A phase I study was conducted to determine the pharmacokinetics, safety, and tolerability of sirolimus, a new immunosuppressive drug, in 45 healthy men between 19 and 36 years of age. Nine subjects in each group were randomly assigned to receive single oral doses of either sirolimus (n = 6) or placebo (n = 3) in group I (0.3 mg/m2), group II (1 mg/m2), group III (3 mg/m2), group IV (5 mg/m2) and group V (8 mg/m2). No serious adverse events occurred during the study. Twenty-eight of the 45 volunteers (62%) reported an adverse event; 19 of 30 (63%) were in the sirolimus group and 9 of 15 (60%) were in the placebo group (ns). Asthenia was the most common adverse event, occurring in 7 of 30 (23%) in the sirolimus group compared with 6 of 15 (40%) in the placebo group (ns). Absorption occurred within 1 hour in all volunteers. Whole blood peak concentration and area under the concentration-time curve increased proportionally with dose. Mean (+/- SD) whole blood terminal disposition half-life (t1/2), apparent oral dose clearance (Cl/F), and volume of distribution (Vss/F) were 82 +/- 12 hours, 278 +/- 117 mL/h x kg and 23 +/- 10 L/kg, respectively. Distribution of sirolimus into formed blood elements was extensive, with a mean whole blood-to-plasma ratio of 36. Single oral doses of sirolimus (0.3 to 8 mg/m2) solution were well tolerated in healthy male volunteers.

The pharmacokinetics of 2 mg ketotifen from four different oral dosage forms were examined in two randomized, balanced cross-over studies. Forty healthy male subjects participated. Each of 20 subjects received two capsule formulations and each of the other 20 subjects received two syrup formulations. Ketotifen concentrations in plasma were determined by a modified GC-MS method. The limit of quantitation was 40 pg ml-1. Inter-day precision and accuracy calculated from quality control samples were 16.3 per cent (-1.9 per cent), 19.8 per cent (+4.5 per cent) and 23.6 per cent (+5.9 per cent) at plasma concentration levels of 86 (n = 18), 215 (n = 19) and 343 (n = 18) pg ml-1, respectively. Ketotifen was rapidly absorbed from all dosage forms reaching Cmax in the order of 400 pg ml-1 after the syrup formulations and 300 pg ml-1 after the capsule formulations within 2 to 4 h. The syrup formulations showed a significantly more rapid rate of absorption as assessed by Tmax. No significant differences in extent of absorption between dosage forms were observed. The terminal elimination half-life of ketotifen varied between subjects from 7 to 27 hours with a mean of about 12 h. The minor pharmacokinetic difference between dosage forms observed in this study is unlikely to be of clinical significance.

What is already known about this subject • The functionality of the HPA axis through cortisol production has been the subject for several investigations.• Modelling of cortisol production has been described by endogenous substance models utilizing a combination of indirect response functions and sum of cosine functions.• The effect of glucocorticoid drugs on cortisol production has been investigated using these models.What this study adds • Previous investigations (models) have not primarily considered the combined action of ACTH and cortisol.• Since ACTH drives cortisol production we adopted, for our modelling, the same approach as previous investigations but we distinguished between two types of models for the production of cortisol (driven by ACTH), one being the sum of cosine functions, the other being described by surges.• The presented surge-based model can serve as a tool for further understanding of the HPA axis and may also prove useful in the development of drugs interacting with the axis. AimsBudesonide, a glucocorticosteroid, is used as a first-line treatment for asthma. The aim of the study was to develop a PK/PD model for the effect of budesonide on ACTH and cortisol. MethodsThe modelling data were generated by conducting a single-blind, randomized, placebo-controlled cross-over study. Ten healthy volunteers inhaled placebo (Placebo Turbohaler) and 1600 mg budesonide (Pulmicort Turbohaler), with a wash-out period of 7 days between treatments. Baseline concentrations of cortisol and ACTH were measured after placebo treatment and concentrations of cortisol, ACTH and budesonide were assessed after budesonide treatment. A one-compartment disposition model was used for budesonide disposition. Based on indirect response models, two types of models, distinguishing between production driven by a sum of cosine functions and production driven by surges, were used in parallel to describe the data. ResultsThe surge-based approach was the most appropriate, based on goodness-of-fit, objective function values and number of parameters. The surge-based model that integrated both ACTH and cortisol data was chosen as the final model. The estimated half-lives of endogenous ACTH and cortisol were 9 and 113 min, respectively. The budesonide and ACTH concentrations producing 50% of the maximal response (IC50 and A50) were 0.325 mg l -1 and 4.96 pmol l -1 . ConclusionsThe present PK/PD model of the effect of budesonide on ACTH and cortisol can serve as a tool for further understanding of the hypothalamic-pituitary-adrenal (HPA) axis and be useful in the development of drugs interacting with the axis.

The results of the present study show that FP-DH suppresses plasma cortisol more than BUD-TBH on a equivalent basis with regard to both magnitude and duration.