How it works
Emtricitabine (FTC) and tenofovir disoproxil fumarate (TDF) are nucleoside and nucleotide analogue reverse-transcriptase inhibitors (NRTIs). Both are prodrugs that require intracellular phosphorylation in target cells to become active: FTC is converted to emtricitabine-triphosphate (FTC-TP) and tenofovir to tenofovir-diphosphate (TFV-DP). These active triphosphate forms compete with the natural substrates of HIV reverse transcriptase — dCTP and dATP respectively — and, once incorporated into the growing viral DNA chain, cause chain termination. Because the active triphosphate forms are trapped inside cells, they provide prolonged antiviral activity: the intracellular half-life of TFV-DP is approximately 150 hours (about 6 days) and FTC-TP about 39 hours, which supports daily dosing and provides some forgiveness for occasional late doses [NCT00458393; PMCID PMC3019086]. The landmark iPrEx trial (NCT00458393) — a phase 3, double-blind, randomised, placebo-controlled study of 2,499 men who have sex with men and transgender women across 11 sites in the Americas, South Africa and Thailand — demonstrated that daily oral FTC/TDF reduced HIV acquisition by 44% overall. Among participants with detectable drug levels in blood, the risk reduction exceeded 90%, underscoring that adherence is the dominant determinant of efficacy. The primary endpoint was time to confirmed HIV seroconversion. The trial did not measure efficacy in people who inject drugs, in heterosexual women independently, or against non-sexual routes of transmission [NCT00458393]. The principal toxicity concern with tenofovir disoproxil is renal: tenofovir is taken up into renal proximal tubule cells via organic anion transporters OAT1 and OAT3, where high intracellular concentrations can cause mitochondrial toxicity and subsequent proximal tubulopathy. Clinically, this manifests as decreased phosphate reabsorption, which can alter bone mineral metabolism and reduce bone mineral density — hence the monitoring of kidney function and the caution when co-prescribing other nephrotoxic medicines [PMCID PMC3019086]. Tenofovir disoproxil also has activity against hepatitis B virus. In someone with unrecognised chronic hepatitis B, starting and then stopping PrEP could lead to a flare of hepatitis, which is why hepatitis B status is checked before the first dose [PMCID PMC3019086].How to use
Two things hold for as long as you are on PrEP: the daily tablet, and the fact that the schedule itself is set clinically.One 200 mg/245 mg tablet once daily
Taken every day, preferably with food, at a time that can be maintained
consistently. Daily PrEP protection depends strongly on adherence.
Tablets are not shared, and another person’s schedule is not used.
Starting, stopping or switching schedules is a medical decision
A documented negative HIV assessment is required before starting and
during follow-up. The clinician confirms when protection can be relied
on and how long to continue after the last exposure.
Event-based dosing is not appropriate for every person or exposure.
Before the first dose
Complete HIV testing, kidney assessment, hepatitis B review, medication interaction check, and STI screening. Symptoms of recent HIV infection can require additional testing before PrEP starts.Ongoing monitoring
One tablet is taken daily, with repeat HIV, kidney and STI checks at the interval set by the service — commonly every 3 months for HIV review. A refill is arranged before tablets run out.What has been reported
Contact your doctor if
- Fever, rash, sore throat, swollen glands, marked tiredness, or another symptom appears after a recent HIV exposure — seek prompt testing advice
- Reduced urination, swelling, severe weakness, persistent vomiting, bone pain, or a severe allergic reaction occurs
- Several doses are missed, tablets are about to run out, a new kidney-affecting medicine is needed, or stopping is being considered
Storage
Keep in the original package, away from moisture and direct heat, and out of children’s reach. Follow the temperature limit printed on the pack and do not use it after the expiry date.What to expect
Daily emtricitabine/tenofovir PrEP substantially reduces the risk of sexually acquired HIV when taken consistently as part of a monitored prevention plan, but it does not prevent every infection and does not protect against other STIs. Adherence, testing, condoms where appropriate, vaccination, and prompt post-exposure advice all have roles.How Hi-Doctor handles it
A questionnaire covering sexual health history, current medication and exposure risk is reviewed by an EU-licensed doctor — see how eligibility works and how safety checks run. Sexual health consultations are offered as a one-off review; the cost is set out on pricing.Start a consultation
Sexual health consultation
Answer the sexual health questionnaire and a registered doctor reviews it.
They decide whether treatment is appropriate, which one, and at what dose —
and declining is a normal outcome. See what it costs
and how the review works.