Warfarin drug interactions with

Morkunas A, Graeme K. Zafirlukast warfarin drug interaction with gastrointestinal bleeding. J Toxicol 1997 35 501. 

Inform the patient about the potential drug-drug interactions with warfarin, including over-the-counter medications and dietary supplements (Tables 7-8, 7-9, and 7-10). Instruct the patient to call the health care practitioner responsible for monitoring warfarin therapy before starting any new medications or dietary supplements. 

While generally not of major concern, omeprazole may inhibit the metabolism of warfarin, diazepam, and phenytoin lansoprazole may decrease theophylline concentrations. Drug interactions with omeprazole are of particular concern in patients who are considered slow metabolizers, as are approximately 3% of the Caucasian population. Unfortunately, it is unclear which patients have the polymorphic gene variation that makes them slow metabolizers.17 The metabolism of esomeprazole may also be altered in patients with this polymorphic gene variation. Patients on potentially interacting drugs should be monitored for development of drug-related problems. 

There are several important drug-drug interactions with allopurinol. The effects of both theophylline and warfarin may be potentiated by allopurinol. Azathioprine and 6-mercaptopurine are purines whose metabolism is inhibited... 

Numerous potential drug interactions are possible clinically significant drug interactions with oral contraceptives, warfarin, and oral dexametha-sone have been described. 

Azithromycin Drugs that may interact with azithromycin include antacids, cyclosporine, HMG-CoA reductase inhibitors, pimozide, tacrolimus, theophyllines, and warfarin. Also consider all drug interactions with erythromycin. 

All quinolones interact with multivalent cations, forming chelation complexes resulting in reduced absorption. Major offenders are antacids vitamins containing calcium and iron can also be problematic. All fluoroquinolones interact with warfarin, didanosine (ddi), and phenytoin, resulting in decreased absorption or metabolism. Ciprofloxacin and other second-generation drugs interact with theophylline by decreasing its clearance, which leads to theophylline toxicity. 

Clinicians should be aware of a few drug interactions with Zolpidem. Flumazenil acts as an antagonist to the hypnotic effects of zolpidem. There is decreased alertness when zolpidem is combined with cimetidine. There is an increase in anterograde amnesia in volunteers treated with a combination of imipramine and zolpidem. Haloperidol, ranitidine, chlorpromazine, warfarin, and digoxin, along with cimetidine and flumazenil, do not alter the pharmacokinetics of zolpidem (Salva and Costa, 1995). 

Significant drug interactions with theophylline [268], itraconazole [269], warfarin, yS-acetyldigoxin, ranitidine, probenecid and oral contraceptives have not been reported with moxifloxacin [12,237]. 

Breckenridge A, Orme ML, Thorgeirsson S, Davies DS, Brooks RV. Drug interactions with warfarin studies with dichloralphenazone, chloral hydrate and phenazone (anti-pyrine). Clin Sci 1971 40(4) 351-64. 

Warfarin is rapidly and nearly completely absorbed by the oral route. Peak plasma levels typically occur within 2-8 h. Warfarin is highly protein bound 97-99%. The volume of distribution approximates 0.151 kg Warfarin is extensively metabolized by hepatic microsomal enzymes. The primary metabolites are 6- and 7-hydroxy warfarin via oxidation and several warfarin alcohols via reduction. The warfarin alcohols retain weak anticoagulant activity. The metabolites undergo enterohepatic circulation. Approximately 85 % of warfarin appears in the urine as metabolites. Less than 1% or 2% appears in the urine unchanged. Warfarin metabolites are also excreted in the stool. The plasma half-life varies widely, from 10 to 80 h it is typically 36-44 h. The duration of clinical effects can significantly exceed the half-life of warfarin. (Note There are many drug interactions with warfarin the reader is referred to a standard pharmacology text for further details.)... 

Drug interactions with acetaminophen can occur for example, iso-niazid can increase the risk of hepatotoxicity. Chronic ingestion of maximal doses of acetaminophen may intensify the anticoagulant effect in patients taking warfarin, so that such individuals may require closer monitoring. Food decreases the maximum serum concentration of acetaminophen by approximately one-half. 

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