MECHANISM OF ACTION

SULFONAMIDES

INTRODUCTION: -

Sulfonamides, commonly known as sulfa drugs, are a group of antibiotics that inhibit the growth and multiplication of bacteria. they are synthetic antimicrobial agents that contain the sulfonamide group.

The mechanism of action process in 5 steps they are:

1. Inhibition of folic acid synthesis:

Sulfonamides act as competitive inhibitors of the enzyme dihydropteroate synthase (DHPS).
DHPS is critical in the synthesis of dihydrofolic acid, a precursor to folic acid, which bacteria need for the synthesis of nucleotides (the building blocks of DNA and RNA) and certain amino acids.
Bacteria synthesize their own folic acid; they cannot absorb it from the environment, unlike humans who obtain folic acid from their diet.

Here is the image below for a clear understanding. ↓

2. Competitive inhibition:-

Sulfonamides are structural analogs of para-aminobenzoic acid (PABA), a substrate of DHPS.
They compete with PABA for binding to the DHPS enzyme when sulfonamides bind to DHPS, the enzyme is inhibited, leading to a blockade in the production of dihydropteroate.
This results in a reduction in dihydrofolic acid and subsequently tetrahydrofolic acid, which is essential for DNA synthesis and cell replication.

3. Bacteriostatic Effect:-

By inhibiting folic acid synthesis, sulfonamides extract a bacteriostatic effect, meaning they prevent bacteria from multiplying but do not kill them directly.
The immune system then helps to clear the infection.

4. Selective Toxicity:-

Sulfonamides are selectively toxic to bacteria because human cells do not synthesize folic acid but obtain it from the diet.
This selective inhibition ensures that the drug targets bacterial cells without affecting human cells.

5. Combination Therapy:-

Sulfonamides are often used in combination with trimethoprim, another antibiotic that inhibits the enzyme dihydrofolate reductase (DHFR), which further blocks the pathway leading to the production of tetrahidrofolic acid.
This combination (e.g., co-trimoxazole) enhances the antibacterial effect and reduces the likelihood of resistance development.

CONCLUSION

Sulfonamides inhibit bacterial growth by targeting the folic acid synthesis pathway. they act as competitive inhibitors of the enzyme dihydropteroate synthase, blocking the production of dihydrofolic acid, essential for DNA synthesis. this mechanism is effective because bacteria must synthesize their own folic acid, unlike humans who obtain it from their diet.

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