Which over-the-counter medication should a patient taking phenytoin avoid?

Phenytoin is an anticonvulsant medication used to control seizures, and it has a narrow therapeutic index, meaning that its effective dosage is very close to the dose that could cause toxicity. When a patient is on phenytoin, it’s crucial to avoid interactions that could alter its effectiveness or increase the risk of side effects.

Calcium carbonate can interfere with the absorption of phenytoin when taken together. Calcium binds to phenytoin in the gastrointestinal tract, which can reduce the amount of phenytoin that is available for absorption into the bloodstream. This can lead to subtherapeutic levels of phenytoin, potentially allowing seizures to occur or causing issues with the control of seizures.

In contrast, medications like acetaminophen, ibuprofen, and ranitidine are generally considered safe for use with phenytoin, provided they are used within recommended dosages. Acetaminophen is often used for pain relief and fever reduction without significantly influencing phenytoin levels. Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that, while requiring caution due to potential effects on renal function and bleeding when used long-term with other drugs, does not interact directly with phenyto