Absorption by oral administration is rapid. Bioavailability at reception on an empty stomach makes 45%, with simultaneous intake with food - 65% - 70%. There is an effect of "first passage" through the liver. Time to reach the maximum concentration - 1-1,5h. Average maximum concentration (Cmax) in plasma: about 5 μmol / l at the end 1 Weeks of admission in a dose 200 mg every 8 hours and about 11 μmol / l at the end 1 Weeks of admission in a dose 400 mg every 8 hours. Dependence of the area under the pharmacokinetic curve (AUC) from the dose linear; from Cmax - nonlinear.
C plasma proteins ribavirin binds slightly. When administered orally 600 mg 2 an equilibrium concentration (Css) is reached by the end 4 weeks and is 2200 ng / ml.
The drug is intensively distributed to organs and tissues; penetrates the blood-brain barrier, is found in the brain, in the cerebrospinal fluid, in the secretion of the airways and red blood cells. The half-distribution period is 3,7 h. The amount of distribution (Vd) from 647 before 5000 l. A large amount of ribavirin triphosphate accumulates in erythrocytes. Next, almost no output from them; therefore, considering the negative impact on the reproductive system, until the pool of red blood cells is fully updated (no less than 6 months), patients of reproductive age should carefully observe contraception. Significant concentration of the drug (67% from that in plasma) is found in the cerebrospinal fluid. The ratio of bioavailability indicators for course and single admission is equal to 6:1.
The metabolism of ribavirin occurs in two ways: reversible phosphorylation and cleavage (deibosylation and amide hydrolysis with the formation of a triazole carboxyl metabolite).
Ribavirin is excreted slowly from the body. The half-life (T1/2) after a single dose 200 mg is from 1 before 2 hours from plasma to 40 days from erythrocytes. After discontinuing admission T1/2 is about 300 h. Ribavirin and its metabolites are excreted primarily through the kidneys. For the first 24 h in unchanged form is displayed near 7% preparation for 48 h - about 10%. Through the intestine, only 10% unchanged ribavirin.
When taking the drug, patients with renal insufficiency AUC and Cmax Ribavirin increase, which is due to a decrease in true clearance. In liver failure (A, B and C Child-Pugh classes), the pharmacokinetics of ribavirin does not change.
On the cytochrome P450 system ribavirin does not affect.