[Durgical](https://durgical.com/en/) › [DurgiPedia](https://durgical.com/en/durgipedia/) › [Pharmacology](https://durgical.com/en/pharmacology/) › [HIV entry inhibitors](https://durgical.com/en/pharmacology/classes/hiv-entry-inhibitors/) › Fostemsavir

# Fostemsavir

## HIV entry inhibitors?

HIV entry inhibitors

An oral HIV attachment inhibitor for heavily treated adults with multidrug-resistant HIV. Its active form, temsavir, binds the viral gp120.

Updated Nov 1, 2026

## Quick facts

**Group**
[HIV entry inhibitors](https://durgical.com/en/pharmacology/classes/hiv-entry-inhibitors/)

**Target**
HIV-1 envelope glycoprotein gp120

**Used for**
HIV-1 infection

**Key effects**
Nausea

**Monitor**
HIV viral load · ECG when QT risk factors exist

**ATC**
J05AX29

No doses: the clinician sets them by the current guideline.

On this page

- The basics Mechanism of action
- Indications
- Adverse effects
- Pharmacokinetics
- Memory aid

- Safety Contraindications
- Key interactions
- What is monitored
- Administration and safety
- Pregnancy and breastfeeding
- Nursing care

- Study Test yourself

- Connections Connections

## Mechanism of action

◆**HIV-1 envelope glycoprotein gp120**Fostemsavir

ⓘ The figure shows temsavir (BMS-626529), the active form of fostemsavir, bound to the HIV-1 envelope trimer.

**Target in 3D:** HIV-1 envelope glycoprotein gp120. PDB structure 5U7O (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/5U7O) · Drag to rotate · pinch to zoom

Fostemsavir is a phosphate prodrug that is quickly converted to temsavir. Temsavir binds gp120 on the viral envelope, so the virus cannot attach to the CD4 receptor and enter the cell. Because the target is new, it keeps activity against virus resistant to other classes. Natural gp120 polymorphisms can reduce susceptibility.

- Fostemsavir is converted to temsavir
- Temsavir binds viral gp120
- gp120 cannot attach to CD4
- HIV cannot enter the T cell

## Indications

- HIV-1 infection in heavily treatment-experienced adults with multidrug resistance, with other antiretrovirals [HIV infection and AIDS →](https://durgical.com/en/conditions/hiv-infection-and-aids/)

## Adverse effects

### Common

- Nausea

### Serious (rare, important)

- QT prolongation at high exposure (fainting, irregular heartbeat)
- Raised liver enzymes, especially with hepatitis B or C
- Immune reconstitution syndrome

## Contraindications

- Strong CYP3A inducers such as rifampicin
- Hypersensitivity to fostemsavir

## Key interactions

**Rifampicin and other strong CYP3A inducers**
Lower temsavir and cause treatment failure; not combined

**Statins carried by OATP1B1/3**
Temsavir inhibits these transporters and raises statin levels; avoided or chosen carefully

**QT-prolonging drugs**
Added QT risk

## What is monitored

- HIV viral load
- ECG when QT risk factors exist
- Liver enzymes, especially with viral hepatitis

## Administration and safety

- Oral, twice a day, with or without food
- Tablets are swallowed whole, not split, chewed or crushed

## Pregnancy and breastfeeding

Human data are limited; benefit and risk are weighed with the HIV team.

## Nursing care

- Check heart history and other QT-prolonging drugs
- Teach to report fainting, palpitations or dizziness
- Teach to report new signs of infection after starting
- Reinforce adherence: options are few in multidrug resistance

## Pharmacokinetics

**Absorption**
Oral tablet; food and stomach pH have little effect

**Metabolism**
Temsavir is cleared by esterases and CYP3A4; a substrate of P-gp

**Elimination**
Partly unchanged in the urine; no adjustment for kidney or liver disease

**Half-life**
Short, so it is taken twice a day

## Memory aid

FOS-TEM-savir: the TEMplate gets stuck closed, so gp120 cannot shake hands with CD4.

## Test yourself

Think of the answer, then tap the question to see it.

## What is the active form of fostemsavir?

Temsavir.

## Which viral protein does temsavir bind?

gp120, preventing attachment to CD4.

## Which antimycobacterial must not be combined with fostemsavir?

Rifampicin, a strong CYP3A inducer.

[Add to my cards (3)](https://durgical.app/estudiar/?add=/en/pharmacology/fostemsavir/)

[More Pharmacology questions →](https://durgical.com/en/practice/?f=pharmacology)

## Connections

## Related drugs 3

- [Maraviroc](https://durgical.com/en/pharmacology/maraviroc/)
- [Enfuvirtide](https://durgical.com/en/pharmacology/enfuvirtide/)
- [Ibalizumab](https://durgical.com/en/pharmacology/ibalizumab/)

## Related conditions 1

- [HIV infection and AIDS](https://durgical.com/en/conditions/hiv-infection-and-aids/)

[← Back to the class: HIV entry inhibitors](https://durgical.com/en/pharmacology/classes/hiv-entry-inhibitors/)

Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: [Fostemsavir: MedlinePlus Drug Information](https://medlineplus.gov/druginfo/meds/a620046.html) (MedlinePlus (U.S. National Library of Medicine), 2026); [Crystal Structure of HIV-1 BG505 SOSIP.664 Prefusion Env Trimer Bound to Small Molecule HIV-1 Entry Inhibitor BMS-626529 in Complex with Human Antibodies PGT122 and 35O22 at 3.8 Angstrom](https://www.rcsb.org/structure/5U7O) (RCSB Protein Data Bank, 2017); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=J05AX29) (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.

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