Evaluation of the frequency and intensity of favipiravir-associated yellow-green fluorescence in lunulae, hair, and face.

Background: We detected yellow-green fluorescence in the face, hair and lunulae of patients using favipiravir.

Aim: We evaluated the frequency and intensity of favipiravir-associated fluorescence.

Patients/methods: The participants comprised patients who had taken at least a single dose of favipiravir and been examined no later than 30 days after the last dose. The gender, age, body mass index (BMI), Fitzpatrick's skin-type, hair color, N-acetylcysteine use, presence and the intensity of fluorescent reflection under Wood's light in the lunulae of the fingernails, hair, and the face were recorded.

Results: There were 275 patients, 144 (52.4%) of whom were women. 165 (57.9%) had used treatment for a maximum of 5 days, 99 (34.7%) for 6-10 days, and 21 (7.4%) for more than ten days. Using more than 22 tablets of favipiravir increased the probability of detecting fluorescence in the lunulae by 6.72 (2.61-17.23) times. Using more than 28 tablets increased the risk of fluorescence in hair and the T-zone by 5.92 (2.43-14.71) and 2.88 (1.11-7.47) times, respectively. No relationship was found between the fluorescence intensity in any localization and the total dose. However, we determined a negative correlation between the elapsed time after the last dose and the fluorescence intensity in the lunulae and the T-zone (p=0.036; p=0.031; respectively). It was noted that BMI negatively correlated with the fluorescence intensity in the lunulae (p=0.001). Skin type was related to intensity for all localizations (p<0.001). Fluorescence was found in the lunulae with significantly less frequency in patients using N-acetylcysteine (p=0.040).

Conclusions: We must be aware of favipiravir-induced phototoxicity.