The action of some
anticonvulsant drugs as the causal agents of attacks of
acute porphyria has been widely documented in the literature. However, little attention has been paid to the effect of these drugs on the urinary excretion of
porphyrins in non-porphyric subjects. In a sample of 82 epileptic patients treated with
phenobarbital (n = 54),
phenytoin (n = 64),
carbamazepine (n = 33), and
valproate (n = 8), the daily doses were expressed according to a drug score that would reflect the capacity of these drugs as enzymatic inducers when administered in polytherapy. A significantly increased urinary excretion of
D-glucaric acid (DGA) and
porphyrins was found in this group of patients (P<0.001), with coproporphyrin being the major fraction in all cases (>60%). Urinary DGA had a highly significant correlation with the drug score (r = 0.783, P<0.001); however, no significant correlations were found between the urinary
porphyrins and DGA (r = 0.005) or the drug score (r = 0.053). Neither was any significant relationship found between the urinary
porphyrins and the serum activity of
5'-nucleotidase (r = 0.066) or the presence of a
cholestasis objectivized through the presence of the
isoform of
gamma-glutamyltransferase with
beta-globulins electrophoretic mobility. However, in a group of 10 patients a significant correlation was found between the urinary excretion of
porphyrins and
beta-N-acetylhexosaminidase (r = 0.790, P<0.01). Therefore, it does not appear that the liver enzyme induction, or even a subclinical
cholestasis, produced by the
antiepileptic drugs administered to these patients may serve to explain the increase in the urinary excretion of
porphyrins. A possible renal origin is proposed for the increase of urinary
porphyrins in these cases.