Which of the following do not increase the action of warfarin?
Reference: KDT, Essentials of Medical Pharmacology, 7th ed., Pg. 623 and Katzung, Basic & Clinical Pharmacology, 13th ed., Pgs. 876 & 877.
 
Barbiturates (but not benzodiazepines), carbamazepine, rifampin and griseofulvin induce the metabolism of oral anticoagulants. The dose of anticoagulant determined during therapy with these drugs would be higher: if the same is continued after withdrawing the inducer—marked hypoprothrombinemia can occur—fatal bleeding is on record.
Metronidazole, fluconazole, and trimethoprim-sulfamethoxazole also stereoselectively inhibit the metabolic transformation of S-warfarin, whereas amiodarone, disulfiram, and cimetidine inhibit metabolism of both enantiomorphs of warfarin. Barbiturates and rifampin cause a marked decrease of the anticoagulant effect by induction of the hepatic enzymes that transform racemic warfarin.
Cimetidine
Isoniazid
Rifampicin
Cotrimoxazole