Antimicrobials — Penicillin vs Fluconazole

Current · V5 (2025) → O2.i Historical · V4 (2023) → T2.ii 1 exam appearance

2016B Q23

Exam question

Compare and contrast the mechanism of action, spectrum of activity and adverse effects of benzyl penicillin and fluconazole.

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Field	BENZYL PENICILLIN Anti-infectives · Anti-infectives · Level 1	FLUCONAZOLE Anti-infectives · Anti-infectives · Level 3
Mechanism of action	β lactam antibiotic Binds to penicillin binding protein (transpeptidase) and prevents crosslinking of bacterial peptidoglycan impairs cell wall synthesis	fluorinated bis-triazole reduction of ergosterol synthesis by inhibition of fungal cytochrome P450 enzymes (greater affinity for fungal than for human)
Absorption	Orally not absorbed (need penicillin V)	Well absorbed orally
Distribution	CSF and bone penetration if inflammation present	good CSF penetration
Protein binding	60% PB	—
Volume of distribution	Vd <1L/kg	—
Metabolism	Inactive metabolite penicollic acid	not metabolized well
Excretion	90% excreted in urine by tubular secretion 25% unchanged	Urine unchanged
Adverse Effects Toxicity	GIT– abdominal pain, N/V/D, pseudomembranous colitis, hepatitis HAEM- agranulocytosis CNS- confusion, seizure, encephalopathy HYPERSENSITIVITY- rash, anaphylaxis	N/V/D, Abdominal pain Headache Skin rash Reversible alopecia Rare: Hepatic failure, SJS Should be avoided in Pregnancy Drug interactions: (inhibitor of CYP3A4, CYP2C9)
Antimicrobial Spectrum	Narrow-Spectrum Natural Penicillin Highly bactericidal, only gram positives/anaerobes, susceptible to betalactamases Targets GPC: Streptococci, Meningococcus Listeria (GPB) GNC: Neisseria, Clostridia Treponemma (Spiral) Synergistic effects with aminoglycosides	Candida Cryptococcus Coccidia (No activity against histoplasma, blasto, sporotrichosis, Aspergillus, mucormycosis)
Class Group	ANTIBIOTIC: PENICILLIN	ANTIFUNGAL: AZOLE
Introduction	Narrow spectrum naturally occurring penicillin	Triazole
Legacy Cicm Level	Level 1	Level 3
Resistance Mechanism	Resistance MRSA Many Staph -Betalactamase prod Gram Negatives	Some candida species, Decreased drug concentration Target site alteration Up-regulation of target enzyme Development of bypass pathways
Special Points	—	potent CYP inhibitors with a wide range of drug interactions (including warfarin)

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Exam appearances

1 appearance

Exam	Exact exam wording	Candidate success
2016B Q23	Compare and contrast the mechanism of action, spectrum of activity and adverse effects of benzyl penicillin and fluconazole.	8%