Acyclovir is a synthetic substance, close in structure to guanine (a constituent part of nucleic acids, is complementary to cytosine), when interacting with specific enzymes, acyclovir is converted into a pharmacologically active substance. In cells Generic Zovirax 5% infected with viruses, a specific enzyme, thymidine kinase, is produced, which, through several chemical reactions, converts acyclovir into acyclovir triphosphate. Due to the saturation of the cytoplasm of the infected cell with acyclovir triphosphate, replication of DNA from viruses occurs, which leads to disruption of normal virus multiplication and the formation of nonviable viral units. The mechanism of action of the drug is based on its structural similarity with deoxyguanosine triphosphate, due to which there is a competitive replacement of the nucleotide with acyclovir triphosphate during the synthesis of viral DNA. The drug does not affect healthy cells of the body, because they lack the enzyme thymidine kinase and acyclovir remains inactive form. In addition, the concentrations of acyclovir in infected cells are significantly higher than in healthy cells. The drug exhibits virostatic activity with respect to herpes simplex virus type I and II, a virus that causes varicella. Acyclovir is moderately active against cytomegaloviruses.
With prolonged use of the drug, especially in patients with immunodeficiency, the development of resistance of viruses to drugs containing acyclovir was observed. Resistant strains of viruses are characterized by a low content or disorder of thymidine kinase structure, changes in the structure of the viral DNA polymerase. When using the drug in the form of eye ointment, acyclovir is rapidly absorbed through the cornea and creates high concentrations in the intraocular fluid. Systemic absorption of the drug when applied to the cornea is insignificant, Acyclovir is practically not detected in the blood plasma, some amount of acyclovir is determined in the urine. When using the preparation in the form of an ointment, the systemic absorption of acyclovir is negligible. At intravenous infusion introduction of a preparation the maximum concentration in a blood plasma was marked in 1 hour after infusion. The half-life in adults is 2.9 hours, in newborns 3.8 hours. After oral administration of the drug, the active substance is partially absorbed into the total blood flow. When taking the drug at a dose of 200 mg every 4 hours, the maximum equilibrium concentration of the drug in the blood plasma is about 3.1 μmol, and the minimum equilibrium concentration of the drug is about 1.8. The degree of association with plasma proteins is low (from 9 to 33%). The drug in high concentrations is determined in the cerebrospinal fluid. Acyclovir is partially metabolized in the liver. It is excreted mainly by the kidneys, both in unchanged form and in the form of metabolites. In elderly people, the half-life of acyclovir increases somewhat.
Increased individual sensitivity to the components of the drug. Increased individual sensitivity to acyclovir and / or valaciclovir.
Relative contraindications to the use of the drug are dehydration and impaired renal function.
Be wary appoint patients suffering from neurologic disorders, and with the development of undesirable effects with the use of cytotoxic drugs.
When applying excessive doses of the drug cause an increase in the amount of urea, and serum creatinine in the blood, as well as the development of renal failure. In addition, with an overdose of the drug, neurological disorders are noted in the form of hallucinations, arousal, convulsions and confusion. With a strong dose exceeding the development of coma.
There is no specific antidote. In case of an overdose, hemodialysis is indicated.
When applying the cream, it is possible to develop local side effects, such as itching, burning, irritation of the skin at the application site. In addition, the patients noted dryness and flaky skin, the development of contact dermatitis. Very rarely there were allergic reactions in the form of angioedema.