Efficacy of adjunctive oral Janus kinase inhibitors in hospitalized patients with extensive or difficult-to-control drug eruptions: a retrospective observational case series

Background Evidence for Janus kinase (JAK) inhibition in severe or difficult-to-control drug eruptions remains limited, particularly regarding early response kinetics and corticosteroid reduction. Methods This single-center retrospective observational case series included nine hospitalized patients with extensive or difficult-to-control drug eruptions treated with adjunctive oral JAK inhibitors between March 2023 and January 2026. Cases 1–7 formed a rescue treatment subgroup because active progression persisted after at least 48 h of systemic corticosteroids. The primary outcome was the first documented absence of new lesions within 72 h. Secondary outcomes included serial changes in Worst Itch Numerical Rating Scale (WI-NRS) and body surface area (BSA), time to corticosteroid reduction, recurrence, and safety. Within-patient changes were assessed using Friedman tests, with exact Wilcoxon signed-rank tests and Holm correction for post hoc comparisons. Results The rescue subgroup received systemic corticosteroids for a median of 72 h before JAK inhibitor initiation (IQR, 48–96 h). New lesions were first documented as absent within 24 h in 6/7 patients and within 48 h in all seven. All seven began corticosteroid reduction within 96 h (median, 48 h). Across all nine patients, median WI-NRS decreased from 6 at baseline to 1 at 72 h [Friedman χ 2 (4) = 35.04, P < 0.001; Kendall's W = 0.973], and all patients achieved a reduction of at least 3 points. Median BSA decreased from 55% at baseline to 30% at day 3 and 10% by day 7 or discharge [Friedman χ 2 (2) = 18.00, P < 0.001; Kendall's W = 1.000]. Two herpes simplex-related events occurred during combined immunosuppression. Conclusion Adjunctive oral JAK inhibitors were associated with rapid control of new-lesion formation, substantial improvement in pruritus and cutaneous involvement, and early corticosteroid reduction. These findings support JAK inhibition as a promising rescue or steroid-sparing option for selected difficult-to-control drug eruptions and warrant prospective controlled evaluation.