Fostemsavir Side Effects

Medically reviewed by Drugs.com. Last updated on Feb 9, 2025.

Applies to fostemsavir: oral tablet extended release.

Common side effects of fostemsavir

Some side effects of fostemsavir may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common side effects

• diarrhea
• nausea
• tiredness or weakness

Less common side effects

• belching
• burning, numbness, tingling, or painful sensations
• change in or loss of taste
• difficulty in moving
• dizziness
• drowsiness
• headache
• heartburn
• indigestion
• joint pain or swelling
• muscle pain, cramps, or stiffness
• stomach discomfort, upset, or pain
• trouble sleeping
• unsteadiness or awkwardness
• vomiting
• weakness in the arms, hands, legs, or feet

Serious side effects of fostemsavir

Along with its needed effects, fostemsavir may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking fostemsavir:

Less common side effects

• fainting
• irregular heartbeat, recurrent
• itching, skin rash

For healthcare professionals

Applies to fostemsavir: oral tablet extended release.

General adverse events

The most common side effects reported were diarrhea, headache, nausea, rash, abdominal pain, and vomiting. Most (81%) of the side effects reported were of mild or moderate severity. This drug was discontinued due to a side effect in 7% of patients at week 96; the most common side effects leading to discontinuation were related to infections. Serious drug reactions were reported in 3% of patients and included a few cases of severe immune reconstitution inflammatory syndrome.^[Ref]

Gastrointestinal

• Very common (10% or more): Diarrhea (up to 24%), nausea (up to 15%), abdominal pain (included abdominal discomfort, abdominal pain, upper abdominal pain; up to 12%), vomiting (up to 11%)
• Common (1% to 10%): Elevated lipase, dyspepsia, flatulence^[Ref]

Elevated lipase (greater than 3 times the upper limit of normal [3 x ULN]) has been reported in up to 10% of patients.^[Ref]

Renal

• Very common (10% or more): Elevated blood creatinine (19%)^[Ref]

Elevated creatinine (greater than 1.8 x ULN or 1.5 x baseline) has been reported in 19% of patients.

Clinically relevant increases in serum creatinine have been reported primarily in patients with identifiable risk factors for reduced renal function, including preexisting medical history of renal disease and/or concomitant agents known to increase creatinine; a causal association between this drug and elevated serum creatinine was not established. Asymptomatic elevations in creatinine were primarily grade 1 or 2 and did not require interruption of therapy.^[Ref]

Nervous system

• Very common (10% or more): Headache (up to 17%)
• Common (1% to 10%): Dizziness, peripheral neuropathy (included peripheral neuropathy, peripheral sensory neuropathy), somnolence, dysgeusia^[Ref]

Hepatic

• Very common (10% or more): Elevated direct bilirubin (up to 14%), elevated ALT (up to 14%), elevated AST (up to 14%)
• Common (1% to 10%): Elevated bilirubin, transaminases increased (included increased ALT, increased AST, increased hepatic enzymes, increased transaminases)^[Ref]

Elevated direct bilirubin (greater than ULN), ALT (greater than 5 x ULN), and AST (greater than 5 x ULN) have each been reported in up to 14% of patients; elevated bilirubin (at least 2.6 x ULN) has been reported in up to 6% of patients.

Increases in direct (conjugated) bilirubin have been reported after treatment with this drug. Clinically significant cases were uncommon and were confounded by intercurrent serious comorbid events (e.g., sepsis, cholangiocarcinoma, other complications of viral hepatitis coinfection); in the remaining cases, elevations in direct bilirubin (without clinical jaundice) were generally transient, occurred without increases in liver transaminases, and resolved on continued therapy.

Grade 3 and 4 elevations in ALT and AST have each been reported in 14% of patients with hepatitis B and/or C virus coinfection compared with 3% (ALT) and 2% (AST) of patients without viral hepatitis coinfection; in some cases, these transaminase elevations were consistent with hepatitis B reactivation, especially when antihepatitis therapy was stopped.

Asymptomatic elevations in liver enzymes were primarily grade 1 or 2 and did not require interruption of therapy.^[Ref]

Dermatologic

• Very common (10% or more): Rash (included rash, erythematous rash, generalized rash, macular rash, maculopapular rash, papular rash, pruritic rash, vesicular rash, allergic dermatitis; up to 12%)
• Common (1% to 10%): Pruritus (included pruritus, generalized pruritus)^[Ref]

Other

• Common (1% to 10%): Elevated triglycerides, fatigue, asthenia, elevated cholesterol, elevated low-density lipoprotein (LDL) cholesterol^[Ref]

Elevated triglycerides (greater than 500 mg/dL), cholesterol (at least 300 mg/dL), and LDL cholesterol (at least 190 mg/dL) have been reported in up to 10%, 5%, and 4% of patients, respectively.^[Ref]

Hematologic

• Common (1% to 10%): Decreased neutrophils, decreased hemoglobin, decreased leukocytes^[Ref]

Decreased neutrophils (up to 599 cells/mm3) and hemoglobin (less than 9 g/dL) have been reported in up to 7% and 6% of patients, respectively.^[Ref]

Metabolic

• Common (1% to 10%): Hyperglycemia, elevated urate^[Ref]

Hyperglycemia (greater than 250 mg/dL) and elevated urate (greater than 12 mg/dL) have been reported in 4% and 3% of patients, respectively.^[Ref]

Psychiatric

• Common (1% to 10%): Sleep disturbance (included insomnia, sleep deficit, sleep disorder, abnormal dreams), insomnia^[Ref]

Immunologic

• Common (1% to 10%): Immune reconstitution inflammatory syndrome (included central nervous system immune reconstitution inflammatory response, immune reconstitution inflammatory syndrome)^[Ref]

Musculoskeletal

• Common (1% to 10%): Elevated blood creatine phosphokinase, myalgia
• Frequency not reported: Musculoskeletal complaints^[Ref]

Elevations in creatine phosphokinase (CPK) were seen after use of this drug, which were primarily mild or moderate; these changes were rarely associated with musculoskeletal complaints and were not considered clinically relevant. Asymptomatic elevations in CPK were primarily grade 1 or 2 and did not require interruption of therapy.

Elevated CPK (at least 10 x ULN) has been reported in 2% of patients.^[Ref]

Cardiovascular

• Common (1% to 10%): Prolonged ECG QT^[Ref]

All reports of prolonged ECG QT were asymptomatic.^[Ref]

Further information

Fostemsavir side effects can vary depending on the individual. Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Note: Medication side effects may be underreported. If you are experiencing side effects that are not listed, submit a report to the FDA by following this guide.

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