Cimetidine adverse effects

The H2RAs are generally well tolerated. The most common adverse effects are headache, somnolence, fatigue, dizziness, and either constipation or diarrhea. Cimetidine may inhibit the metabolism of theophylline, warfarin, phenytoin, nifedipine, and propranolol, among other drugs. 

Fig. 8.27 Structures of the thiourea-containing H2 antagonist metiamide, which caused blood dyscrasias in man, Cimetidine and its cyanoimino-containing analogue cimetidine which did not show similar adverse effects.

Il.b.l.1. Adverse effects of anti-secretory treatment. Histamine H2 antagonists and proton pump inhibitors are very safe as well as effective treatments. Cimetidine has small effects on hepatic drug metabolism which are only of clinical signiflcance with drugs used in doses close to toxic levels, notably phenytoin, aminophylline and warfarin. Other adverse effects such as headache, rash and thrombocytopenia are rare. 

Cimetidine (Tagamet) CNS adverse effects, including confusion. Low... 

CCB Dose 10-60 mg/d PO 4- start doses w/ elderly or hepatic impair Caution [C, ] Disp Tabs SE Edema, HA, flushing Interactions T Effects W/ antihypertensives, cimetidine, nitrates, EtOH, high-fat foods 4- effects W/ phenytoin, St. John s wort EMS T Adverse effects w/ grapefruit juice and EtOH use fentanyl and nitro w/ caution T risk of photosensitivity Rxn OD May cause hypotension, tach, and CV collapse calcium salts can be given as antidote... 

Biguanides This class of antidiabetics may cause acute poisoning with adverse effects such as acidosis and may be treated by supportive therapy. These drugs have therapeutic interactions with other antidiabetic drugs, alcohol, drugs that affect kidney function, and cimetidine. 

Cimetidine can impair benzodiazepine metabolism and lead to adverse effects (SEDA-18, 43). In contrast, a few benzodiazepines are metabolized exclusively by glucuro-nide conjugation (lorazepam, oxazepam, temazepam), and are therefore unaffected by concomitant therapy with cimetidine and other oxidation inhibitors (123). 

Omeprazole, like cimetidine, can impair benzodiazepine metabolism and lead to adverse effects (SEDA-18, 43). Other drugs, including antibiotics (erythromycin, chloramphenicol, isoniazid), antifungal drugs (ketoconazole, itraconazole, and analogues), some SSRIs (fluoxetine, paroxetine), other antidepressants (nefazodone), protease inhibitors (saquinavir), opioids (fentanyl), calcium channel blockers (diltiazem, verapamil), and disulfiram also compete for hepatic oxidative pathways that metabolize most benzodiazepines, as well as zolpidem, zopiclone, and buspirone (SEDA-22,39) (SEDA-22,41). 

SSRIs H2 RECEPTOR BLOCKERS -CIMETIDINE t efficacy and adverse effects, e.g. nausea, diarrhoea, dyspepsia, dizziness, sexual dysfunction t bioavailability Use with caution, monitor for t side-effects. 1 dose may be necessary... 

TCAs H2 RECEPTOR BLOCKERS-CIMETIDINE T efficacy and adverse effects, e.g. dry mouth, urinary retention, blurred vision, constipation 1 metabolism Use alternative acid suppression or monitor more closely and i dose. Rapid hydroxylators may be at t risk... 

CARBAMAZEPINE H2 RECEPTOR BLOCKERS -CIMETIDINE, FAMOTIDINE, RANITIDINE t plasma concentrations of phenytoin and risk of adverse effects including phenytoin toxicity, bone marrow depression and skin reactions Inhibition of metabolism via CYP2C9 and CYP2C19 Use alternative acid suppression (e.g. ranitidine) or warn patients that effects last about 1 week. Consider monitoring carbamazepine levels, and adjust dose as necessaiy... 

ALMOTRIPTAN, ELETRIPTAN, ZOLMITRIPTAN H2-RECEPT0R BLOCKERS -CIMETIDINE t efficacy and adverse effects of zolmitriptan, e.g. flushing, sensations of tingling, heat, heaviness, pressure or tightness of any part of body including the throat and chest, dizziness Inhibition of metabolism via CYP1A2 Consider alternative acid suppression, e.g. H2 antagonist or proton pump inhibitors (not omeprazole or lansoprazole), or monitor more closely and l maximum dose of zolmitriptan to 5 mg/24 hours... 

PRAMIPEXOLE, ROPINIROLE H2-RECEPTOR BLOCKER-CIMETIDINE T efficacy and adverse effects of pramipexole 1 renal excretion of pramipexole by inhibition of cation transport system. Inhibition of CYP1A2-mediated metabolism of ropinirole Monitor closely i dose of pramipexole may be required. Adjust dose of ropinirole as necessaiy or use alternative acid suppression, e.g. H2 antagonist proton pump inhibitor (not omeprazole or lansoprazole)... 

ANTIPSYCHOTICS-CHLORPROMAZINE, CLOZAPINE, HALOPERI-DOL, OLANZAPINE, PERPHENAZINE, RISPERIDONE, SERTINDOLE, THIORIDAZINE, ZUCLOPENTHIXOL H2 RECEPTOR BLOCKERS -CIMETIDINE t plasma concentrations of these antipsychotics, with risk of associated adverse effects Cimetidine is an inhibitor of CYP3A4 (sertindole, haloperidol, risperidone), CYP2D6 (chlorpromazine, risperidone, zudopenthixol, thioridazine, perphenazine) and CYP1A2 (clozapine, olanzapine, sertindole, haloperidol) Avoid concomitant use. Choose an alternative acid suppression, e.g. H2 antagonist... 

BZDs (NOT LORAZEPAM OR TEMAZEPAM) H2 RECEPTOR BLOCKERS -CIMETIDINE, RANITIDINE t efficacy and adverse effects of BZD, e.g. sedation Cimetidine is an inhibitor of CYP3A4, CYP2D6, CYP2C19 and CYP1A2 Not clinically significant for most patients. Conflicting information for some BZDs. Monitor more closely, and i dose if necessary... 

---