Acyclovir for Bell's Palsy
Acyclovir alone should NOT be prescribed for Bell's palsy, and the addition of acyclovir to corticosteroids provides no proven benefit and is not recommended as standard therapy. 1
Primary Treatment Recommendation
Oral corticosteroids are the only proven effective treatment for Bell's palsy in patients 16 years and older. The American Academy of Otolaryngology-Head and Neck Surgery clinical practice guideline makes a strong recommendation AGAINST antiviral monotherapy and provides only an "option" (not a recommendation) for combination therapy with steroids 1.
Evidence Against Acyclovir
The highest quality evidence comes from the BELLS study (2009), a large randomized controlled trial of 551 patients that definitively showed:
- Prednisolone alone: 83% recovery at 3 months, 94.4% at 9 months
- Acyclovir alone: 62.5% recovery at 3 months, 78.1% at 9 months (no better than placebo)
- Combination therapy: 79.7% at 3 months, 92.7% at 9 months (no additional benefit over prednisolone alone) 2, 3
The study found no significant difference between aciclovir comparison groups (71.2% for aciclovir vs 75.7% for no aciclovir, adjusted P=0.50 at 3 months) 3.
Treatment Algorithm
For patients presenting within 72 hours of symptom onset:
Prescribe oral corticosteroids (strong recommendation):
- Prednisolone 50 mg daily for 10 days, OR
- Prednisone 60 mg daily for 5 days, then taper over 5 days 1
Do NOT prescribe acyclovir alone (strong recommendation against) 1
Combination therapy with acyclovir MAY be offered (option only, not recommended):
For patients presenting >72 hours after onset:
- Benefit of any treatment is unclear 1
- Steroids may still be considered, but evidence is weaker
Key Clinical Nuances
Why the Guideline Allows Combination Therapy as an "Option"
Despite the BELLS study showing no benefit, the guideline acknowledges two smaller trials suggested possible benefit:
- One trial (221 patients) showed 96.5% recovery with valacyclovir+prednisolone vs 89.7% with prednisolone alone 1
- Another trial (34 patients) showed higher recovery rates with famciclovir+prednisolone, though this study had methodological flaws 1
However, the most recent and highest quality evidence (the BELLS study) should guide practice, and it showed no benefit 2, 3.
Most Recent Evidence (2025)
A 2025 prospective randomized study of 63 patients confirmed no advantage of acyclovir+prednisolone (86.6% improvement) over prednisolone alone (90% improvement, p>0.05) 5. This reinforces that combination therapy offers no additional benefit.
Common Pitfalls to Avoid
Do not prescribe acyclovir monotherapy - This is definitively ineffective and delays appropriate steroid treatment 1
Do not routinely add acyclovir to steroids - While allowed as an option, the evidence does not support this practice. The cost and medication burden are not justified by outcomes 2, 3, 5
Do not delay steroid treatment - The 72-hour window is critical. Treatment initiated within 24 hours shows best outcomes 1
Do not confuse Bell's palsy with zoster sine herpete - If there is clinical suspicion for herpes zoster (severe pain, vesicles, involvement of other cranial nerves), antiviral therapy IS indicated, but this is not Bell's palsy 6
Pediatric Considerations
In children, evidence for any treatment is limited. Spontaneous recovery rates are higher than in adults. If treatment is pursued, steroids may be considered with caregiver involvement in decision-making, but acyclovir has no established role 1.
Bottom Line
Prescribe oral corticosteroids alone within 72 hours of symptom onset. Acyclovir provides no benefit as monotherapy and no proven additional benefit when combined with steroids. The guideline's allowance of combination therapy as an "option" reflects minor conflicting evidence, but the strongest and most recent data support steroids alone 1, 2, 3, 5.