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aciclovir

aciclovir

introduction

  • aciclovir is an antiviral agent which is active against Herpes simplex virus (HSV) types I and II and varicella-zoster virus (chickenpox/shingles)).
  • in infected cells, HSV or VZV coded thymidine kinases facilitate the conversion of aciclovir to the active aciclovir monophosphate which then acts as an inhibitor of, and substrate for, the herpes specified DNA polymerase, preventing further viral DNA synthesis.
  • plasma half-life is ~3hrs
  • 60% is excreted unchanged in urine, thus adjust dose in renal impaired patients
  • probenecid increases the half life by ~18%
  • high doses are cytotoxic in animal studies
  • may cause reversible renal impairment in high iv doses - administer over 1 hour to reduce this issue
  • crosses the placenta readily and is excreted in breast milk
  • category B3 for pregnant women
  • use in lactating women if benefits outweigh risks

indications for aciclovir

Australian PBS authority 2011 approved indications for varicella/zoster

  • herpes zoster within 72hrs of onset of rash (800mg tabs x 35)
  • herpes zoster ophthalmicus (800mg tabs x 35)
  • mod-severe primary genital herpes within 1st 72hrs (200mg tabs x 25 x 2)
  • episodic Rx of recurrent genital herpes after PCR proof (200mg tabs x 90)
  • HIV patients with CD4 counts < 150 million/L (800mg tabs x 120)

Australian Therapeutic Guidelines indications 2011

  • pregnant women with varicella within 72hrs of onset of rash
  • immunocompromised patients with varicella irrespective of duration of rash
  • normal patients with severe chickenpox (eg. pneumonitis, encephalitis or hepatitis) irrespective of duration of rash
  • primary or recurrent genital herpes
  • severe primary or recurrent herpes on any part of skin or mucosa:
    • 400mg 5/day for 7 days or normal dose regime iv
    • NB. sun protection is important in preventing recurrences
  • suppressive Rx for severe disabling, recurrent herpetic episodes (eg. frequent episodes assoc. with erythema multiforme, or for immunocompromised patients with chronic lesions):
    • 400mg bd for up to 6 months

iv dose given over 1 hour

  • most patients are given a 5-7 day iv course, then oral course for total of 10 days

high dose regime

  • varicella zoster infection in immunocompromised patients
  • severe chickenpox pneumonitis, encephalitis, etc.
  • herpes simplex encephalitis (10 day iv course)
  • adult dose: 10mg/kg 8hrly iv
  • paediatric dose: 250mg/m2 body surface area 8hrly iv

normal dose regime

  • severe shingles in immunocompetent patient
  • HSV infection
  • adult dose: 10mg/kg 8hrly iv
  • paediatric dose: 500mg/m2 body surface area 8hrly iv

renally impaired patients

  • reduce iv dosing frequency as follows:
    • creatinine clearance 25-50ml/min: 12hrly dosing
    • creatinine clearance 10-25ml/min: 24hrly dosing
    • creatinine clearance <10ml/min or anuric: 24hrly dosing and after dialyis, and halve dose

oral dosing

  • primary genital herpes:
    • 200mg 5/day (every 4 waking hours) for 10 days
  • recurrent genital herpes:
    • suppressive Rx: 200mg tds for up to 6 months
    • intermittent Rx: 200mg 5/day (every 4 waking hours) for 10 days
  • acute herpes zoster (shingles) within 72hrs of rash or acute herpes zoster ophthalmicus:
    • 800mg 5/day (every 4 waking hours) for 10 days
  • advanced, symptomatic HIV patients with CD4 counts < 150 million/L:
    • 800mg qid

topical aciclovir

  • 5% cream (eg. Stoxil) are very useful for Mx of cold sores if started early and applied frequently (5/day for 4 days)
  • avoid topical antivirals to the eye for HSV keratitis without ophthalmology consult as they are cytotoxic to the cornea.

other herpes virus and varicella virus antiviral agents

aciclovir.txt · Last modified: 2011/12/30 15:10 (external edit)