Which class of antibiotics was first effective and introduced around 1935?

• A. Penicillin
• B. Sulfa-class antibiotics
• C. Tetracycline
• D. Macrolides

Answer: (B)

Sulfonamide (the sulfa-class) antibiotics were the first to prove effective and were introduced around 1935. They are synthetic compounds that block bacterial folic acid synthesis, a pathway bacteria must use to make DNA and RNA. They do this by mimicking the natural substrate PABA and inhibiting the enzyme dihydropteroate synthase, which stops production of essential folate derivatives. Humans don’t synthesize folate the same way, obtaining it from the diet, so these drugs can target bacteria with selective toxicity. Although penicillin was discovered earlier (in 1928), its widespread clinical use began in the 1940s, while tetracycline and macrolides appeared later, in the mid-20th century. This combination of early, effective antibacterial action and the 1935 introduction makes the sulfa-class the correct reference.