marrow.
• Mental-state changes in older, critically ill or renally impaired patients.
• Renal and hepatic status when propylene-glycol-containing liquids present additional risk.

Clinical pharmacology

Cimetidine is a reversible competitive H2-receptor antagonist. It is rapidly absorbed orally, undergoes first-pass metabolism and is eliminated mainly by the kidneys, much of it unchanged. It inhibits several cytochrome P450 enzymes and can modestly raise plasma creatinine through effects on renal handling without necessarily reducing glomerular filtration.

Formulation and product differences

• Film-coated tablets are swallowed with water and are essentially sodium-free according to the selected tablet product information.
• The generic oral solution contains sorbitol, maltitol, propylene glycol, parabens and Sunset Yellow.
• The syrup contains sorbitol, propylene glycol, parabens, Sunset Yellow, ethanol, sucrose and sodium.
• Peri-anaesthetic licensing differs: the selected tablets and syrup include an acid-aspiration indication, while the selected generic oral solution advises avoiding treatment before general anaesthesia and during labour.

Oral solution

Route: Oral

Strengths: 200 mg/5 mL

Tablet

Route: Oral

Strengths: 200 mg, 800 mg