Those with persistent nausea and vomiting.
Those with severe dysphagia or swallowing disorders.
Those with delirium, confusion, stupor, or other mental status changes that make oral administration contraindicated because of concerns about pulmonary aspiration in an unprotected airway.
Those on high doses of oral medications necessitating numerous tablets.
Those who experience undesirable side effects in relation to each dose of an "as-needed" medication.
Those who require rapid incremental doses of analgesia.
The benefits of opioid infusions, compared with those of intermittent "as-needed" doses by intramuscular or subcutaneous injection, include less pain on injection, fewer delays awaiting preparation and administration of medication, and improved effectiveness (Bruera, Benneis, and MacDonald, 1987; Portenoy, 1986, 1987). The intravenous route provides the most rapid onset of analgesia, but the duration of analgesia after a boles dose is shorter than with other routes.
A continuous intravenous infusion provides the most consistent level of analgesia and is easily accomplished for patients who have permanent intravenous access for other purposes such as hydration, alimentation, chemotherapy, or antibiotic administration. If intravenous access is not available or desirable, continuous subcutaneous opioid infusion offers a practical alternative in the hospital and home. The subcutaneous administration of opioids provides levels in blood comparable to those with intravenous doses; therefore, the intravenous dose recommendations can be used (Table 9and Table 10) (Moulin, Kreeft, Murray-Parsons, et al., 1991).
Intraspinal drug delivery systems
General comments and cautions regarding the use of opioid analgesics
Drugs and routes of administration not recommended for treatment of cancer pain