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Galanthamine hydrobromide (Nivalin®, dose 10 mg) was given subcutaneously and orally to 8 volunteers. Galanthamine and its metabolites were quantified in plasma and urine by reversed-phase HPLC. An unusual two-stage absorption and biexponential drug decline were observed. Galanthamine plasma peaks (1.24 µg/ml after subcutaneous and 1.15 µg/ml after oral doses) were reached 2 h following administration, the t_½(β) values being 5.70 and 5.26 h, respectively. Minor epigalanthamine and galanthaminone plasma levels were detected. An almost complete urinary recovery of galanthamine and its metabolites was obtained within 72 h. The plasma AUC, C_max, t_max and k_a suggest that the subcutaneous and oral Nivalin formulations are bioequivalent.

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Based on precise analysis of the acid-base equilibrium, a new approach in the treatment of experimental data from a potentiometric titration is proposed. A new general formula giving explicitly the relation V=f([H(+)]) is derived, valid for every acid-base titration, which includes mono- and polyfunctional protolytes and their mixtures. The present study is the first practical application of this formula for the simplest case, the analysis of one monofunctional protolyte. The collected mV data during the titration are converted into pH-values by means of an auto pH-calibration procedure, thus avoiding preliminary preparation of the measuring system. The mentioned pH-calibration method is applicable also in water-organic mixtures and allows the quantitative determination of sparingly soluble substances (particularly pharmaceuticals). The treatment of the data is performed by means of ready-to-use software products, which makes the proposed approach accessible for a wide range of applications.

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