Combination of Trimethoprim a dihydrofolate reductase inhibitor (16.7%), and Sulfamethoxazol an sulfonamide antibiotic (83.3%).

Has both oral, and intravenous routes of administration.

Trimethoprim/sulfamethoxazole or co-trimoxazole, abbreviated as SXT, TMP-SMX, TMP-SMZ, or TMP-sulfa.

A sulfonamide antibiotic.

It consists of 1 part trimethoprim to 5 parts sulfamethoxazole.

Trimethoprim and sulfamethoxazole have a greater effect when given together than when given individually.

Trimethoprim and sulfamethoxazole inhibit successive steps in the folate synthesis pathway.

Used for the treatment of bacterial upper and lower respiratory tract infections, renal and urinary tract infections, gastrointestinal tract infections, otitis media, skin and wound infections.

Recommended to treat or prevent: lung infections, including pneumonia, caused by Pneumocystis jirovecic and infections caused by Toxoplasma organisms.

Used to treat bladder or urinary tract infections, lung infections, bronchitis, ear infections such as otitis media, and skin and soft tissue infections.

Often prescribed to immunocompromised patients as a prophylaxis against Pneumocystis jirovecii pneumonia.

Used to treat norcardiosis.

Effective agent against both gram-positive and gram-negative organisms including: Listeria monocytogenes, Nocardia spp., Xanthomonas maltophilia, Staphylococcus saprophyticus, Staphylococcus aureus, including some MRSA strains, and susceptible strains of Escherichia coli.

Efficacious for traveler’s diarrhea, Whipple’s disease, Shigellosis, acne, Protozoan infections, and cyclospora infections.

Useful for prophylaxis against cerebral toxoplasmosis in HIV patients.

Associated with frequent allergic reactions, Stevens–Johnson syndrome, myelosuppression, mydriasis, agranulocytosis, and severe liver damage and fulminant liver failure.

Exposure during the last six weeks of pregnancy it is associated with increased risk of kernicterus in the fetus due to displacement of bilirubin from albumin.

Renal impairment, to include acute renal failure, and anuria have been reported, especially in the elderly and may be fatal.

May elevate creatinine without causing renal damage, by the inhibition of the tubular secretion of creatinine by the trimethoprim component.

Folic acid and folinic acid are equally effective in reducing the adverse effects of trimethoprim/sulfamethoxazole.

As trophoblasts in the early fetus are sensitive to changes in the folate cycle, there is a doubling in the risk of miscarriage in women exposed to trimethoprim in early pregnancy.

Trimethoprim/sulfamethoxazole may give rise to the following adverse reactions:

Allergic: Stevens–Johnson syndrome, toxic epidermal necrolysis, anaphylaxis, allergic myocarditis, erythema multiforme, exfoliative dermatitis, angiodema, drug fever, chills, Henoch–Schönlein purpura, serum sickness-like syndrome, generalized allergic reactions, generalized skin eruptions, photosensitivity, conjunctival and scleral injection, pruritus, urticaria and rash.

Has been reported to cause periarteritis nodosa and systemic lupus erythematosus.

As sulfonamides have chemical similarities to some goitrogens, diuretics and oral hypoglycemic agents, such that cross-sensitivity may exist with these agents.

Diuresis and hypoglycemia have occurred rarely in patients receiving sulfonamides.

Gastrointestinal side effects include hepatitis, cholestatic jaundice, hepatic necrosis, elevation of serum transaminase and bilirubin, pseudo-membranous enterocolitis, pancreatitis, stomatitis, glossitis, nausea, emesis, abdominal pain, diarrhea, constipation, anorexia.

Genitourinary associated problems include renal failure, interstitial nephritis, elevation of BUN and serum creatinine, toxic nephrosis with oliguria and anuria, and crystalluria.

Hematologic toxicity includes: agranulocytosis, aplastic anemia, thrombocytopenia, leukopenia, neutropenia, hemolytic anemia, megaloblastic anemia, hypoprothrominemia, methemoglobinemia, and eosinophilia.

Metabolic changes include hyperkalemia, and hyponatremia.

Arthralgia and myalgia may occur.

Aseptic meningitis, convulsions, peripheral neuritis, ataxia, vertigo, tinnitus, and headache can occur.

Psychiatric manifestations include hallucinations, depression, apathy, and nervousness.

May be associated with cough, shortness of breath, and pulmonary infiltrates.

Sulfamethoxazole acts as a false-substrate inhibitor of dihydropteroate synthetase.

Sulfamethoxazole is an analogue of p-aminobenzoic acid (PABA) and competitive inhibits the production of dihydropteroic acid.

Trimethoprim acts by interfering with bacterial dihydrofolate reductase, inhibiting synthesis of tetrahydrofolic acid.

Folic acid is an essential precursor in the de novo synthesis of the DNA/RNA nucleosides thymidine and uridine.

Bacteria cannot take up folic acid from the environment and are dependent on their own de novo synthesis, so inhibition of the enzyme prevents bacteria from DNA replication and transcription.

Used for prophylaxis and treatment of pneumocystis jiroveci.

Adverse reactions occur in 8% of patients.

3.3% of patients have hypersensitivity reactions.

In HIV patients adverse reactions and hypersensitivity reactions occur with much higher frequency and can be as history as 50%.

Proposed that a metabolite hydroxylamine may accumulate, along with a deficiency of glutathione in patients with HIV may increase toxicity in HIV infected patients.

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