A nurse is reviewing the medication list of a patient who is taking carbamazepine (Tegretol) for seizures. Which of the following drugs may interact with carbamazepine and require dosage adjustments? (Select all that apply.)

- Choice A is correct because warfarin (Coumadin) may interact with carbamazepine and require dosage adjustments. Carbamazepine can increase the metabolism of warfarin and decrease its anticoagulant effect, which can increase the risk of blood clots or stroke¹⁴. The nurse should monitor the patient's international normalized ratio (INR) and prothrombin time (PT) and adjust the warfarin dose accordingly¹⁵.

- Choice B is correct because erythromycin (Erythrocin) may interact with carbamazepine and require dosage adjustments. Erythromycin can inhibit the metabolism of carbamazepine and increase its blood levels, which can increase the risk of toxicity or adverse effects, such as drowsiness, dizziness, nausea, or rash¹⁴. The nurse should monitor the patient's carbamazepine levels and signs of toxicity and adjust the carbamazepine dose accordingly¹⁵.

- Choice E is correct because metformin (Glucophage) may interact with carbamazepine and require dosage adjustments. Carbamazepine can decrease the absorption of metformin and reduce its blood glucose-lowering effect, which can increase the risk of hyperglycemia or diabetes complications¹⁴. The nurse should monitor the patient's blood glucose levels and adjust the metformin dose accordingly¹⁵.

- Choice C is wrong because ibuprofen (Advil) does not interact with carbamazepine and does not require dosage adjustments. Ibuprofen is a nonsteroidal anti-inflammatory drug (NSAID) that does not affect the metabolism or blood levels of carbamazepine or be affected by it²³. The nurse should advise the patient to use ibuprofen as needed for pain or inflammation, but to avoid taking it with other NSAIDs or aspirin to prevent bleeding or stomach ulcers²³.

- Choice D is wrong because levothyroxine (Synthroid) does not interact with carbamazepine and does not require dosage adjustments. Levothyroxine is a thyroid hormone replacement that does not affect the metabolism or blood levels of carbamazepine or be affected by it²³. The nurse should advise the patient to take levothyroxine on an empty stomach, at least 30 minutes before or 4 hours after any other medications, to ensure optimal absorption²³.

This statement is incorrect because grapefruit juice does not interact with phenytoin and has no effect on its metabolism or blood levels¹. The patient does not need to avoid grapefruit juice while taking phenytoin, unless they are also taking another drug that is affected by grapefruit juice, such as some statins, calcium channel blockers, or cyclosporine²³.

The other statements by the patient are correct and indicate an understanding of the teaching.

- Choice A is correct because the patient should brush their teeth gently with a soft toothbrush to prevent gingival hyperplasia, which is an overgrowth of the gums that can occur with phenytoin use. The patient should also floss regularly and visit a dentist every 3 to 4 months.

- Choice B is correct because the patient should wear a medical alert bracelet that says they have epilepsy and are taking phenytoin. This can help emergency personnel to provide appropriate care and avoid drug interactions if the patient has a seizure or another medical problem.

- Choice C is correct because the patient should check their blood pressure regularly while taking phenytoin, as this drug can cause hypotension, especially when given intravenously or in high doses. The patient should also monitor their heart rate and rhythm, as phenytoin can cause bradycardia or arrhythmias.