[Therapeutic drug monitoring of itraconazole--a report of experiences]. / Therapeutisches Drug-Monitoring von Itraconazol--ein Erfahrungsbericht.

Itraconazole possesses nonlinear pharmacokinetics. We used the Michaelis-Menten model for calculating dosing rates under steady-state conditions. We determined a Michaelis-Menten constant of about 0.3 micrograms/ml from the data of two publications and from our own investigations. From the steady-state concentrations we calculated the necessary amount for the realization of a desired concentration of 1.0 micrograms/ml. The interindividual differences and intraindividual changes of the pharmacokinetics were high (median: 6.9 mg/kg/d (2.7-17.1), n = 110). The intraindividual stability of the pharmacokinetics of repeatedly investigated patients (n = 20, individual time of observation: 4 to 296 days, median: 30 d) depended on various pathophysiological factors of influence. The individual duration of pharmacokinetically stable periods in relation to the respective observation time ranged between 0 and 100% (median: 75%, n = 23). In the initial days of treatment the course of itraconazole concentrations in repeatedly investigated patients (n = 6) was not uniform. Under constant dosage only one patient showed the increase in concentrations described in the literature during the first week of treatment. In this period of treatment probably three pharmacokinetic processes overlap one another: the establishment of the steady state, and systematic changes as well as changes caused by pathophysiological factors of the underlying disease. The development of therapeutic drug monitoring (with the calculation of the needed dosages) was unproblematic with the use of standard procedures. Necessity and frequency of therapeutic drug monitoring depend on the accepted ranges of concentration during long-term therapy, on the expected deviation of the pharmacokinetics during the course of the basic illness of the individual patient and on potential drug interactions.

Capillary blood, dried on filter paper, as sample for monitoring cyclosporin A concentrations.

For monitoring the immunosuppressive drug cyclosporin A by radioimmunoassay (Sandoz Ltd.) we propose a simple method of sampling in which 20 microL of capillary blood is dried on filter paper. Patients can collect their own samples and mail or bring them to the laboratory. Results for such samples, and their variability, correspond to those for conventional methods of sampling (collection of venous or capillary blood into buffer). Capillary blood can be stored on paper at room temperature for more than four weeks with no effect on assay results.

[Blood level oriented ambulatory cyclosporin A therapy following kidney transplantation]. / Blutspiegelorientierte ambulante Cyclosporin-A-Therapie nach Nierentransplantation.

It is reported on the blood level-oriented oral long-term therapy with cyclosporin-A (Sandimmun) in 20 patients after kidney transplantation. The Cy-A-concentrations were measured in the whole blood by means of a radioimmunoassay (Sandoz) under steady state conditions. The mathematical analysis of the steady state daily minimum concentrations in the whole blood depending upon the dosage rate allows individual calculations of the dosage for the stabilisation of the therapeutic concentration desirable for the individual patient in each case. In the majority of the patients a non-linear relation between the steady state blood concentration and the dosage rate was present. The observation of a defined therapeutic area under the conditions of the ambulatory treatment could be achieved without any problems. The control intervals were 4-6 weeks. The long-term stability of the individual pharmacokinetic parameters can at present not be judged reliably, since the average observation time is still too short. In 6 patients who are controlled on the way demonstrated already for several months no systemic changes in the behaviour of the blood level were to be seen.

Sodium flux and lipid spectrum in the erythrocyte membrane in essential hypertension.

In the erythrocyte membranes of normotensive individuals and patients with essential hypertension, sodium flux behavior, cholesterol content, phospholipid spectrum, and the fatty acid composition of the phospholipids were measured. There was no difference between normotensives and hypertensives in sodium influx in the erythrocyte. In both groups, 1 microM norepinephrine resulted in a significantly equal increase of sodium influx after an incubation period of 15 min. Compared with normotensives, erythrocytes in essential hypertensive patients showed a decreased sodium efflux. The cholesterol/phospholipid quotient of the erythrocyte membrane of hypertensive subjects increased in comparison with that of normotensive individuals. No differences between the two groups were found in the phospholipid pattern and in the fatty acid composition of phosphatidylserine/-inositol, -choline, and sphingomyelin. However, in phosphatidylethanolamine of the erythrocyte membrane in essential hypertensives in contrast to normals, a decreased content of the fatty acid fraction 22:0/20:3 and in increased content of the fatty acid fraction of 20:5/22:2/22:3 was found. The dependence of the Na turnover on the lipid spectrum of the erythrocyte membrane is discussed. The altered lipid composition of the erythrocyte membrane in essential hypertensives does not seem to cause the altered Na efflux behavior.

Electrochemical investigations on the oxygen activation by cytochrome P-450.

The application of cytochrome P-450 in substrate conversion is complicated both due to the limited stability and the cofactor regeneration problems. To overcome the disadvantages of NADPH consumption the transfer of the reduction equivalents from an electrode into the cytochrome P-450-system was studied: 1. NADPH was cathodically reduced at a mercury pool electrode. By immobilization of NADP on dialdehyde Sephadex the reductive recycling was possible. 2. Different forms of reduced oxygen were produced by the cathode: a) The reaction of O2- with deoxycorticosterone yields a carboxylic acid derivative. In contrast the cytochrome P-450 catalyzed NADPH-dependent reaction with the same substrate gives corticosterone, O2- represents only an intermediate in the activation of oxygen and is not the "activated oxygen" species. b) Molecular oxygen was reduced to HO2- and H2O2, respectively. The interaction of adsorbed cytochrome P-450 on the electrode surface with the reduced oxygen species in the absence of NADPH was studied. The electrochemically generated peroxide seems to be more active than added H2O2. 3. In a model of electro-enzyme-reactor several substrates were hydroxylated by microsomal cytochrome P-450 with cathodically reduced oxygen which substitutes NADPH.

Studies on electron transfer between mercury electrode and hemoprotein.

The electrochemical behaviour of ferricytochrome c, metmyoglobin and methemoglobin was studied using d.c., a.c. and differential pulse polarography, and controlled potential electrolysis. 1. The three hemoproteins yield d.c. polarographic steps, and peaks in differential pulse polarograms, the height of which is proportional to concentration. The charge transfer is influenced by strong adsorption. 2. The concentration dependence of the a.c. polarograms indicates structural changes in the adsorbed molecules. 3. The reduction products of controlled potential electrolysis of metmyoglobin and methemoglobin have absorption spectra identical with the native control samples. The affinity for oxygen and the cooperativity in hemoglobin are not affected by the reaction at the electrode. 4. The charge transfer proceeds via adsorbed, already reduced, molecules to freely diffusible proteins.

[Polarographic studies on the peroxidase activity of liganded deuterohemin]. / Polarographische Untersuchungen zur Peroxidaseaktivität von ligandiertem Deuterohämin

The peroxidase activity of deuterohemin and deuterohemin complexes relative to the substrates pyrogallol and ascorbic acid was studied using d.c. polarography in aqueous solution. Imidazole and pyridine served as complex ligands. In the absence of the ligands, a continual rise in the substrate conversion rate with increasing H2O2 initial concentration is observed. Imidazole or pyridine were found to considerably increase the peroxidase activity of deuterohemin at low H2O2 concentrations. At high H2O2 concentrations, the dependence of the reaction rate on H2O2 concentration shows a bend, the reaction rate being in each case higher than that of free hemin under the same conditions. The reason of this fact is discussed to be a retarded formation of activated H2O2 hemin-ligand complexes at high H2O2 concentrations.