Opiates and Respiratory Function in Advanced Cancer
Oral administration of opiates is the preferred method of relieving chronic pain in advanced cancer. Morphine, methadone and diamorphine (heroin) are the main drugs used for severe pain. Saunders (1979, personal communication) and Mount (1980) reported that respiratory depression in such patients is uncommon when oral morphine (in aqueous solution) is given 4-hourly in individually determined doses, titrated against the patient’s level of pain. These reports were surprising in view of the known effect of opiates on respiratory function (Bellville et al. 1968) and the clinical condition of the patient population in question. Oral morphine is known to provide effective pain relief in up to 95% of cancer patients (Mount 1980) despite low relative bioavailability (Brunk and Delle 1974) compared with parenteral administration. It is likely too that oral administration is associated with lower peaks and less rapid change in morphine plasma levels. Examination of the literature on the effects of opiates on respiratory function (Murray and Grant 1966) reveals that studies have been largely conducted on surgically treated patients following parenteral administration (Rigg 1978) of opiates. The methodology employed has not always had direct clinical relevance, nor have the impairments in respiratory function demonstrated clinical significance (Betcher and Barber 1966).
KeywordsRespiratory Function Parenteral Administration Oral Morphine Morphine Equivalent Respiratory Tract Disease
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