M Coffin | PubMed Health

PubMed1999

Vitamin E-TPGS increases absorption flux of an HIV protease inhibitor by enhancing its solubility and permeability.

PURPOSE: To investigate the effect of vitamin E-TPGS, d-alpha-tocopheryl polyethylene glycol 1000 succinate, on the solubility and permeability of amprenavir, a potent HIV protease inhibitor. METHODS: The aqueous solubility of amprenavir was measured as a function of vitamin E-TPGS concentration. Directional transport through Caco-2 cell monolayers was determined in the presence and absence of vitamin E-TPGS and P-glycoprotein inhibitors. Absorption flux was estimated from Caco-2 cell permeability and aqueous solubility. RESULTS: The solubility of amprenavir in a pH 7 buffer at 37 degrees C was 0.036+/-0.007 mg/mL. The solubility linearly increased with increasing vitamin E-TPGS concentration (above 0.2 mg/mL). Polarized transport was demonstrated in the basolateral to apical direction, exceeding apical to basolateral transport by a factor of 6. The active efflux system was inhibited by vitamin E-TPGS and known P-glycoprotein inhibitors verapamil and GF120918. CONCLUSIONS: The solubility of amprenavir was improved in the presence of vitamin E-TPGS through micelle solubilization. Vitamin E-TPGS inhibits the efflux system and enhances the permeability of amprenavir. Overall, vitamin E-TPGS enhanced the absorption flux of amprenavir by increasing its solubility and permeability. The enhancement is essential to the development of the novel soft gelatin capsule formulation of amprenavir for use in the clinic.

Algorithms↗

PubMed1997

Receiver operating characteristic studies and measurement errors.

A receiver operating characteristic (ROC) curve expresses the probability of a true positive (PTP) as a function of the probability of a false positive (PFP) for all possible values of the cutoff between cases and controls. Theta, the area under ROC curve, is a measure of the diagnostic ability of the separator variable. The usual nonparametric estimate of theta is shown to be based when the separator is measured with error. An expression for the largest-order term of the bias is found. The observed values and the measurement error variance are used to form a kernel estimate of the underlying distribution. These kernel estimates are used to estimate the bias. Monte Carlo simulation indicates that, for several families of distributions, the bias-corrected estimators have smaller bias and comparable MSE to the usual estimator. An application to the data of Clayton, Moncrieff, and Roberts (1967, British Medical Journal 3, 133-136) illustrates the technique.

Bias↗