Opioid poisoning classically presents with an altered level of consciousness. The triad of acute toxicity consists of CNS depression, respiratory depression, and constriction of the pupils or “pinpoint pupils.” CNS depression ranges from mild sedation to stupor and coma. Patients are typically hypotensive, hypothermic, bradycardic, and hyporeflexic. Many patients experience central-mediated vomiting. This, coupled with respiratory depression and a diminished gag reflex, places the patient at risk for aspiration pneumonitis. Other respiratory effects may also include bronchospasm from histamine release or from insufflating or inhaling fumes of opioid compounds cut with impurities or adulterants. In massive overdoses, the respiratory toxicity can also cause severe hypoxia, hypercarbia, and acute lung injury.
While miotic or “pinpoint” pupils are a classic opioid-induced clinical finding, mydriasis or pupillary dilation has been described with meperidine, propoxyphene, and diphenoxylate-atropine (Lomotil®) overdoses. With Lomotil® overdose, a two-phase toxicity has been described. Phase I manifests with anticholinergic symptoms such as dry mouth, flushing, and mydriasis, whereas phase II consists of opioid effects causing respiratory and central nervous system depression, with associated miosis.
Less common effects of opioid toxicity include generalized seizure activity following overdose of propoxyphene, meperidine, tramadol,9 fentanyl, or pentazocine. Neonates receiving continuous intravenous morphine can also suffer seizures from toxicity or during acute opioid withdrawal.10
Dermatologic effects include flushing and pruritus secondary to histamine release. Gastrointestinal effects include decreased gut motility and constipation. Finally, medical complications common among chronic users arise from adulterants found in street drugs and the nonsterile practices of injecting drugs. Patients who chronically use opioids intravenously or by “skin popping” can contract bacterial endocarditis, septic pulmonary emboli, skin infections, tetanus, wound botulism, hepatitis, and human immunodeficiency virus infection.