Opioids are used in clinical practice for sedation,
anesthesia, and analgesia. Their effects depend on their pharmacokinetic and pharmacodynamic characteristics. The liver is the major site for the biotransformation of most
opioids. The major metabolic pathway is oxidation. Metabolism influences distribution, clearance, onset, and offset of
opioid drugs. Action also depends on the coupling of
opioids with the class of receptors involved and on localization of specific receptors. Three major types of
opioid receptors, designated as mu, delta, and kappa, present in the central nervous system, are coupled to
G proteins and inhibit
adenylyl cyclase.
Down's syndrome is a congenital condition characterized by
mental retardation and particular physical features. Neurotransmission alterations are important. Alteration in the concentration of
opioids in the cortex of these patients has been demonstrated. Neurobiological abnormalities and, in some, abnormalities in the neurotransmission systems, anxiety, and, in particular, nociception all suggest that structural and functional alterations of
opioid receptors may be present. A clear knowledge of these
multiple abnormalities is essential for skillful management of the
perioperative period and for a good outcome for patients with
Down's syndrome.