BACKGROUND: Nitroglycerin (NTG) has been shown to be a useful adjunct for pain treatment without increasing adverse side effects. The effects of NTG on postoperative morphine consumption after knee replacement were evaluated.METHODS: After undergoing total knee replacement, patients receiving patient-controlled morphine analgesia were randomly assigned to receive either an NTG or a placebo patch. The blinded investigator assessed each patient using a visual analogue scale at rest and while moving, as well as the patient’s morphine requirements, sedation score, sleep quality, nausea and vomiting, vital signs and postoperative bleeding.RESULTS: Two of the patients in the NTG group suffered postoperative myocardial infarctions after removal of the patch. Because of these two serious adverse effects, the study was stopped prematurely. In the subset of patients studied, NTG conferred no advantage over placebo in pain control (visual analogue scale at rest or during movement) and in satisfaction scores.CONCLUSIONS: The use of NTG patches conferred no advantage over the use of placebo in patients receiving patient-controlled morphine analgesia after total knee replacement. Two myocardial infarcts occurred in this group. Therefore, the safety of postoperative NTG patch use for pain control must be questioned.