6 - Antivirals

Question 1

Aciclovir ointment
- Can kill which virus?
- Mechanism?
- Dose?
- Concentration?
- Side effects
- Contraindication

Answer 1

• Kills HSV (doesn’t respond to adenovirus)
• Highly specific for herpes. Virus-specific thymidine kinase phosphorylates aciclovir 3 times which activates it to inhibit DNA synthesis.
• 5x daily over 10 days. 1cm ribbon on lower eyelid fornix so it rubs the eye to temporarily blur it.
• 3%, 4.5g tube.
• Bit greasy, min systemic asborbed.
• Mild stinging (common)
• SPK (common) (can make eye itchy so have to warn Px)
• Hypersensitivity (uncommon)
• Known hypersensitivity to aciclovir
• Renal impairment (check with GP first)
• Avoid in CLs use
• If pregnant, refer to GP first and tell Px the issue.

Question 2

Oral aciclovir
- Concentrations?
- Reasons to avoid over ointment?
- Uses?
- Side effects?

Answer 2

• 200, 400, and 800mg pills
• Less effect on active corneal dendrites in HSV as hard to reach cornea
• Hard to get on surface of lids compared w/ drops
• Suppress flare of virus e.g. if Px often flares up with HZV
• If sight-threatening, can be used alongside topical aciclovir to maxmise effects of topical.
• Not much side effects. Just remember to check for kidney disease and check w/ GP if so.

Question 3

Valacyclovir?
- Bioavailability?
- Dose

Answer 3

Prodrug of acyclovir.
- 50% more bioavailability
- 500mg once a day prevents recurrence
- 500 – 1000mg to Tx active HSK
- Subisidised (only for 500 and 1000mg versions)

Question 4

HZO Tx?
- Dose

Answer 4

• Prevent shingles (painful)
• If have shingles, still helps and reduces pain

If HZO (eye involved)
- 800mg orally 5x daily for 10 days (ointment doesn’t reach nerves so can’t suppress pain if ointment)
- Doesn’t actually help against ocular involvement, only reduces pain (post herpetic neuralgia)

Question 5

Aciclovir in epithelial vs stromal HSK

Answer 5

Epithelial - HSV recurrence drops to almost half. Recurrence reduction only applies as long as they’re actively on aciclovir so Tx is up to patient.
Stromal – Also halves recurrence. However, due to chances of scarring which impairs vision, recommendation is better option