Table 4.

Types of drugs concurrently prescribed with warfarin known to have interaction and their potential effect on INR values (n = 91)

Drugs	Effect on INR	Severity
Norfloxacin, Metronidazole, Clarithromycin	Increase	Major
Rifampin	Decrease	Major
Isoniazid, Omeprazole, Tramadol, Ceftriaxone, Cimetidine, Allopurinol, Azithromycin	Increase	Moderate
Nevirapine, Neurobion, Mercaptopurine	Decrease	Moderate
Efavirenz, Hydrocortisone, Prednisolone	Increase/Decrease	Moderate
Methotrexate, Vincristine, Furosemide, Simvastatin	Increase	Minor
Hydrochlorothiazide	Decrease	Minor