Comparative pharmacology of antibiotics

Both Question 3 from the second paper of 2006 and Question 9 from the second paper of 2003 asked the candidates to compare and contrast the pharmacology of ceftriaxone, gentamicin and meropenem. The answer to this specific question comes first in this chapter. It is not followed by a more indepth discussion of antibiotic pharmacology, because this would be something of a waste. it is unlikely that - after nine years of neglect - the college would bring this sort of question back into the papers.

A comparison of the selected antibiotics which the college was interested in:






3rd gen cephalosporin




IV – 1g; up to 3g/day

IV; daily dosing 5-7mg/kg

IV 1-2g – up to 6g/day


Cleared both renally (unchanged) and via biliary excretion (33%)

Cleared renally; rapidly and unchanged

Cleared renally

Mechanism of action

Inhibition of bacterial cell wall synthesis by binding to penicillin-binding proteins

Inhibition of bacterial protein synthesis by binding to the 30S subunit of the bacterial ribosome

Inhibition of bacterial cell wall synthesis by binding to penicillin-binding proteins



Infections by susceptible gram-positive organisms;
Some gram-negative cover

Infections by susceptible gram-negative organisms;
Little role in treatment of gram-positive infections (with the exception of enterococcal endocarditis)

Infection by susceptible gram-positive and gram negative aerobic and anaerobic organisms; broad cover


Seizures in overdose
Bone marrow suppression in chronic high-dose use
Rapid development of microbial resistance

Accumulation in renal failure increases risk of toxicity
Potentiates neuromuscular blockade

Seizures in overdose