[Use of opioids in the elderly -- pharmacokinetic and pharmacodynamic considerations].

Perioperative management of geriatric patients is becoming an important component in anaesthetic practice in the 21st century. This phenomenon is due to the fact that people aged 65 and over are the segment with the fastest growing population. Thus, it is estimated that by the year 2025 20 % of the population in the western hemisphere will be > 65 years of age. Currently, elderly patients comprise one-third of all operations, and one out of two patients older than 65 years of age will undergo an operation in their lifetime. The dramatic change in demographics of surgical patients will have a tremendous impact on the use of anaesthetics. Older patients facing surgery can generally be expected to be a more complex case than their younger counterparts. They have more systemic diseases (e. g. cardiac, pulmonary, endocrine), and usually these diseases have advanced to more serious stages. These patients may suffer disability, both physical and mental, and may show differences in the pharmacokinetic as well as the pharmacodynamic of compounds such as opioids. While neuronal numbers, dendrites and synapses decline with age and the ventricular volume triples, cerebral circulation is similar to young adults, although there is a reduction in cerebral blood flow (CBF). This is because of the lower unit weight, lower CBF and CMRO (2), which are tightly coupled in aging where autoregulation is preserved. However, because of a decline in dopaminergic, serotonergic, cholinergic and GABAergic transmitters, anticholinergic compounds (atropine, scopolamine) as well as some anaesthetics such as ketamine, benzodiazepines or even propofol may produce delirium and/or an increase in efficacy when given together with opioids. Therefore it is mandatory to consider a pharmacologic interaction with a potentiation and/or an addition in effects of other drugs when judging the net action of opioids in the elderly. Physicians and nurses treating geriatric patients tend to have an unfounded level of fear of complications associated with treating perioperative pain. Although it is known that inadequate analgesia may delay recovery, the treatment of perioperative pain in the geriatric patient remains inadequate, even relative to younger patients. It is well established that there is increased responsiveness to the effects of opioids in the elderly. This may result in an increased risk of respiratory depression, while especially the elderly female patient demonstrates an increase in the duration of effects, but the risk of nausea is not augmented. Increased sensitivity of older patients to systemic opioids mostly involves pharmacokinetic factors such as a higher proportion of unbound and active substances as well as changes in drug redistribution. Because of a 40 % reduction in stroke volume in the elderly, there is a protracted redistribution of opioids to the liver. This results in a prolonged metabolisation, a lesser inactivation over time followed by an increase in duration of effects, mainly impairment of respiration. To a much lesser extent, pharmacodynamic factors with an increased response at opioid receptor sites have to be considered. Although the mechanisms causing differences of opioid action in the elderly may be complex, the clinical implications are not. They include slow titration of opioids to allow for long circulation times, lower total doses because of increased sensitivity, and anticipation of a longer duration of action because of reduced clearance. Since elderly patients present multimorbidity, therapy of chronic pain has to be considered in the light of multidrug intake, which, due to interaction, results in marked side-effects, and a prolonged duration of action. Those opioids should be used which, due to their pharmacokinetic properties, have a reduced volume of distribution, present a low plasma protein binding and finally result in the formation of no pharmacologically active metabolites.