Adjuvant treatment of anogenital warts with systemic interferon: a systematic review and meta-analysis

Interferons are natural messenger proteins that are used to treat various disease entities. Due to their immunomodulating, antiviral and antiproliferative effects, the systemic administration of interferons after ablative treatment for anogenital warts (AGWs) has been advocated to increase clearance and decrease recurrence rates. However, studies investigating the efficacy of adjuvant systemic interferon have yielded inconsistent results. The objective of this systematic review and meta-analysis was to comprehensively assess and evaluate the available evidence from randomised controlled trials.

A literature search was conducted in Cochrane Central Register of Controlled Trials, Embase and MEDLINE. Available data were classified according to the interferon type and dosage. Pooled effect estimates were calculated for predefined outcomes. The Cochrane Collaboration's risk of bias tool was used to assess the included trials and the Grading of Recommendations Assessment, Development and Evaluation (GRADE) approach to evaluate our confidence in the effect estimates.

Twelve trials were identified that met the inclusion criteria and assessed immunocompetent patients with external AGW. Compared with placebo, adjuvant alpha-, beta- and gamma-interferon were generally not significantly superior in terms of complete clearance over the short, intermediate or long term, nor with regard to intermediate- or long-term recurrence. However, the low-dose subgroup of adjuvant alpha-interferon was significantly superior compared with placebo regarding intermediate-term complete clearance and recurrence. Further data were available for the comparison of different dosages of alpha- and beta-interferon and for comparisons of the three interferon types. No significant differences were seen in these comparisons regarding efficacy. Data on quality of life were not available.

The GRADE quality of the evidence ranged from 'very low' to 'high'. The significantly higher efficacy of low-dose alpha-interferon compared with placebo was based on a single trial, and our confidence in the effect estimates rated as 'low'. Overall, we found no reliable evidence favouring the systemic use of interferon after ablative treatment of AGW.