Sulphamethoxazole + Trimethoprim

Introduction

Sulphamethoxazole + Trimethoprim is a combination antibiotic used to treat a variety of bacterial infections. This fixed-dose combination leverages the synergistic effects of two drugs to enhance antibacterial activity and reduce the potential for resistance.

Uses

This combination is used to treat:

Urinary tract infections (UTIs)
Respiratory tract infections
Gastrointestinal infections
Certain types of pneumonia, including Pneumocystis jirovecii pneumonia (PCP) in immunocompromised patients
Shigellosis and traveler's diarrhea caused by susceptible bacteria

Brand Name	Sulphamethoxazole + Trimethoprim
Type
Weight
Generic	Sulphamethoxazole + Trimethoprim
Manufacturer
Available in	English বাংলা

Mechanism of Action

Sulphamethoxazole and Trimethoprim work together to inhibit bacterial folic acid synthesis. Sulphamethoxazole is a sulfonamide that blocks the bacterial enzyme dihydropteroate synthase, preventing the formation of folate. Trimethoprim inhibits dihydrofolate reductase, another enzyme involved in folate synthesis. The combined inhibition of these pathways results in potent antibacterial activity.

How Long Does It Take to Work?

Patients may start to feel improvement within a few days of starting treatment. Full therapeutic effects typically become evident within 7 to 10 days, depending on the type and severity of the infection.

Absorption

Both Sulphamethoxazole and Trimethoprim are well absorbed from the gastrointestinal tract. Peak plasma concentrations are generally reached within 1 to 4 hours after oral administration.

Route of Elimination

Sulphamethoxazole is primarily metabolized in the liver and excreted via the kidneys. Trimethoprim is also metabolized in the liver and excreted mostly in the urine. Both drugs are eliminated primarily through the renal route.

Dosage

Cotrimoxazole double strength tablet: Over 12 years

For mild to moderate infections: 1 tablet twice daily.
For severe infections: 1.5 tablets twice daily.
Long term therapy (>14 days): 0.5 tablet twice daily.
Gonorrhoea: 2 tablets every 12 hours for two days or 2.5 tablets followed by a further dose of 2.5 tablets after 8 hours.

Cotrimoxazole tablet: over 12 years

For mild to moderate infections: 2 tablets twice daily.
For severe infections: 2 tablets thrice daily.
Long term therapy: (>14 days): 1 tablet twice daily.

Cotrimoxazole suspension: Under 12 years

6-12 years: 2 teaspoonful twice daily.
6 month-5 years: 1 teaspoonful twice daily.
6 weeks-6 months: 0.5 teaspoonful twice daily.

The typical dosage for adults is:

One tablet of the combination product (usually containing 800 mg of Sulphamethoxazole and 160 mg of Trimethoprim) twice daily.
The dosage may be adjusted based on the infection type, patient weight, and renal function.

For children, dosage is based on body weight and the specific infection being treated.

Administration

Take Sulphamethoxazole + Trimethoprim with or without food. It is generally recommended to take the medication at evenly spaced intervals to maintain effective drug levels in the body. Drink plenty of fluids to help prevent crystalluria (crystals in the urine).

Side Effects

Common side effects include:

Nausea and vomiting
Diarrhea
Rash
Loss of appetite

Serious side effects may include:

Allergic reactions (e.g., severe rash, itching, swelling)
Hematological reactions (e.g., thrombocytopenia, leukopenia)
Hepatic reactions (e.g., elevated liver enzymes, hepatitis)

Toxicity

Overdose may lead to toxicity, manifesting as severe gastrointestinal disturbances, central nervous system effects (e.g., dizziness, headache), or hematological abnormalities. In case of suspected overdose, seek immediate medical attention.

Precautions

Use with caution in patients with:

Renal impairment
Hepatic impairment
History of blood disorders
Known allergies to sulfonamides or Trimethoprim

Regular monitoring of blood counts and renal function may be required during prolonged therapy.

Interaction

Interactions with other drugs may occur, including:

Warfarin and other anticoagulants, increasing the risk of bleeding
Other renal-excreted drugs, potentially altering their clearance
Certain diuretics, which may enhance the risk of adverse effects

Disease Interaction

Use with caution in patients with:

Chronic renal or hepatic disease
G6PD deficiency, as it may increase the risk of hemolytic anemia
Severe allergies or asthma

Drug Interaction

Notable drug interactions include:

Increased risk of hyperkalemia with potassium-sparing diuretics
Potential interactions with antidiabetic agents
Increased risk of adverse effects when used with other drugs that affect bone marrow

Food Interactions

No significant food interactions are noted. However, avoiding excessive alcohol consumption may help reduce the risk of gastrointestinal side effects.

Pregnancy Use

Sulphamethoxazole + Trimethoprim should generally be avoided during pregnancy, especially during the first trimester. Potential risks to the fetus include teratogenic effects. Consult a healthcare provider to assess the risks versus benefits.

Lactation Use

Both Sulphamethoxazole and Trimethoprim are excreted in breast milk. The use of this medication during lactation should be carefully considered, and alternative treatments may be recommended if necessary.

Acute Overdose

In cases of acute overdose, seek medical attention immediately. Treatment may involve supportive care and symptomatic management, including hydration and monitoring for potential adverse effects.

Contraindication

Contraindications include:

Hypersensitivity to Sulphamethoxazole, Trimethoprim, or any component of the formulation
Severe renal or hepatic impairment
Pregnancy, especially during the first trimester

Use Direction

Follow the prescribed dosage and administration guidelines. Do not use for longer than prescribed, and complete the full course of therapy even if symptoms improve. Contact your healthcare provider if symptoms persist or worsen.

Storage Conditions

Store at room temperature, away from moisture and heat. Keep the medication in its original container, tightly closed, and out of reach of children.

Volume of Distribution

The volume of distribution for Sulphamethoxazole and Trimethoprim is approximately 0.2 to 0.3 L/kg for both drugs. These values may vary depending on individual patient characteristics.

Half Life

The half-life of Sulphamethoxazole is approximately 10 hours, while the half-life of Trimethoprim is about 8 to 11 hours. The elimination half-life may be prolonged in patients with renal impairment.

Clearance

Sulphamethoxazole and Trimethoprim are primarily cleared through renal excretion. Clearance rates may be reduced in patients with renal dysfunction, necessitating dose adjustments.

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