Antiepileptic agents (hydantoin, barbiturates, primidone, carbamazepine), anti-TB drugs (rifampicin, rifabutin), oxcarbazepine, topiramate, felbamate, ritonavir, antibiotics (penicillin, griseofulvin, tetracyclines), St. John's wort, ketoconazole, erythromycin, cyclosporin. ACE inhibitors, AIIA & indomethacin may increase K blood levels.