Dose-dependent kinetics of orally administered 6-mercaptopurine in children with leukemia

To determine whether the pharmacokinetics of 6-mercaptopurine (6-MP) would show dose dependency, we studied three different single oral doses in eight children (aged 3.6 to 15.1 years) with acute leukemia in remission. Marked interindividual differences in maximum plasma concentration (Cmax) and the area under the plasma concentration-time curve (AUC) were observed when children received the 50 mg/m2 dose. This variability decreased when the doses were increased. Six of the eight children showed a disproportionate increase in the AUC with increasing doses; the other two had a proportionate relationship between the AUC and dose. Overall mean (+/- SD) Cmax and AUC values increased disproportionately (88 +/- 123, to 326 +/- 194, to 653 +/- 344 ng/ml for Cmax, and 147 +/- 180, to 451 +/- 177, to 1291 +/- 415 ng/ml per hour for AUC, respectively) when the dose increased from 50 to 87.5 mg/m2 and then to 175 mg/m2. The results suggest that a saturable first-pass metabolism of oral 6-MP occurs with increasing oral doses in some, but not all, children. Whether and to what extent this pharmacokinetic character of oral 6-MP affects the interindividual difference in systemic exposure to the drug in children with leukemia receiving maintenance therapy require further studies.

Morphology of sickle cells produced in solutions of varying osmolarities

The effect of varying osmolarities (0.6% to 1.5% NaCl solutions, 213 to 492 mOsm/kg H2O) on the morphology of deoxygenated sickle cells was studied quantitatively with a computer-assisted image analysis system. Discocyte-rich, less dense fractions of sickle cells (density less than or equal to 1.11) were suspended in buffered NaCl solutions (pH 7.4) of various osmolarities, deoxygenated at room temperature for up to 5 hours, and stained by Wright's solution. Microscopic images were analyzed by circular shape factor (CSF = 4 pi x [area]/[perimeter]2) and elliptical shape factor (ESF = [short axis]/[long axis]). Since these two parameters yield different values for elongated cells and for cells of other shapes, such as maple-leaf- or star-shaped cells, the morphologic changes of sickle cells can be analyzed numerically. We found that both the rate and the degree of deformation depended highly on the osmotic pressure of the media in which the cells were suspended. In hypertonic solution, most sickle cells assumed a maple-leaf shape. The deformation occurred quickly, but the degree of deformation (circular shape factor and elliptical shape factor) was lower than that found in isotonic and slightly hypotonic solutions. Although elongated cells were formed in hypotonic and isotonic solutions, deformation was slower in these solutions than in hypertonic solutions. These results indicate that the shape and the degree of deformation of deoxygenated sickle cells are highly dependent on the osmolarity of the suspending medium and that the rate of deformation is inversely related to osmolarity. The relationship between morphology of deoxygenated sickle cells and osmotic pressure of the suspending media is discussed.

[Pharmacokinetics of 6-mercaptopurine in children with acute lymphoblastic leukemia--interindividual and intraindividual variations]

The pharmacokinetics of oral 6-mercaptopurine (6-MP) was assessed in ten children with acute lymphoblastic leukemia during maintenance chemotherapy. The doses were 175 mg/m2, 87.5 mg/m2, and 50 mg/m2. The relation between doses and the means of AUC (area under the curve) and Cmax (maximum concentration) suggested a non-linear pharmacokinetics. Our results demonstrated wide interindividual variability as reported by others. We demonstrated individual variation between clinically stable patients. The relationships between predicted and observed concentrations were variable among four patients studied. Some of the patients showed discrepancy between the both concentrations, whereas others did not. The results indicate that serum concentration after oral administration is predictable by further analysis of therapeutic drug monitoring.

[Clinical effect of prostaglandin E1 on liver dysfunction due to high-dose methotrexate]

The effect of prostaglandin E1 (PGE1) on liver dysfunction due to high-dose methotrexate (HD-MTX) was investigated in children with malignant diseases. Eight children received 45 doses of HD-MTX. Group 1 (33 cases) received no PGE1. Group 2 (4 cases) received PGE1 intravenously 8 times every 12 hours for 3 consecutive days. Group 3 (8 cases) received infusion of PGE1 continuously for 4 days (1 day before and 3 consecutive days after MTX infusion). No significant difference was observed among the serum levels of transaminase in these 3 groups as well as the corresponding levels in the same patients who were treated with or without PGE1. There are reports suggesting that in spite of the lack of any difference in serum transaminase levels in rats with drug-induced hepatic injury given PGE1 infusion, data on DNA synthesis and survival ratio indicate the existence of 'hepatocytoprotection'. Further investigation will be necessary in order to decide whether PGE1 infusion is indeed effective.