16B23: Exam Report
Compare and contrast the mechanism of action, spectrum of activity and adverse effects of benzyl penicillin and fluconazole.
8% of candidates passed this question.
To pass this question each of the three components needed to be compared and contrasted for both agents. A tabulated answer helped in this regard but was not essential. Some answers included information that could not gain marks, as it was not directly relevant to the question asked (e.g. presentation and dose).
In spectrum of activity, as well as what important organisms the agents were effective against, marks were also given for the important organisms that they were not effective against (e.g. MRSA and beta-lactamase producing organisms for penicillin G; and aspergillus for fluconazole).
In general, of the two agents, fluconazole was the least well answered. For example, a common omission either in mechanism of action or in adverse effects was that fluconazole inhibits microsomal P450 enzymes.
Some candidates confused fluoroquinalone with fluconazole.
T2i / 16B23: Compare and contrast the mechanism of action, spectrum of activity and adverse effects of benzyl penicillin and fluconazole
- B lactam ring mimics shape of D-Ala-D-Ala sequence that is the substrate for cell wall transpeptidases
This is the final step in bac cell wall synthesis that allows cross linking
By pretending to be D-Ala-D-Ala, it binds transpeptidases -> inhibits enzyme activity → bac without cell wall → die
- Exerts bacterial autolytic effect
Inhibits certain penicillin binding proteins (PBP) related to the activation of autolysis →promotes bac lysis & cell death
Inhibits the fungal cytP450 enzyme that syntheses ergosterol
Inhibits cell memb formation
Leakage -> cell death
C Krusei (Kompletely resistant)
High Na+, Low K+
Hepatic toxicity – watch LFTs; hepatic failure, hepatitis, abnormal LFTs
GI – nausea, vomiting, diarrhea, abdm pain
CVS – pallor angioedema
CNS – headache, dizziness
Haem: thrombocytopenia, leukopenia
Derm – skin rashes, alopecia