Intraindividual variability in the relative systemic availability of cyclosporin after oral dosing.

We have measured total and unbound plasma concentrations of cyclosporin A in seven healthy men after single oral doses (12 mg per kg body weight) on two occasions at least two weeks apart. There was an up to two-fold intraindividual and a more than three-fold interindividual variation in the AUCs of both total and unbound drug. The intraindividual variability in the AUC of cyclosporin is similar to that of many other drugs and needs to be taken into account in the planning of pharmacokinetic studies.