1. Departments of Pharmaceutics and of Analysis and Toxicology, Faculty of Pharmacy, Utrecht Institute of Pharmaceutical Sciences (UIPS), Universiteit Utrecht, Participant in the Groningen Utrecht Institute of Drug Exploration (GUIDE), P.O. Box 80.082, 3508 TB Utrecht, The Netherlands, and Department of Pharmaceutics and Pharmaceutical Chemistry, 108 Biomedical Polymers Research Building, University of Utah, Salt Lake City, Utah 84112