Terbinafine Warfarin

While terbinafine had no effect on warfarin in healthy volunteers, it can prolong the prothrombin time in some individuals (74-77), prompting intensification of laboratory control during terbinafine therapy. 

A 71-year-old woman taking a stable dose of warfarin and cimetidine was treated with terbinafine, and 32 days later developed profuse intestinal bleeding associated with a prothrombin time of 120 seconds, suggestive of an interaction between warfarin and terbinafine, either directly or through the mediation of cimetidine (which can reduce terbinafine clearance by 33%) (74). 

Since a pharmacokinetic study of a single dose of warfarin in 26 healthy volunteers treated with terbinafine showed no significant interaction, and since a large postmarketing study of terbinafine did not find any cases of interaction of warfarin with terbinafine, the manufacturers (78) and others (77) have cautioned about any generalization regarding an interaction between terbinafine and warfarin. 

Gupta AK, Ross GS. Interaction between terbinafine and warfarin. Dermatology 1998 196(2) 266-7. 

Warwick JA, Corrall RJ. Serious interaction between warfarin and oral terbinafine. BMJ 1998 316(7129) 440. 

Guerret M, Francheteau P, Hubert M. Evaluation of effects of terbinafine on single oral dose pharmacokinetics and anticoagulant actions of warfarin in healthy volunteers. Pharmacotherapy 1997 17(4) 767-73. 

Clarke MF, Boardman HS. Interaction between warfarin and oral terbinafine. Systematic review of interaction profile of warfarin is needed. BMJ 1998 317(7152) 205-6. 

Terbinafine did not interact with warfarin in a study in healthy subjects, and patients have received the combination without apparent problems. However, two isolated cases describe reduced and increased anticoagulation, respectively. A cohort study found no increased risk of over-anticoagulation when acenocoumarol or phenprocoumon were given with terbinafine. 

Normally no interaction occurs between coumarins and terbinafine, while the two isolated cases cited are rarities, and unexplained. There appears therefore to be no reason for avoiding concurrent use, but bear these cases in mind if terbinafine is given to patients taking warfarin. 

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