Final answer:
Phenytoin causes a decrease in the effects of certain medications by inducing hepatic cytochrome P450 enzymes, which accelerates the metabolism of these drugs, reducing their plasma concentrations and efficacy. Commonly affected drugs include warfarin, oral contraceptives, corticosteroids, and some chemotherapeutic agents.
Step-by-step explanation:
Phenytoin is known to decrease the effects of certain medications due to its ability to induce hepatic cytochrome P450 enzymes. This action accelerates the metabolism of drugs that are substrates for these enzymes, resulting in reduced plasma concentrations and potentially decreased efficacy of the affected medications. Drugs whose effects can be diminished by phenytoin include, but are not limited to, warfarin, oral contraceptives, corticosteroids, and some chemotherapeutic agents.
It is important for healthcare professionals to monitor patients receiving phenytoin in conjunction with other medications and adjust doses as necessary. The interactions between phenytoin and other drugs are an important consideration in clinical practice to ensure therapeutic effectiveness and avoid potential drug interactions.