A 35-year-old male is brought to the emergency department 6 hours after consuming approximately 100 mL of methanol-contaminated alcohol at a local gathering in Delhi. He is conscious but complains of blurred vision and severe headache. Vital signs are stable. Arterial blood gas shows pH 7.28, HCO₃⁻ 12 mEq/L, and anion gap of 18. What is the most appropriate immediate next step in management?