is no benefit to continuing lamivudine treatment in patients with lamivudine resistance. A better explanation of the data is that lamivudine continues to have a partial anti-viral effect even in the presence of the M184V mutation. In hepatitis B, lamivudine resistance was first described in the YMDD (tyrosine-methionine-aspartate-aspartate) locus of the HBV reverse transcriptase gene. The HBV reverse transcriptase gene is 344 amino acids long and occupies codons 349 to 692 on the viral genome. The most commonly encountered resistance mutations are M204V/I/S. The change in amino acid sequence from YMDD to YIDD results in a 3.2 fold reduction in the error rate of the reverse transcriptase, which correlates with a significant growth disadvantage of the virus. Other resistance mutations are L80V/I, V173L and L180M. Side effects Minor side effects may include nausea, fatigue, headaches, diarrhea, cough and nasal congestion. Do not prescribe lamivudine/zidovudine, abacavir/lamivudine, or abacavir/lamivudine/zidovudine to patients taking emtricitabine. Long-term use of lamivudine can trigger a resistant hepatitis B virus (YMDD) mutant. HIV or HBV-infected women on lamivudine are warned to discontinue breastfeeding as this puts the baby at risk for HIV transmission and medication side effects. Patients who are infected with HIV and HCV and are on both interferon and lamivudine can experience liver damage. The drug can trigger an inflammatory response to opportunistic infections (e.g., Mycobacterium avium complex [MAC], M. tuberculosis, cytomegalovirus [CMV], Pneumocystis jirovecii [formerly P. carinii). Autoimmune disorders have been reported and symptoms can occur many months after initiation of the antiretroviral therapy. Use with caution for patients with impaired renal function and do not prescribe this treatment to patients with impaired hepatic function. Mechanism of action Lamivudine is an analogue of cytidine. It can inhibit both types (1 and 2) of HIV reverse transcriptase and also the reverse transcriptase of hepatitis B virus. It is phosphorylated to active metabolites that compete for incorporation into viral DNA. They inhibit the HIV reverse transcriptase enzyme competitively and act as a chain terminator of DNA synthesis. The lack of a 3'-OH group in the incorporated nucleoside analogue prevents the formation of the 5' to 3' phosphodiester linkage essential for DNA chain elongation, and therefore, the viral DNA growth is terminated. Lamivudine is administered by mouth, and it is rapidly absorbed with a bio-availability of over 80%. Some research suggests that lamivudine can cross the blood–brain barrier. Lamivudine is often given in combination with zidovudine, with which