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The size of the breakthrough dose should be 5-15% of the patient's 24-hour baseline dose. In an inpatient setting, rescue doses can be provided IV every 15-30 minutes. Oral rescue doses can be offered as needed over the normal dosing interval of the drug (typically every 4 hours).
For example, if your reduced IV morphine dose was 50mg, the equivalent IV hydromorphone dose is 10mg. Divide this number by the bioavailability of the new drug to get a bigger number, that being the oral 24 hour dose of the new drug. Some rounding of numbers is fine.
The equianalgesic chart indicates that 7.5 mg of oral hydromorphone is equal to 30 mg of oral morphine. The patient’s calculated dose of 25 mg of oral hydromorphone is equal to 100 mg of oral morphine.
Table 1: Pharmacokinetic Data for Oral Opioids . Starting Dose Onset Peak Duration Half life Codeine 30 - 60 mg q 4 hr 30 min 1.5 hr 6 hours 2-4 hr Morphine SA 10 - 15 mg q 3 - 4 hr 15 min 1.5-2 hr 4 hr 1.5-2 hr Hydrocodone 5-10 mg q 4-6 hr 60 min 2 hr 4-6 hr 4 hr Oxycodone 5-10 mg q 4-6 hr 15-30 min 1-2 hr 4-6 hr 4 hr
Consider the need to adjust dose for conditions that increase opiate risk (eg elderly, co-morbidities, renal or hepatic impairment). Where dose equivalence is expressed as a range, use the value that produces the lowest equivalent dose and titrate as necessary.
The Morphine Milligram Equivalents (MME) Calculator calculates total daily morphine milligram equivalents.
Use the equianalgesic ratio: 25 mg PO morphine = 5 mg PO hydromorphone, which is a 5:1 ratio. Calculate new dose using ratios: 180/5 = 36 mg oral hydromorphone/24 hours. For this example, reduce dose 50% for cross-tolerance: 36 x 0.5 = 18 mg/24 hours = 3 mg q4h.
