Bactrim is a brand name for the generic co-trimoxazole, a British Approved Name. It is a sulfonamide antibiotic drug that is a 1-to-5 blend of Trimethoprim and Sulfamethoxazole used for treating a range of ailments caused by bacterial infections. The Bactrim brand is manufactured by Roche but the generic co-timoxazole is also marketed as the Septra brand from GlaxoSmithKline. Bactrim comes in tablet form and is available in two strengths: regular strength formulated with 80 mg Trimethoprim and 400 mg Sulfamethoxazole, and DS or double strength formulated with 160 mg Trimethoprim and 800 mg Sulfamethoxazole. The drug is available from online UK drugstores with or without prescription.
Synonyms: Trimethoprim


Bactrim DS is indicated for treating bladder and urinary tract infections (UTI), lung infections such as pneumonia and bronchitis, ear infection such as acute otitis media, traveler’s diarrhea, shigellosis, and other bacterial infections vulnerable to Trimethoprim and Sulfamethoxazole antibiotics. In addition, Bactrim can also treat infections caused by Tocoplasma organisms, Listeria monocutogenes, Stenotrophomonas, Staphylococcus saprophyticus and some strains of Escherichia coli. It can also treat Nocardiosis infection that affect the brain, skin and lungs as well as Acne vulgaris that cause pimples.

Mechanism of action

Sulfonamides like Sulfamethoxazole inhibit dihydropteroate synthetase and serve as analogues of p-aminobenzoic acid (PABA) inhibiting the production of dihydropteroic acid. Trimethoprim interferes with bacterial dihydrofolate reductase and inhibits the synthesis of tetrahydrofolic acid. Trimethoprim and sulfamethoxazole working together has a synergetic action that is greater when taken together than separately due to their abilities to inhibit successive processes in folate synthesis.


For treating Urinary tract Infections (UTI) or acute otitis media, the recommended dose is one or two Bactrim DS (double strength every 12 hours over a period of two weeks or less. For children, the suggested dose is 40mg/kg of Sulfamethoxazole and 8mg/kg of Trimethoprim every 24 hours administered 12 hours apart for 10 days.

For treating Shigellosis, a similar dosage for adults and children is recommend but for a shorter 5-day period.

For patients suffering from renal ailment, a reduced dosage is recommended for adults aged 30 and over and halved for patients aged 15-30. For children with renal impairment, the drug is not recommended at all.

For adult patients with acute aggravation of Chronic Bronchitis, the recommended dosage is 1 or 2 Bactrim DS tablet taken every 12 hours over a two week period.

For both adults and children with Pneumocystis Carinii Pneumonia, the recommended dosage is 15-20 mg/kg Trimethoprim or 75-100 mg/kg Sulfamethoxazole every 24 hours taken on equal does every 6 hours for 2-3 weeks.

For prophylaxis, the recommend dosage for adults is 1 Bactrim DS daily for 12 days, while for children, the dose is 750 mg/kg of Sulfamethoxazole and 150 mg/kg of Trimethoprim administered twice dialy for 3 consecutive days in a week.

For treating traveler’s diarrhea, the adult dosage is 1-2 Bactrim DS every 12 hours for 5 days.

It is important to consult with your doctor to arrive at a more specific dosage for your age, gender and medical condition even if the drug is easily obtainable online with or without a doctor’s prescription. Knowing the right dosage can help you buy the right amount of Bactrim tablets for a one-time purchase with discounts on a volume orders.

Side Effects

Commonly reported side effects of the drug revolve around gastrointestinal discomforts such as nausea, loss of appetite, and vomiting, as well a mild allergic reaction. Other known side effects include bleeding or brusiing, mouth sores, joint aches, skin rashes and itching, as well as sore throat and flu-like symptoms. Kernicterus of the fetus may also develop during pregnancy in the last 6 weeks. There have been reported cases of severe liver damage like hepatic necrosis, cholestatic hepatosis, fulminant liver failure, and hepatitis, as well as acute renal failure, anuria and renal impairment. These serious side effects, however, are most commonly experienced by the elderly and while they may be fatal at advance age, the serious side effects can be moderated by the administration of folic and folnic acid.


Patients allergic to sulfa compounds should not take Bactrim. The drug passes into breast milk and is therefore not recommended for nursing mothers. It is also not approved to be used for infants below 2 months old. It has not be clinically established that Bactrim may harm the unborn child but it affects folic acid production which is vital in fetal development.

Bactrim interacts with drugs to diminish their curative effects or that of Bactrim. Some of these drugs are folic acid, albuterol, aspirin, metoprolol, gabapentin, furosemide drugs like Lasix, esomeprazole drugs, simvastin, levothyroxin drugs, metformin, lisinopril, acetominophen drugs like Tylenol, tramadol, prednisone, sertraline drugs like Zoloft, and atorvastatin drugs, to mention some. Be sure to let your doctor know any drug you are taking to assess potential interactions with Bactrim even if you can buy the drug online without prescription.