Tolterodine Warfarin

Colucci VJ, Rivey MP. Tolterodine-warfarin drug interaction.. dn/jP/ianmacoi/ier (1999) 33, 1173-6. 

Drugs that may affect fluconazole include cimetidine, hydrochlorothiazide, and rifampin. Drugs that may be affected by fluconazole include alfentanil, benzodiazepines, buspirone, carbamazepine, cisapride, oral contraceptives, corticosteroids, cyclosporine, haloperidol, HMG-CoA reductase inhibitors, losartan, nisoldipine, phenytoin, protease inhibitors, rifabutin, sirolimus, sulfonylureas, tacrolimus, theophylline, tolterodine, tricyclic antidepressants, vinca alkaloids, warfarin, zidovudine, and zolpidem. 

In healthy subjects, tolterodine did not aiter the pharmacokinetics or pharmacodynamics of warfarin, but isoiated cases of raised INRs have been reported. 

In a placebo-controlled study in healthy subjects, tolterodine 2 mg twice daily for 7 days did not affect the pharmacokinetics oiR- or 5-warfarin after a single 25-mg dose of warfarin given on day 4, nor were the pharmacokinetics of tolterodine altered by warfarin. In addition, the prothrombin time and factor Vn activity were not altered by tolterodine. ... 

However, a report describes two patients on stable warfarin doses who had elevated INRs shortly after tolterodine 2 mg daily was started and stopped one had an INR of 6.1 one day after stopping 13 days of tolterodine, and the other had an INR of 7.4 two days after stopping 8 days of tolterodine. In both cases no bleeding occurred and warfarin was withheld for three doses and successfully reinstated at the original dose. Another case has been reported of a patient who required a 15% reduction in warfarin dose while taking tolterodine 4 mg daily. Her maximum INR had been 3.9. However, she had undergone several warfarin dose increases over the previous 2 months and her INR had been fluctuating. ... 

The controlled study suggests that no warfarin dose adjustment would expected to be needed when tolterodine is added to warfarin therapy. However, the 3 cases introduce a note of caution. Although additional monitoring would seem over-cautious on the basis of these cases, bear them in mind in the case of an unexpected response to warfarin. 

RahirnyM, Hallen B, Narang P. Effect of tolterodine on the anticoagulant actions and pharmacokinetics of single-dose warfarin in healthy volunteers. Arzneimittelforschung (2002) 52, 890-5. 

Taylor JR. Probable interaction between tolterodine and warfarin. Pharmacotherapy (2006) 26,719-21. 

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