Rather than bolus re-dosing for those long acting opiod overdoses, consider using a narcan drip. It can be a bit easier on the nurses. A reasonable place to start for the hourly IV dose is two-thirds of the initial bolus dose that achieved the desired reversal effect. So for example, if the initial bolus dose that awoke the patient was 1.5 mg, then the drip rate should be started at (2/3) x 1.5 = 1 mg/hour.
Source
Roberts: Clinical Procedures in Emergency Medicine, 4th ed.