Which antibiotic among the following is a third-generation cephalosporin?

• A. Cephalexin
• B. Ceftriaxone
• C. Dicloxacillin
• D. Tobramycin

Answer: (B)

Cephalosporin generations reflect how broad the Gram-negative coverage and tissue penetration become within the class. Ceftriaxone is a third-generation cephalosporin, which means it has strong activity against many Gram-negative bacteria and good penetration into the central nervous system, making it a go-to for serious infections like meningitis and sepsis. The other drugs listed are not third-generation cephalosporins: one is a first-generation cephalosporin with mainly Gram-positive coverage, another is a penicillinase-resistant penicillin, and the last is an aminoglycoside. So ceftriaxone best fits the third-generation cephalosporin profile.