Co-trimoxazole injection is used to treat certain infections that are caused by bacteria such as infection of the intestine, lungs (pneumonia), and urinary tract. Co-trimoxazole should not be used in children younger than 2 months of age. Co-trimoxazole injection is in a class of medications called sulfonamides. It works by killing bacteria.

Antibiotics such as co-trimoxazole injection will not work for colds, flu, or other viral infections. Taking antibiotics when they are not needed increases your risk of getting an infection later that resists antibiotic treatment.

Co-trimoxazole injection comes as a solution (liquid) to be mixed with additional liquid to be injected intravenously (into a vein) over 60 to 90 minutes. It is usually given every 6, 8, or 12 hours. The length of your treatment depends on the type of infection you have and how your body responds to the medication.

You may receive co-trimoxazole injection in a hospital or you may administer the medication at home. If you will be receiving co-trimoxazole 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.

You should begin to feel better during the first few days of treatment with co-trimoxazole injection. If your symptoms do not improve or get worse, call your doctor.

Use co-trimoxazole injection until you finish the prescription, even if you feel better. If you stop using co-trimoxazole injection too soon or skip doses, your infection may not be completely treated and the bacteria may become resistant to antibiotics.

Co-trimoxazole injection is also sometimes used to treat other serious bacterial infections. Talk to your doctor about the risks of using this medication for your condition.

Before receiving co-trimoxazole injection,

• Tell your doctor and pharmacist if you are allergic to sulfamethoxazole, trimethoprim, benzyl alcohol, any other sulfa drugs, any other medications, or any of the ingredients in co-trimoxazole 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 any of the following: amantadine (Symmetrel), angiotensin converting enzyme inhibitors such as benazepril (Lotensin), captopril (Capoten), enalapril (Vasotec), fosinopril (Monopril), lisinopril (Prinivil, Zestril), moexipril (Univasc), perindopril (Aceon), quinapril (Accupril), ramipril (Altace), and trandolapril (Mavik); anticoagulants (‘blood thinners’) such as warfarin (Coumadin); cyclosporine (Gengraf, Neoral, Sandimmune); oral medications for diabetes; digoxin (Digitek, Lanoxicaps, Lanoxin); diuretics (‘water pills’); indomethacin (Indocin); leucovorin (Fusilev); methotrexate (Rheumatrex, Trexall); phenytoin (Dilantin, Phenytek); pyrimethamine (Daraprim); and tricyclic antidepressants (mood elevators) such as amitriptyline (Elavil), amoxapine (Asendin), clomipramine (Anafranil), desipramine (Norpramin), doxepin, imipramine (Tofranil), nortriptyline (Aventyl, Pamelor), protriptyline (Vivactil), and trimipramine (Surmontil). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
• Tell your doctor if you have or have ever had thrombocytopenia (less than normal number of platelets) caused by taking sulfonamides or trimethoprim or megaloblastic anemia (abnormal red blood cells) caused by folate deficiency (low blood levels of folic acid). Your doctor may tell you not to use co-trimoxazole injection.
• Tell your doctor if you drink or have ever drunk large amounts of alcohol, if you have malabsorption syndrome (problems absorbing food), or are taking medication to treat seizures. Tell your doctor if you have or have ever had asthma, low levels of folic acid in the body, severe allergies, a glucose-6-phosphate dehydrogenase (G-6-PD) deficiency (an inherited blood disease), human immunodeficiency virus (HIV) infection, phenylketonuria (PKU, an inherited condition in which a special diet must be followed to prevent damage to your brain that can cause severe intellectual disability), porphyria (an inherited blood disease that may cause skin or nervous system problems), or thyroid, liver, or kidney disease.
• Tell your doctor if you are pregnant, plan to become pregnant, or are breastfeeding. If you become pregnant while using co-trimoxazole injection, call your doctor immediately. Co-trimoxazole can harm the fetus.
• Plan to avoid unnecessary or prolonged exposure to sunlight and to wear protective clothing, sunglasses, and sunscreen. Co-trimoxazole injection may make your skin sensitive to sunlight.

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

Drink plenty of fluids during your treatment with co-trimoxazole injection.

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

• Nausea
• Vomiting
• Loss of appetite
• Diarrhea
• Joint or muscle pain
• Pain or irritation at the site of injection

Some side effects can be serious. If you experience any of these symptoms, call your doctor immediately or get emergency medical treatment:

• Rash or skin changes
• Peeling or blistering skin
• Hives
• Itching
• Red or purple skin discolorations
• A return of fever, sore throat, chills, or other signs of infection
• Cough
• Shortness of breath
• Severe diarrhea (watery or bloody stools) that may occur with or without fever and stomach cramps (may occur up to 2 months or more after your treatment)
• Fast heartbeat
• Hunger, headache, tiredness, sweating, shaking of a part of your body that you cannot control, irritability, blurry vision, difficulty concentrating, or loss of consciousness
• Yellowing of the skin or eyes
• Swelling of the face, throat, tongue, lips, eyes, hands, feet, ankles, or lower legs
• Hoarseness
• Difficulty breathing or swallowing
• Unusual bleeding or bruising
• Paleness
• Swelling at the injection site
• Decreased urination
• Seizure

Co-trimoxazole injection 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).

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:

• Loss of appetite
• Nausea
• Vomiting
• Dizziness
• Headache
• Drowsiness
• Confusion
• Fever
• Blood in urine
• Yellowing of the skin or eyes
• Loss of consciousness

Keep all appointments with your doctor and the laboratory. Your doctor will order certain lab tests to check your body’s response to co-trimoxazole injection.

Before having any laboratory test, tell your doctor and the laboratory personnel that you are receiving co-trimoxazole injection.

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.