Suramin: development of a population pharmacokinetic model and its use with intermittent short infusions to control plasma drug concentration in patients with prostate cancer.

PURPOSE

This study aimed to (1) develop a population pharmacokinetic model for suramin; (2) use Bayesian methods to assess suramin pharmacokinetics in individual patients; (3) use individual patients' pharmacokinetic parameter estimates to individualize suramin dose and schedule and maintain plasma suramin concentrations within predetermined target ranges; and (4) assess the feasibility of outpatient administration of suramin by intermittent, short infusions.

METHODS

Plasma suramin concentrations were measured by high-performance liquid chromatography (HPLC), and compartmental pharmacokinetic models were fit using a Bayesian algorithm. Population pharmacokinetic models were developed using an iterative two-stage approach. Estimates of each patient's central-compartment volume were used to calculate suramin dosage. Simulation of that patient's suramin clearance was used to predict the time of his next dose. Using this approach, plasma suramin concentration was maintained at between 200 and 300, 175 and 275, 150 and 250, or 100 and 200 microgram/mL in four sequential patient cohorts. The ability of two- and three-compartment, open, linear models to fit the pharmacokinetic data was compared. Population pharmacokinetic parameters were estimated, using both two- and three-compartment structural models in 69 hormone-refractory prostate cancer patients.

RESULTS

Target plasma suramin concentrations in individual patients were rapidly achieved. Concentrations were maintained within desired ranges for > or = 85% of treatment duration in all cohorts. A three-compartment, open, linear model described suramin pharmacokinetics better than did a two-compartment, open, linear model. Population pharmacokinetic estimates generated for two- and three-compartment pharmacokinetic models demonstrated modest interpatient pharmacokinetic variability and the long terminal half-life of suramin.

CONCLUSION

Suramin can be administered by intermittent short infusion. Adaptive-control-with-feedback dosing facilitated precise control of plasma suramin concentrations and allowed a number of different concentration ranges to be studied. This approach is expensive and labor-intensive. Although we have demonstrated the ability to control drug exposure, simpler dosing schedules require critical evaluation. Population pharmacokinetic parameters generated in men with hormone-refractory prostate cancer will facilitate rational design of such schedules.