Valsartan: Reversible increases in serum conc & toxicity of lithium. Monitor K plasma levels when given w/ K-sparing diuretics, K supplements, salt substitutes containing K & other substances that may increase K levels. Attenuation of antihypertensive effect w/ NSAIDs (including selective COX-2 inhibitors, acetylsalicylic acid (>3 g/day & nonselective NSAIDs). May increase antihypertensive effects w/ TCAs & α-blockers. Amlodipine: Inhibits metabolism w/ diltiazem. May increase plasma conc w/ CYP3A4 inhibitors ie, ketoconazole, itraconazole, ritonavir. Reduced plasma conc w/ CYP3A inducers [anticonvulsants (eg, carbamazepine, phenobarb, phenytoin, fosphenytoin, primidone), rifampicin,
H. perforatum].