PROPRIETARY INFORMATION
CONFIDENTIAL MATERIAL
Not for Customer Distribution Assays/Reagents
AEROSET
®
System Troubleshooting Guide 91
94816-107—November 2004
Why is Phenytoin compared to
high-performance liquid chromatography
(HPLC) methodology, but not the other TDM
assays?
HPLC is commonly considered the gold
standard in immunoassay. Phenytoin is
extensively metabolized and the major
pathway is para-hydroxylation of the phenyl
ring. The resulting metabolite,
p-hydroxyphenytoin (HPPH) is inactive and
present largely as a glucuronide conjugate
(HPPG). Both metabolites are structurally
similar to phenytoin, and may interfere with
immunoassays. This is especially true in renal
insufficiency, where HPPG clearance is
decreased and plasma levels of HPPG may be
increased 10 times the phenytoin
concentration.
Frequently Asked Questions (FAQ) (Continued)
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