The correct answer is A. Tinnitus. 💡 Clinical Explanation Tinnitus (ringing or buzzing in the ears) is classic and typically the earliest clinical sign of acute salicylate (aspirin) toxicity. It often develops when serum salicylate concentrations exceed 30 mg/dL, even before overt systemic metabolic derangements become prominent. ⏱️ Progression of Aspirin Toxicity Symptoms Earliest Sign (~30 mg/dL): Tinnitus, impaired hearing, nausea, vomiting, and dizziness. Early Systemic Phase: Direct stimulation of the respiratory center in the medulla leads to hyperventilation, causing an early Respiratory Alkalosis. Late / Severe Phase: Uncoupling of oxidative phosphorylation leads to an accumulation of organic acids (lactic acid, ketoacids), resulting in a classic High Anion Gap Metabolic Acidosis. (Note: Adults typically present with a mixed Respiratory Alkalosis + Metabolic Acidosis). End-Stage / Severe Toxicity: Central nervous system depression and eventual respiratory depression occur as toxic levels become severe. 🚫 Why the Other Options are Incorrect B. Metabolic Acidosis: Occurs later as cellular metabolism uncouples; it is not the earliest sign. C. Reye's Syndrome: A rare, severe complication (hepatic failure and encephalopathy) seen when aspirin is given to children/children during active viral infections (like varicella or influenza), not an acute manifestation of salicylate overdose in adults. D. Respiratory Depression: Occurs in late, severe toxicity stages due to severe CNS depression. Early toxicity causes respiratory stimulation (hyperventilation), not depression.