Phase I trial using adaptive control dosing of hexamethylene bisacetamide (NSC 95580)

Abstract

Hexamethylene bisacetamide (HMBA), a potent differentiating agent, was administered to patients with refractory malignant tumors. Thirteen patients received 30 evaluable courses. HMBA was given by continuous i.v. infusion for 5 days. Therapy was repeated every 28 days, if patients had recovered from toxicity. The starting dose was 24 g/m2/day. Because our previous trial had shown wide interpatient variability in HMBA pharmacokinetics and excess toxicity at HMBA plasma concentrations greater than 2 mM (HMBA doses between 24 and 33.6 g/m2/day), we attempted to individualize each patient's dose based on a dosing scheme using an adaptive (feedback) control algorithm, which assumed linear clearance for HMBA. In all courses, a plasma sample was assayed daily and infusion rates were adjusted to achieve an HMBA plasma concentration of 1.5-2.0 mM (300-400 mg/liter). The patients included 12 men and 1 woman with a median age of 56 years (range, 34-76) and median Karnofsky performance status of 90% (range, 60-100). All patients had received prior chemotherapy and 9 patients had also received radiation therapy. The linear adaptive control algorithm was reasonably precise, with a mean absolute error of 0.28 (SE 0.04) mM. However, adjustments in infusion rate systematically overshot the desired change in steady state concentration, probably due to nonlinear clearance of HMBA. For levels within 24 h of a change in infusion rate, this resulted in significant bias, with a mean error of 0.24 (SE 0.09) mM. The mean absolute error was 0.40 (SE 0.06) mM. A second adaptive control algorithm, using a pharmacokinetic model with parallel first-order (renal) clearance and Michaelis-Menten (nonrenal) clearance and using Bayesian parameter estimation with a priori estimates based on our previous phase I trial, proved to be much more precise than the linear method and was unbiased when applied retrospectively to the same observations, with a mean error (within 24 h of a change in infusion rate) of 0.02 (SE 0.06) mM and a mean absolute error of 0.22 (SE 0.03) mM. Toxicity was reversible in all cases. Neurotoxicity, consisting of hallucinations, agitation, somnolence, or confusion, was seen in 2 patients. Four patients complained of insomnia or anxiety. Mild asymptomatic acidosis was seen in 3 patients. Other toxicity included grade 1-2 nausea and vomiting (10 patients), grade 2 diarrhea (2 patients), grade 3 thrombocytopenia (3 patients), grade 1-3 leukopenia (3 patients), and oral herpes simplex infection (4 patients). Mild reversible renal insufficiency (measured by creatinine clearance) was seen in 8 patients.(ABSTRACT TRUNCATED AT 400 WORDS)