Can new blisters develop with shingles despite treatment with aciclovir (antiviral medication)?

New Blisters in Shingles Despite Acyclovir Treatment

Yes, new blisters can continue to develop in shingles despite acyclovir treatment, especially during the first 24-72 hours after starting therapy. This is particularly true if treatment was initiated more than 72 hours after the onset of rash 1.

Mechanism and Timeline of New Lesion Formation

When treating herpes zoster (shingles) with acyclovir, it's important to understand the expected clinical course:

1. Early Treatment Window:

   • Acyclovir is most effective when started within 72 hours of rash onset 1
   • Even with prompt treatment, new lesions may continue to appear for 24-72 hours after starting therapy

2. Normal Disease Progression:

   • In immunocompetent patients, new lesions typically stop forming within 4-6 days
   • With acyclovir treatment, this period is shortened but not immediately halted 1
   • Complete healing takes approximately 2 weeks in healthy individuals

3. Immunocompromised Patients:

   • Lesions may continue to develop over a longer period (7-14 days) even with treatment 1
   • Healing generally occurs more slowly unless effective antiviral therapy is administered

Factors Affecting Continued Lesion Development

Several factors influence whether new blisters will continue to form despite acyclovir treatment:

• Timing of treatment initiation: Starting treatment after 48 hours of rash onset significantly reduces efficacy 2
• Immune status: Immunocompromised patients experience more prolonged viral replication 1
• Dosing adequacy: Standard dosing is 800 mg five times daily for 7-10 days 3
• Treatment adherence: Missing doses can reduce effectiveness
• Viral sensitivity: Though rare in immunocompetent patients (<0.5%), acyclovir resistance can occur 1

Clinical Implications and Management

If new blisters continue to develop beyond the expected timeframe (>72 hours after starting treatment):

1. Evaluate treatment adequacy:

   • Confirm proper dosing (800 mg five times daily for immunocompetent adults) 1
   • Assess patient adherence to prescribed regimen

2. Consider immune status:

   • Immunocompromised patients may require IV acyclovir instead of oral therapy 1
   • Higher doses may be needed for patients with HIV or other immunocompromising conditions 3

3. Watch for complications:

   • Secondary bacterial infection of lesions
   • Dissemination of infection (more common in immunocompromised hosts)

4. Monitor for treatment failure:

   • If lesions persist beyond 7-10 days of treatment, consider resistance
   • Resistance is more common in immunocompromised patients (7% vs <0.5% in immunocompetent) 1

Expected Treatment Outcomes

With appropriate acyclovir treatment, patients should experience:

• Reduction in time to last new lesion formation 2
• Faster loss of vesicles and full crusting 2
• Reduction in acute pain during treatment 2
• Accelerated resolution of cutaneous manifestations 1

Common Pitfalls

1. Delayed treatment initiation: Starting acyclovir after 72 hours significantly reduces its effectiveness in preventing new lesions 2

2. Inadequate dosing: The full recommended dose is necessary (800 mg five times daily for adults) 1

3. Misdiagnosis: Ensuring the diagnosis is truly herpes zoster and not another vesicular condition

4. Unrealistic expectations: Patients should be counseled that treatment does not immediately stop all new lesion formation but rather shortens the disease course

5. Overlooking immunocompromised status: These patients may require IV therapy or longer treatment courses 1

Remember that while acyclovir speeds healing and reduces pain, it does not completely prevent all new lesion formation, especially in the first few days of treatment. The continued appearance of some new blisters within the first 72 hours of therapy is within the expected course of treated shingles.