Dosing and Intervals
A number of factors should be taken into consideration when choosing a starting dose. Polypharmacy is prevalent in many patients with multiple medical conditions, and this increases the risk of drug interactions and unexpected side effects. In the opioid-naïve patient, consideration should be made to commencing with a low dose. By monitoring progress frequently at the onset and titrating the dose as tolerated, side effects can be monitored and the minimum required dose can be used. A reasonable starting dose in a patient with moderate pain (requiring an opioid) might be the equivalent of 1 mg of hydromorphone at a time (the equivalent of one 30 mg codeine-containing combination tablet).
When a patient begins taking an opioid, it should be given on an as-needed (PRN) basis, until the need for a standing dose is established. The frequency of PRN dosing is based on the time to maximal effect of the drug (onset of action) and depends on the route ( Table 3 ). Traditionally, PRN dosing has been ordered every 4-6 hours; however, there is a risk that the patient may require more medication and remain in pain until the next dose can be given.
When monitoring of PRN dosing reveals a regular need for opioids, a standing dose should be calculated based on the cumulative dose of the preceeding 24 hours. The interval for standing opioids is every 4 hours, based on the kinetics of their metabolism. The PRN dose should be roughly 10% of the total daily dose. In cases where the regular dose is quite low (such as 0.5 or 1 mg of hydromorphone), the PRN dose can be the same as the standing dose. Periodically, the prescriber should calculate the cumulative daily dose to determine whether the standing dose needs to be increased.
When a stable standing dose is established, a long-acting (slow-release) formulation can be substituted. For instance, a 15 mg capsule of slow-release morphine every 12 hours can replace 5 mg of immediate-release morphine taken every 4 hours. The calculation of breakthrough (PRN) dosing remains the same. One advantage of long-acting opioids is that they can improve compliance by increasing convenience. Another is that the continuous release avoids the peaks and troughs of the immediate-release dosing, to which older adults may be sensitive.
Initial prescription of long-acting opioids for opioid-naïve patients may seem to be a time-saving measure, but substantial risks may be incurred if a stable dose is not established first. For instance, if too many pills are accidentally ingested, the danger to the patient and need for monitoring extend for 12 hours instead of 4. For this reason, long-acting formulations are contraindicated for patients who have widely fluctuating pain levels or for whom a stable 24-hour dose has not yet been established.
Geriatrics and Aging. 2009;12(1):48-52. © 2009 1453987 Ontario, Ltd.
Cite this: Prescribing Opioids to Older Adults: A Guide to Choosing and Switching Among Them - Medscape - Jan 01, 2009.