Abacavir and lamivudine

Uses

Abacavir is an antiviral nucleoside reverse transcriptase inhibitor used in combination with other antiretrovirals for the treatment of HIV.

For the treatment of HIV-1 infection, in combination with other antiretroviral agents.

Lamivudine is used for the treatment of chronic hepatitis B associated with evidence of hepatitis B viral replication and active liver inflammation.

Abacavir and lamivudine is also used to associated treatment for these conditions: Human Immunodeficiency Virus Type 1 (HIV-1) InfectionHepatitis B Chronic Infection, Human Immunodeficiency Virus (HIV) Infections

How Abacavir and lamivudine works

Abacavir is a carbocyclic synthetic nucleoside analogue and an antiviral agent. Intracellularly, abacavir is converted by cellular enzymes to the active metabolite carbovir triphosphate, an analogue of deoxyguanosine-5'-triphosphate (dGTP). Carbovir triphosphate inhibits the activity of HIV-1 reverse transcriptase (RT) both by competing with the natural substrate dGTP and by its incorporation into viral DNA. Viral DNA growth is terminated because the incorporated nucleotide lacks a 3'-OH group, which is needed to form the 5′ to 3′ phosphodiester linkage essential for DNA chain elongation.

Lamivudine is a synthetic nucleoside analogue and is phosphorylated intracellularly to its active 5'-triphosphate metabolite, lamivudine triphosphate (L-TP). This nucleoside analogue is incorporated into viral DNA by HIV reverse transcriptase and HBV polymerase, resulting in DNA chain termination.

Dosage

Abacavir and lamivudine dosage

The recommended oral dose of Lamivudine for the treatment of chronic hepatitis B in adults is 100 mg once daily.

Side Effects

Several serious adverse events reported with lamivudine (lactic acidosis and severe hepatomegaly with steatosis, post treatment exacerbations of hepatitis B, pancreatitis, and emergence of viral mutants associated with reduced drug susceptibility and diminished treatment response). Malaise, fatigue, fever, ENT infections, sore throat, nausea, vomiting, abdominal discomfort, pain, diarrhea, myalgia, arthralgia, headache, skin rashes may occur. Lactic acidosis and severe hepatomegaly with steatosis, have been reported.

Toxicity

Some myocardial degeneration has been noticed in rats and mice. The most commonly reported adverse reactions of at least moderate intensity (incidence ≥10%) in adult HIV-1 clinical trials were nausea, headache, malaise and fatigue, nausea and vomiting, and dreams/sleep disorders. Serious hypersensitivity reactions have been associated with abacavir which has been strongly linked to the presence of the HLA-B*57:01 allele. This reaction manifests itself in patients within the first 6 weeks of treatment. Patients should be tested for the presence of this allele as recommended by the U.S Food and Drug Administration (FDA).

The most common reported adverse reactions (incidence ≥15%) in adults were headache, nausea, malaise and fatigue, nasal signs and symptoms, diarrhea, and cough.

Precaution

Patients should be assessed before beginning treatment and during treatment with lamivudine by a physician experienced in the management of chronic hepatitis B.

Interaction

Trimethoprim 160 mg / Sulfamethoxazole 800 mg once daily has been shown to increase lamivudine exposure (AUC). The effect of higher doses of trimethoprim /sulfamethoxazole on lamivudine pharmacokinetics has not been investigated.

Volume of Distribution

• 0.86 ± 0.15 L/kg [IV administration]

Apparent volume of distribution, IV administration = 1.3 ± 0.4 L/kg. Volume of distribution was independent of dose and did not correlate with body weight.

Elimination Route

Rapid and extensive after oral administration (83% bioavailability, tablet). When a 300 mg tablet is given twice daily to subjects, the peak plasma concentration (Cmax) was 3.0 ± 0.89 mcg/mL and the area under the curve (AUC 0-12 hours) was 6.02 ± 1.73 mcg•hr/mL.

Lamivudine was rapidly absorbed after oral administration in HIV-infected patients. Absolute bioavailability in 12 adult patients was 86% ± 16% (mean ± SD) for the 150-mg tablet and 87% ± 13% for the oral solution. The peak serum lamivudine concentration (Cmax) was 1.5 ± 0.5 mcg/mL when an oral dose of 2 mg/kg twice a day was given to HIV-1 patients. When given with food, absorption is slower, compared to the fasted state.

Half Life

1.54 ± 0.63 hours

5 to 7 hours (healthy or HBV-infected patients)

Clearance

• 0.80 ± 0.24 L/hr/kg [asymptomatic, HIV-1-infected adult patients receiving single (IV dose of 150 mg]

• Renal clearance = 199.7 ± 56.9 mL/min [300 mg oral dose, healthy subjects]
• Renal clearance = 280.4 ± 75.2 mL/min [single IV dose, HIV-1-infected patients]
• Total clearance = 398.5 ± 69.1 mL/min [HIV-1-infected patients]

Elimination Route

Elimination of abacavir was quantified in a mass balance study following administration of a 600-mg dose of 14C-abacavir: 99% of the radioactivity was recovered, 1.2% was excreted in the urine as abacavir, 30% as the 5′-carboxylic acid metabolite, 36% as the 5′-glucuronide metabolite, and 15% as unidentified minor metabolites in the urine. Fecal elimination accounted for 16% of the dose. Renal excretion of unchanged abacavir is a minor route of elimination in humans.

The majority of lamivudine is eliminated unchanged in urine by active organic cationic secretion. 5.2% ± 1.4% (mean ± SD) of the dose was excreted as the trans-sulfoxide metabolite in the urine. Lamivudine is excreted in human breast milk and into the milk of lactating rats.

Pregnancy & Breastfeeding use

There is no adequate and well-controlled study in pregnant women. Lamivudine should be used during pregnancy only if the potential benefits outweigh the risks. Although it is not known if lamivudine is excreted in human milk, there is the potential for adverse effects from lamivudine in nursing infants. Mothers should be instructed not to breast feed if they are receiving lamivudine.

Contraindication

Lamivudine is contraindicated in patients hypersensitive to any of the components of the product.

Special Warning

It is recommended that doses of Lamivudine should be adjusted in accordance with renal function. Dosage adjustment of Lamivudine in accordance with creatinine clearance is as follows:

• CrCl 50 ml/min: 100 mg once daily
• CrCl 30-49 ml/min: 100 mg first dose, then 50 mg once daily
• CrCl 15-29 ml/min: 100 mg first dose, then 25 mg once daily
• CrCl 5-14 ml/min: 35 mg first dose, then 15 mg once daily
• CrCl <5 ml/min: 35 mg first dose, then 10 mg once daily

Use in children: Safety and efficacy of lamivudine for the treatment of chronic hepatitis B in children have not been established.

Storage Condition

Store below 30˚C. Protect from light. Keep out of the reach of children.

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