Alertness, cognition and morphine in patients with advanced cancer

Abstract

Oral morphine is widely used for pain control in advanced cancer. Amongst the adverse effects of morphine, sedation is often expected by cancer patients and their families (1). However, the fear of excessive sedation from oral morphine is probably exaggerated (2). Clinical experience suggests that sedation occurs in approximately 20% of patients, and tolerance develops to it within days on the same dose (3). Some patients, although no longer drowsy, complain of difficulty in concentrating, but the incidence of this effect, its extent and the speed of tolerance to it are not known. The main studies looking at alertness and cognitive function in cancer patients are shown in Table 1. It will be clear from this table that the effects of morphine are often complex and variable, with some tests showing marked impairment of function whilst others show no detriment at all. The assessment of cognitive function in these patients is confounded by a number of factors (Table 2). First is the difficulty in measuring psychological variables perse. This will be covered in greater detail below. Measurements in these patients will also be affected by other drugs that the patients may be taking. Indeed, in patients thought to be suffering from troublesome sedation, all medications that they are taking should be reviewed, e.g. hypnotics and anti-emetics with central effects. Other important agents include neuroleptic drugs (41, non-steroidal anti-inflammatory drugs (51, tricyclic anti-depressants and anti-convulsants (6,7). Advanced cancer by its very nature is often a systemic disease which in turn may directly affect psychomotor functions (e.g. brain metastases), or more indirectly through biochemical disturbances from hypercalcaemia and renaI/hepatic impairment, or even as a paraneoplastic effect. Some subjects will also have marked diurnal variations in cognitive abilities (so called ‘owls & larks’). The influence of the patient’s personality and motivation may also be