Lamivudine

BRAND NAMES

• Epivir is the main brand name for lamivudine when used to treat HIV.

• Epivir-HBV is a specific brand of lamivudine formulated for the treatment of hepatitis B infections.

MECHANISM OF ACTION

Lamivudine is a synthetic nucleoside analogue that is phosphorylated inside cells to form its active metabolite, lamivudine triphosphate (L-TP). This active form is incorporated into viral DNA by HIV reverse transcriptase and HBV polymerase, leading to the termination of the DNA chain.

PHARMACOKINETICS

Absorption

Lamivudine is quickly absorbed following oral administration in patients with HIV. In a study of 12 adult patients, the absolute bioavailability was found to be 86% ± 16% (mean ± SD) for the 150-mg tablet and 87% ± 13% for the oral solution.

Distribution

The apparent volume of distribution following intravenous administration is 1.3 ± 0.4 L/kg. This volume of distribution is dose-independent and shows no correlation with body weight. Lamivudine is less than 36% bound to plasma proteins, and metabolism plays a minor role in its elimination.

Metabolism

Lamivudine is primarily eliminated through other pathways, with metabolism playing a minor role in its elimination. In humans, the only identified metabolite of lamivudine is the trans-sulfoxide metabolite. This biotransformation is catalyzed by sulfotransferases.

Excretion:

Lamivudine is primarily excreted unchanged by the kidneys, with a minor portion metabolized in the liver. This heavy reliance on renal clearance means that proper kidney function is essential for its elimination from the body

PHARMACODYNAMICS

Lamivudine is a nucleoside reverse transcriptase inhibitor (NRTI) that is used to treat HIV-1 and chronic hepatitis B virus (HBV) infections. Its pharmacodynamics describe the biochemical effects and the mechanism by which it inhibits these viruses.

ADMINISTRATION

For adults infected with HIV-1, the recommended dose of lamivudine tablets is 300 mg per day. This can be taken as 150 mg orally twice a day or 300 mg orally once a day, with or without food.

DOSAGE AND STRENGTHS

The dosage of this medicine varies depending on the patient and condition, so always follow your doctor’s instructions or the label directions. For hepatitis B, adults typically take 100 mg once daily, while children’s doses are based on body weight, usually around 3 mg/kg per day, not exceeding 100 mg. For HIV treatment, adults usually take 300 mg once daily or 150 mg twice daily. Children's doses, whether in solution or tablet form, depend on their weight and age, with doctors adjusting as needed. Use and dosing for children under 2 years (hepatitis B) or under 3 months (HIV) must be determined by a doctor.

DRUG INTERACTIONS

While some medications should never be taken together, there are instances where two different drugs may be used simultaneously despite potential interactions. In such cases, your doctor might adjust the dosage or take other precautions. It is especially important to inform your healthcare provider about any medications you are currently taking while using this medicine. The interactions listed below are chosen based on their potential importance but do not represent a complete list.

FOOD INTERACTIONS

Lamivudine can be taken with or without food, as there are no known significant food interactions. While taking it with food can slow its absorption, the overall amount of the drug absorbed into the body (systemic exposure) is not affected.

CONTRAINDICATIONS

The primary contraindication for lamivudine is a known hypersensitivity or allergic reaction to lamivudine or any of the components in the medication. For fixed-dose combination drugs that contain lamivudine (like abacavir/lamivudine), there are additional contraindications related to the other components.

SIDE EFFECTS

• Headache

• Diarrhea

• Heartburn

• Trouble falling asleep or staying asleep

• Depression

• Nasal congestion

• Cough

• Joint pain

OVER DOSE

An overdose of lamivudine can cause serious side effects, including severe nausea, vomiting, and unusual tiredness. In rare but severe cases, an overdose may lead to life-threatening conditions like lactic acidosis or severe liver problems

TOXICITY

Lamivudine is a nucleoside analogue antiretroviral medication recognized for its low toxicity at clinically recommended doses. However, the toxicity, underlying mechanisms, and effects on target tissues during long-term use of higher doses have received limited investigation in laboratory studies.