VIVA: Pharmacology - Antimicrobials

Question 1

What are the indications for acyclovir in the ED?

Answer 1

HSV encephalitis*
VZV
Genital herpes
Patients with HIV

• needed to pass

Question 2

Describe the mechanism of action of acyclovir

Answer 2

Inhibition of viral DNA synthesis*
- Irreversible binding to viral DNA polymerase
- Incorporation into viral DNA with termination
- Specificity for virus-infected cells (virus-specific thymidine kinase)

• needed to pass + one other

Question 3

Describe the pharmacokinetics of acyclovir

Answer 3

• Short half-life of 2.5hrs (5x daily dosing oral)*
• Low oral bioavailability
• Mostly excreted unchanged in urine
• CSF 20-50% of plasma
• Wide distribution
• needed to pass + one other

Question 4

Name some side effects of acyclovir

Answer 4

2 to pass:
- Nausea
- Vomiting
- Diarrhoea
- Headache
- Reversible renal toxicity
- Neurological: tremor, delirium, seizures

Question 5

Name some macrolide antibiotics

Answer 5

2 to pass:
- Erythromycin
- Roxithromycin
- Azithromycin
- Clarithromycin

Question 6

Describe the mechanism of action of macrolides

Answer 6

Inhibits bacterial protein synthesis* by binding to 50S ribosomal RNA, which blocks aminoacyl translocation reaction and formation of initiation complexes (transpeptidation)
May be inhibitory or bactericidal, particularly at higher concentrations

• needed to pass

Question 7

What organisms are macrolides effective against?

Answer 7

3 to pass:
- Gram positive organisms: pneumococci, streptococci, staphylococci, corynebacteria
- Atypicals: Mycoplasma, Legionella, Chlamydia sp, Listeria, some mycobacteria
- Gram negative organisms: Neisseria sp, Bordatella pertussis, Treponema pallidum, Campylobacter sp, bartonella (Haemophillus less susceptible)

Question 8

What are the adverse effects of erythromycin?

Answer 8

Gastrointestinal*: anorexia, nausea, vomiting, diarrhoea
Liver toxicity: acute cholestatic hepatitis (particularly with estolate)
Allergic reaction: fever, eosinophilia, rash
Drug interactions: inhibits CP450

• needed to pass + one other

Question 9

Describe the mechanism of action of ceftriaxone

Answer 9

Binds to bacterial cell wall peptidases leading to inhibition of bacterial growth and death of the bacterium
Bacteriocidal antibiotics

• description of effect on cell wall to be at standard

Question 10

What is the spectrum of activity of ceftriaxone?

Answer 10

Broad spectrum third generation cephalosporin with good tissue penetration and effective against a broad range of Gram positive and Gram negative organisms including Haemophilus and Neisseria
Not effective against anaerobes, Pseudomonas, Listeria, and MRSA

• Gram positive and Gram negative (name each group or one examples from eaach group and at least one non-susceptible organism to be at standard

Question 11

Describe the pharmacokinetics of ceftriaxone

Answer 11

3/7 to pass:
- Administration: IV and IM, <1% bioavailability orally
- Excretion: 35-70% excreted unchanged in urine, remainder excreted in bile with some hepatic/gut metabolism
- Half-life: 6-9hrs
- Distribution: penetrates tissues and body fluids well, including CSF
- Volume of distribution: 5.8-13.5L
- Negligible protein binding
- Duration of action: 24hrs