Evidence of an absorption phase after short intravenous suramin infusions.

Suramin was given as an intravenous infusion to 16 cancer patients in a phase I trial. Individual pharmacokinetic parameters were calculated from a test dose given 1 week prior to the administration of a full-dose (350-700 mg/m2) regimen of 1-h loading and maintenance infusions. A distribution phase of 3.8 h was found. Plasma suramin concentrations were noted to increase following cessation of the intravenous test infusion in eight subjects. A model is proposed in which high-capacity, low-affinity binding of suramin to a shallow compartment adjacent to the intravascular space occurs rapidly during infusion, followed by absorption back into the measured blood pool with binding to plasma albumin. Despite the observable presence of this postinfusion peak shortly after the cessation of the brief suramin infusion, the pharmacokinetics of suramin were best characterized by a traditional two-compartment model. The dose-adjusted area under the concentration-time curve (AUC) increased with dose, supporting a hypothesis of sustained absorption of suramin to vascular endothelium but also raising the possibility of dose-dependent clearance.