Sulfamethoxazole + Trimethoprim information from DrugsUpdate  

Pharmacodynamics

Pharmacokinetics

Sulfamethoxazole act by inhibiting dihydropteroate synthetase where as trimethoprim act by inhibiting trihydrofolate reductase there by inhibiting the synthesis of tetrahydrofolic acid. Thus interfering with nucleic acid synthesis.

Sulfamethoxazole and Trimethoprim is rapidly absorbed following oral administration. Both Sulfamethoxazole and Trimethoprim exist in the blood as unbound, protein-bound and metabolized forms; sulfamethoxazole also exists as the conjugated form.
Approximately 70% of sulfamethoxazole and 44% of trimethoprim are bound to plasma proteins.
Peak blood levels for the individual components occur 1 to 4 hours after oral administration. The mean serum half-lives of Sulfamethoxazole and Trimethoprim are 10 and 8 to 10 hours, respectively. However, patients with severely impaired renal function exhibit an increase in the half-lives of both components, requiring dosage regimen adjustment

Sulfamethoxazole + Trimethoprim Indications / Sulfamethoxazole + Trimethoprim Uses

Susceptible infections, Gastrointestinal infections, Respiratory tract infections, Urinary tract infections, Pneumocystis carinii pneumonia, prophylaxis of susceptible infections in AIDS patients.

Sulfamethoxazole + Trimethoprim Adverse Reactions / Sulfamethoxazole + Trimethoprim Side Effects

Renal failure, nausea, vomiting, diarrhoea, anorexia, skin rashes, urticaria. Stevens-Johnson syndrome, toxic epidermal necrolysis, hepatic necrosis.

Precautions

Prescribing Sulfamethoxazole and Trimethoprim tablets in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.
Sulfamethoxazole and Trimethoprim should be given with caution to patients with impaired renal or hepatic function, to those with possible folate deficiency (e.g., the elderly, chronic alcoholics, patients receiving anticonvulsant therapy, patients with malabsorption syndrome, and patients in malnutrition states) and to those with severe allergies or bronchial asthma. In glucose-6-phosphate dehydrogenase deficient individuals, hemolysis may occur. This reaction is frequently dose-related.

Special Precautions

Patients with renal dysfunction, liver disease, malnutrition or those receiving high doses of Sulfamethoxazole and Trimethoprim are particularly at risk.

Other Drug Interactions

Reduced ciclosporin concentrations in blood when used concurrently.
Increases toxicity of methotrexate.
Inhibits phenytoin clearance.
Potentiates warfarin and oral hypoglycaemics.
Co-administration with pyrimethamine causes megaloblastic anaemia.
Enhancement of renal damage by ciclosporin.

Other Interactions

Information Not Available

Dosage

Adult: 960mg bid, upto 2.88g daily given in 2 divided doses in severe cases.
Child: 6wk-5mth: 120mg bid.
6mth-5yr:240mg bid.
6-12yr: 480mg bid.

Food(before/after)

Information Not Available

Sulfamethoxazole + Trimethoprim and Pregnancy

Sulfamethoxazole and Trimethoprim is contraindicated in pregnant patients because sulfonamides passes the placenta.

Sulfamethoxazole + Trimethoprim and Lactation

Sulfamethoxazole and Trimethoprim is contraindicated in nursing mothers because are excreted in the milk and may cause kernicterus.

Sulfamethoxazole + Trimethoprim and Children

Sulfamethoxazole and Trimethoprim is contraindicated in pediatric patients less than 2 months of age.

Sulfamethoxazole + Trimethoprim and Geriatic

Sulfamethoxazole and Trimethoprim is also contraindicated in patients with marked hepatic damage or with severe renal insufficiency when renal function status cannot be monitored.

Sulfamethoxazole + Trimethoprim and Other Contraindications

Information Not Availabe

Storage

Store below 25°C

Lab interference

Store below 25°C