## Investigation of Drug-Induced Ototoxicity **Key Point:** Pure tone audiometry is the gold standard for detecting and quantifying sensorineural hearing loss caused by ototoxic antitubercular drugs (streptomycin, ethionamide, linezolid). ### Why Pure Tone Audiometry? **High-Yield:** Pure tone audiometry provides: - Objective measurement of air and bone conduction thresholds across frequencies (250–8000 Hz) - Early detection of high-frequency hearing loss (typically 4–6 kHz) — the hallmark of ototoxicity - Quantification of severity and progression - Documentation for medicolegal purposes and treatment modification decisions ### Ototoxic Antitubercular Drugs | Drug | Mechanism | Frequency Affected | Reversibility | |------|-----------|-------------------|----------------| | Streptomycin | Aminoglycoside; damages cochlear hair cells | 4–6 kHz initially | Irreversible | | Ethionamide | Direct toxicity to 8th nerve | High frequencies | Irreversible | | Linezolid | Mitochondrial toxicity | Broad spectrum | Partially reversible if caught early | **Clinical Pearl:** Baseline audiometry should be performed BEFORE starting ototoxic drugs, and repeated every 2–4 weeks during treatment. If high-frequency hearing loss is detected, the offending drug should be discontinued immediately. ### Why Other Options Are Incorrect - **Tympanometry:** Measures middle ear compliance and ossicular chain function — useful for conductive hearing loss, not sensorineural ototoxicity. - **Rinne and Weber tuning fork test:** Bedside screening tools that are insensitive and non-quantitative; cannot detect early high-frequency loss or document progression. - **Caloric test:** Assesses vestibular function (balance); while streptomycin does cause vestibulotoxicity, it does not confirm cochlear ototoxicity specifically.
Sign up free to access AI-powered MCQ practice with detailed explanations and adaptive learning.