Drug Interactions between mavacamten and mephenytoin

Grapefruit juice may increase the blood levels of mavacamten and increase the risk of heart failure, a condition where the heart is unable to pump blood adequately to meet the body's needs. Your risk may be further increased if you develop a serious infection or irregular heartbeat during treatment with mavacamten. You should avoid the consumption of grapefruit and grapefruit juice while taking this medication. Talk to your doctor if you have any questions or concerns. You should seek medical attention if you experience signs and symptoms of heart failure such as shortness of breath, chest pain, fatigue, swelling in your legs, palpitations, or rapid weight gain. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Do not stop using any medications without first talking to your doctor.

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Mephenytoin levels may decrease when the suspension is given with enteral feedings. This could lead to a loss of seizure control. You could interrupt the feeding for 2 hours before and after the mephenytoin dose. Alternatively, you may give the mephenytoin suspension diluted in water and flush the tube with water after administration. These would make it easier for your body to absorb the medication. However, this still may not entirely avoid the interaction and may not always be feasible. You should have your mephenytoin levels checked upon starting and stopping of enteral feedings. In addition, using mephenytoin together with food may alter the effects of mephenytoin. Contact your doctor if you experience worsening of seizure control or symptoms of toxicity, including twitching eye movements, slurred speech, loss of balance, tremor, muscle stiffness or weakness, nausea, vomiting, feeling light-headed, fainting, and slow or shallow breathing. If your doctor does prescribe these medications together, you may need a dose adjustment or special test to safely use both medications. It is important to tell your doctor about all other medications you use, including vitamins and herbs. Ask your doctor before making any changes to your therapy.

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