Pharmacokinetics of naproxen in the dog

The pharmacokinetics of naproxen was studied in mongrel dogs. After IV injection of a 5 mg/kg dose, plasma concentrations decreased biexponentially, with an average elimination half-life of 74 hours. The drug was highly protein-bound (greater than 99%) and had a correspondingly low apparent volume of distribution (0.13 L/kg). After naproxen was given orally, absorption was rapid, and the bioavailability ranged between 68% and 100%. With an initial dose of 5 mg/kg given orally, therapeutic plasma concentrations could be maintained by giving 1 daily dose of 1.2 to 2.8 mg/kg.