Treating the pain of ambulatory surgical patients can be problematic. Concerns over the safety of analgesics often lead physicians to use small doses of these drugs with consequent sacrifices in efficacy. In particular, the respiratory depression, together with the prevalent nausea and vomiting, caused by opioids severely limit their value in this setting. However, other groups of analgesics are limited in terms of strength and duration of effect. One established approach to circumventing these problems is to use combinations of analgesics in single formulations. However, until recently, such combination formulations of analgesics have generally proved to be disappointing in practice, especially in treating moderate-to-severe pain.