Relationship between morphine rescue dose and respiratory safety during breakthrough cancer pain in lung cancer patients treated with high-dose opioids.

To investigate the efficacy and safety of different morphine rescue doses for breakthrough cancer pain (BTcP) in lung cancer patients receiving high-dose opioid therapy. Between August 2023 and January 2025, 150 hospitalized patients with at least one documented BTcP episode were retrospectively assigned to three groups based on their initial rescue dose: a fixed 10 mg dose (Group A, n=47), 5% of their daily opioid dose (Group B, n=62), and 10% of their daily opioid dose (Group C, n=41). Pain intensity (numerical rating scale, NRS) and vital signs were recorded at baseline and up to 180 minutes after administration. The primary outcome was the proportion of patients with a ≥30% or ≥50% reduction in NRS at 60 minutes; safety outcomes included a ≥5% reduction in respiratory rate or oxygen saturation (SpO). The pain relief rates in groups B and C were significantly higher (≥30% reduction: 95.2% and 95.1%, respectively, compared to 68.1% in group A, P<0.001; ≥50% reduction: 83.9% and 90.2%, respectively, compared to 57.4% in group A, P<0.001), and the onset of relief was faster. Multivariate logistic regression confirmed that proportional dosing was an independent predictor of successful analgesia (adjusted odds ratio (aOR) for ≥50% relief: 4.63 in group B and 8.00 in group C, both P=0.001). No significant differences were observed among the three dosage groups in terms of respiratory rate or SpO reduction (both P>0.05). However, brain metastasis (65.52% vs. 4.96%, P<0.001) and background opioid dose >720 mg/day (35.14% vs. 14.16%, P=0.005) were significant risk factors for respiratory depression. For lung cancer patients receiving high-dose opioid therapy, a rescue dose of 5%-10% of the daily opioid dose provides superior analgesia compared with a fixed dose of 10 mg, and has acceptable respiratory safety in patients without brain metastasis.