Naproxen (NPX) is a frequently used nonsteroidal anti-inflammatory drug (NSAID) for rheumatoid arthritis (RA). Lack of quantitative information about the drug exposure-response relationship has resulted in empirical dosage regimens for use of NPX in RA. Few studies included sex as a factor, although RA predominates in women. A pharmacokinetic, pharmacodynamic, and disease progression (PK/PD/DIS) model described the anti-inflammatory effects of NPX in collagen-induced arthritic (CIA) male and female rats. Three groups of rats were included for each sex: healthy animals, CIA controls, and CIA rats given 50 mg/kg single dose NPX intraperitoneally (IP). Paw volumes of healthy rats indicated natural growth and disease status was measured by paw edema. An innovative minimal physiologically based pharmacokinetic (mPBPK) model incorporating nonlinear albumin binding of NPX in both plasma and interstitial fluid (ISF) was applied. Arthritic rats exhibited lower plasma and ISF albumin concentrations and reduced clearances of unbound drug to explain PK profiles. The unbound ISF NPX concentrations predicted by the mPBPK model were used as the driving force for pharmacological effects of NPX. A logistic growth function accounting for natural paw growth and an indirect response model for paw edema and drug effects (inhibition of kin) was applied. Female rats showed higher incidence of CIA, earlier disease onset, and more severe symptoms. NPX had stronger effects in males owing to higher unbound ISF NPX concentrations and lower IC50 values. The model described the PK, unbound NPX in ISF, time-course of anti-inflammatory effects, and sex differences in CIA rats.
- The American Society for Pharmacology and Experimental Therapeutics