A 35-year-old woman undergoes elective total abdominal hysterectomy under general anesthesia. Postoperatively, she is prescribed intravenous patient-controlled analgesia (PCA) with morphine. The PCA pump is programmed with a bolus dose of 2 mg, lockout interval of 10 minutes, and a 4-hour maximum cumulative dose of 30 mg. On postoperative day 1, she reports inadequate pain relief despite requesting analgesia 18 times in 4 hours (achieving only 12 mg of the maximum allowed dose). Her vital signs are stable, respiratory rate 16/min, SpO₂ 98% on room air, and she is alert and oriented. Which of the following adjustments would be most appropriate?