Isoforms of serum gamma-glutamyltransferase in epileptic patients treated with enzyme-inducing anticonvulsant drugs.
OBJECTIVE
The increase of serum activity of gamma-glutamyltranferase (gammaGT) through the action of enzyme-inducing anticonvulsant drugs has been widely documented; however, the behaviour of its multiple forms and its relationship with the degree of enzyme induction has received little coverage. This subject is the major aim of our paper.


METHODS
An electrophoretic study of the serum gammaGT isoforms was made in 90 adult epileptic patients under chronic treatment with phenobarbital, phenytoin and carbamazepine in polytherapy.


RESULTS
A significant correlation was found (p<0.001) between the drug score and urinary excretion of D-glucaric acid (DGA) (r=0.773), total gammaGT (r=0.382), gammaGT1 (r=0.398) and gammaGT2 (r=0.361). In a group of 11 patients with the gammaGT3 isoforms, considered a sensitive test for cholestasis, serum activities of total gammaGT, gammaGT1, gammaGT2 and 5 -nucleotidase were found that were significantly higher than in the 79 patients without the gammaGT3 isoform (p<0.001); however, for the drug score and excretion of DGA, no significant differences were found, suggesting a similar degree of enzyme induction in both groups of patients.


CONCLUSIONS
The presence of cholestasis, at least biochemically detectable in some of these patients, appears to be a factor of paramount importance when interpreting the effect of enzyme-inducing anticonvulsant drugs on serum gammaGT. This fact may contribute towards explaining its highly varied response to the administration of these drugs.
Tutor-Crespo
María
M
Laboratorio Central, Hospital Clínico Universitario, Santiago de Compostela, Spain.
Hermida
Jesús
J
Tutor
Carlos
C
D000328:Adult; D000927:Anticonvulsants / Q000494:pharmacology* / Q000627:therapeutic use; D002220:Carbamazepine / Q000494:pharmacology / Q000627:therapeutic use; D004827:Epilepsy / Q000097:blood* / Q000188:drug therapy / Q000201:enzymology; D005260:Female; D006801:Humans; D007527:Isoenzymes / Q000097:blood*; D008297:Male; D010634:Phenobarbital / Q000494:pharmacology / Q000627:therapeutic use; D010672:Phenytoin / Q000494:pharmacology / Q000627:therapeutic use; D005723:gamma-Glutamyltransferase / Q000097:blood*
D000927:Anticonvulsants; D007527:Isoenzymes; D002220:Carbamazepine; D010672:Phenytoin; D005723:gamma-Glutamyltransferase; D010634:Phenobarbital