Rash Onset — The Clock Starts Ticking
Placeholder: dermatomal vesicular rash marks hour zero of the treatment window.
- 1–5 days: Typical prodrome (Placeholder pain/tingling phase)
- Dermatomal: Rash pattern (Placeholder unilateral band)
- Day 3–5: Peak vesicle stage (Placeholder crusting follows)
- Dorsal root ganglia: VZV reactivation site (Placeholder latent virus site)
Detecting rash onset
Placeholder: onset marks the reference point for the 72-hour clock.
The 72-Hour Treatment Window
Placeholder: antivirals are most effective when started within 72 hours.
- 72 hours: Critical window (Placeholder from rash onset)
- IDSA/AAD: Guideline source (Placeholder clinical guidance)
- Efficacy drops: Window closes (Placeholder sharp decline)
- <48h: Best case start (Placeholder optimal timing)
Why 72 hours matters
Placeholder: viral replication in ganglia slows after this point, reducing drug impact.
Early Antiviral Initiation Benefit
Placeholder: early dosing flattens the severity curve and shortens illness.
- Up to 45%: Rash duration cut (Placeholder with early start)
- Up to 60%: PHN risk cut (Placeholder with early start)
- >90%: Viral suppression (Placeholder early treatment)
- Marked: Pain reduction (Placeholder acute neuritis)
Mechanism of benefit
Placeholder: nucleoside analogs block viral DNA polymerase early in replication.
Late Initiation — Reduced Benefit
Placeholder: starting after 72 hours yields diminishing therapeutic return.
- Sharp: Efficacy decay (Placeholder past 72h)
- Some to 120h: Residual benefit (Placeholder fading window)
- Minimal: Beyond 120h (Placeholder little added value)
- Elevated: Complication risk (Placeholder higher PHN odds)
Why delay hurts
Placeholder: viral replication has largely peaked, limiting antiviral effect.
Outcome Comparison — Duration & PHN Risk
Placeholder: compare treated vs untreated outcomes across timing scenarios.
- ~20%: Untreated PHN risk (Placeholder older adults)
- ~8%: Early-treated PHN risk (Placeholder within window)
- Faster: Rash resolution (Placeholder early treatment)
- Famciclovir/Valacyclovir: Best drug choice (Placeholder higher potency)
Summary comparison
Placeholder: timing matters more than drug choice, but both compound benefit.
Placeholder: earliest treatment within the window gives the best combined outcome.