Opioids are the mainstay of treatment for moderate to severe pain.  However, opioid therapy in the elderly is often associated with significant morbidity because of excessive ventilatory depression.  The large amount of interindividual variability in opioid dose–response relationships makes it difficult to individualise the dose and dosing interval to provide safe and effective analgesia.  By examining how aging affects the pharmacokinetics (PK) and pharmacodynamics (PD) of opioids, it is possible to provide a rational basis for age adjustment in opioid dosing.

Authors conclude that 'simulations with PK–PD models confirm the clinical impression that elderly patients need a reduction in opioid dose without a change in dosing interval, although this has not been tested in clinical trials.  Compiling a library of PK–PD models for other opioids and using a reliable biomarker of clinical effect could lead to individualisation of opioid therapy at the bedside.  PK–PD simulations such as these can help guide the candidate dosing regimens that are to be evaluated in future clinical trials.'