Dosing
CrCl > 80: 200 - 800 mg 2-5 x day po depending on syndrome. IV for the immunoincompetent.
Genital Herpes
Initial treatment: 200 mg po 5 x daily for 10 days or 400 mg po q8 for 7-10 days.
Intermittent treatment for recurrence: 200 mg po 5 x daily for 5 days; initiate at the earliest sign or symptom of recurrence.
Chronic suppression for recurrence: 400 mg po bid or 200 mg 3-5 times daily.
Herpes Zoster
Shingles: 800 mg 5 times a day for 7-10 days.
10-15 mg/kg iv q 8 for Herpes simplex encephalitis for 2-3 weeks.
CrCl 80-50: 5-12 mg/kg q 8 h iv.
CrCl 50-10: 5-12 mg/kg q 12-24 h iv.
CrCl < 10: 2.5 - 6 mg/kg q 24 h iv.
Hemodialysis: 500 mg after dialysis.
Peritoneal dialysis: 2.5 mg/kg/day.
Important side effects
Keep well hydrated, causes acute renal failure from IV acyclovir crystal deposition in the kidneys. I have seen it with po acyclovir.
Nephrotoxicity is associated with obesity and vancomycin (PubMed).
Agitation, confusion, dizziness, hallucinations, somnolence (more common in the elderly).
Important drug interactions
Cyclosporine increases nephrotoxicity; aminoglycosides increase nephrotoxicity and/or neurotoxicity; cimetidine increases acyclovir toxicity; increases meperidine effect; decreases phenytoin effect; zidovudine increases neurotoxicity (drowsiness and lethargy (:the Grand Rounds Effect:))
Rants and Screeds
Note: valacyclovir, famciclovir are better-absorbed acyclovir. Same drug though.
Use for
Herpes simplex 1 and 2; Varicella Zoster (aka shingles or chickenpox).
In terms of the MIC for herpes virus, from most to least sensitive: HSV 1 < HSV 2 < VZV.
Thymidine kinase negative mutant HSV can occur and are resistant.
Class
Thymidine analog.
Curious Cases
Relevant links to my Medscape blog
Last Update: 04/26/19.