Background: Respiratory depression is the opioid adverse effect feared most by physicians. This may hinder adequate dosing in cancer pain. The study was conducted to examine the respiratory function of patients with advanced cancer receiving significant doses (>100 mg/24 h) of oral morphine.
Patients and methods: Consecutive pain-free hospice inpatients with advanced cancer receiving high-dose immediate-release oral morphine were evaluated. A single assessment of respiratory rate (RR), arterial blood gas (ABG), and peak flow rate (PFR) was made at assumed morphine steady state. Venous blood was drawn for a trough morphine plasma level.
Results: Of 31 patients who consented to examination, 20 completed the study assessment; 12 had chronic bronchitis. The median morphine dose was 30 mg 4-hourly (range 20 to 90 mg). Only one patient had evidence of ventilatory impairment.
Conclusions: Morphine does not commonly cause chronic ventilatory impairment when given in this way in this population even in the presence of pre-existing or concurrent respiratory disease. Oral morphine given repeatedly in individualized dosage is a safe and efficacious analgesic in the majority of those with advanced cancer.