Serum SH reactivity: A simple assessment of D-penicillamine absorption?

A simple biochemical technique is described, which reflects the levels of D-penicillamine in the serum of patients with rheumatoid arthritis treated with this drug. The assay is based on the ability of D-penicillamine to stimulate the rate of reaction between serum sulphydryl groups and Ellman's reagent (DTNB). Using this technique, co-administration of oral ferrous sulphate has been shown to block D-penicillamine absorption. The assay provides useful information for the evaluation of a patient's clinical response to D-penicillamine treatment.