Biomedical subjects

R Süverkrüp

Publications and source records attributed to R Süverkrüp.

6 recordsLinked to original sources

PubMed1990

[Bioequivalence of theophylline retard capsules in children and relation of metabolism to administration route].

The bio-availability of two slow-release theophylline capsules employing different sustained-release principles, was investigated in 12 children suffering from bronchial asthma, on this basis of the renal excretion of the unchanged active substance. With the aid of a model-bound convolution procedure, the completeness and the variability of absorption on multiple dosaging under non-steady-state conditions were established. Depending upon the retardation principle, both the mean bioavailability and its scatter differed from one preparation to the other, one of them being, on average, more completely absorbed than the other, while, at the same time, showing an appreciably more variable bio-availability. In consequence of the first pass metabolisation, the percentage of theophylline that was excreted unchanged in the urine, was greater with the intravenous route of administration than with peroral application. In the case of the secondary metabolite 3-methylxynthine, the situation was reversed.

Adolescent↗

PubMed1989

Numerical stability of pharmacokinetic deconvolution algorithms.

The sensitivity of pharmacokinetic deconvolution algorithms with respect to simulated experimental error has been studied. Approximations of cumulative absorption profiles reconstructed from simulated data sets with normally distributed random error were compared with corresponding known input functions. The coincidence of both functions was assessed in 600 numerical experiments by the nonparametric Kolmogorov-Smirnov test. A constrained iterative nonlinear regression procedure based on the analytical convolution of multiphasic zero-order input functions with linear disposition models was found to perform well under conditions where the results of direct numerical deconvolution and model-based mass balance methods were unsatisfactory.

Absorption↗

PubMed1989

Renal clearance of theophylline and its major metabolites: age and urine flow dependency in paediatric patients.

The renal clearance of theophylline (TH) and its metabolites 1,3-dimethyluric acid (1,3-DMU), 3-methylxanthine (3-MX), and 1-methyluric acid (1-MU) has been studied in 10 children aged 8 months to 14 years. Individual renal clearances were calculated from serum levels and amounts excreted in urine after i.v. administration of the parent drug. The clearance of 1,3-DMU was found to depend both upon urine flow rate and age, which are interrelated. An effect of urinary pH was expected, but was not studied. Consistent age-dependent changes in the relative quantities of metabolites excreted were not observed.

Adolescent↗

PubMed1987

Total theophylline clearance in childhood: the influence of age-dependent changes in metabolism and elimination.

Theophylline metabolism and elimination during childhood are age-dependent. The total clearance, which is the sum of metabolic and renal clearances is highest in infants and young children. To differentiate between the two pathways, theophylline concentrations were measured in both serum and urine in 16 children aged 2 weeks-16 years using the fluorescence polarization immunoassay. It was found that both partial clearances assume maximal values at about the same age, but the fraction of total clearance attributable to the renal route decreases continuously.

Adolescent↗

PubMed1985

Segmentally continuous input functions in linear multicompartment systems.

The convolutions of segmentally continuous zero- and first-order input functions with the general form of pharmacokinetic multicompartmental disposition functions can be used to analyze and simulate the time course of drug invasion into the central compartment of mammillary models and certain physiologically relevant recirculating systems. The generalized model equations may be used to assess the reliability and intercorrelations of parameter estimates directly, since partial derivatives with respect to all model constants can be computed explicitly. In combination with curve-fitting algorithms, input functions identical to those of the point-area deconvolution can be obtained, although at the expense of significantly longer computing times. On the other hand, the range of potential applications goes far beyond the reconstruction of the time course of drug absorption.

Bile↗

PubMed1979

Discontinuous absorption processes in pharmacokinetic models.

The limited contact time of absorbable drug with absorbing surfaces is, in some cases, a significant factor determining the fraction of the dose absorbed. A simple modification of customary linear compartmental models is presented to account for this situation, and a general input function in the Laplace domain for truncated first-order absorption is derived. An extension to series of truncated absorption processes is discussed.

Absorption↗