Final answer:
The initial dose of atropine for a patient with sinus bradycardia and a heart rate of 42 is typically 0.5 to 1 mg IV, which can be repeated every 3 to 5 minutes until the desired heart rate is achieved or a maximum dose of 3 mg is reached.
Step-by-step explanation:
The initial dose of atropine for a patient with sinus bradycardia and a heart rate of 42 would depend on the severity of symptoms and the patient's overall condition. However, a typical starting dose is 0.5 to 1 mg IV, which can be repeated every 3 to 5 minutes until the desired heart rate is achieved or a maximum dose of 3 mg is reached.