Trough cyclosporine (CsA) blood levels obtained just before administration of the next dose are monitored to guide dosage adjustments. However, these levels may not be the best indicator of total drug exposure. In a study of de novo renal transplant patients, pharmacokinetic profiles of CsA after administration of the traditional CsA formulation (Sandimmune [CsA-SIM] Novartis, E. Hanover, NJ) or the new formulation, cyclosporine capsules for microemulsion (Neoral [CsA-ME] Novartis, E. Hanover, NJ), were compared at 1, 4, 8, and 12 weeks posttransplantation under fasting and fed conditions. The data were analyzed to assess the degree of correlation between total drug exposure, indicated by the area under the concentration-versus-time curve at the end of a 12-hour dosing interval (AUC12h), and drug exposure calculated from concentrations obtained at different time points (abbreviated AUC [AAUC]). With AAUCs calculated from trough levels and levels at 4 hours postdose, the average degree of correlation with AUC12hwasr= 0.915 for CsA-ME andr= 0.853 for CsA-SIM. The degree of correlation was smaller with CsA-SIM and additional sampling times may be required. With CsA-ME, these two sampling time points appear to provide a reliable indication of total CsA exposure; CsA-ME may thus provide advantages in terms of blood level monitoring and patient management.