Modified Irwin Test (rat)

The modified Irwin test or Functional Observation Battery (FOB) assay is used to identify potential toxic and therapeutic effects of a test compound by examining its effect on behavior and physiologic functions of the treated animals. Before testing, animals are handled over two days to familiarize them with the experimenter(s). Animals are visually evaluated by two independent observers for impaired autonomic (e.g., salivation, porphyrin), neuromuscular (e.g., ataxia, tremors), sensorimotor (e.g., hyperesthesia, loss of righting reflex), and behavioral (e.g., vocalizations, grooming) function at multiple timepoints (e.g., 0.25, 0.5, 1, 2, and 4 hours) following administration of a single dose of the drug. Animals are also evaluated 24 hours post-compound administration to assess recovery from any impairment seen the previous day. A numerical score is assigned for the severity, from normal to extreme, for each functional parameter. Usually four animals/dose are used in the test and in addition to the vehicle control, an unblinded control is used to establish baseline activity and to account for environmental variables that may affect the behaviors of the healthy animal.


Mathiasen JR, Moser VC. The Irwin test and functional observational battery (FOB) for assessing the effects of compounds on behavior, physiology, and safety pharmacology in rodents. Curr Protoc Pharmacol. 2018;83:e43