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Etanercept Has Similar Pharmacokinetics In Ankylosing Spondylitis As In Rheumatoid Arthritis: Presented at ACCP

By Mike Fillon

TAMPA, FL -- October 6, 2003 -- According to a new study, etanercept may benefit ankylosing spondylitis patients as much as those with rheumatoid arthritis. The poster study was presented here on September 21^st at the 32^nd Annual Meeting of the American College of Clinical Pharmacology (ACCP).

Ankylosing spondylitis, or AS, is a chronic inflammatory disease characterised by axial skeletal ankylosis, inflammation at the insertions of tendons and occasionally peripheral arthritis. It occurs primarily in men and produces pain and stiffness due to inflammation of the sacroiliac, intervertibral and costovertebral joints.

In the multicentre, double-blind, parallel, placebo-controlled randomised study, 43 eligible AS patients received 25 mg etanercept or placebo twice weekly for 12 weeks. Serum samples were collected at weeks four and 12. The median age of the subjects was 45 years, and their median body weight was 75 kg. Most of the subjects were male (79%), and 93% were Caucasian.

A final covariate population pharmacokinetic (PK) model was developed based on the etanercept data from 265 rheumatoid arthritis patients and healthy subjects who received either intravenous or subcutaneous etanercept in 10 previous clinical studies. This model was used to predict the Bayesian-estimated etanercept PK parameters in AS patients from the current trial.

"Based on the assumption that the AS disease state would not result in significantly different PK from those in patients with RA [rheumatoid arthritis]," said lead researcher Honghui Zhou, PhD, "the current data set was merged with the data used to obtain post hoc estimates of PK parameters of etanercept in AS patients. Whether or not the presence of AS had significant impact on the PK parameters of etanercept was tested in the model."

No improvement in objective function value (OFV) was observed when AS was incorporated, which, according to Dr. Zhou, suggested no significant difference was expected in PK between patients with rheumatoid arthritis and those with AS. Based on a typical 45 year old 75 kg man, the mean Bayesian-predicted etanercept clearance in AS patients was estimated to be 0.072 L/h, and the steady-state trough concentration was estimated to be 2004 ng/mL. For rheumatoid arthritis patients, the clearance was 0.066 L/h and steady-state trough concentration was and 2069 ng/mL.

Funding for the study was provided by Wyeth Research, Collegeville, Pennsylvania.


[Study title: Pharmcokinetics Of Etanercept in Ankylosing Spondylitis Patients: A Population-Based Investigation.]

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