Statins Phenytoin

Murphy Ml, Dominiczak MH. Efficacy of statin therapy possible effect of phenytoin. Postgrad Med J 1999 75 359-60. 

Telithromycin has several clinically significant drug interactions similar to those for erythromycin. It is both a substrate and a strong inhibitor of CYP3A4. Coadministration of rifampin, a potent inducer of CYP, decreases the serum concentrations of telithromycin by 80%. CYP3A4 inhibitors (e.g., itraconazole) increase peak serum concentrations of telithromycin. Serum concentrations of CYP3A4 substrates (e.g., pimozide, cisapride, midazolam, statins, cyclosporine, phenytoin) are increased by telithromycin. Telithromycin also increases peak serum concentrations of metoprolol and digoxin. 

Evidence of an interaction currently appears to be limited to these two reports and the clinical significance remains unclear. The change in phenytoin levels seems unlikely to be clinically significant. There is a small risk that the concurrent use of fluvastatin and phenytoin could result in myopathy. Patients should be told to report any signs of myopathy and possible rhabdomyolysis (i.e. otherwise unexplained muscle pain, tenderness or weakness or dark coloured urine). If myopathy does occur, the statin should be stopped immediately. See also muscle toxicity , (p.l086), for further guidance on monitoring, and risk factors for muscle toxicity. 

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