protein binding

valproate + aspirin

Aspirin (and other salicylates) displace valproate from plasma albumin binding sites and also inhibit valproate's beta-oxidation, leading to increases in the free (active) valproate fraction by up to fourfold. Even total valproate levels may not rise dramatically, masking the increase in pharmacologically active free drug and raising the risk of valproate toxicity (sedation, tremor, hyperammonemia, hepatotoxicity).