Tackling the non-linearizeable dose-response relationship in clotting time assays of heparin.

Heparin sodium was assayed by turbidimetric measurement of the clotting time of bovine citrate plasma with thromboplastin, between the moment of recalcification and the moment of maximal speed of polymerization of the fibrinogen monomer, as marked by the turning-point of the trace of the turbidimetric record. Most assays were practiced in the range of 0.2-2.0 units per test volume. The lower end of the range could be extended by decreasing the thromboplastin dose, the higher end by increasing this dose. The dose-response relationship for heparin sodium, i.e. between the nominal heparin activity x and the clotting time y, was non-linear in such a way that no uniform mathematical transformation could provide a valid linearization over the whole range. A non-linear regression in the form of a cubic fit, applied to the data pairs (x, y) of both standard and test sample, proved to be satisfactory. The two non-linear regression curves were compared at varying levels of x by computing the quotient of nominal and actual activity for equal clotting times, and by computing the quotient of the slopes (tangents) of the curves for these times. The percentual deviation of the test sample potency from the standard's potency as obtained from the former quotient was termed Za, and the deviation as computed from the latter quotient was termed Ztg, Za and Ztg as functions of x were plotted and were found to intersect invariably at critical points of Za(x) within the range of the experiment. This seems to be a theorem.(ABSTRACT TRUNCATED AT 250 WORDS)

Simple monitoring of low salicylate concentrations in capillary blood. An appraisal of ultraviolet spectrophotometric methods.

The differential ultraviolet spectrophotometric determination of salicylate according to Williams et al. (11) and the single extraction ultraviolet spectrophotometric method of Stevenson (9) are subject to interference by serotonin. Probably as a result of this interference, the results are erratic when low concentrations of salicylate are monitored in capillary blood. Owing to a peculiarity of the ultraviolet absorbance spectrum of serotonin, there is no appreciable interference by serotonin, if the double extraction method of Stevenson (9) is used, in which the spectrophotometry is carried out in phosphate buffer of pH 6.86. With due precautions and standardization, reliable results are obtained, so that this comparatively simple and rapid method can be recommended wherever capillary blood sampling (finger tip, the heel in pediatrics) is preferable to venous blood sampling. Pharmacokinetical results, obtained by this method, are given for three human subjects after a single oral dose of 500 mg aspirin.

[On the inhibition of thrombocyte aggregation by bupranolol / Aggregometric and electron microscopic study in vitro (author's transl)]. / Zur Hemmung der Thrombozytenaggregation durch Bupranolol. Eine aggregometrische und elektronenmikroskopische In-vitro-Studie.

The ADP-induced primary aggregation of human thrombocytes in vitro was inhibited by 1.5X10(-4) mol/l (+/-)bupranolol. At this concentration a strong desaggregation was obtained. The stereoisomers of bupranolol did not differ in effectiveness. Fractional addition was just as effective as a single dose. Not beta-receptor blocking but a membrane stabilizing effect is, therefore, the probable mechanism -- as in the case of propranolol. The less lipophilic metabolites hydroxybupranolol and carboxybupranolol were one-fourth and one-fifth as effective, respectively, as bupranolol. 5X10(-4) mol/l ASA (final concentration) showed the same inhibition of primary aggregation as did 1.5X10(-4) mol/l bupranolol but elicited less desaggregation. Doubling this dose of ASA resulted in a weaker inhibition than the subsequent addition of the aforementioned doses of bupranolol and ASA or vice versa, while this combination, in turn, inhibited less than a double dose of bupranolol. 1.5X10(-4) mol/l bupranolol inhibited the formation of pseudopodia by thrombocytes not stimulated with ADP. At 3X10(-4) mol/l this inhibition was drastic but no morphological damage was seen.