Lack of inhibition of purine nucleoside phosphorylase and adenosine deaminase in patients treated with azathioprine.

Deficiency of the purine salvage enzymes purine nucleoside phosphorylase (PNP) and adenosine deaminase (ADA) are known causes of immunodeficiency. Evidence for inhibition of these enzymes was sought in 16 patients on azathioprine therapy by testing for deoxyguanosine (PNP deficiency) and deoxyadenosine (ADA deficiency) in urine using a novel phosphorescence method. These abnormal nucleosides were not found in urine of azathioprine treated patients or in 30 normal controls but were easily detected in urine from proven cases of PNP and ADA deficiency suggesting lack of in vivo inhibition of PNP and ADA by azathioprine.