After oral famciclovir is rapidly converted to penciclovir, which has activity against human herpes viruses including Varicella zoster and Herpes simplex types 1 and 2 virus, and test enanthate virus and cytomegalovirus.
Penciclovir misses the virus-infected cells, where the action of viral rapidly converted into thymidine monophosphate which is in turn transferred to the triphosphate. Penciclovir triphosphate inhibits the replication of viral (deoxyribonucleic acid).
Period intracellular half-life of penciclovir triphosphate cell culture infected simplex 1 is 10 hours; simplex 2-20 hours;
The concentration of penciclovir triphosphate in uninfected cells does not exceed the minimum determined, however at therapeutic concentrations penciclovir no effect on uninfected cells.
As with acyclovir resistance Penciclovir is most often associated with mutations in the gene for viral thymidine kinase, leading to a deficiency disruption or substrate specificity of the enzyme. Significantly less frequent changes in the DNA polymerase gene.
Use of the drug for the treatment of herpes zoster (caused by the virus Varicella zoster) in immunocompetent patients and patients with reduced immunity marked acceleration of healing of the skin and mucous membranes. Famciclovir is effective in treating various ophthalmic manifestations caused by the virus Varicella zoster. The drug significantly reduces the severity and duration of postherpetic neuralgia in patients with herpes zoster.
One-day treatment with famciclovir in immunocompetent patients in a dose of 1500 mg 1 time per day or 750 mg 2 times per day contributes to the rapid resolution of the manifestations of recurrent labial herpes (caused by the virus simplex).
The use of the drug in immunocompetent patients at a dose of 1000 mg two times a day for one day, 125 mg 2 times a day for 5 days or 500 mg two times a day for 3 days accelerates the healing of skin and mucous membranes for recurrent genital herpes (caused by the virus herpes simplex ).
Famciclovir 500 mg 2 times a day for 7 days is effective in the treatment of various manifestations of herpes zoster in patients with reduced immunity due to the infection with the human immunodeficiency . In test enanthate patients in the drug dose of 500 mg 2 times a day for 7 days accelerates healing of skin and mucous membranes for recurrent genital herpes, and also reduces the number of days of viral simplex (both symptomatic and without them). The use of famciclovir in patients with reduced immunity due to other reasons, has not been studied.
The effectiveness of one day receiving famciclovir at a dose of 1000 mg 2 times a day for treatment of recurrent genital herpes in immunocompetent patients blacks is not higher than that for the placebo.The safety profile of the one-day administration of the drug at a dose of 1000 mg two times daily in these patients was similar to that previously established.
Absorption Famciclovir is a prodrug. After oral administration, famciclovir is rapidly and almost completely absorbed and rapidly converted to the pharmacologically active metabolite – penciclovir. Bioavailability of penciclovir after administration of the drug Famvir inside is 77%. Increased plasma concentration of penciclovir takes place proportionally to the single dose of famciclovir in the range 125-1000 mg. According to research the maximum concentration ) after oral administration of penciclovir 125 mg, 250 mg or 500 mg of famciclovir is achieved on average after 45 minutes and an average of 0.8 mg / ml, 1.6 ug / ml and 3.3 ug / ml, respectively. Another study shows the maximum concentration (C max ) after oral administration of penciclovir 250 mg, 500 mg or 1000 mg of famciclovir in values of 1.5 mg / ml, 3.2 ug / ml and 5.8 ug / ml, respectively. Systemic bioavailability penciclovir is independent of meal times. Of penciclovir at single dose of famciclovir and the separation of the daily dose into two or three doses are the same, indicating a lack of accumulation of penciclovir on repeated applications of famciclovir.
Metabolism After oral administration, famciclovir and quickly completely transformed into a pharmacologically active metabolite -. penciclovir Distribution plasma protein binding of penciclovir and its 6-deoxy precursor is less than 20%. Withdrawal Famciclovir is displayed mainly in the form of penciclovir and its 6-deoxy precursor, which are excreted through the kidneys in unchanged form ; famciclovir in the urine can not be detected. The of penciclovir from the plasma in the final phase after a single and repeated doses of about 2 hours. Pharmacokinetics in special cases, patients with infections caused by the virus Varicella zoster in patients with uncomplicated infection caused by the Varicella zoster virus, is not detected significant changes in pharmacokinetic parameters of penciclovir . Patients with impaired renal function after a single and repeated doses of famciclovir observed a linear relationship between the decrease in plasma clearance, renal clearance, the rate of excretion of penciclovir from blood plasma and the degree of renal dysfunction. The pharmacokinetic characteristics of the drug in patients with severe (decompensated) impaired renal function have not been studied. Patients with impaired liver function in patients with impaired function of mild to moderate severity of the liver is observed to increase the test enanthate of penciclovir. The pharmacokinetics of penciclovir in patients with severe hepatic impairment has not been studied. The conversion to an active metabolite of famciclovir penciclovir in these patients may be impaired, resulting in lowering of penciclovir concentrations in plasma and, as a consequence, inefficiency of famciclovir. Patients ≥65 years of age in patients aged 65 to 70 years there has been increasing average penciclovir AUC by about 40% and reduces its renal clearance is about 20% compared with those younger than 65 years. These pharmacokinetic characteristics of penciclovir may be partly due to age-related changes in renal function in patients older than 65 years. Gender patient Gender has no significant effect on the pharmacokinetic parameters of the drug (slight differences in the clearance of penciclovir in men and women). Race In applying famciclovir (single or multiple receive a dose of 500 mg of 1, 2 or 3 times a day), the pharmacokinetic parameters of the drug in healthy volunteers and patients blacks blacks with impaired renal or hepatic function did not differ from those of enanthate individuals.