May cause hypotension (use with caution in hypovolemia, cardiovascular disease (including acute myocardial infarction), or drugs which may exaggerate hypotensive effects (including phenothiazines or general anesthetics)). Opioid agonist toxicities. Caution when administering to patients with bradyarrhythmias. Potential for drug dependency exists. Exaggerated elevation of intracranial pressure may occur (use with extreme caution in head injury, intracranial lesions, or elevated intracranial pressure). Caution in morbidly obese patients. Use with caution in the following situations: respiratory disease (hypoxia and/or hypercapnia), chronic obstructive pulmonary disease or other obstructive pulmonary disease, and kyphoscoliosis or other skeletal disorder which may alter respiratory function). Hypotension has occurred in neonates with respiratory distress syndrome. Rapid intravenous infusion may result in skeletal muscle and chest wall rigidity, impaired ventilation, or respiratory distress/arrest.