Prospective evaluation of a model for predicting etoposide plasma protein binding in cancer patients.
Etoposide protein binding in cancer patients is variable and has been related mathematically to a linear model consisting of serum albumin and total bilirubin [percentage unbound = (1.4 x total bilirubin) - (6.8 x albumin) + 34.4]. In this prospective evaluation of the model, plasma samples were obtained following the administration of etoposide in 31 patients, and the unbound percentage (% unbound) of etoposide in plasma was determined by equilibrium dialysis. The mean measured % unbound was 15.3 +/- 11.6 (SD), and the mean model predicted % unbound was 16.7 +/- 10.1. The relation between predicted and measured etoposide % unbound was highly correlated (r2 = 0.92, P = 0.001). The model was precise but with a slight bias toward overpredicting % unbound (mean prediction error, 1.36%; 95% confidence interval, 0.09 to 2.6%). In patients with abnormal total bilirubin (i.e., greater than 1.5 mg/dl) or with hypoalbuminemia (i.e., less than 3.3 g/dl), the model was both precise and unbiased. These results demonstrate that etoposide % unbound can be predicted using serum albumin and total bilirubin. This model should be useful in prospectively identifying patients at increased risk of experiencing altered pharmacological effects due to altered protein binding of etoposide.
Department of Clinical Pharmacy, University of Tennessee, Memphis 31863.
C F
CF
Stewart
R A
RA
Fleming
S G
SG
Arbuck
W E
WE
Evans
D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001663:Bilirubin / Q000097:blood; D001798:Blood Proteins / Q000378:metabolism*; D005047:Etoposide / Q000097:blood*; D005069:Evaluation Studies as Topic; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D008954:Models, Biological; D009369:Neoplasms / Q000097:blood* / Q000188:drug therapy; D011446:Prospective Studies; D011485:Protein Binding; D012709:Serum Albumin / Q000378:metabolism
D001798:Blood Proteins; D012709:Serum Albumin; D005047:Etoposide; D001663:Bilirubin