Fostemsavir is an HIV-1 gp120-directed attachment inhibitor, indicated for the treatment of adult patients with extensive treatment experience who have multiply drug-resistant HIV-1 infection.

What Are the Side Effects of Fostemsavir?

Common Side Effects

Gastrointestinal reactions: Nausea (10%) is the most common adverse reaction; others include diarrhea (4%), abdominal pain (3%), dyspepsia (3%), and vomiting (2%).

Neurological reactions: Headache (4%), somnolence (2%).

Skin reactions: Rash (3%), pruritus.

Systemic reactions: Fatigue (3%).

Sleep disorders: The incidence is approximately 3%, including insomnia, insufficient sleep, and abnormal dreams.

Abnormal laboratory test results: Increased ALT (5%), increased AST (4%), increased direct bilirubin (7%), increased cholesterol (5%), increased creatinine (19%), increased triglycerides (5%), etc.

Severe Side Effects of Fostemsavir That Require Vigilance

Immune Reconstitution Syndrome

Fostemsavir, when used in combination with other antiretroviral drugs for treatment, may trigger immune reconstitution syndrome.

In the early stage of treatment, the immune system's response may lead to an inflammatory reaction to latent or residual opportunistic infections (such as Mycobacterium avium complex infection, cytomegalovirus infection, Pneumocystis jirovecii pneumonia, or tuberculosis).

Autoimmune diseases (such as Graves' disease, polymyositis, Guillain-Barré syndrome, and autoimmune hepatitis) may also occur, and these conditions may not appear until several months after the start of treatment.

QT Interval Prolongation

At a dose 4 times the recommended dose (2400 mg twice daily), Fostemsavir can significantly prolong the QTc interval on the electrocardiogram (with an average increase of 11.2 milliseconds).

Special caution is required for patients with the following conditions: A history of QT interval prolongation.

Patients who are taking drugs known to induce torsades de pointes.

Patients with relevant underlying heart diseases.

Elderly patients may be more sensitive to drug-induced QT interval prolongation.

Elevated Liver Enzymes in Patients Co-Infected with HBV/HCV

The proportion of patients with elevated liver transaminases (14%) is significantly higher in those co-infected with hepatitis B virus (HBV) or hepatitis C virus (HCV) than in patients with HIV monoinfection (3% with elevated ALT and 2% with elevated AST). Some cases of transaminase elevation are associated with HBV reactivation after discontinuing anti-hepatitis treatment.

Recommendation: Monitor liver function in patients co-infected with HBV/HCV.

Special attention should be paid to initiating or maintaining effective HBV treatment when starting Fostemsavir therapy.

Precautions for Fostemsavir Administration

Important Drug Interactions

HCV direct-acting antiviral drugs: May increase the blood concentrations of grazoprevir or voxilaprevir; it is recommended to switch to alternative HCV treatment regimens whenever possible.

Oral contraceptives: The daily dose of ethinyl estradiol should not exceed 30 mcg.

Statins: Should be initiated at the lowest starting dose, and statin-related adverse reactions should be monitored.

Drugs that prolong the QT interval: Caution is required when used in combination with drugs known to induce torsades de pointes.

Other Precautions

Dosage: 600 mg tablets, taken twice daily; swallow the tablets whole, and do not chew, crush, or split them.

Effect of diet: A high-fat meal can increase the AUC by 81%, and a standard meal can increase it by 10%; it is recommended to maintain a consistent way of taking the medication.

Management of overdose: There is no specific antidote; supportive treatment should be administered, including monitoring of vital signs and electrocardiogram (QT interval).