A 32-year-old farmer from Punjab is brought to the emergency department 45 minutes after accidental exposure to an organophosphate pesticide (malathion) during crop spraying. He presents with profuse salivation, lacrimation, muscle fasciculations, and pinpoint pupils. Respiratory rate is 28/min with audible bronchospasm. Blood pressure is 110/70 mmHg and heart rate is 92/min. What is the most appropriate immediate next step in management?