Valtrex

Valtrex is an effective antiviral drug.

Indications Valtrex

The drug is indicated in the situations described below:

• to eliminate the shingles form of herpes (which is caused by the chickenpox virus) - helps to alleviate pain and reduce its duration, and in addition, the percentage of patients with such pain (among them neuralgia in the acute or post-herpetic stage);
• elimination of infectious processes on the mucous membrane along with the skin, which are provoked by common herpes types 1 and 2 (including acquired for the first time or recurrent form of genital herpes);
• elimination of herpes localized on the lips;
• prevention of the formation of skin lesions (if the medication is taken immediately after the initial signs of a relapse of simple herpes appear);
• prevention of relapses of diseases of the mucous membranes together with the skin, which are provoked by common herpes (types 1 and 2), including genital type;
• reducing the risk of infection of a healthy partner with genital herpes (when taken as a preventive measure and with the use of contraception);
• prevention against the development of the cytomegalovirus form of infection, which develops as a result of organ transplantation (reduces the manifestation of a response reaction of severe rejection of the transplanted organ in people with kidney transplants, and in addition, the risk of the occurrence of opportunistic and other types of viral infections, which are provoked by chickenpox and common herpes).

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Release form

Available in tablet form - on blisters of 10 pieces. One package contains 1 blister plate.

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Pharmacodynamics

Inside the body, the component valacyclovir is fully and fairly quickly converted into the substance acyclovir (through the action of valacyclovir hydrolase). In vitro, the substance demonstrates specific suppressive activity against common herpes (types 1 and 2), chickenpox virus, and also Epstein-Barr with herpes type VI, as well as cytomegalovirus.

Acyclovir inhibits the process of binding viral DNA immediately after the phosphorylation reaction with conversion into the active element - acyclovir triphosphate. At the 1st stage of the phosphorylation process, virus-specific enzymes act. For the above-mentioned viruses (except for cytomegalovirus with herpes type VI), such an enzyme is viral thymidine kinase, the presence of which is observed inside the cells affected by the virus. Partial selectivity of phosphorylation remains in cytomegalovirus and is carried out indirectly - with the participation of the product produced by the UL 97 kinase gene. Since acyclovir is activated with the assistance of a specific viral enzyme, this mainly explains its selectivity.

At the final stage of phosphorylation of the active component (conversion from mono- to triphosphate component) cellular kinases are present. The newly formed substance competitively suppresses DNA polymerase inside the virus and, because it is an analogue of nucleoside, penetrates its DNA, promoting complete rupture of this chain and stopping the process of DNA binding. As a result, viral replication is blocked.

In people with preserved immunity, chickenpox and common herpes viruses, as well as low sensitivity to valacyclovir, are observed very rarely (the rate is less than 0.1%). Occasionally, they can occur in patients with severe disorders in the immune system (for example, with a bone marrow transplant, undergoing chemotherapy, as well as in people infected with the HIV virus).

Resistance is due to a deficiency in viral thymidine kinase, which allows the virus to spread widely throughout the body. In some cases, decreased sensitivity to acyclovir is due to the emergence of viral strains that disrupt the structure of DNA polymerase or thymidine kinase of the virus. The pathogenicity of these types of virus is similar to that of the wild strain of this pathogenic organism.

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Pharmacokinetics

After oral administration, valacyclovir and acyclovir acquire identical pharmacokinetic properties.

Once inside the body, valacyclovir is effectively absorbed from the gastrointestinal tract - almost completely and very quickly converted into valine with acyclovir. The catalyst for this process is the enzyme valacyclovir hydrolase, which is produced by the liver.

With a single dose of 0.25-2 g of valacyclovir, peak acyclovir levels in healthy subjects (with normal renal function) taking the drug were (average) 10-37 μmol (or 2.2-8.3 μg/ml), and the time required to reach this level was 1-2 hours.

Following administration of 1+ g of valacyclovir, the bioavailability of acyclovir was 54% (regardless of food intake).

The peak plasma concentration of valacyclovir is only 4% of that of acyclovir. The drug reaches this level on average 30-100 minutes after taking a dose. After 3 hours, this indicator remains at the same level or decreases.

Acyclovir is weakly synthesized with plasma protein – only 15%.

With normal renal function, the half-life of acyclovir is approximately 3 hours. Valaciclovir is excreted in the urine, mostly as acyclovir (80+ percent of the total dose), as well as its breakdown product: 9-carboxymethoxymethylguanine. Less than 1% of the drug is excreted unchanged.

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Dosing and administration

To eliminate the shingles form of herpes, adults need to take the medicine in the amount of 1 g three times a day for 1 week.

When treating pathologies caused by the herpes simplex virus, it is necessary to take the medicine in the amount of 500 mg twice a day. If relapses occur, the course of treatment should last 3 or 5 days. In more severe forms of primary diseases, therapy should be started as quickly as possible, increasing its duration to 10 days. In case of relapse of the disease, it is optimal to start taking the medicine in the prodromal period or immediately after the first signs appear.

As an alternative remedy for eliminating labial herpes, Valtrex is prescribed in a dose of 2 g twice a day. The next dose after the first dose should be taken approximately 12 hours later (but it should be taken into account that earlier than 6 hours) after it. Treatment in this mode should not last longer than 1 day, since it has no additional therapeutic benefits. Such a course should begin immediately upon the appearance of the first signs - burning, itching and tingling on the lips.

As a preventive measure against relapses of infectious diseases caused by the herpes simplex virus, adults with normal immunity should take the medicine at 500 mg per day once. If relapses are extremely frequent (10+ times per year), it is considered more appropriate to take the daily dose of the drug in 2 doses (250 mg each). People with immunodeficiency are prescribed 500 mg twice per day. This course lasts 4-12 months.

When preventing infection of a healthy partner with genital herpes (adults with preserved immunity with the number of exacerbations no more than 9 per year), the medicine must be taken once at 500 mg per day for 1+ years. The drug must be taken daily with regular sexual contacts. If contacts are irregular, you should start taking the drug 3 days before possible sexual contact.

For the prevention of cytomegalovirus, children aged 12 and over and adults should take the medicine 4 times a day in the amount of 2 g. The medicine should be taken as soon as possible after the transplant. The dosage is reduced depending on the CC indicators. The course duration is 90 days, but it can be increased in patients who are predisposed to infections.

In case of renal failure, the dosage is calculated depending on the creatinine clearance rate and the indications.

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Use Valtrex during pregnancy

There is limited information on the use of Valtrex in pregnant women. It is only approved for use when the potential benefit to the woman outweighs the risk of adverse effects to the fetus.

Contraindications

Contraindications include patient intolerance to acyclovir and valacyclovir, as well as other substances contained in the drug.

Caution is required when prescribing to patients with clinically expressed forms of HIV.

Side effects Valtrex

The use of the drug may provoke the appearance of such side effects:

• CNS organs: most often – headaches. In isolated cases, dizziness appears, as well as hallucinations, a feeling of confusion, and deterioration of mental abilities. Tremor, a feeling of excitement, or dysarthria and ataxia occur isolatedly, and in addition, convulsions, symptoms of psychotic disorders, as well as a state of coma and encephalopathy develop;

(these effects are reversible and often develop in patients with kidney problems or other health conditions that predispose them to their occurrence; in patients with a transplanted organ who take Valtrex as a prophylactic against cytomegalovirus (and in high doses - 8 g per day), neurological reactions occur more often than when using smaller doses)

• respiratory system: shortness of breath occasionally appears;
• Digestive system organs: occasionally diarrhea, vomiting or abdominal discomfort develop; isolated cases – reversible degree of disturbances in liver function tests (they are sometimes mistaken for signs of hepatitis);
• skin reactions: rashes may appear, as well as symptoms of photosensitivity; itching may occasionally develop;
• allergies: isolated cases – Quincke’s edema or urticaria;
• urinary system organs: occasionally kidney dysfunction; isolated cases – acute renal failure;
• Others: in people with severe immune disorders (especially in the late stages of AIDS), who take valacyclovir in high doses (8 g daily) for a long time, renal failure, thrombocytopenia, and mechanical hemolytic anemia (in some cases in combination) have been observed. The same negative reactions are also determined in patients with similar pathologies who do not take valacyclovir.

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Overdose

There is not enough information about drug overdoses.

In the case of a single oral intake of a large dose of acyclovir (20 g), it is partially absorbed through the gastrointestinal tract, without causing toxic effects. Continued use of large doses of acyclovir over several days causes gastrointestinal disorders (in the form of nausea and vomiting), as well as neurological manifestations (a feeling of confusion, as well as headaches). High doses of the substance administered intravenously increase serum creatinine levels and, subsequently, the development of renal failure. Neurological symptoms include the appearance of hallucinations, feelings of excitement or confusion, the development of seizures, and a comatose state.

The patient must be under constant medical supervision to determine the presence of intoxication symptoms. Hemodialysis accelerates the process of excretion of acyclovir from the blood, so it can be considered an appropriate option for treating patients with an overdose of this drug.

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Interactions with other drugs

No significant clinical interactions of Valtrex with other drugs have been identified.

Unchanged acyclovir is excreted in urine due to the active process of tubular secretion. When using the drug (1 g) in combination with probenecid and cimetidine (they are tubular secretion blockers), the AUC of acyclovir increases, and its clearance inside the kidneys decreases. But there is no need to adjust the dosage of the drug, because acyclovir has a wide therapeutic index.

Valtrex should be used with caution in an increased daily dose (4 g), in combination with drugs that compete with acyclovir for the elimination pathway, because there is a risk of increasing the levels of one of these drugs (or their breakdown products) or both of them together in the blood plasma. In the case of a combination with an inactive breakdown product of mycophenolate mofetil (an immunosuppressant used in organ transplants), an increase in the AUC of this drug and acyclovir is observed.

It is necessary to combine the drug (in doses of 4+ g per day) with drugs that impair kidney function (including cyclosporine and tacrolimus) with caution.

Storage conditions

The medicine is kept in standard conditions for medicines, inaccessible to small children. Temperature – no more than 30°C.

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Shelf life

Valtrex is suitable for use for 3 years from the date of release of the drug.

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