Valtrex 500 mg Tablets

Brand name

The trade name of the drug is Valtrex. This is the registered name under which the drug is known in medical practice and is available in the pharmacy network.

International Nonproprietary Name (INN)

The international nonproprietary name is valacyclovir. It denotes the active active ingredient and is used in pharmacology at the international level.

Form of release

Valtrex is available as film-coated tablets with dosages of 500 mg and 1000 mg. Tablets have a white color, oval shape and are packed in blisters of 7, 10 or 42 pieces. This form provides ease of administration and accurate dosing for patients requiring systemic antiviral therapy.

Composition

Active substance

The main active ingredient is valacyclovir hydrochloride. One tablet contains 500 mg or 1000 mg of valacyclovir hydrochloride, which is equivalent to 445 mg or 890 mg of valacyclovir, respectively.

Auxiliary Components

The tablets include substances such as microcrystalline cellulose, crospovidone, povidone, magnesium stearate, colloidal anhydrous silicon dioxide, and a coating of hypromellose, titanium dioxide, polyethylene glycol, and carnauba wax. These components ensure stability and bioavailability of the active substance.

Pharmacologic Properties

Pharmacodynamics

Valacyclovir, the active ingredient of Valtrex, is a prodrug that is converted in the body into acyclovir, a potent inhibitor of viral DNA polymerase. After oral administration, valacyclovir is rapidly metabolized in the liver and intestine by the enzyme valacyclovirhydrolase to acyclovir. Acyclovir then penetrates into infected cells where it is phosphorylated by viral thymidine kinase to acyclovir triphosphate. This active form competitively blocks viral DNA polymerase, preventing DNA chain elongation and viral replication.

The drug is highly selective to viral enzymes, minimally affecting human cellular processes, which ensures its safety. Valtrex is active against herpes simplex virus types 1 and 2 (HPV-1, HPV-2), varicella-zoster virus (VZV), and partially against cytomegalovirus (CMV) and Epstein-Barr virus. Therapeutic effects include shortening the duration of rashes, reducing pain and itching, and reducing the risk of transmission. Maximum efficacy is maximized when treatment is initiated within the first 24-48 hours after the onset of symptoms.

Pharmacokinetics

Absorption

Valacyclovir is rapidly absorbed from the gastrointestinal tract after oral administration. The maximum plasma concentration of acyclovir is reached in 1-2 hours, and the bioavailability of acyclovir after conversion is about 54%, which is significantly higher than that of direct acyclovir administration (15-20%). Food intake slightly slows absorption, but does not affect the overall efficacy, which allows the drug to be taken independently of meals.

Distribution

Acyclovir weakly binds to blood plasma proteins (about 15-20%). The volume of distribution is approximately 0.7 L/kg, indicating penetration into tissues including skin, mucous membranes, lungs and nervous system. The active form of the drug accumulates in infected cells, where its concentration can be 100 times higher than in plasma, providing a prolonged antiviral effect.

Metabolism

Valacyclovir is metabolized to acyclovir by the enzyme valacyclovirhydrolase in the liver and intestine. About 85-90% of the administered dose is converted to acyclovir, the remainder to the inactive metabolite 9-(carboxymethoxymethoxymethyl)guanine (CMMG) with the participation of the enzymes alcohol dehydrogenase and aldehyde dehydrogenase.

Excretion

The elimination half-life of acyclovir is 2.5-3.3 hours in patients with normal renal function. The drug is excreted mainly through kidneys (about 80-90% in the form of acyclovir and CMMG) by tubular filtration and tubule secretion. Complete excretion takes about 24 hours, but in renal insufficiency this period increases.

Indications for Use

Valtrex is indicated for the treatment of the following conditions:

• Shingles (herpes zoster), including the acute phase and postherpetic neuralgia;
• Genital herpes (HPV-2) - primary and recurrent episodes, as well as suppressive therapy;
• Labial herpes (HPV-1) - recurrent rashes on the lips;
• Prevention of herpetic infections in immunodeficient patients (e.g., HIV, post-transplant);
• Treatment and prevention of skin and mucosal herpes recurrences.

The drug is effective in controlling acute symptoms and preventing exacerbations.

Contraindications

The use of Valtrex is prohibited in:

• Hypersensitivity to valacyclovir, acyclovir or auxiliary components;
• Severe renal insufficiency (creatinine clearance less than 15 ml/min) without dose adjustment;
• Children under 12 years of age (for shingles) or under 18 years of age (for genital herpes);
• Severe hepatic insufficiency with impaired metabolism;
• Pregnancy and lactation without strict indications.

Cautiously prescribe in dehydration, neurologic disorders, immunodeficiency.

Method of Administration and Dosage

How to take

Valtrex tablets are taken orally, drinking water (100-150 ml), regardless of meals. Tablets are not chewed and crushed to preserve the stability of the active ingredient. For maximum efficacy, treatment should be started as soon as possible after the onset of symptoms, preferably within 24-48 hours.

Dosages for adults and children

Adults

For shingles: 1000 mg 3 times daily for 7 days. In genital herpes: primary episode - 1000 mg 2 times a day for 10 days; relapse - 500 mg 2 times a day for 3 days or 1000 mg once; suppression - 500 mg once a day (or 250 mg 2 times a day in case of frequent relapses). In labial herpes: 2000 mg 2 times a day at 12-hour intervals for 1 day.

Children over 12 years of age

For shingles: 1000 mg 3 times a day for 7 days. For other indications in children the drug is not used.

Dose adjustment in certain conditions

In renal insufficiency: creatinine clearance 30-49 ml/min - 1000 mg 2 times a day (shingles) or 500 mg once a day (genital herpes); 15-29 ml/min - 1000 mg once a day or 500 mg once. In hepatic insufficiency, correction is usually not required.

Side Effects

Possible adverse reactions include:

• Nervous system: headache, dizziness, confusion;
• Gastrointestinal system: nausea, abdominal pain, diarrhea;
• Hematopoietic system: thrombocytopenia, leukopenia (rare);
• Skin: rash, itching, photosensitization;
• Allergic reactions: urticaria, rarely - angioedema;
• Other: fatigue, increase in creatinine level.

The side effects are usually mild and pass independently.

Overdose

Symptoms of overdose

Doses above 4000 mg/day may cause nausea, vomiting, confusion, and acute renal failure.

First aid measures

Stop taking, call a doctor. Gastric lavage (if it has been less than an hour), give activated charcoal. If necessary, hemodialysis.

Drug Interactions

Influence on the effect of other drugs

Valtrex has no significant effect on the metabolism of other drugs. Probenecid and cimetidine slow down the excretion of acyclovir, increasing its concentration. Nephrotoxic drugs (cyclosporine) increase the risk of renal failure.

Compatibility with alcohol and food

Alcohol does not affect efficacy but may increase dizziness. Food does not alter absorption.

Special Precautions

Use in pregnancy and breastfeeding

Valtrex is used in pregnancy only for strict indications; lactation should be discontinued due to penetration into milk.

Influence on driving and mechanisms

The drug may cause dizziness, which requires caution when driving.

Particularities of use in the elderly and children

In the elderly, the dose is adjusted in case of impaired renal function. In children under 12 years of age it is used only for shingles.