RESUMO
The effects of temperature, albumin, pH and Ca2+ on the binding of phenobarbitone and phenytoin to human serum albumin in buffer have been investigated using equilibrium dialysis. The free fractions of both anticonvulsants were much increased by raising the temperature. Lower free fractions were observed by increasing the albumin concentration from 5-8 g litre-1 and by raising pH from 6 to 9. No significant effect on the free fractions was observed by changing (at pH 7.4) the Ca2+ concentration from 0 to 5 mM. The observed differences in free fractions at 37 degrees C, as determined in phosphate, borate and Krebs-Ringer buffer at pH 7.4, indicate that great care is needed in the choice of dialysis fluid for dialysis of clinical samples.
Assuntos
Fenobarbital/sangue , Fenitoína/sangue , Cálcio/sangue , Diálise , Humanos , Concentração de Íons de Hidrogênio , Albumina Sérica/metabolismo , TemperaturaRESUMO
In this study, three techniques for measuring the free fractions of phenobarbital and phenytoin were compared: equilibrium dialysis, ultrafiltration, and the Hummel and Dreyer method for gel permeation chromatography. In their therapeutic range (15-40 and 10-20 mg/L, respectively) the free fractions of phenobarbital and phenytoin were independent of the drug concentrations. Free fractions of phenobarbital as determined by equilibrium dialysis, ultrafiltration, and gel permeation chromatography were 58.7 +/- 1.8, 58.3 +/- 1.5, and 55.1 +/- 1.7%, respectively. Free fractions of phenytoin were 18.1 +/- 1.1, 17.0 +/- 2.1, and 19.4 +/- 1.2%, respectively. On lowering the albumin concentration, a similar increase in the free fractions of both drugs was observed with all three techniques. The results of this study show that all three techniques are suitable for the determination of free fractions of phenobarbital and phenytoin. Moreover, these techniques seem to be suitable for the investigation of physiological factors that may influence albumin drug binding.
