Which of the following sulphonamides is available as an oral preparation?
**Core Concept**
Sulphonamides are a class of antimicrobials that inhibit bacterial growth by competing with para-aminobenzoic acid (PABA) for the enzyme dihydropteroate synthase, thereby preventing folic acid synthesis. Oral preparations of sulphonamides are used to treat various bacterial infections, including urinary tract infections, skin infections, and respiratory tract infections.
**Why the Correct Answer is Right**
The correct answer is a sulphonamide that is available in an oral formulation, making it suitable for outpatient treatment of bacterial infections. This sulphonamide is well-absorbed from the gastrointestinal tract and undergoes extensive hepatic metabolism.
**Why Each Wrong Option is Incorrect**
* **Option A:** This sulphonamide is typically administered intravenously or intramuscularly due to its poor oral bioavailability.
* **Option B:** This sulphonamide is not commonly used as an oral preparation, and its use is often limited to severe infections due to its potential for toxicity.
* **Option D:** This sulphonamide is not typically used as an oral preparation, and its use is often limited to topical applications due to its poor oral bioavailability and potential for skin irritation.
**Clinical Pearl / High-Yield Fact**
When choosing an oral sulphonamide, consider the patient's renal function, as some sulphonamides are primarily excreted by the kidneys and may accumulate to toxic levels in patients with impaired renal function.
**Correct Answer:** B. Sulfamethoxazole