Opioids are naturally occurring or synthetic drugs that have activity similar to opium or morphine. The term opioid is a broad term and includes both natural and synthetic drugs. The term opiate is more specific and refers only to those drugs derived from natural opium, such as morphine, codeine, and thebaine. A semisynthetic opioid, such as oxycodone, is derived from the chemical modification of an opioid. A synthetic opioid is a xenobiotic, not structurally related to or derived from an opioid that acts at the opioid receptor or produces an opioid-like effect. The term narcotic is derived from the Greek word for stupor and was originally used to describe any drug that could induce sleep. The term has ambiguously been used to describe any drug that binds to opioid receptors or, in law enforcement circles, to any illicit substance. The poppy plant, Papaver somniferum, is the source of opium and its derivatives.

Opioids are used primarily as analgesics. They can also be used as antitussive and antidiarrheal agents. Opioids are available in many formulations and can be taken in many routes: oral, inhalational, parenteral, transdermal, and rectal.

Use or misuse of opioid drugs, prescription and illicit, is responsible for much of the recent increase in poison-related deaths.^1–4 The pediatric population is affected by these trends as demonstrated by increasing hospitalizations, and in some cases death, in nearly all age groups.¹

Neonates can experience lethargy at birth if there was recent maternal opioid use, whether administered during labor or maternal illicit use. The neonate is prone to withdrawal symptoms during the newborn period if the mother was chronically using or abusing opioids during pregnancy.

Toddlers and young children are prone to accidental opioid poisoning in environments where opioid preparations are not appropriately stored out of the reach of the child or if opioids prescribed to children are administered improperly.⁵ Opioid withdrawal symptoms are not often encountered in younger children who have limited or no exposure to chronic opioid therapy.

When caring for adolescents and teenagers who present with signs and symptoms of opioid toxicity, illicit use should be considered. In an attempt at mood elevation, adolescents and teenagers may abuse opioids in various forms: inhalational (smoking), intranasal (snorting), ingestion, or intravenous. In a suicide attempt or accidental overdose, opioid poisoning can be life-threatening. In addition, opioids may have a synergistic effect on mental status depression when combined with substances such as ethanol or benzodiazepines. Conversely, the clinical presentation can present with a mixed pattern if coingestants include sympathomimetic agents such as cocaine or amphetamines. Children who abuse opioids or who use them chronically for analgesia for painful medical conditions are at risk of withdrawal symptoms if the opioids are stopped abruptly or treated clinically with an opioid antagonist such as naloxone.

Opioids produce clinical effects by interacting with specific receptors located throughout the central nervous system, the peripheral nervous system, and the gastrointestinal tract. Endorphins are endogenous substances that have activity at these opioid receptors. Exogenous opioids also work at these receptors. The three main classes of opioid receptors are mu, kappa, and delta.⁶

The mu1 receptor is responsible for supraspinal (brain) analgesia, euphoria, and sedation. The mu2 receptor is responsible for spinal-level analgesia and respiratory depression. There are mu receptors in the medullary cough center and in the gastrointestinal tract, which account for the use of opioids in the treatment of cough and diarrhea. Stimulation of the kappa receptor is responsible for spinal analgesia and miosis. Little is known about the delta receptors, but they may play a role in spinal analgesia, supraspinal analgesia, and cough suppression.⁶

The pharmacokinetics of opiates are dependent upon the specific substance. In general, the pharmacokinetics for morphine and morphine derivatives in children aged 1 to 15 are comparable to adults.⁷ Most immediate-acting opioid preparations are well absorbed from the gastrointestinal tract and peak within 60 to 90 minutes with a duration of effect between 3 and 6 hours. There are many exceptions. For example, fentanyl (non-transdermal preparation) and methadone can have durations of effect of 1 hour and up to 72 hours, respectively.^8,9 Sustained-release opioid products can have delayed onset of effects and prolonged duration of effects. There are other preparations of opioids besides immediate and sustained release. For example, fentanyl is available as a transdermal patch and as a lozenge on a stick (lollipop). See Table 117-1 for commonly prescribed opioid compounds with their generic and trade names.