['The objective of this study was to evaluate the effects of abacavir on intracellular ribavirin triphosphate and plasma ribavirin trough concentrations.', 'Hepatitis C virus-infected subjects who had been cured or failed prior treatment were randomized to 8 weeks of ribavirin alone (N\u200a=\u200a14; weight-based dosing) or weight-based ribavirin\u200a+\u200aabacavir (N\u200a=\u200a14; 300 mg orally every 12 h). Ribavirin trough concentrations were measured on days 14, 28, 42 and 56; PBMCs for ribavirin triphosphate determination were sampled on days 28 and 56, pre-dose and at 6 and 12 h post-dose. ClinicalTrials.gov: NCT01052701.', 'Twenty-six subjects completed the study (24 males, 17 Caucasians, median age 52 years); 2 were excluded for missed pharmacokinetic visits. Fourteen subjects received ribavirin\u200a+\u200aabacavir and 12 received ribavirin alone. Mean\u200a±\u200aSD plasma ribavirin trough concentrations (μg/mL) on days 14, 28, 42 and 56, respectively, were not significantly different with coadministration of abacavir (1.54\u200a±\u200a0.60, 1.93\u200a±\u200a0.54, 2.14\u200a±\u200a0.73 and 2.54\u200a±\u200a1.05) compared with ribavirin alone (1.48\u200a±\u200a0.32, 2.08\u200a±\u200a0.41, 2.32\u200a±\u200a0.47 and 2.60\u200a±\u200a0.62) (P\u200a>\u200a0.40). Mean ribavirin triphosphate intracellular concentrations (pmol/10(6) cells) on days 28 and 56, respectively, did not differ statistically between abacavir users (11.98\u200a±\u200a9.86 and 15.87\u200a±\u200a12.52) and non-users (15.91\u200a±\u200a15.58 and 15.93\u200a±\u200a12.69) (P\u200a>\u200a0.4). Adverse events were mild or moderate, except for three grade 3 occurrences of transaminitis, cholecystitis and low absolute neutrophil count that resolved and were judged not attributable to study medications.'] Are plasma and intracellular ribavirin concentrations significantly altered by abacavir in hepatitis C virus-infected patients?