Quinine Ototoxicity - Cinchonism

A 52-year-old woman presents with sudden bilateral hearing loss, high-pitched tinnitus, blurred vision, and mild vertigo three days after starting quinine sulfate 300 mg TDS for nocturnal leg cramps. She also reports headache, nausea, and flushing. Audiometry shows bilateral symmetric sensorineural hearing loss with a characteristic pattern marked **A** in the diagram—near-normal thresholds at low frequencies (250–500 Hz) but moderate-to-severe loss (60–70 dB) at high frequencies (4000–8000 Hz). Tympanometry is type A bilaterally, and otoacoustic emissions are absent at high frequencies. Which of the following best explains the mechanism of quinine-induced ototoxicity in this patient?