Severe Renal Impairment and End Stage Renal Disease
No dose recommendation can be given for patients with severe renal impairment (estimated Glomerular Filtration Rate (eGFR) <30 mL/min/1.73m2) or with end stage renal disease (ESRD) due to higher exposures (up to 20-fold) of the predominant sofosbuvir metabolite.

WARNINGS AND PRECAUTIONS

Use with Potent P-gp Inducers
Drugs that are potent P-gp inducers in the intestine (e.g., rifampin, St. John’s wort) may significantly decrease sofosbuvir plasma concentrations and may lead to a reduced therapeutic effect of SOVALDI.  Rifampin and St. John’s wort should not be used with SOVALDI.

ADVERSE REACTIONS
The most common adverse events (≥ 20%) for SOVALDI + ribavirin combination therapy were fatigue and headache. The most common adverse events (≥ 20%) for SOVALDI + peginterferon alfa + ribavirin combination therapy were fatigue, headache, nausea, insomnia and anemia.

DRUG INTERACTIONS
Potential for Drug Interactions
After oral administration of SOVALDI, sofosbuvir is rapidly converted to the predominant circulating metabolite GS-331007 that accounts for greater than 90% of drug related material systemic exposure, while the parent sofosbuvir accounts for approximately 4% of drug related material. In clinical pharmacology studies, both sofosbuvir and GS-331007 were monitored for purposes of pharmacokinetic analyses.

Sofosbuvir is a substrate of drug transporter P-gp and breast cancer resistance protein (BCRP) while GS-331007 is not. Drugs that are potent P-gp inducers in the intestine (e.g., rifampin or St. John’s wort) may decrease sofosbuvir plasma concentration leading to reduced therapeutic effect of SOVALDI and thus should not be used with SOVALDI.  Coadministration of SOVALDI with drugs that inhibit P-gp and/or BCRP may increase sofosbuvir plasma concentration without increasing GS-331007 plasma concentration; accordingly, SOVALDI may be coadministered with P-gp and/or BCRP inhibitors. Sofosbuvir and GS-331007 are not inhibitors of P-gp and BCRP and thus are not expected to increase exposures of drugs that are substrates of these transporters.

The intracellular metabolic activation pathway of sofosbuvir is mediated by generally low affinity and high capacity hydrolase and nucleotide phosphorylation pathways that are unlikely to be affected by concomitant drugs.

7.2       Potentially Significant Drug Interactions
Drug interaction information for SOVALDI with potential concomitant drugs is summarized in Table 5. The drug interactions described are based on potential drug interactions that may occur with SOVALDI. The table is not all-inclusive.

Table 5  Potentially Significant Drug Interactions: Alteration in Dose or Regimen May Be Recommended Based on Drug Interaction Studies or Predicted Interactiona

Concomitant Drug Class: Drug Name Effect on Concentrationb
 Clinical Comment
 
Anticonvulsants:
carbamazepine                    phenytoin                       &nbs