Foscarnet injection is used alone or with ganciclovir (Cytovene) to treat cytomegalovirus (CMV) retinitis (an eye infection that can cause blindness) in people who have human immunodeficiency virus (HIV) infection. Foscarnet injection is also used to treat herpes simplex virus (HSV) infections of the skin and mucus membranes (mouth, anus) in people whose immune system is not working normally and when treatment with acyclovir did not help. Foscarnet is in a class of medications called antivirals. It works by slowing the growth of CMV and HSV. Foscarnet controls CMV retinitis and HSV infections of the skin and mucus membranes but does not cure these infections.

Foscarnet may cause serious kidney problems. The risk of kidney damage is greater in people that are dehydrated. Your doctor will order laboratory tests before and during your treatment to see if your kidneys are affected by this medication. Tell your doctor if you have or have ever had kidney disease or if you have a dry mouth, dark urine, decreased sweating, dry skin, and other signs of dehydration or recently have had diarrhea, vomiting, fever, infection, excessive sweating, or have been unable to drink enough fluids. Tell your doctor and pharmacist if you are taking acyclovir (Zovirax); aminoglycoside antibiotics such as amikacin, kanamycin, neomycin, paromomycin, streptomycin, and tobramycin; amphotericin (Abelcet, Ambisome); cyclosporine (Gengraf, Neoral, Sandimmune); methotrexate (Otrexup, Rasuvo, Trexall); pentamidine (Nebupent, Pentam), or tacrolimus (Astagraf, Prograf). Your doctor may not want you to receive foscarnet injection. If you experience any of the following symptoms, call your doctor immediately: decreased urination; swelling of the face, arms, hands, feet, ankles, or lower legs; unusual tiredness; or weakness.

Foscarnet may cause seizures. Tell your doctor if you have or have ever had seizures, other nervous system problems, or if you have ever had a low level of calcium in your blood. Your doctor will probably check the level of calcium in your blood before you receive foscarnet injection and during treatment. If you experience any of the following symptoms, call your doctor immediately: seizures; numbness or tingling around the mouth or in fingers or toes; fast, pounding, or irregular heartbeat; or muscle spasms.

Keep all appointments with your doctor, including your eye doctor, and the laboratory. Your doctor will order certain tests, including periodic eye examinations, before and during your treatment to check your body's response to foscarnet. Your doctor may also order an electrocardiogram (ECG; test that measures the electrical activity in the heart) before and during your treatment.

Foscarnet injection comes as a liquid to be intravenously (into a vein). It is usually infused slowly over 1 to 2 hours every 8 or 12 hours. The length of your treatment depends on how you respond to the medication.

You may receive foscarnet injection in a hospital or you may administer the medication at home. If you will be receiving foscarnet injection at home, your healthcare provider will show you how to use the medication. Be sure that you understand these directions, and ask your healthcare provider if you have any questions

Ask your pharmacist or doctor for a copy of the manufacturer's information for the patient.

Before using foscarnet injection,

• tell your doctor and pharmacist if you are allergic to foscarnet, any other medications, or any of the ingredients in foscarnet injection. Ask your pharmacist for a list of the ingredients.
• tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking or plan to take. Be sure to mention the medications listed in the IMPORTANT WARNING section and any of the following: amiodarone (Cordarone, Nexterone, Pacerone); azithromycin (Zithromax); clarithromycin (Biaxin); diuretics ('water pills') such as bumetanide, ethacrynic acid (Edecrin), furosemide (Lasix), or torsemide (Demadex); dofetilide (Tikosyn); erythromycin (E-mycin, Ery-Tab, others); fluoroquinolone antibiotics including ciprofloxacin (Cipro), gatifloxacin (Tequin), levofloxacin (Levaquin), moxifloxacin (Avelox), and ofloxacin (Floxin); medications for mental illness or nausea; procainamide; quinidine (in Nuedexta); ritonavir (Norvir, in Kaletra); saquinavir (Invirase); sotalol (Betapace, Sorine); and tricyclic antidepressants ('mood elevators') such as amitriptyline, desipramine (Norpramin), doxepin (Silenor), or nortriptyline (Pamelor). Your doctor may need to change the doses of your medications or monitor you carefully for side effects. Many other medications may also interact with foscarnet injection, so be sure to tell your doctor about all the medications you are taking, even those that do not appear on this list.
• tell your doctor if you have or have ever had QT prolongation (an irregular heart rhythm that can lead to fainting, loss of consciousness, seizures, or sudden death); low levels of potassium or magnesium in your blood; heart disease; or if you are on a low salt diet.
• tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while receiving foscarnet injection, call your doctor.
• you should know that foscarnet may make you drowsy or dizzy. Do not drive a car or operate machinery until you know how this medication affects you.

In case of overdose, call the poison control helpline at 1-800-222-1222. Information is also available online at https://www.poisonhelp.org/help. If the victim has collapsed, had a seizure, has trouble breathing, or can't be awakened, immediately call emergency services at 911.

Symptoms of overdose may include the following:

• seizures
• numbness or tingling around the mouth or in fingers or toes
• decreased urination
• swelling of the face, arms, hands, feet, ankles, or lower legs
• unusual tiredness or weakness

Unless your doctor tells you otherwise, continue your normal diet.

Foscarnet may cause side effects. Tell your doctor if any of these symptoms are severe or do not go away:

• itching, redness, pain, or swelling in the place where you received your injection
• nausea
• stomach pain
• back pain
• loss of appetite or weight
• constipation
• headache
• vision changes
• redness, irritation, or sores on the penis
• redness, irritation, or sores around the vagina

Some side effects can be serious. If you experience any of these symptoms or those listed in the IMPORTANT WARNING section, call your doctor immediately or get emergency medical treatment:

• rash
• hives
• swelling of the eyes, face, lips, tongue, or throat
• difficulty breathing or swallowing
• chest pain
• fast, pounding, or irregular heartbeat
• fainting
• lightheadedness
• loss of consciousness
• vomiting
• diarrhea
• fever, chills, cough, or other signs of infection
• unusual bleeding or bruising
• black and tarry stools
• bloody vomit or vomited material that looks like coffee grounds
• pale skin
• shortness of breath
• confusion
• muscle pain or cramps
• increased sweating

Foscarnet may cause other side effects. Call your doctor if you have any unusual problems while using this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online (http://www.fda.gov/Safety/MedWatch) or by phone (1-800-332-1088).

Foscarnet injection is also sometimes used to treat and prevent CMV infections in patients with human immunodeficiency virus (HIV). Talk to your doctor about the risks of using this medication for your condition.

This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

It is important for you to keep a written list of all of the prescription and nonprescription (over-the-counter) medicines you are taking, as well as any products such as vitamins, minerals, or other dietary supplements. You should bring this list with you each time you visit a doctor or if you are admitted to a hospital. It is also important information to carry with you in case of emergencies.