Pharmacokinetics and anti-inflammatory effect of naproxen in rats with acute and subacute spinal cord injury

Previous reports have warned about the influence of spinal cord injury (SCI) on the pharmacokinetics of various drugs. However, the role of SCI in the efficacy and safety of pharmacotherapy remains unknown. Thereby, our aim was to explore the role of SCI on pharmacokinetics and anti-inflammatory effect of naproxen in response to a local inflammatory challenge. Rats received a severe contusive SCI at T9 or sham injury. Pharmacokinetics of a single intravenous dose of naproxen (10 mg kg(-1)) was studied at days 1 and 15 post-surgery. For the anti-inflammatory assessment, carrageenan was subcutaneously injected in forelimb and hindlimb paws at the same post-surgery periods, and naproxen efficacy was evaluated measuring paw swelling. Plasma protein concentrations and body weight changes were also determined. Plasma naproxen levels and pharmacokinetic parameters were unchanged by acute injury, but subacute injury generated alterations in volume of distribution, clearance, and bioavailability, resulting in significantly reduced plasma naproxen concentrations, in the absence of changes in plasma proteins. Assessment of naproxen anti-inflammatory activity during the acute stage of injury could not be determined because of carrageenan failure to elicit swelling. During the subacute stage, naproxen anti-inflammatory effect on forelimbs (above injury) was similar to that observed in sham-injured animals, while it was almost absent in paralyzed hindlimbs. Under conditions of SCI and peripheral inflammation, pharmacokinetics and anti-inflammatory activity of naproxen vary according to post-injury timing and neurological status of the assessed region.