LASSBio-873

Route-of-administration selection in mammals is a pharmacokinetic, pharmacodynamic, formulation, animal-welfare, and translational decision, not a default technical choice. The selected route should match the study goal: intravenous dosing is most useful when complete systemic exposure and rapid onset are required, oral dosing is most translational for orally intended medicines but is affected by absorption and first-pass metabolism, subcutaneous or intramuscular dosing can provide slower systemic exposure, and intraperitoneal dosing can be useful in rodent proof-of-concept studies but may have limited clinical translation. Published route-comparison studies show that the same compound can produce different exposure, onset, bioavailability, tissue distribution, and tolerability depending on route; therefore, route choice should be supported by pilot pharmacokinetic or pharmacodynamic evidence when the literature is insufficient. Unresolved questions include how to standardize route sel

The formalin-induced paw inflammation/nociceptive test is a chemical persistent pain model in rodents in which subcutaneous injection of formalin into the hind paw produces spontaneous nocifensive behaviors such as flinching and licking. The response is classically biphasic, consisting of an early acute phase (Phase I) reflecting direct activation of peripheral nociceptors (particularly C-fiber afferents), followed by a later prolonged phase (Phase II) associated with central sensitization in the spinal dorsal horn driven by sustained afferent input and inflammatory signaling. This model is widely used to evaluate analgesic and anti-inflammatory interventions because it captures both peripheral nociception and central sensitization processes within a single assay system.