The patient: A 6-month-old boy in Bangkok The symptoms: The child was brought to a hospital after he'd had a fever and cough for 24 hours. The plan was for the child to be administered favipiravir tablets on the first day of hospitalization and then given the drug in liquid form for the next four days. But about 18 hours after he began the treatment, the boy's mother noticed that his eyes, which were normally dark brown, had turned bluish-purple. The corneas — the transparent, dome-shaped barriers covering the fronts of the eyes — appeared blue in sunlight. There was no visible discoloration of his skin, nails or hair, according to a report of the case. The diagnosis: Doctors suspected that favipiravir might be causing the blue tint. A year earlier, in 2021, physicians in Goa, India, described the case of a 20-year-old man who also developed a bluish tinge in his corneas after he began favipiravir treatment for COVID-19. The side effect had never been documented before, they wrote in a report of his case .…