Sulphamethoxazole is antibacterial sulfonamide. Sulphamethoxazole is classified as an intermediate-acting sulfonamide and is longer-acting than sulfisoxazole, which allows it to be given 2-3 times daily, possibly aiding in compliance. Although it was once an extremely useful antibiotic, the development of resistance and the availability of newer agents has made sulfamethoxazole almost obsolete as a single agent. Today, clinical use of sulfamethoxazole occurs primarily in combination with trimethoprim. It was approved by the FDA in 1961 as an antibecterial agent. Sulphamethoxazole is effective against gram positive, gram negative bacteria and some protozoan.


Primary Characterstics

Molecular Structure of Sulphamethoxazole
Sulphamethoxazole also known as Sulfamethoxazole. . It is of Synthetic origin and belongs to Sulphonamide. It belongs to Dihyropteroate synthetase inhibitor pharmacological group on the basis of mechanism of action and also classified in Antibacterial pharmacological group.The Molecular Weight of Sulphamethoxazole is 253.30.
Its pKa is 5.7.


Oral absorption of Sulphamethoxazole is found to be 100% . Volume of distribution is found to be 0.21 l/kg and plasma protien binding is 65%. and metabolism is reported Hepatic. Renal Excretion accounts for 80 - 85% and plasma half life is 7-12 hr.


Sulphamethoxazole is primarily indicated in conditions like Bacterial infections, Lymphogranuloma venereum, Respiratory tract infections, Urinary tract infection.


Sulphamethoxazole is contraindicated in conditions like Renal diseases,Liver diseases.

Drug Interactions

Sulphamethoxazole is known to interact with other drugs, the details of drug interactions is as follows:

Para Aminobenzoic AcidShould not be used concurrently except on medical advice.
Phenytoin (Na)
ProcaineDecreased effect of sulfonamides with the PABA metabolite of procaine.
Warfarin (Na)Sulphamethoxazole may decrease the metabolism of Warfarin. ModerateMonitor for increased effects of Warfarin if Sulphamethoxazole is initiated/dose increased, and decreased effects if Sulphamethoxazole is discontinued/dose decreased.

These interactions are sometimes beneficial and sometimes may pose threats to life. Always consult your physician for the change of dose regimen or an alternative drug of choice that may strictly be required.

Interference in Pathology

  • Measurement of serum Theophylline levels by HPLC

Side Effects

The severe or irreversible adverse effects of Sulphamethoxazole, which give rise to further complications include Hepatic damage, Renal failure, Crystalluria.

Sulphamethoxazole produces potentially life-threatening effects which include Stevens Johnson syndrome. which are responsible for the discontinuation of Sulphamethoxazole therapy.

The signs and symptoms that are produced after the acute overdosage of Sulphamethoxazole include Nausea, Vomiting, Confusion, Dizziness, Abdominal pain.

The symptomatic adverse reactions produced by Sulphamethoxazole are more or less tolerable and if they become severe, they can be treated symptomatically, these include Rashes, Hemolytic anemia, Thrombocytopenia, Eosinophilia, Serum sickness, Hypoprothrombinemia, Hematological disorder.

Available Brands

Multi ingredient

Inj: 800 mg,
Susp: 200 mg/5ml, 400 mg/5ml, 800 mg/5ml,
Tabs: 80 mg, 200 mg, 400 mg, 800 mg,


Sulphamethoxazole's dosage details are as follows:
Dose Single Dose Frequency Route Instructions

Adult Dosage

800 mg800 (800)12 hourlyPOIn Combination with trimethoprim 160 mg/day.

Paedriatic Dosage ( 20 Kg. )

25 to 30 mg/kg28 (27.5)12 hourlyOralMaintenance, As required
50 to 60 mg/kg55 (55)24 hourlyOralInitial

Neonatal Dosage ( 3 Kg. )

Should not be used in this age group

High Risk Groups

Drug should not be given to Paediatrics, Pregnant Mothers, patients suffering from Kidney dysfunction, patients suffering from Liver Malfunction, Geriatrics, and Neonates.

If prescribing authority justifies the benefits of the drug against the possible damages he/she should reevaluate them and consult the reference material and previous studies.

Warning / Precautions

Sulphamethoxazole should be used with caution in patients with medical history including liver or kidney disease, blood disorders or of any drug allergy. This may makes patients more prone to sunburn, wear protective clothing and (PABA-free) sunscreen when outdoors. It should be used only if clearly needed during pregnancy or lactation.

Storage Conditions


Store at room temperature. Do not Freeze. Protect from Sunlight.

Tab, Susp

Store at room temperature. Protect from Sunlight and Moisture.

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