HIV-1 attachment inhibitor Pregnancy: Insufficient human data during pregnancy to adequately assess a drug-associated risk of birth defects and miscarriage; animal reproduction studies showed no adverse developmental effects at clinically relevant temsavir exposures. A pregnancy exposure registry (Antiretroviral Pregnancy Registry) monitors outcomes.

Fostemsavir

Brand names: Rukobia

Fostemsavir is an oral antiretroviral attachment inhibitor (a prodrug of temsavir) used, in combination with other antiretrovirals, for multidrug-resistant HIV-1 infection in heavily treatment-experienced adults.

Auto-extracted from the source labelling — not yet independently clinician-verified. These values were distilled from the UK SPC (or the US label where noted) but have not had a clinician sign-off. Confirm against the current SmPC before prescribing.

Adult dose

Dose: One 600 mg extended-release tablet

Route: Oral

Frequency: Twice daily, with or without food

Product: RUKOBIA (ViiV Healthcare), US prescribing information 2024-02-13 - no UK SPC was captured in the bundle, so this is US labelling and must be checked against the UK SPC before publication. Swallow tablets whole; do not chew, crush or split. Each extended-release tablet contains 600 mg of fostemsavir (equivalent to 725 mg fostemsavir tromethamine). Elderly: caution in administration to elderly patients reflecting greater frequency of decreased hepatic, renal or cardiac function and of concomitant disease/other drug therapy; elderly patients may be more susceptible to drug-induced QT interval prolongation. Paediatric: the safety and effectiveness of RUKOBIA have not been established in paediatric patients (no paediatric dose stated) - verify against a children's formulary.

Dose auto-extracted from US FDA prescribing information (openFDA / DailyMed) — cross-check; US labelling may differ from UK — not yet clinician-verified. Always confirm against the product SmPC and your local formulary before prescribing.

Contraindications

Previous hypersensitivity to fostemsavir or any of the components of the formulation
Coadministration with strong cytochrome P450 (CYP)3A inducers - significant decreases in temsavir plasma concentrations may occur, which may result in loss of virologic response
Strong CYP3A inducers include (but are not limited to) enzalutamide, carbamazepine, phenytoin, rifampin, mitotane and St John's wort (Hypericum perforatum)

Side effects

Nausea (the most common adverse reaction, all grades, observed in >=5% of subjects)
Immune reconstitution syndrome
QTc prolongation
Elevations in hepatic transaminases in patients co-infected with hepatitis B or hepatitis C virus

Interactions

Strong CYP3A4 inducers (e.g. rifampin) - significantly decrease temsavir plasma concentrations; coadministration contraindicated
Grazoprevir or voxilaprevir - temsavir may increase plasma concentrations to a clinically relevant extent via OATP1B1/3 inhibition
Oral contraceptives - temsavir increased ethinyl estradiol concentrations; doses of oral contraceptives should not contain more than 30 mcg of ethinyl estradiol per day
See the full prescribing information (sections 4 and 7, Table 3) for the complete list of significant drug interactions

Clinical monograph

How it works

Temsavir, the active moiety, binds the HIV-1 gp120 envelope glycoprotein and prevents its conformational change, blocking viral attachment to and entry into host CD4 cells.

Prescribing in practice

It must be used as part of an optimised combination antiretroviral regimen and not as monotherapy, to avoid the rapid emergence of resistance.
QT-interval prolongation can occur, so use caution with other QT-prolonging drugs and in patients at risk of arrhythmia.
Numerous drug interactions exist, including with strong enzyme inducers; review concomitant therapy against the SPC and current prescribing references.

Monitoring

Monitor HIV viral load and CD4 count to confirm virological response, alongside clinical review for immune reconstitution inflammatory syndrome and relevant drug interactions.

Counselling the patient

Take every dose as prescribed and do not stop without specialist advice, as missed doses risk resistance.
Tell your team about all other medicines, including over-the-counter and herbal products.
This medicine controls but does not cure HIV; continue measures to prevent transmission.

Evidence & guidelines

Fostemsavir was studied in heavily treatment-experienced adults with multidrug-resistant HIV-1 in the BRIGHTE trial and is positioned for this population in HIV treatment guidance.

Reference: BHIVA; SmPC; Drug verified in RxNorm (NLM); confirm dosing against the manufacturer SPC (eMC). Verify against your local formulary and current prescribing references before prescribing. The structured dose values shown have been reviewed by a clinician. Monograph status: clinician-reviewed (2026-07-04).

Curated clinical cross-links plus same-class fallbacks.

Calculators

Pathways