Some of the views expressed in the following notes on newly approved products should be regarded as preliminary, as there may have been limited published data at the time of publication, and little experience in Australia of their safety or efficacy. However, the Editorial Executive Committee believes that comments made in good faith at an early stage may still be of value. Before new drugs are prescribed, the Committee believes it is important that more detailed information is obtained from the manufacturer's approved product information, a drug information centre or some other appropriate source.
3TC (Glaxo Wellcome)
150 mg tablets
10 mg/mL oral solution
Indication: HIV infection
The treatment of HIV infection with a nucleoside analogue, such as zidovudine, is only temporarily effective. There are also the problems of toxicity and the emergence of resistant viral strains. These problems are being addressed by treating patients with combinations of drugs.
Lamivudine, an analogue of cytidine, has been studied in combination with zidovudine. Both drugs act by inhibiting viral reverse transcriptase and lamivudine is active against strains which are resistant to zidovudine. Compared to zidovudine alone, the combination results in a significant increase in CD4 lymphocyte counts. Patients who have been previously treated with zidovudine also benefit.
Patients take lamivudine twice a day. The drug is well absorbed with a bioavailability over 80%. Food delays absorption. Lamivudine is cleared mainly by the kidneys so the dose is adjusted if there is renal impairment. The half-life is 5-7hours.
Adverse effects are common and similar to those seen in patients treated with zidovudine. The most common complaints are nausea, abdominal discomfort, headache, malaise and fatigue. Abnormal liver function tests and anaemia can occur during treatment. When lamivudine is used alone, resistant viral strains can develop rapidly.
The pivotal efficacy studies in adults only lasted 24 weeks and the outcomes are not clinical end-points. Although the combination of lamivudine and zidovudine is effective, it is unclear when the combination should be used in the course of a HIV infection. For example, should all patients be given the combination when their CD4 counts fall to levels that were studied in the trials?