Delayed increase in serum acetaminophen concentration after ingestion of a combination medications: a case report.

Acetaminophen is absorbed rapidly after oral intake, and serum concentration peaks within 4 hours. The Rumack-Matthew (RM) nomogram is widely used to identify the potential risk of liver dysfunction. However, the RM nomogram was intended for use only when a single agent was ingested. We report the case of a patient with overdose ingestion of an over-the-counter combination cold medication that contained acetaminophen, where the patient's serum concentration increased over time. Over-the-counter combination cold medications are designed to relieve cold symptoms. However, the possibility that other agents that were present in the drug may change gastrointestinal kinetics should also be considered. The risk of liver dysfunction cannot be accurately determined from a single serum acetaminophen concentration measurement. Because of the risk of a delayed increase in the serum acetaminophen concentration, monitoring for liver dysfunction and developing a treatment strategy that includes N-acetylcysteine are required. This case report is targeted to clinical physicians who treat patients with acetaminophen overdose resulting from ingestion of multiple agents, and it reviews points of consideration when using the RM nomogram in acute intoxication.