Pseudoephedrine (PSE) is a drug with a long history of medical use; it is helpful in treating symptoms of the common cold and flu, sinusitis, asthma, and bronchitis. Due to its central nervous system (CNS) stimulant properties and structural similarity to amphetamine, it is also used for non-medical purposes. The substance is taken as an appetite reducer, an agent which eliminates drowsiness and fatigue, to improve concentration and as a doping agent. Due to its easier availability, it is sometimes used as a substitute for amphetamine or methamphetamine. Pseudoephedrine is also a substrate (precursor) used in the production of these drugs. Time will tell whether legal restrictions on the sale of this drug will reduce the scale of the problem associated with its misuse.

Background. Modern pharmacotherapy requires an individual approach to patients, taking into account changes in pharmacokinetics in pathological states and between-subject variability. This procedure is of particular importance in immunosuppressive drug therapy. In recent years, the attention has been paid to the usefulness of calculating the kinetic parameters of the drug in the optimization of the immunosuppressive treatment. Objectives. To assess the possibility of using mycophenolic acid (MPA) concentration measurements in order to optimize pharmacotherapy in patients with kidney diseases or after kidney transplantation. Materials and methods. The study included 103 patients with renal diseases (group 1) and after kidney transplantation (group 2), treated at the Department of Nephrology and Transplantation Medicine at the University Clinical Hospital, Wroclaw, Poland. The concentrations of MPA were measured using Enzyme Multiplied Immunoassay Technique (EMIT (R)) method. A total of 193 pharmacokinetic profiles were performed. Results. The median of initial (C0) concentration for all patients was 2.09 mg/L, in group 1 - 2.06 mg/L and in group 2 - 2.11 mg/L. The median concentration at 30 min after drug administration (C30) was 11.72 mg/L in the whole study group, in group 1 - 11.52 mg/L and in group 2 - 12.72 mg/L. The median concentration at 120 min after the drug administration (C-120) was 4.73 mg/L, 4.45 mg/L and 5.57 mg/L, respectively. The median area under the curve from C-0 to C-120 (AUC)(0-120) was 15.77 h x mg/L for the entire study group, in group 1 - 15.46 h x mg/L and in group 2 - 16.78 h x mg/L. Using the Spearman's rank correlation coefficient for both groups, statistically significant (p < 0.05) correlations were found between 1) C-0 and C-30, 2) C-0 and C-120, 3) C0 and AUC(0-120), 4) C-0 and the daily dose, 5) C30 and AUC(0-120), and 6) C-30 and the morning dose. There were also statistically significant correlations between C-120 and AUC(0-120). Moreover, in group 1, a statistically significant correlation (p < 0.05) was found between 1) C-120 and the daily dose, 2) C-120 and albumin, 3) C-120 and C-30, and 4) C-120 and AUC(0-120). In the group 2, a statistically significant correlation was found between C-120 and the morning dose. Conclusions. Measurements of MPA concentrations are useful for optimizing immunosuppression in patients requiring an individualized treatment.