Primidone 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 primidone 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 primidone levels may increase or decrease is uncertain. Contact your doctor if your conditions worsen or you experience excessive effects of primidone such as drowsiness, confusion, hallucinations, restlessness, depression, loss of balance or coordination, twitching eye movements, blurred vision, and shallow or impaired breathing. 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 phenobarbital and efavirenz may affect the plasma concentrations of both drugs. Theoretically, efavirenz levels may decrease due to induction of the CYP450 3A4 and 2B6 enzymatic pathways by phenobarbital, whereas phenobarbital levels may increase or decrease according to the product labeling for efavirenz. Pharmacokinetic data are not currently available. Phenobarbital is a substrate of CYP450 2C19 and 2C9, both of which are inhibited by efavirenz. However, the extent to which inhibition of these pathways may affect the overall clearance of phenobarbital is unknown. 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 phenobarbital.

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 phenobarbital or primidone, the latter of which is partially metabolized in vivo to phenobarbital. 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 phenobarbital 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 increased side effects of phenobarbital such as drowsiness, confusion, hallucinations, restlessness, depression, ataxia, lethargy, nystagmus, and respiratory depression.

Primidone

Generic Name: primidone

Brand name: Mysoline

Synonyms: n.a.

What is Primidone?

Sustiva

Generic Name: efavirenz

Brand name: Sustiva

Synonyms: n.a.

What is Sustiva?