Bioavailability of oral vitamin E formulations in adult volunteers and children with chronic cholestasis or cystic fibrosis.

PURPOSE: To test bioequivalence of oral vitamin E formulations, water-soluble tocofersolan (test) and water-miscible (reference), in healthy adult volunteers, and their bioavailability in children with chronic cholestasis or cystic fibrosis. METHODS: In a two-way open randomized single dose cross-over design, 1200 IU were administered in 12 healthy volunteers and 100 IU/kg in 12 children with chronic cholestasis or cystic fibrosis. RESULTS: In healthy volunteers, formulations were not bioequivalent with a higher exposure to tocofersolan. In cholestatic children tocofersolan bioavailability was significantly higher than reference formulation (maximum plasma concentration: P = 0.008 and AUC: P = 0.0026). Bioavailability was not statistically different in cystic fibrosis. CONCLUSIONS: Oral tocofersolan was more bioavailable than the reference formulation in children with chronic cholestasis and similarly bioavailable in cystic fibrosis. Tocofersolan may represent an alternative to painful intramuscular vitamin E injections in chronic cholestasis, or to other oral formulations in cystic fibrosis.

Prediction of sotalol-induced maximum steady-state QTc prolongation from single-dose administration in healthy volunteers.

The relationship between racemic sotalol plasma concentrations and QTc interval prolongation after both single-dose and repeated administration of three sotalol oral doses was studied in a randomized crossover protocol performed in 10 healthy volunteers. QTc interval increase was significant after the three single-dose sotalol administrations and was significantly related to the administered dose (p < 0.0001). In 21 of 30 analyses, QTc interval was linearly correlated with sotalol plasma concentrations. After the 320 mg dose, the linear model was a best fit for 90% of the cases, and no hysteresis was observed. After repeated sotalol administration, 69 of 87 QTc interval measurements at steady state could be predicted from the plasma concentration versus effect relationship established after single-dose 320 mg administration. Seventeen of 18 errors (94%) corresponded to QTc intervals that were significantly lower than predicted. These findings suggest that a short-term individual linear model determined after a 320 mg test dose of sotalol allows a good prediction of expected maximal increase in QTc duration in healthy subjects.

Effect of ibuprofen on bilirubin-albumin binding in vitro at concentrations observed during treatment of patent ductus arteriosus.

BACKGROUND: In vitro studies have shown that ibuprofen (IBU) may interfere with bilirubin-albumin binding at concentrations of 100 microg/mL and above. OBJECTIVES: The present study evaluates the in vitro bilirubin displacement over the range of IBU plasma concentrations observed in vivo during curative treatment of patent ductus arteriosus in preterm infants. METHODS: Considering that individual plasma concentrations obtained during the clinical development of IBU in preterm infants were ranging between 10 and 70 microg/mL and exceptionally above 100 microg/mL, we used the modified peroxidase method to determine total and unbound bilirubin concentrations without IBU and with IBU over this specific concentration range. RESULTS: Total bilirubin and albumin concentrations were respectively 6.6 mg/dL and 2.87 g/dL in pooled newborn plasma. No displacement of bilirubin from its albumin binding sites by IBU was observed over a range of concentrations from 10 to 100 microg/mL. Only a concentration of 200 microg/mL significantly increased the unbound bilirubin by 1.5-fold (p=0.0008). CONCLUSIONS: This in vitro study confirms displacement of bilirubin by a high IBU concentration of 200 microg/mL, however it retrieves no significant displacement over a range of concentrations up to and including 100 microg/mL, i.e. within the range of in vivo concentrations at the recommended dose regimen.

Rate dependence of sotalol-induced prolongation of ventricular repolarization during exercise in humans.

Studies in animals have shown that drug-induced action potential prolongation with class III antiarrhythmic agents increases with slow pacing rates. We studied the physiological rate dependence of sotalol effects on ventricular repolarization, measured as QT interval duration on the surface electrocardiogram at rest and during a maximal exercise test, in 10 normal volunteers. In a randomized, crossover study, three dosages of sotalol (160 mg/24 hr, 320 mg/24 hr, and 640 mg/24 hr) were administered during 4 days to each subject. In a control period, no drug was administered. During each period, 50-100 QT intervals were measured over a wide range of RR intervals recorded at rest and during the course of a maximal exercise test. Plasma sotalol concentration and beta-adrenoceptor blockade (percent reduction in peak exercise heart rate from control) were also measured. The QT-versus-RR relation was fitted to several formulas, and the overall best fit was used to calculate QT interval duration normalized for a heart rate of 60 beats/min (QTc) and to analyze the rate dependence of QT prolongation with sotalol. Sotalol-induced beta-adrenoceptor blockade and QTc prolongation were dose and concentration dependent. Sotalol reduced peak exercise heart rate by 13.8 +/- 7% at the dosage of 320 mg/24 hr and by 25.4 +/- 8% at the dosage of 640 mg/24 hr (both p less than 0.01). Sotalol prolonged QTc interval by 5.8 +/- 3.7% and 11.8 +/- 3% at these respective dosages (both p less than 0.01). The concentration of sotalol required to produce minimal (mean QTc prolongation, 5.6%; confidence interval, 0-11.2%) QTc prolongation (680 ng/ml) tended to be lower than that required for minimal (mean percent reduction in maximal exercise heart rate, 13.9%; confidence interval, 0-27.8%) beta-blockade (840 ng/ml). QT prolongation with sotalol increased with increasing RR intervals (i.e., decreasing heart rate) at all dosages. QT prolongation became statistically significant for RR of 800 msec or more at all dosages and for RR intervals of 600 msec or more at the dosage of 640 mg/24 hr. This rate dependence altered the relation between QT interval duration and sotalol plasma concentrations. These results suggest that sotalol prolongs QTc interval in humans at dosages and concentrations similar to those required to produce beta-adrenoceptor blockade, QT prolongation with sotalol is more pronounced when heart rate decreases and is not apparent during exercise-induced tachycardia, and the relation between QT prolongation with sotalol and plasma concentrations of the drug depends on the heart rate at which measurements are made.