Okay, let's tackle this question. The patient is on ATT, which stands for Anti-Tubercular Therapy. The question is about which drug in the regimen causes tinnitus and hearing loss. The correct answer is probably one of the aminoglycosides like streptomycin.

First, I need to recall the common drugs in ATT. The first-line drugs are Isoniazid, Rifampin, Pyrazinamide, Ethambutol, and Streptomycin. Now, among these, which ones have ototoxic effects? Streptomycin is known for causing ototoxicity, leading to tinnitus and hearing loss. Ethambutol is associated with optic neuritis, so that's not it. Isoniazid can cause peripheral neuropathy. Rifampin is more about hepatotoxicity and drug interactions. Pyrazinamide can cause hyperuricemia and hepatotoxicity. So the answer should be Streptomycin, which is option C or D depending on the options given.

Wait, the options here are A to D, but the user didn't list them. Hmm, but the correct answer given by the user is option C. So assuming that the options are structured with C being Streptomycin. Let me double-check the ototoxic drugs. Aminoglycosides like gentamicin, tobramycin, and streptomycin are all ototoxic. Since streptomycin is part of ATT, that's the culprit here. The mechanism is thought to be due to damage to the cochlear hair cells in the inner ear. So the explanation should highlight that streptomycin's ototoxicity is a known adverse effect, and other drugs in ATT don't have this side effect. The clinical pearl is to monitor for hearing changes in patients on streptomycin. Also, remember that aminoglycosides are nephrotoxic and ototoxic, so if the question mentions those, it's a clue towards aminoglycosides.

**Core Concept**
Ototoxicity is a known adverse effect of aminoglycoside antibiotics. Streptomycin, an aminoglycoside used in anti-tubercular therapy (ATT), can damage cochlear hair cells in the inner ear, leading to tinnitus and sensorineural hearing loss.

**Why the Correct Answer is Right**
Streptomycin causes ototoxicity by disrupting the function of cochlear hair cells through mitochondrial dysfunction and oxidative stress. This damage is often irreversible and dose-dependent. Its mechanism involves binding to the 30S ribosomal subunit of bacteria, but off-target effects on human cells (particularly in the inner ear) are responsible for toxicity.

**Why Each Wrong Option is Incorrect**
**Option A:** Isoniazid causes peripheral neuropathy (via pyridoxine deficiency), not ototoxicity.
**Option B:** Rifampin is associated with hepatotoxicity and orange discoloration of body fluids, not hearing loss.
**Option D:** Ethambutol causes optic neuritis (visual field defects), not tinnitus.

**Clinical Pearl / High-Yield Fact**
Aminoglycosides (e.g., streptomycin, gentamicin) are classic "oto-nephrotoxic" agents. Always monitor patients on these drugs for hearing changes and renal function.

**Correct Answer: C

✓ Correct Answer: C. Streptomycin