What types of drugs an foods interfere with the coagulation test of prothrombin time?

Depends on : Circumstances. In a normal person, usual drugs and foods do not affect pt measurably. In patients on warfarin, foods both prolong pt, e.g., grapefruit, or shorten it, e.g., green leafy vegetables. Many drugs affect pt, e.g., birth control pills, isoniazid, anti-fungals, antibiotics, and many other drugs metabolized through cytochrome p450 system, and barbiturates and alcohol.