CIMETIDINE

Gastroesophageal reflux disease: Oral: 400 mg 4 times/day or 800 mg twice daily for 12 weeks

Short-term treatment of active ulcers:
  300 mg 4 times/day or 800 mg at bedtime or 400 mg twice daily for up to 8 weeks
    
Duodenal ulcer prophylaxis: 400 mg at bedtime
Heartburn, acid indigestion, sour stomach (OTC labeling):  200 mg up to twice daily; may take 30 minutes prior to eating foods or beverages expected to cause heartburn or indigestion

DOSING IN  RENAL IMPAIRMENT –decrease by 50%

DOSING IN  HEPATIC IMPAIRMENT Safe in mild liver disease but use with caution and in reduced dosage in severe liver disease

DOSAGE FORMS 

Tablet: 200 mg [OTC], 300 mg, 400 mg, 800 mg
  Tagamet® HB 200: 200 mg

ADMINISTRATION

Administer with meals so that the drug’s peak effect occurs at the proper time

SIGNIFICANT  ADVERSE REACTIONS

Headache
Dizziness
Gynecomastia
 
Diarrhea
Hypotension
Pancreatitis
Confusion

CONTRAINDICATIONS — Hypersensitivity to cimetidine, any component of the formulation, or other H2 antagonists

DRUG INTERACTIONS 

Amiodarone: Serum concentration of amiodarone is increased; avoid concurrent use.
Antiretrovirals: Histamine H2 antagonists may decrease the absorption of atazanavir
Benzodiazepines (except lorazepam, oxazepam, temazepam): Serum concentration of the benzodiazepine is increased; consider alternative H2 antagonist or monitor for benzodiazepine toxicity.
Beta-blockers (except atenolol, betaxolol, bisoprolol, nadolol, penbutolol): Effects of the beta-blocker may be increased
Calcium channel blockers (except amlodipine and nicardipine): Serum concentration of the CCB is increased
Carbamazepine: Plasma concentration of carbamazepine may increase transiently (1 week). Monitor for carbamazepine toxicity or use an alternative H2 antagonist.
Citalopram: Serum concentration of citalopram is increased
Clozapine: Cimetidine may increase levels/effects; consider alternative H2 antagonist
Cyclosporine: Serum concentration of cyclosporine may increase; monitor cyclosporine levels.
CYP1A2 substrates: Cimetidine may increase the levels/effects of CYP1A2 substrates. Example substrates include aminophylline ropinirole, theophylline, and trifluoperazine.
CYP2C19 substrates: Cimetidine may increase the levels/effects of CYP2C19 substrates. Example substrates include citalopram, diazepam, phenytoin, propranolol, and sertraline.
CYP2D6 substrates: Cimetidine may increase the levels/effects of CYP2D6 substrates. Example substrates include amphetamines, selected beta-blockers, fluoxetine, lidocaine, mirtazapine, nefazodone, risperidone, ritonavir, tricyclic antidepressants, and venlafaxine.
CYP2D6 prodrug substrates: Cimetidine may decrease the levels/effects of CYP2D6 prodrug substrates. Example prodrug substrates include codeine, hydrocodone, oxycodone, and tramadol.
CYP3A4 substrates: Cimetidine may increase the levels/effects of CYP3A4 substrates. Example substrates include benzodiazepines, calcium channel blockers, cyclosporine, mirtazapine, nateglinide, nefazodone, sildenafil ,tacrolimus, and venlafaxine.
Ketoconazole, fluconazole, itraconazole (especially capsule): Decreased serum concentration; avoid concurrent use with H2 antagonists.
Lidocaine: Serum concentration of lidocaine is increased; use alternative H2 antagonist.
Metformin: Serum levels/effects may be increased by cimetidine; monitor for hypoglycemia.
Phenytoin: Serum levels/effects may be increased by cimetidine; avoid concurrent use.
Procainamide: Cimetidine may increase levels/effects; monitor.
Quinolones: Renal elimination of quinolone antibiotics may be decreased.
Selective serotonin reuptake inhibitors (eg, paroxetine, citalopram): Serum concentrations may be increased by cimetidine; monitor.
Sulfonylureas: Cimetidine may increase levels/effects; monitor for hypoglycemia
Tricyclic antidepressants: Serum concentration is increased; consider alternative H2 antagonist or monitor for TCAs toxicity.
Thioridazine: Serum levels/effects may be increased by cimetidine; concurrent use contraindicated by manufacturer.
Warfarin: INR is increased; cimetidine’s effect is dose related. Use an alternative H2 antagonist if possible or monitor INR closely and adjust warfarin dose as needed.

PREGNANCY RISK FACTOR — B

LACTATION — Enters breast milk/not recommended.