Question:
Sulphonamide injection causes decrease in folic acid by?
Sulphonamide injection causes decrease in folic acid by?
Show Hint
The drug mimics PABA and fights for the same enzyme site.
Updated On: Jun 24, 2026
- Competitive inhibition
- Non competitive inhibition
- Uncompetitive inhibition
- Allosteric inhibition
Show Solution
Verified By Collegedunia
The Correct Option is A
Solution and Explanation
Step 1: Bacteria cannot use preformed folic acid from the host and must synthesise it themselves. A key building block in this synthesis is para-aminobenzoic acid (PABA).
Step 2: Sulphonamides are structural analogues of PABA. Because they resemble the natural substrate, they bind to the active site of the bacterial enzyme dihydropteroate synthase (folate synthase).
Step 3: Since the drug and PABA compete for the same active site, this is competitive inhibition. Increasing the amount of PABA can overcome the block, which is the hallmark of a competitive mechanism.
Step 4: Non-competitive, uncompetitive and allosteric inhibition all involve binding at sites other than the substrate site or do not allow reversal by excess substrate, so they do not describe the PABA-analogue mechanism. Hence competitive inhibition is correct.
Step 2: Sulphonamides are structural analogues of PABA. Because they resemble the natural substrate, they bind to the active site of the bacterial enzyme dihydropteroate synthase (folate synthase).
Step 3: Since the drug and PABA compete for the same active site, this is competitive inhibition. Increasing the amount of PABA can overcome the block, which is the hallmark of a competitive mechanism.
Step 4: Non-competitive, uncompetitive and allosteric inhibition all involve binding at sites other than the substrate site or do not allow reversal by excess substrate, so they do not describe the PABA-analogue mechanism. Hence competitive inhibition is correct.
Was this answer helpful?
0
0
Top NEET PG Pharmacology Questions
- A bronchial asthma patient on inhalational steroids presented with white patchy lesions on the tongue and buccal mucosa. What is the drug that can be used to treat this condition?
- A pregnant woman with a history of bronchial asthma is in the third stage of labor. Which drugs should be avoided in managing postpartum hemorrhage in this mother?
- Name the drug that acts on both the marked areas.
- A patient with a previous history of myocardial infarction and ventricular arrhythmia is ontreatment for a few months. He developed fatigue, dyspnea, and weight gain. He had also developed pulmonary fibrosis. Which of the following drugs is responsible for the side effects mentioned above?
- A young female comes to the emergency department after consuming 100 aspirin tablets.What should be the next step in management?
View More Questions
Top NEET PG Sulphonamides classification Questions
Top NEET PG Questions
- A patient hailing from Delhi presents with fever, arthralgia, and extensive petechial rash for 3 days. Lab investigations revealed a hemoglobin of 9 g/ dL, a white blood cell count of 9000 cells/mm3, a platelet count of 20000 cells/mm3, and a prolonged bleeding time. The clotting time was normal. What is the most likely diagnosis?
- Which of the following statements is true about Trichomonas vaginalis?
- A lady from West Rajasthan presented with an ulcer surrounded by erythema on the right leg. Microscopy of the biopsy from the edge of the ulcer showed organisms with dark staining nuclei and kinetoplast. What is the most likely causative agent?
- A child presents with a fever and a rash. Urine examination showed cells with owl's eye appearance. What is the most likely diagnosis?
- Infection with Clonorchis sinensis is associated with an increased risk of__?
View More Questions