HIV infection
Lamivudine: Intracellularly, Lamivudine is phosphorylated to its active 5’-triphosphate metabolite, Lamivudine triphosphate (L-TP). The principal mode of action of L-TP is inhibition of reverse transcription (RT) via DNA chain termination after incorporation of the nucleoside analogue. Following oral administration, Lamivudine is rapidly absorbed and extensively distributed. Binding to plasma protein is low.
Zidovudine: Intracellularly, Zidovudine is phosphorylated to its active 5’-triphosphate metabolite, Zidovudine triphosphate (ZDV-TP). The principal mode of action of ZDV-TP is inhibition of RT via DNA chain termination after incorporation of the nucleoside analogue. Following oral administration, Zidovudine is rapidly absorbed and extensively distributed. Binding to plasma protein is low. Zidovudine is eliminated primarily by hepatic metabolism.
Nevirapine: Nevirapine binds directly to reverse transcriptase (RT) and blocks the RNA-dependent and DNA-dependent DNA polymerase activities by causing a disruption of the enzyme’s catalytic site. The activity of nevirapine does not compete with template or nucleoside triphosphates.
Adult dose: One tablet twice daily. This fixed dose combination is not recommended for patients who have not been on initial lower dose of Nevirapine 200 mg once daily for 2 weeks and /or have not tolerated this dose. After successful therapy with low dose Nevirapine for two weeks, patients can be switched over to 200 mg bid dose provided they have not demonstrated any hypersensitivity reaction (rash, abnormal liver function tests) during their initial exposure to Nevirapine. Monitoring of patients for their liver function tests etc. is desirable prior to initiating therapy with Nevirapine and monitoring at frequent intervals once therapy with fixed dose combination is continued.
Dosage adjustment:
- Lamivudine: For patients with low body weight (<50 kg) where dosage adjustment may be required, it is preferable not to use this fixed dose combination.
- Zidovudine: Because it is a fixed dose combination, this should not be prescribed for patients requiring dosage adjustment such as those with reduced renal function (creatinine clearance 50 ml/min) or those experiencing dose imiting adverse events.
- Nevirapine: For patients who experience severe rash or rash with constitutional complaints during the initial low dose Nevirapine phase of 14 days with once daily dose of 200 mg; neither, dose should be increased to twice daily nor they should receive triple fixed dose combination until the rash is resolved. Similarly for patients with abnormal liver function tests, Nevirapine therapy should be stopped till liver function return to normal and careful restart is advisable after extended observation. In event of recurrence, Nevirapine therapy can not be restarted.
- For patients where Nevirapine therapy has to be restarted after an interruption, daily dose of Nevirapine 200 mg for 14 days should be followed with twice daily dose in absence of any hypersensitivity reaction. Studies have not been documented to suggest dosage of Nevirapine in patients with hepatic dysfunction, renal insufficiency or undergoing dialysis.
Lamivudine: Increased risk of hepatic decompensation or haematologic toxicities with interferon and ribavirin (also increases risk of mitochondrial toxicity, pancreatitis and lactic acidosis). Ganciclovir and valganciclovir may increase effects and toxicity; sulfamethoxazole/ trimethoprim may increase AUC and decrease clearance (increasing levels and effects).
Zidovudine: Headache (which may be severe, has been reported in up to 63% of patients receiving Zidovudine and asthenia has been reported in 9-69%), malaise and fatigue, fever or chills, nausea (61% cases), diaphoresis, dyspnoea, rash and taste perversion have been reported. Skin rashes and myalgia has been reported in patients receiving Zidovudine. Myopathy and myositis with pathologic changes similar to that produced by HIV infection, have been associated with prolonged use of Zidovudine. The major adverse effect is bone marrow toxicity resulting in severe anaemia and/or neutropenia. Patients with low serum folate or vitamin B12 concentrations may be at increased risk for developing bone marrow toxicity during Zidovudine therapy. There also are limited data suggesting that bone marrow of patients with fulminant acquired immunodeficiency syndrome (AIDS) may be more sensitive to Zidovudine induced toxicity than that of patients with less advanced disease (eg, AIDS related complex). Anaemia and granulocytopenia usually resolve when Zidovudine is discontinued or when dosage is decreased. Lactic acidosis (in the absence of hypoxaemia) and severe hepatomegaly with steatosis, including some fatalities, have been reported in patients receiving Zidovudine.
Nevirapine: More frequent incidences are skin rash, diarrhoea, gastrointestinal problems, headache, nausea and stomach pain. Incidence of less frequents are aphthous stomatitis, fever, hepatitis and Stevens Johnson syndrome.
