**Core Concept**
Lamivudine is a nucleoside reverse transcriptase inhibitor (NRTI) used in the treatment of HIV infection and chronic hepatitis B. It works by inhibiting the reverse transcriptase enzyme, which is essential for the replication of retroviruses and hepadnaviruses.

**Why the Correct Answer is Right**
Lamivudine is a prodrug that undergoes intracellular conversion to its active metabolite, lamivudine triphosphate. This active form competes with the natural nucleotide substrates for incorporation into the viral DNA, thereby inhibiting viral replication. Lamivudine has a high genetic barrier to resistance, making it a favorable option for long-term treatment.

**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because lamivudine is indeed used in the treatment of chronic hepatitis B, in addition to HIV infection. Its efficacy in treating hepatitis B is well established.
**Option B:** Incorrect because lamivudine is not primarily a prodrug; it is converted to its active form within the cell, but it is not a prodrug in the classical sense.
**Option C:** Incorrect because lamivudine is actually a pyrimidine nucleoside analog, not a purine nucleoside analog.

**Clinical Pearl / High-Yield Fact**
Lamivudine is often used in combination with other antiretroviral agents to achieve optimal suppression of viral replication in patients with HIV infection. Its use in chronic hepatitis B treatment has also been shown to improve liver histology and reduce the risk of liver cancer.

**Correct Answer:** C.