Lamivudine Dosage Calculator
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Epivir (Lamivudine) is a nucleoside reverse transcriptase inhibitor (NRTI) used primarily to treat HIV‑1 infection and chronic hepatitis B. It works by mimicking the natural nucleoside cytidine, inserting itself into the viral DNA chain and halting replication. In the UK, the NHS typically provides 150mg tablets for adults, priced around £12 per month. The drug was approved by the U.S. Food and Drug Administration (FDA) in 1995 and has been a staple of combination therapy ever since.
How Lamivudine Fits Into Antiretroviral Therapy
Lamivudine belongs to the broader class of reverse transcriptase inhibitors, which target the enzyme HIV uses to copy its RNA into DNA. By joining the viral chain prematurely, the drug introduces a dead‑end that prevents new viral particles from forming. Because the virus can quickly develop resistance, lamivudine is almost never given alone; it’s paired with at least two other agents from different classes.
Key Attributes of Lamivudine
- Dosage: 150mg once daily for hepatitis B, 100mg twice daily for HIV (or 50mg in paediatric suspensions).
- Half‑life: Approximately 5-7 hours, allowing flexible dosing.
- Renal excretion: 70% unchanged in urine; dose adjustment needed for eGFR<30mL/min.
- Cost (NHS): £12‑£15 per month for the adult tablet.
- Safety: Generally well‑tolerated; common side effects include headache, nausea, and mild fatigue.
Why Compare? The Main Alternatives
Clinicians often weigh lamivudine against other NRTIs that share a similar potency but differ in resistance patterns, dosing convenience, and side‑effect profiles. The most common comparators are:
- Tenofovir disoproxil fumarate (TDF) - a staple of once‑daily regimens, noted for its high barrier to resistance but linked to renal and bone toxicity.
- Emtricitabine (FTC) - chemically similar to lamivudine, often paired with TDF in the popular “Truvada” combo.
- Zidovudine (AZT) - the first approved NRTI, with a long history but notable for anaemia and mitochondrial toxicity.
- Abacavir (ABC) - prized for once‑daily dosing; however, it carries a risk of hypersensitivity in patients with HLA‑B*57:01.
Side‑Effect Profiles Compared
Below is a concise view of how lamivudine stacks up against its peers on the most clinically relevant adverse events.
| Attribute | Lamivudine | Tenofovir (TDF) | Emtricitabine | Zidovudine | Abacavir |
|---|---|---|---|---|---|
| Typical Dose | 100mg BID (HIV) / 150mg QD (HBV) | 300mg QD | 200mg QD | 300mg QD | 600mg QD |
| Half‑life (hours) | 5‑7 | 17 | 10 | 1‑2 | 8‑10 |
| Key Toxicities | Mild GI, headache | Renal dysfunction, bone loss | Similar to lamivudine | Anaemia, lipoatrophy | Hypersensitivity (HLA‑B*57:01) |
| Resistance Barrier | Low - M184V mutation | High - few mutations alone | Low - M184V (shared) | Medium - multiple thymidine analog mutations | Medium - K65R can affect |
| Cost (UK NHS) | £12‑£15 / month | £25‑£30 / month | £20‑£25 / month | £10‑£12 / month | £30‑£35 / month |
Clinical Scenarios: When Lamivudine Shines
Lamivudine’s low cost and solid safety make it attractive in a few specific settings:
- Pregnant women with HIV: The drug crosses the placenta safely and has a long safety record in the World Health Organization (WHO)‑recommended regimens.
- Patients with chronic hepatitis B: It is one of only two agents (the other being tenofovir) approved for monotherapy, providing durable viral suppression.
- Resource‑limited settings: Its affordability aligns with national treatment programmes that rely on generic supply chains.
- Renal‑impaired individuals (eGFR>30mL/min): Dose adjustment is straightforward, unlike tenofovir which may be contraindicated.
Resistance Considerations
The most common lamivudine‑related mutation is M184V, which reduces susceptibility by >100‑fold. Interestingly, this mutation also hampers viral fitness, so patients who develop it often see a slower disease progression. When M184V appears, clinicians typically add a high‑barrier agent such as tenofovir or a boosted protease inhibitor to maintain suppression.
Drug‑Interaction Landscape
Lamivudine has a clean interaction profile because it is not metabolised by cytochrome P450 enzymes. However, a few cautions are worth noting:
- Co‑administration with didanosine increases the risk of pancreatitis - avoid the combo.
- Nephrotoxic agents (e.g., aminoglycosides) can exacerbate renal clearance issues; monitor serum creatinine closely.
- Vaccines containing live attenuated viruses should be deferred until immune reconstitution is confirmed.
Prescribing Tips & Monitoring
- Baseline labs: HIV viral load, CD4 count, hepatitis B surface antigen, renal function, and CBC.
- Follow‑up schedule: Viral load at weeks 4 and 12, then every 3-6months; renal function every 6months.
- Adherence counseling: Because lamivudine is often part of a twice‑daily regimen, encourage pill‑box use or fixed‑dose combinations (e.g., Triumeq - abacavir/lamivudine/dolutegravir) to simplify dosing.
- Switching strategies: If a patient develops renal insufficiency, consider moving to emtricitabine/tenofovir alafenamide (TAF) based regimens, which have lower renal impact.
Related Topics Worth Exploring
While this article focuses on lamivudine, the broader antiretroviral landscape includes:
- Integrase strand transfer inhibitors (INSTIs) - the current backbone of first‑line therapy.
- Dolutegravir - a high‑potency INSTI often paired with lamivudine in single‑tablet regimens.
- HIV treatment guidelines from the WHO and the British HIV Association (BHIVA) - essential for staying up‑to‑date.
- Hepatitis B management - especially relevant when lamivudine is the sole HBV agent.
TL;DR - Quick Reference
- Lamivudine is cheap, well‑tolerated, and works for both HIV and HBV.
- Best for pregnant women, HBV monotherapy, and low‑resource settings.
- Watch for M184V resistance; combine with a high‑barrier drug.
- Renal dose‑adjust if eGFR<30mL/min.
- Cost‑effective alternative to tenofovir in many scenarios.
Frequently Asked Questions
Can lamivudine be used alone for HIV?
No. Current guidelines recommend it only as part of combination antiretroviral therapy (cART). Using it alone leads to rapid resistance, particularly the M184V mutation.
Is lamivudine safe during pregnancy?
Yes. Both the WHO and BHIVA list lamivudine as a Category B drug, meaning there is no evidence of fetal harm in well‑conducted studies. It is commonly included in first‑line regimens for pregnant women.
How does lamivudine compare cost‑wise with tenofovir?
Lamivudine is roughly half the price of tenofovir on the NHS (£12‑£15 vs £25‑£30 per month). The cheaper price makes it attractive in budget‑constrained programmes, though the higher resistance barrier of tenofovir may justify its cost in some patients.
What monitoring is needed for patients on lamivudine?
Baseline viral load and CD4 count, liver function tests, and renal function are essential. Follow‑up viral load at weeks4 and12, then every 3-6months. Renal function should be checked at least twice a year, more often if eGFR is borderline.
Can lamivudine treat both HIV and hepatitis B at the same time?
Yes. In co‑infected patients, lamivudine suppresses both viruses. However, hepatitis B can develop resistance faster, so many clinicians add tenofovir for a more durable HBV response.
I am a pharmaceutical expert with over 20 years of experience in the industry. I am passionate about bringing awareness and education on the importance of medications and supplements in managing diseases. In my spare time, I love to write and share insights about the latest advancements and trends in pharmaceuticals. My goal is to make complex medical information accessible to everyone.