A drug fever is the occurrence of a fever whose onset correlates closely to the taking of medication and spontaneously resolves soon after the responsible agent is discontinued. It is thought to be more common than is realized and is often misdiagnosed as something else, frequently an infection, often in the context of a pyrexia of unknown origin. It is usually a diagnosis of exclusion, clinical recognition finally arising when the temporal relationship between the onset of the pyrexia and usage of the precipitating medication is noted.
The time for the febrile response to appear varies considerably, typically 7-10 days post-administration of the drug, with a quick cessation of the increased body temperature soon after the agent has been stopped. Early diagnosis is favorable as these patients can be subjected to a whole panoply of resource-intensive tests, including multimodality, whole body imaging, frequently entailing a significant ionizing radiation dose. Unfortunately at times patients may also undergo futile and expensive therapeutic interventions.