Ribavirin has recently been demonstrated to have efficacy in combination with alpha interferon for treatment of relapsed hepatitis C. The marked improvement in the response rate after treatment with the combination regimen (10-fold higher versus that from monotherapy with alpha interferon) highlights the importance of determining the absolute bioavailability of ribavirin as a first step in beginning to investigate the pharmacodynamics of the combination. The objective of this study was to determine the absolute bioavailability of ribavirin with an intravenous formulation containing ribavirin labeled with the stable isotope 13 C 3 ( 13 C 3ribavirin) and unlabeled oral ribavirin. Six healthy volunteers received 150 mg of intravenous 13 C 3 -ribavirin followed 1 h later by a 400-mg oral dose of ribavirin. Samples of blood and urine were collected up to 169 h postdosing. Concentrations of 13 C 3 -ribavirin and unlabeled ribavirin were determined by a high-performance liquid chromatography tandem mass spectrometric method. All plasma and urine data were comodeled for labeled and unlabeled ribavirin by using both the two-and three-compartment models in the program ADAPT II. A three-compartment model was chosen for the pharmacokinetic analysis with the Akaike Information Criterion. The mean maximum concentrations of drug in plasma for intravenous and oral ribavirin were 4,187 and 638 ng/ml, respectively. The mean bioavailability was 51.8% ؎ 21.8%, and the mean ␥-phase half-life was 37.0 ؎ 14.2 h. The mean renal clearance, metabolic clearance, and volume of distribution of the central compartment were 6.94 liters/h, 18.1 liters/h, and 17.8 liters, respectively. The use of the stable-isotope methodology has provided the best estimate of the absolute bioavailability of ribavirin that is currently available, as there was neither a period bias nor a washout effect to confound the data. The study demonstrated that the mean bioavailability for a 400-mg dose of ribavirin was 52%, which is higher than that previously reported in other investigations.

The purpose of this study to compare the long-term clinical outcome of early versus delayed rasagiline treatment in early Parkinson's disease (PD). Subjects (N = 404) were randomly assigned to initial treatment with rasagiline (early-start group) or placebo for 6 months followed by rasagiline (delayed-start group) in the TEMPO study. Subjects who chose to participate in an open-label extension (N = 306) continued to receive rasagiline as well as other PD medications as needed. Average (+/-SD) duration in the study was 3.6 +/- 2.1 years; 177 subjects received rasagiline for > or =5.0 years. Over the entire 6.5-year follow-up period, the adjusted mean difference in change from baseline in total UPDRS scores was 2.5 units (SE 1.1; P = 0.021) or 16% (SE 5.7; P = 0.006) in favor of the early-start versus delayed-start rasagiline group. Although the interaction between treatment and time was significant, values for the early-start group were better than the delayed-start group across all time points. Significantly less worsening (percent change) in total UPDRS scores was observed in the early-start group at the time points 0.5, 1.5, 2.0, 3.0, 4.5, 5.0, and 5.5 years (P < 0.05). Compared to delayed start, early initiation of rasagiline provided long-term clinical benefit, even in the face of treatment with other dopaminergic agents. This might reflect enduring benefits due to neuroprotection or effects on compensatory mechanisms in early PD.

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