This drug is used with other HIV medications to help control HIV infection. It helps to decrease the amount of HIV in your body so your immune system can work better. This lowers your chance of getting HIV complications (such as new infections, cancer) and improves your quality of life. Fostemsavir is changed in your body to its active drug form. It works by helping to prevent attachment of and entry of the (HIV-1) virus into healthy cells in your body.

Fostemsavir is not a cure for HIV infection. To decrease your risk of spreading HIV disease to others, continue to take all HIV medications exactly as prescribed by your doctor. Use an effective barrier method (latex or polyurethane condoms/dental dams) during sexual activity as directed by your doctor. Do not share personal items (such as needles/syringes, toothbrushes, and razors) that may have contacted blood or other body fluids. Consult your doctor or pharmacist for more details.

Read the Patient Information Leaflet if available from your pharmacist before you start taking fostemsavir and each time you get a refill. If you have any questions, ask your doctor or pharmacist.

Take this medication by mouth with or without food as directed by your doctor, usually twice daily. Swallow the tablets whole. Do not chew, crush, or split the tablets. Doing so can release all of the drug at once, increasing the risk of side effects. The dosage is based on your medical condition and response to treatment.

You may smell a slight odor (like vinegar) from the tablets. This is normal.

It is very important to keep taking this medication (and other HIV medications) exactly as prescribed by your doctor. Do not skip any doses.

For the best effect, take this medication regularly. To help you remember, take this medication at the same times every day.

Do not take more or less of this drug than prescribed or stop taking it (or other HIV medicines) even for a short time unless directed to do so by your doctor. Doing so may cause the amount of virus to increase, make the infection more difficult to treat (resistant), or worsen side effects.

Nausea or drowsiness may occur. If either of these effects lasts or gets worse, tell your doctor or pharmacist promptly.

Remember that this medication has been prescribed because your doctor has judged that the benefit to you is greater than the risk of side effects. Many people using this medication do not have serious side effects.

As your immune system gets stronger, it can begin to fight off infections you already had, possibly causing disease symptoms to come back. You could also have symptoms if your immune system becomes overactive. This reaction may happen at any time (soon after starting HIV treatment or many months later). Get medical help right away if you have any serious symptoms, including:

• unexplained weight loss
• severe tiredness
• muscle aches/weakness that doesn't go away
• headaches that are severe or don't go away
• joint pain
• numbness/tingling of the hands/feet/arms/legs
• vision changes
• signs of infection (such as fever, chills, swollen lymph nodes, trouble breathing, cough, non-healing skin sores)
• signs of an overactive thyroid (such as irritability, nervousness, heat intolerance, fast/pounding/irregular heartbeat, bulging eyes, unusual growth in the neck/thyroid known as a goiter)
• signs of a certain nerve problem known as Guillain-Barre syndrome (such as unsteadiness, loss of coordination, trouble swallowing/speaking/chewing, trouble moving your eyes)
• signs of liver disease (such as nausea/vomiting that doesn't stop, loss of appetite, stomach/abdominal pain, yellowing eyes/skin, dark urine)

Get medical help right away if you have any very serious side effects, including:

• fast/irregular heartbeat
• severe dizziness
• fainting

A very serious allergic reaction to this drug is rare. However, get medical help right away if you notice any symptoms of a serious allergic reaction, including:

• rash
• itching/swelling (especially of the face/tongue/throat)
• severe dizziness
• trouble breathing

This is not a complete list of possible side effects. If you notice other effects not listed above, contact your doctor or pharmacist.

In the US - Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088 or at www.fda.gov/medwatch.

In Canada - Call your doctor for medical advice about side effects. You may report side effects to Health Canada at 1-866-234-2345.

Before taking fostemsavir, tell your doctor or pharmacist if you are allergic to it; or if you have any other allergies. This product may contain inactive ingredients, which can cause allergic reactions or other problems. Talk to your pharmacist for more details.

Before using this medication, tell your doctor or pharmacist your medical history, especially of:

• liver problems (especially hepatitis B, hepatitis C infection)

This drug may make you drowsy. Alcohol or marijuana (cannabis) can make you more drowsy. Do not drive, use machinery, or do anything that needs alertness until you can do it safely. Limit alcoholic beverages. Talk to your doctor if you are using marijuana (cannabis).

Fostemsavir may cause a condition that affects the heart rhythm (QT prolongation). QT prolongation can rarely cause serious (rarely fatal) fast/irregular heartbeat and other symptoms (such as severe dizziness, fainting) that need medical attention right away.

The risk of QT prolongation may be increased if you have certain medical conditions or are taking other drugs that may cause QT prolongation. Before using fostemsavir, tell your doctor or pharmacist of all the drugs you take and if you have any of the following conditions:

• certain heart problems (heart failure, slow heartbeat, QT prolongation in the EKG)
• family history of certain heart problems (QT prolongation in the EKG, sudden cardiac death)

Low levels of potassium or magnesium in the blood may also increase your risk of QT prolongation. This risk may increase if you use certain drugs (such as diuretics/"water pills") or if you have conditions such as severe sweating, diarrhea, or vomiting. Talk to your doctor about using fostemsavir safely.

Before having surgery, tell your doctor or dentist about all the products you use (including prescription drugs, nonprescription drugs, and herbal products).

Older adults may be more sensitive to the side effects of this drug, especially QT prolongation (see above).

During pregnancy, this medication should be used only when clearly needed. Treatment can lower the risk of passing HIV infection to your baby, and fostemsavir may be part of that treatment. Discuss the risks and benefits with your doctor.

It is unknown if this medication passes into breast milk. Because breast milk may transmit HIV, consult your doctor before breastfeeding.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Other medications can affect the removal of fostemsavir from your body, which may affect how fostemsavir works. Examples include apalutamide, butalbital, enzalutamide, lumacaftor, mitotane, rifamycins (such as rifampin, rifapentine), secobarbital, St. John's wort, drugs used to treat seizures (such as carbamazepine, fosphenytoin, phenytoin), among others.

This medication can slow down the removal of other medications from your body, which may affect how they work. Examples of affected drugs include grazoprevir, voxilaprevir, among others.

If someone has overdosed and has serious symptoms such as passing out or trouble breathing, call 911. Otherwise, call a poison control center right away. US residents can call 1-800-222-1222. Canada residents can call 1-844-764-7669.

Do not share this medication with others.

Lab and/or medical tests (such as viral load, T-cell counts, liver function) should be done while you are taking this medication. Keep all medical and lab appointments.

If you miss a dose, take it as soon as you remember. If it is near the time of the next dose, skip the missed dose. Take your next dose at the regular time. Do not double the dose to catch up.

Store at room temperature away from light and moisture. Do not store in the bathroom. Keep all medications away from children and pets.

Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company.