[Analysis of decay curves with biphasic kinetics]

Medication of trout and carps with chloramphenicol and sulfadimidine results in tissue residues which best fit by a biexponential decay curve. The analysis of residues does not reveal any systematic deviations of the data from the model. On the basis of this model half lives for the fast and slow drug elimination phases can be estimated. For the assessment of withdrawal times it is necessary to compute confidence limits for the decay curves. A withdrawal time may be defined by the intersection of recommended maximal concentrations with the upper confidence limit. This analysis does not include any metabolites. This model is also suited for monitoring purposes. It is recommended to apply the procedure to all chemicals exhibiting biexponential decay kinetics.

[Pharmacokinetics and pharmacodynamics of proxyphylline in asthmatic children]

In 15 asthmatic children and 3 healthy adult volunteers the pharmacokinetics and pharmacodynamics of proxyphylline under oral treatment, and the pharmacokinetics after intravenous administration were determined. The concentration-time-courses after intravenous application could best be fitted to an open 2-compartment model whereas the pharmacokinetics after oral treatment followed an open 1-compartment model. Under oral administration great inter- and intraindividual variances of the serum levels occurred. These differences which showed no age-dependency were suggested to be due to variations of the absorption velocity and the elimination half-lifes. In order to evaluate the curative efficacy of proxyphylline on lung function parameters all children had to undergo a whole body-plethysmography. No significant antiobstructive effects on the relevant baseline ventilation parameters could be observed. The protective efficacy of proxyphylline was determined in asthmatic children who developed an exercise induced asthma after a 7 minutes run. Only in 3 of 11 children a significant reduction of the enhanced airway resistance occurred. No correlation between serum levels and the protective effects was found. The present results show that there is no positive association between pharmacokinetics and pharmacodynamics of proxyphylline in asthmatic children. A safe antiobstructive therapy appears to be impossible within the dose range recommended so far.

The kinetics of bupivacaine (Carbostesin) plasma concentrations during epidural anesthesia following intraoperative bolus injection and subsequent continuous infusion

Plasma levels of bupivacaine were measured in 25 patients undergoing major abdominal surgery. The pharmacokinetic analysis of these data shows: (1) under a short term treatment, i.e. in the initial phase where multiple injections are given, the kinetic properties are in accordance with linear kinetic theory. The data can best be fitted to a two-compartment-model. (2) under a longterm treatment, i.e. infusion for more than 50 h, a very high accumulation occurs in contradiction to this theory. Therefore, the calculation of plasma levels from initial kinetic data is not feasible.

The relationship between pharmacodynamics and pharmacokinetics in asthmatic children receiving a sustained-release formulation of theophylline

Pharmacodynamic response as well as serum and saliva concentrations of theophylline were monitored in 15 children under a long term theophylline treatment. Respiratory parameters, such as vital capacity and total bronchial resistance all related to bronchodilatation, were measured by use of a bodyplethysmograph. Measurements were performed before treatment and during the steady state with respect to serum levels. Due to small differences between peak and trough concentrations, no correlations between serum concentrations and respiratory parameters were found during the steady state. However, some important respiratory parameters exhibit considerable differences with respect to pretreatment values. In conclusion, one can state that during the steady state, theophylline exerts a constant influence on bronchodilatation which depends only slightly on the concentration range achieved.

[A rheumatic disease register in clinical use]

A registry for the documentation of rheumatic diseases has been developed at the University of Düsseldorf. For 3 years more than 450 parameters for each patient have been documented, checked, and stored in a data bank. The registry has made a definite improvement in the diagnosis and long-term follow-up of rheumatic diseases. The use of special statistical procedures to study the frequency of various parameters in different diseases has allowed independent diagnostic criteria to be established.

[Pharmacokinetics of drugs from the breast-feeding mother passing into the body of the infant, using theophylline as an example]

In order to find out whether theophylline medication during the lactation period would produce hazards in the suckling infant or not, the following investigations were performed: 1. After oral application of theophylline to 12 nursing mothers the pharmacokinetics of the translactal passage was determined by simultaneous measurements in serum and milk. 2. For predicting the drug uptake by the suckling infant a pharmacokinetic model was designed allowing estimations of drug uptake by the infant on the basis of the kinetics of the translactal passage and the kinetics of the drug in the infant. The following results were obtained: 1. Theophylline passes the blood milk barrier with a certain delay. The time courses of theophylline in the milk thus were depressed when compared to those in the serum. The milk/plasma-quotient varied within a range of 0.6 to 0.89 and was less when maxima of theophylline in plasma were reached. Elimination half-lifes did not differ, but the apparent volume of distribution was greater in milk. This difference showed a good correlation to the divergent areas under the curves for milks and serum concentrations. 2. The kinetic data of the translactal passage of theophylline and the kinetic data of theophylline in infants were fitted into the kinetic model presuming constant dosage intervals as well as constant amounts and intervals of drinking. Theophylline accumulation occurred highly dependent upon the half-life in the infant. This accumulation reached therapeutic levels and even could surpass these when long half-lifes were assumed. For the estimation of drug transfer from breast feeding mothers to their infants via breastmilk, several pharmacokinetic criteria should be considered.

[Developing a dose-administration schedule for drug therapy in childhood]

For the application of a target concentration strategy for the assessment of dosage regimens pharmacokinetic parameters and their variances must be known. Since pharmacokinetic parameters like the elimination constant or the volume of distribution undergo considerable changes during the perinatal period until early childhood, the application of standard dosage regimens may lead to serious under- or overtreatment. Based on kinetic data of children from the literature and own studies, it is demonstrated, how changes of the volume of distribution and of the elimination constant influence the optimal dosage regimen. The optimal dosage regimen is evaluated using a special criterion of optimality.

Pharmacokinetics of dexamethasone in children

A pharmacokinetic data analysis of plasma level data for dexamethasone obtained from children with various diseases and healthy adults was performed. A total of 33 subjects participated in the study. The results show: The pharmacokinetics of dexamethasone can be described satisfactorily within the frame of classic linear pharmacokinetic theory. The variance of important pharmacokinetic parameters is large. Therefore, if a close relationship between drug levels and therapeutic and adverse effects exists, which still has to be proved, optimal individual dosage regimens have to be calculated, guided by drug-level monitoring. When treating newborns, one should be aware that high drug levels are likely to occur, possibly necessitating a dose reduction.

Concentration of dimethylnitrosamine in the air of smoke-filled rooms

In order to evaluate the contribution of volatile nitrosamines from tobacco smoke to indoor air pollution, N-nitroso-dimethylamine (NDMA) and N-nitroso-diethylamine (NDEA) were measured in indoor air under artificial and natural conditions. In controlled experiments under extreme conditions, we found that tobacco smoke-related NDMA levels above 0.07 ng/liter were associated with a highly irritating atmosphere which was scarcely tolerable to those present. In smoke-filled rooms under natural conditions NDMA levels ranged from 0.02 to 0.05 ng/liter except a minimum value of less than 0.01 ng/liter in a restaurant and a maximum of 0.07 ng/liter in a dancing bar. These NDMA levels are thus below comparable values reported by others. The NDMA/NDEA ratios found in air samples taken from some rooms under conditions of everyday life are quite different from those found in sidestream smoke of cigarettes. Irritation was not reported under natural conditions. From the results it is concluded that NDMA levels, measured under real life conditions, are usually not caused by tobacco smoke alone. Evidence for other sources of volatile nitrosamines is discussed.

Methods for evaluating optimal dosage regimens and their application to theophylline

For a certain class of drugs blood levels can be used to monitor therapy. Based on the concept of a target concentration strategy criteria for optimal treatment schemes are given. The goal of these criteria is to define dose regimens that lead to concentrations within the target concentration range. The performance indices of these criteria are evaluated and applied to the dose regimen assessment for theophylline.

Improved method for routine determination of nicotine and its main metabolites in biological fluids

ExtrelutR extraction and glass capillary gas chromatography were applied to the routine determination of nicotine and its metabolites cotinine, nicotine-1'-N-oxide and cotinine-1-N-oxide in urine and plasma. After extraction of nicotine and cotinine both N-oxides and phendimetrazine-N-oxide (used as internal standard) were reduced to their bases by SO2 on-column and eluted by a mixture of diethyl ether and dichloromethane. The minimum detectable concentrations are 0.03 micrograms/ml for urinary nicotine and cotinine and 0.1 microgram/ml for the N-oxides. In plasma samples the corresponding values are 5 ng/ml and 15 ng/ml, respectively, with sample values as small as 2 ml. The advantage of the direct determination of all four compounds of interest in one sample reduced the amount of plasma required. The straightforward and rapid extraction and reduction procedure as well as the long-term stability of the gas chromatographic separation system make the method suitable for routine application.

[Fibrinolysis and complement-system profiles during aorto-femoral bypass implantation]

In 51 patients undergoing either implantation of an aortofemoral bypass (38 patients) or of an saphenous bypass (13 patients) the fibrinolytic and complement system profiles were determined. During the course of an aortofemoral bypass the plasminogen concentration decreased by 40%, alpha 2-macroglobulin by 25%, the complement factor C3c by 20% and the complement factor C4 by 40%. Antithrombin III concentration remained stable until the third postoperative day. The alpha 1-antitrypsin concentration increased postoperatively by 40% compared to the preoperative control. The concentrations of plasminogen, antithrombin III, alpha 2-macroglobulin and complement factor C4 did not change in the patients undergoing saphenous bypass operation. Intraoperatively the complement factor C3c decreased by 20%, while alpha 1-antitrypsin showed postoperatively an increase by 30%. Anaesthesia (neuroleptanaesthesia, halothane- or continuous thoracal epidural anaesthesia) had no influence on the fibrinolytic and complement system profiles. Neither could a correlation be shown between the intraoperative haemodynamic changes and the concentrations of the factors of the fibrinolytic and complement system.

Linear elimination kinetics but non-linear pharmacodynamics in theophylline intoxication in a child

In an infant's acute theophylline intoxication following a medication error, plasma levels above 80 micrograms/ml were not associated with repetitive seizures, but also with heart rates above 200 bpm. The serum elimination kinetics were characterized by a first-order elimination process with a half-life of 15 h. Despite the exponential decay of plasma levels the heart rate remained at a high level during the first 20 h. This behavior is explained by a saturation phenomenon familiar in receptor and enzyme kinetics.

Kinetics of the translactal passage of digoxin from breast feeding mothers to their infants

In order to find out whether digoxin therapy of nursing mothers might produce discomfort in suckling infants we have investigated the kinetics of the transfer of digoxin from plasma to milk in 11 nursing mothers. After intravenous or oral application of a single dose of 0.5 mg or 0.75 mg digoxin simultaneous serum, fore- and hindmilk samples were taken. Obviously, a rapid equilibrium occurred between the serum and the milk compartments and there was no difference between fore- and hindmilk. All three digoxin concentration profiles ran parallel with a milk to serum ratio of 0.6 to 0.7. The curves could best be fitted by the sum of two exponential functions. For predicting the digoxin intake into the suckling infant, simulations were carried out on the basis of two coupled compartment models. When the kinetic milk data as well as the kinetic data obtained in infants were fitted by this model it could be shown that even in the case of long half-lives only about 3% of the therapeutic drug levels were reached in the baby. Thus, one can conclude that digoxin accumulation to toxic concentrations should not occur in infants of women treated with appropriate doses of digoxin.

Experimental studies on the kinetics of early postmortem decay of the lymphocyte membrane. Remarks about its application to forensic hemogenetics and to cornea transplantation

Tests on human and animal cadavers were carried out to investigate the early postmortem decay of the lymphocyte membrane HLA-typing of cool-kept human cadavers can be performed within the first 36 h after death. Hereby, a possibility is obtained to determine HLA-ABC antigens of the deceased for hemogenetic or cornea transplantation purposes. The data obtained from animal experiments give evidence that the decay of the lymphocyte membrane follows a function of the Verhult's type. Using this function, it is possible to estimate the rate constant as a function of temperature.

[Quantitative laser-nephelometric detection of rheumatoid factor, using IgG coated latex particles (author's transl)]

The laser-nephelometric test (Latex RF test) detects rheumatoid factor activity, and is based on immune complex formation between IgG coated latex particles and rheumatoid factor. This test requires little time and gives qualitative results in good precision. The latex nephelometric test and the frequently used agglutination tests (Waaler-Rose, Latex agglutination test) give the same qualitative results. In the quantitative assay higher nephelometric results correlate on average with higher titers in the Waaler-Rose and Latex agglutination test. The high standard deviation could be explained by the fact that other factors (IgG rheumatoid factor, IgG and IgG-IGM immune complexes), in addition to the IgM rheumatoid factor concentration, influence the immune complex formation in vitro.

Pharmacolinetic and pharmacodynamic data analysis of theophylline for three different drug forms

Theophylline, which is widely used in asthmatics, should be maintained within narrow plasma limits to achieve maximum therapeutic benefit with minimum adverse effects. For the evaluation of drug input schemes it is essential to know the pharmacokinetic parameters and their variation for different dosage forms. Apart from absorption and elimination rates, an appropriate dosage schedule is determined by the extent of bioavailability. The objectives of the study presented here are the assessment of bioavailability, the estimation of pharmacokinetic parameters, and the investigation of the relationship between plasma drug levels and cardiac side effects. Additionally, it was checked whether drug levels in saliva could be used for monitoring drug levels in plasma. The time course of theophylline in plasma and saliva was measured in twelve healthy volunteers on different drug forms: intravenous injection as well as oral application of a fast and a slow release form of theophylline. Pharmacokinetic parameters were estimated using a three-compartment model for the distribution of theophylline. The extent of bioavailability was estimated via the area under the curves and by numerical evaluation of the invasion function. By simultaneous measurements of heart rate and c-AMP levels the drug response was monitored. The results show the following: i) The slow and fast release dosage forms do not differ with respect to extent of bioavailability, whereas bioavailability rates are slower for the sustained release form. ii) Apart from the initial phase (less than or equal to 1 h) plasma and saliva drug levels run approximately parallel. However, the mean concentration ratio has a large variance. iii) The time courses of heart rate are closely related to the time courses of drug level. iv) When the sustained release form is used for a long-term therapy, it is possible to evaluate dosage schedules and dosage regimens that reduce cardiac side effects caused by the fast release form. This was shown by computer simulation carried out on the basis of pharmacokinetic parameters that were estimated from the experimental curves.

[Drug effects on embryo and fetus. 2. Diaplacental transport of drugs]

Drugs administered in pregnancy have primarily as their target the mother, and the embryo or fetus is an unwanted recipient. Only in a few cases therapy of the growing child via the mother is intended. Thus the knowledge of the risk-benefit ratios of various drug regimens during pregnancy is a matter of utmost concern to each physician. Experimental and clinical data show that there is no direct relationship between the chemical structure, the pharmacological activity or the toxicity of a drug in the adult and its specific action on the embryo. Nevertheless, the considerations presently known to be involved in determining whether a drug will be teratogenic and toxic or not mainly depend upon the type of drug, duration of dosage, access to the conceptus, developmental embryonic stage at time of dosage, disposition within the fetus and individual susceptibility. We have attempted to summarize the present knowledge concerning drug disposition in the embryo and fetus. In addition, based upon the mathematical evaluation of some new experimental results the pharmacokinetics of diaplacental drug transfer is demonstrated.