Management of Acute Pain in Children: Pharmacologic

Oral opioids

Codeine is available in an elixir form and is, therefore, the most commonly administered oral opioid in young children. It is often given in combination with acetaminophen but a safe dosage for children under 3 has not be established. In fact, this combined form is not only more effective than the single drug alone, but also may, unlike some opioids in the United States, be prescribed over the phone. The commercially available acetaminophen/ codeine elixir contains the two drugs in a 10:1 ratio (acetaminophen 120 mg with codeine 12 mg in each 5 ml). When given separately, these two drugs are generally given in a 20:1 to 30:1 ratio (i.e.,10 to 15 mg/kg acetaminophen and 0.5 mg/kg codeine). Therefore, additional acetaminophen is often prescribed to improve analgesia. Codeine's analgesic effects derive from its metabolic conversion to morphine. A significant fraction of the general population (ranging from 3% to 14% in different ethnic groups) lacks the enzyme that O-demethylates codeine to generate morphine.³⁸ Thus, if a child fails to show an analgesic effect from standard dosing of codeine, consideration should be given to substituting a different opioid, in order to circumvent this pharmacogenetic barrier. Dosage guidelines for codeine and other opioid analgesics can be found in the table.²⁷ Methadone is also available as an oral elixir and, because of its long half life, can provide excellent analgesia even with infrequent dosing. It has an oral bioavailability of 60% to 90% so dosage ranges for oral and intravenous administration are similar. Due to slow and variable clearance, methadone requires careful assessment and titrated to prevent delayed sedation.

Dosing Guidelines for Commonly Used Opioid Analgesics in Infants and Children