A nurse is monitoring a client who is receiving morphine IV and amitriptyline PO. Which of the following findings indicates an adverse interaction between the prescribed medications?

A. Diarrhea: Diarrhea is not a typical adverse effect of either morphine or amitriptyline. In fact, both medications are more likely to cause constipation by slowing gastrointestinal motility, making this an unlikely indication of a drug interaction. B. Low-grade fever: A low-grade fever may indicate an underlying infection or inflammatory process but is not a known or expected adverse interaction between morphine and amitriptyline. Neither drug typically affects thermoregulation in this manner. C. Tachypnea: Tachypnea is not a usual result of the interaction between morphine and amitriptyline. Morphine typically causes respiratory depression rather than increased respiratory rate, and amitriptyline has no significant direct effect on respiratory rate. D. Urinary retention: Both morphine and amitriptyline can independently cause urinary retention by reducing detrusor muscle tone and decreasing bladder contractility respectively. When used together, these effects may be compounded, increasing the risk of significant urinary retention.