Fostemsavir is an HIV-1 gp120-directed attachment inhibitor, indicated for adult patients with multiply drug-resistant HIV-1 infection. As part of combination antiretroviral therapy, its efficacy and effectiveness depend on strict medication management.

What Are the Side Effects of Fostemsavir?

Common Side Effects

Gastrointestinal reactions: Nausea (10%), diarrhea (4%), vomiting (2%), abdominal pain (3%), and dyspepsia (3%).

Neurological symptoms: Headache (4%), drowsiness (2%), dizziness, and taste disturbance (rare).

Skin reactions: Rash (3%) and pruritus (rare).

Others: Fatigue (3%), sleep disorders (3%), and abnormal laboratory findings (e.g., elevated creatine kinase, elevated cholesterol).

Serious Side Effects of Fostemsavir That Require Vigilance

Immune Reconstitution Syndrome (IRS)

Manifestations: In the early stage of treatment, the recovery of the immune system may trigger inflammatory responses to latent infections (such as tuberculosis, cytomegalovirus, Mycobacterium avium complex) or induce autoimmune diseases (such as Graves' disease, Guillain-Barré syndrome).

Management: Close monitoring for infection symptoms is necessary; anti-infective or immunomodulatory treatment should be administered when needed.

QT Interval Prolongation

Risk: High doses (2400 mg, twice daily) can significantly prolong the QT interval, increasing the risk of arrhythmias (e.g., torsades de pointes).

High-risk populations: Patients with a history of QT prolongation, a history of heart disease, or those concomitantly using other QT interval-prolonging drugs (e.g., antiarrhythmic drugs).

Recommendation: Evaluate the electrocardiogram (ECG) before medication use and avoid concurrent use of high-risk drugs.

Hepatotoxicity

Patients coinfected with hepatitis B/C virus: The risk of transaminase elevation is higher (14% vs. 3% in patients with HIV monoinfection), and some cases are associated with hepatitis B reactivation.

Monitoring: Conduct regular liver function tests at baseline and during treatment, and ensure effective anti-hepatitis B treatment.

Precautions for Fostemsavir Use

Medication Use in Special Populations

Pregnancy: Sufficient human data are not available; the benefits and risks must be weighed.

Lactation: HIV-infected patients should not breastfeed to avoid virus transmission.

Hepatic/renal impairment: No dosage adjustment is required for patients with mild to severe hepatic or renal impairment, but enhanced monitoring is necessary.

Elderly patients: They are more prone to QT interval prolongation, so careful assessment of cardiovascular risks is required.

Management of Drug Interactions

Statins (e.g., rosuvastatin): Fostemsavir may increase their plasma concentrations; it is recommended to start with the lowest dose.

Oral contraceptives: The dose of contraceptives containing ethinyl estradiol should be ≤ 30 mcg/day to reduce the risk of thrombosis.

HCV drugs: Concurrent use of grazoprevir or voxilaprevir should be avoided, as it may increase the risk of hepatotoxicity.

Recommendations for Patient Monitoring

Before treatment: Electrocardiogram (QT interval), liver function, and HIV drug resistance testing.

During treatment: Regular monitoring of HIV RNA, CD4 cell count, liver function, and electrolytes.