The effect of hyperlipidemia on therapeutic drug assays.

Hyperlipidemia interferes with spectrophotometric assays of a number of analytes. No interference was found in the assay of gentamicin, phenytoin, or phenobarbital due to turbidity in levels of triglyceride less than or equal to 2,000 mg/dl with the Abbott TDx or Syva enzyme multiplied immunoassay (EMIT) methods. There is no evidence that lipophilic drugs partition into the lipid phase in severely hyperlipidemic serum. No assay errors due to turbidity or partitioning of phenobarbital in the lipid of serum with a triglyceride concentration of 10,000 mg/dl were found, nor were changes seen in free phenytoin distribution due to hyperlipidemia.