Drug-drug interaction with OTC drugs -The inhibitory effect of NSAIDs and cough suppressants on CYP activities

In general most of NSAIDs and cough suppressants are available as the over the counter drugs (OTC) without prescription. It has been believed that OTC drugs are relatively safe compared to prescription drugs, therefore, OTC drugs have been widely used for self-medication all over the world. However, the reports concerning to their drug-drug interactions are insufficient in fact, although the information especially for that mediated by cytochrome P450 (CYP) is essential for safe medication. In our previous study, the major OTC drugs such as antihistamines and expectorants showed potent inhibitory effects on CYP activities, suggesting the possibility of clinical drug interactions. To avoid the risks of adverse reaction caused by CYP inhibition, it is important to investigate these interactions. Thus, in the present study we evaluated the inhibitory effects of commonly used NSAIDs and cough suppressants on CYP activities in human liver microsomes.