Cimetidine

H2-receptor antagonist for gastric ulcers and excess gastric acid secretion in horses and small animals; historically used for equine PPID (Cushing's). H2 receptor antagonist (histamine H2 blocker). Mechanism: competitively and reversibly blocks histamine H2 receptors on gastric parietal cells → reduces histamine-stimulated gastric acid secretion. Also inhibits CYP450 enzymes (multiple drug interactions). Older H2 blocker; largely superseded by newer H2 blockers and PPIs. Key information Significant drug interactions — inhibits CYP450 enzymes; increases levels of theophylline, lidocaine, warfarin, and many others. Use famotidine or omeprazole when interaction concerns exist. H2 blocker — less effective than PPIs.

Oral tablets: Administer orally. May be given with food to improve compliance and reduce GI upset. Administer with food to reduce GI adverse effects. or without. IV: dilute in 0.9% NaCl; Administer IV slowly; rapid infusion may cause adverse reactions. Administer q6–8h. Store at room temperature; protect from light. If a dose is missed Administer as soon as you remember. If it is almost time for the next scheduled dose, skip the missed dose and resume the normal schedule. Never double up doses to make up for a missed one.

GI: diarrhea, constipation. CNS: confusion, agitation, headache (especially in elderly). Gynecomastia/antiandrogenic effects (prolonged high-dose use). Numerous CYP450 drug interactions (CYP1A2, CYP2D6, CYP3A4 inhibition — increase levels of theophylline, warfarin, benzodiazepines, etc.).

For animals Numerous drug interactions (CYP1A2, CYP2D6, CYP3A4 inhibitor) — increases plasma levels of theophylline, warfarin, lidocaine, metronidazole, and others. Reduce dose or extend interval in renal impairment. — dose-reduce. Use with caution in hepatic impairment. For people handling this medication Wash hands thoroughly with soap and water after handling. Avoid contact with eyes; if contact occurs, flush with water for 15 minutes and seek medical attention. Keep out of reach of children. If accidental ingestion occurs, contact Poison Control (1-800-222-1222). H2 blocker — Wash hands thoroughly with soap and water after handling. after handling. Keep out of reach of children.

Contact your veterinarian. Cimetidine overdose causes GI signs and mental status changes. Numerous drug interactions — monitor other medications. Contact your veterinarian, a veterinary emergency clinic, or the ASPCA Animal Poison Control Center (888-426-4435) immediately. Do not induce vomiting unless specifically directed by a veterinary professional.