Famotidine Warfarin

Deravirdine (Rescnptor) [Antiretroviral/NNRTI] Uses HIV Infxn Action Nonnucleoside RT inhibitor Dose 400 mg PO tid Caution [C, ] CDC recommends HIV-infected mothers not to breast-feed (transmission risk) w/ renal/hepatic impair Contra Use w/ drugs dependent on CYP3A for clearance (Table VI-8) Disp Tabs SE Fat redistribution, immune reconstitution synd, HA, fatigue, rash, T transaminases, N/V/D Interactions T Effects W/ fluoxetine T effects OF benzodiazepines, cisapride, clarithromycin, dapsone, ergotamine, indinavir, lovastatin, midazolam, nifedipine, quinidine, ritonavir, simvastatin, terfena-dine, triazolam, warfarin effects W/ antacids, barbiturates, carbamazepine, cimetidine, famotidine, lansoprazole, nizatidine, phenobarbital, phenytoin, ranitidine, rifabutin, rifampin effects OF didanosine EMS Use of benzodiazepines and CCBs should be avoided may cause a widespread rash located on upper body and arms OD May cause an extension of nl SEs symptomatic and supportive Deferasirox (Exjade) [Iron Chelator] Uses Chronic iron overload d/t transfusion in pts >2 y Action Oral iron chelator Dose Initial 20 mg/kg... 

Drug interactions Cimetidine is a CYP450 inhibitor and can inhibit the metabolism of phenytoin, warfarin, and theophylline. Famotidine, nizatidine, and ranitidine are unlikely to cause clinically significant drug interactions. All antagonists have the potential to interact with other drugs that require gastric acid for absorption (e.g., ketoconazole, itraconazole). 

A 46-year-old woman is prescribed doxycycline for a diagnosis of community-acquired pneumonia. Her PMH is significant for iron-deficiency anemia, peptic ulcer disease, HTN, a recent DVT, and headaches. Her current medications include ferrous sulfate, ibuprofen, enalapril, acetaminophen, famotidine, and warfarin. Which of her following medications is most likely to result in decreased levels of doxycycline ... 

The anticoagulant effects of warfarin can be increased by cimeti-dine. The effect is generally minor to modest, although severe bleeding has been reported in a few cases. Acenocoumarol seems to interact similarly, but phenprocoumon appears not to be affected. In one patient the effects of phenindione were modestly increased by cimetidine. Famotidine, nizatidine, ranitidine and roxatidine normally do not appear to interact, although isolated cases of bleeding have been reported. 

In a study in 8 healthy subjects taking doses of warfarin titrated to prolong the prothrombin time by 2 to 5 seconds (mean dose 4 mg daily), treatment with famotidine 40 mg daily for 7 days did not affect prothrombin times, thrombotest coagulation times or steady-state plasma warfarin levels. No changes in prothrombin times were seen in 3 patients stabilised on acenocoumarol or fluindione when they were given famotidine. ... 

However, in another report 2 patients taking warfarin are said to have had prolonged prothrombin times and bled when they took famotidine. ... 

De Lepeleire I, van Hecken A, Verbesselt R, Tjandra-M a TB, Buntinx A, Distlerath L, De Schepper PJ. Lack of interaction between famotidine and warfarin. IntJ Clin Pharmacol Res... 

Aripiprazole plasma levels are increased by inhibitors, and decreased by inducers, of CYP3A4. Quinidine increases aripiprazole levels. The manufacturers advise caution with drugs that can prolong the QT intervaL Food and famotidine do not have a clinically relevant effect on the pharmacokinetics of aripiprazole, and aripiprazole does not affect the pharmacokinetics of dextromethorphan, omeprazole, and warfarin. 

---