Oral minocycline for the treatment of retinitis pigmentosa–associated cystoid macular edema: results of a phase I/II clinical trial

Purpose The etiology of retinitis pigmentosa (RP)–associated cystoid macular edema (CME) has been related to retinal neuroinflammation and microglial activation. Minocycline, a drug FDA-approved for anti-microbial indications, also inhibits microglial activation and expression of inflammatory mediators. This study investigates the safety and efficacy of oral minocycline as primary treatment for RP-associated CME. Methods A single-center, prospective, open-label phase I/II clinical trial enrolled five participants with RP-associated CME. Participants had lead-in assessments prior to the initiation of oral minocycline 100 mg twice daily for 12 months. Main outcome variables included changes in best-corrected visual acuity (BCVA) and retinal central subfield thickness (CST) measured using spectral domain optical coherence tomography relative to mean of pre-treatment measurements. Results The study drug was well tolerated and not associated with any severe adverse events. No significant changes in mean BCVA from study baseline were noted in either the study eye (+ 0.7 ± 4.1 letters at 6 months, − 1.1 ± 1.7 letters at 12 months) or the qualifying fellow eye (− 0.3 ± 3.4 letters at 6 months, − 0.3 ± 4.6 letters at 12 months) ( p > 0.05 for all comparisons). Mean percentage changes in CST from baseline however decreased progressively with treatment (decreases at 6 and 12 months: study eyes 3.9 and 9.8%; qualifying fellow eyes 1.4 and 7.7%). Considering all eyes ( n = 10), mean percentage CST decrease at 6 and 12 months was 2.7 ± 9.5% ( p = 0.39) and 8.7 ± 9.5% ( p = 0.02) respectively. Conclusion Oral minocycline administration over 12 months was associated with no significant changes in mean BCVA and a small but progressive decrease in mean CST. Trial registration NCT02140164 (05/2014).