When taken orally acyclovir only partially absorbed in the intestine. After a dose of 200 mg 5 times a day, the maximum concentration Acyclovir in blood plasma is 3.2 μmol (0.7 μg / ml), the minimum concentration is 1.8 μmol (0.4 μg / ml).
The concentration of acyclovir in the cerebrospinal fluid is 50% of the concentration in the blood plasma. Binding to plasma proteins is relatively low (9-33%). Acyclovir basically excreted from the body in an unchanged form through the kidneys. The renal clearance of acyclovir is significantly higher than the creatinine clearance, which indicates that it is eliminated not only by glomerular filtration, but also by tubular secretion.
The only metabolite found in the urine is 9-carboxymethoxymethyl guanine (10-15% of the prescribed dose).
When ingested partially absorbed from the gastrointestinal tract, bioavailability - 20% (15-30%),does not depend on the dosage form, decreases with increasing dose; food has no significant effect on the absorption of acyclovir. After oral administration of 200 mg of acyclovir every 4 hours in adults, the average equilibrium values of the maximum concentration of the substance in plasma (serum) of blood - 0,7 mkg / ml and the minimum concentration - 0,4 mkg / ml; the time of maximum concentration in blood plasma is 1.5-2 hours.
After intravenous drip introduction to adults, the mean maximum concentration of the substance in plasma (serum) of blood 1 hour after infusion in a dose of 2.5; 5 and 10 mg / kg were 5.1; 9.8 and 20.7 μg / ml, respectively. The minimum concentration of substance in blood plasma (serum) 7 hours after the infusion, respectively, were 0.5; 0.7 and 2.3 μg / ml. In children older than 1 year, the maximum and minimum concentrations when administered at a dose of 250 and 500 mg / m2 were similar to those in adults at doses of 5 and 10 mg / kg, respectively. In newborns and infants up to 3 months of age, acyclovir was administered at a dose of 10 mg / kg intravenously drip for 1 hour every 8 hours, the maximum concentration in the blood plasma was 13.8 μg / ml, the minimum concentration was 2.3 μg / ml.
Binding to proteins is low (9-33%).Passes through the blood-brain barrier, the placental barrier, is found in breast milk (at a dose of 1 g per day inside with the mother's milk, the child receives 0.3 mg / kg). It penetrates well into the organs, tissues and body fluids, including the brain, kidneys, liver, lungs, watery moisture, lacrimal fluid, intestine, muscles, spleen, uterus, mucous membrane and vaginal secretion, semen, cerebrospinal fluid, the contents of herpetic vesicles . The highest concentrations are found in the kidneys, liver and intestines. The concentration in the cerebrospinal fluid is 50% of that in the blood plasma. Metabolised in the liver, under the influence of alcohol and aldehyde dehydrogenase and, to a lesser extent, aldehyde oxidase in inactive metabolites. Metabolism of acyclovir is not associated with cytochrome P450 enzymes.
The main way of elimination is through the kidneys through glomerular filtration and tubular secretion. When ingested unchanged, about 14% is withdrawn, with intravenous administration - 45-79%. The main metabolite found in urine is 9-carboxymethoxymethylguanine. The share of the main metabolite is up to 14% (with normal kidney function).Less than 2% is excreted with feces, trace amounts are determined in the exhaled air.
Half-Elimination (half-life) when administered orally in adults - 2,5-3,3 hours. PThe half-elimination period (half-life) with intravenous administration: in adults - 2.9 hours, in children and adolescents from 1 to 18 years - 2.6 hours, in children under 3 months - 3.8 hours (with intravenous injection of 10 mg / kg in for 1 hour 3 times a day). In patients with chronic renal insufficiency half-elimination period (half-life) - 19.5 hours, during hemodialysis - 5.7 hours, with constant outpatient peritoneal dialysis - 14-18 hours. With a single hemodialysis session for 6 hours, the concentration of acyclovir in the plasma is reduced by 60%, with peritoneal dialysis, the clearance of acyclovir does not change significantly.
When applied to the affected skin (for example, with herpes zoster), the absorption is moderate; in patients with normal renal function, serum concentrations of up to 0.28 μg / ml, with renal dysfunction up to 0.78 μg / ml. It is excreted by the kidneys (approximately 9% of the daily dose).
Eye ointment easily penetrates the epithelium of the cornea and creates a therapeutic concentration in the eye fluid.