Oral opioid administration and hyperalgesia in patients with cancer or chronic nonmalignant pain

Aims: Previous research has reported on reduced paw withdrawal latencies to heat and mechanical stimuli after parenteral administration of opioids in animals and on increased pain sensitivity in humans subsequent to postoperative infusions of short-acting opioids or in drug addicts. The aim of the present study was to explore the possibility that oral opioid treated patients with cancer-related or chronic non-malignant pain differ in their pain sensitivity from patients treated with non-opioid analgesics. Methods: The study population consisted of 224 patients, including 142 in the opioid-treated group and 82 in the non-opioid-treated group. Pain thresholds for punctuate measured by von Frey filaments (g), mechanical pressure measured by pressure algometer (mmHg), heat stimuli measured by quantitative sensory testing (°C), as well as suprathreshold tonic heat pain intensity (46.5 °C for 1 min) measured by 0-10 numerical pain scale (NPS) were obtained at a nonpainful site (thenar eminence) in all patients. Results: No differences between the groups were found for gender, age, duration of pain, or duration of treatment (independent variables). No significant differences between the groups were found in punctuate (difference = 17.0 g (95% CI -8.8, 42.8), P = 0.19), pressure (2.2 mmHg (-28.7, 33.2), P = 0.89) and heat (-0.3 °C (-1.5, 0.9), P = 0.70) pain thresholds, or in suprathreshold heat pain intensity (difference between maximal pain intensities -0.4 NPS units (95% CI -1.2, 0.4), P = 0.31). Pearson correlations within the opioid-treated group failed to show significant relationships between any of the independent variables and the outcome measures. A further comparison of the outcomes between the 'weak' opioid-treated subgroup and the 'strong' opioid-treated subgroup again revealed insignificant results. Conclusions: These results suggest that the administration of 'commonly used' dosages of oral opioids does not result in abnormal pain sensitivity beyond that of patients receiving non-opioid analgesia.