Equianalgesic doses may differ from oral and parenteral doses because of pharmacokinetic differences. A short-acting opioid should normally be used for initial therapy of moderate to severe pain. Transdermal fentanyl dosage is not calculated as equianalgesic to a single morphine dosage. See the package insert for dosing calculations. Doses above 25 mcg should not be used in opioid-naive patients.
Doses listed are for brief therapy.
Switch to another opioid for long-term therapy. Codeine doses above 65 mg often are not appropriate because of diminishing incremental analgesia with increasing doses but continually increasing nausea, constipation, and other side effects. Because there is not complete cross-tolerance among these drugs, it is usually necessary to use a lower than equianalgesic dose when changing drugs and to retitrate to response. PDQ statements exist for a number of topics. Please consult the PDQ Index .