Phenytoin Capsules and Sustiva

In the database of official manuals used in the service creation an interaction registered by statistical results of studies was found, which can either lead to negative consequences for the patient health or strengthen a mutual positive effect. A doctor should be consulted to address the issue of joint drug administration.

Using efavirenz together with phenytoin can alter the blood levels and effects of both medications. Specifically, efavirenz levels may decrease, which may make the medication less effective in treating HIV infection. Whether phenytoin levels may increase or decrease is uncertain. Contact your doctor if your conditions worsen or you experience excessive effects of phenytoin such as nausea, vomiting, twitching eye movements, blurred vision, slurred speech, loss of balance or coordination, tremors, sluggishness, confusion, or hallucinations. You may need a dose adjustment or more frequent monitoring by your doctor to safely use both medications. 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.

MONITOR: Coadministration of phenytoin and efavirenz may affect the plasma concentrations of both drugs. Specifically, efavirenz levels may decrease due to induction of the CYP450 3A4 and 2B6 enzymatic pathways by phenytoin, whereas phenytoin levels may increase or decrease according to the product labeling for efavirenz. Pharmacokinetic data are not currently available. Phenytoin is a substrate of CYP450 2C9 and 2C19, both of which are inhibited by efavirenz. On the other hand, convulsions have been observed during efavirenz therapy, generally in patients with a known medical history of seizures. This would suggest a possible induction by efavirenz, a known inducer of CYP450 3A4 and possibly other hepatic microsomal enzymes, of the clearance of certain anticonvulsants that are primarily metabolized by the liver such as phenytoin. In two published case reports, patients treated concomitantly with efavirenz and phenytoin had low or undetectable levels of efavirenz despite increasing dosage. Although an early virologic response was observed in both cases, anticonvulsant therapy was changed due to the risk of antiretroviral treatment failure with chronically low efavirenz exposure. In one of the reports, an elevated level of phenytoin was also observed despite no change in dosage.

MANAGEMENT: Given the risk of reduced viral susceptibility and resistance development associated with subtherapeutic antiretroviral drug levels, caution is advised if efavirenz is prescribed in combination with phenytoin. Close clinical and laboratory monitoring of antiretroviral response is recommended, and the efavirenz dosage adjusted as necessary. Alternative treatment that do not affect efavirenz metabolism should be considered whenever possible. Pharmacologic effects and serum phenytoin levels should also be monitored more closely following the addition, discontinuation or change of dosage of efavirenz. Patients should be advised to contact their physician if they experience loss of seizure control or signs and symptoms of phenytoin toxicity such as nausea, vomiting, tremors, ataxia, lethargy, slurred speech, visual disturbances, or changes in mental status.

Phenytoin Capsules

Generic Name: phenytoin

Brand name: Dilantin, Phenytek, Dilantin Infatabs, Phenytoin Sodium, Prompt

Synonyms: Phenytoin

What is Phenytoin Capsules?

Sustiva

Generic Name: efavirenz

Brand name: Sustiva

Synonyms: n.a.

What is Sustiva?