Quinidine-digoxin interaction: cardiac efficacy of elevated serum digoxin concentration.

Cardioactivity due to elevated serum digoxin concentration (SDC) after quinidine (Q) and digoxin (D) was evaluated in six healthy subjects by means of measurement of systolic time intervals (STIs). Each subject randomly received basic treatments with 0.2 mg D and placebo (PL1). Randomized coadministrations with Q (1 gm/day), sparteine (SP) (0.8 gm/day), and placebo (PL2) were given for 7-day periods. A steady-state dose of 0.4 mg D was added. Mean SDC increased from 0.48 ng/ml during 0.2 mg D + PL2 to 1.13 ng/ml on 0.2 mg D + Q (P less than 0.05); it was unchanged by SP. On 0.4 mg D there were further shortenings of STIs compared to those on 0.2 mg D + PL2. Q markedly prolonged STIs; the SP effects were similar but less pronounced. When given with Q or SP, the effect of D was obscured by opposing inotropic properties; consequently, despite increasing SDC, measureable STIs were unchanged. The true glycoside effect was determined by comparing the effects of the pure antiarrhythmic to those of the antiarrhythmic with D. These calculations showed that the glycoside effect of the elevated SDC during Q + D dosing was much the same as the effect of 0.4 mg D.

Sympathomimetic effects of amezinium on the cardiovascular system and plasma catecholamines in man.

The cardiovascular effects of the sympathomimetic agent amezinium were investigated in a double-blind, placebo-controlled, randomized trial in six volunteers. Before and 2 h after oral administration of amezinium 30 mg or placebo the cardiovascular responses to orthostatic stress, induced by 80 degrees passive head-up tilt, were assessed by recording blood pressure, systolic time intervals, and echocardiogram. Plasma catecholamines were also determined. After amezinium treatment, the average supine systolic blood pressure was increased by +30 mm Hg and after tilting it remained above both the pre-treatment and placebo values. Compared to placebo, amezinium elicited only minor changes in heart rate and diastolic blood pressure. The effect of amezinium on the pre-ejection period corrected for heart rate (PEPc) and mean velocity of fiber shortening (VCFmean) indicated positive inotropic properties. Its effects were distinctly more pronounced during tilt than with the subjects supine. Plasma concentrations of noradrenaline and adrenaline were not influenced by amezinium during rest or tilt. From these results and previous research it is concluded that amezinium induces its sympathomimetic effects by preferentially inhibiting the re-uptake of noradrenaline which is released by the drug itself, or by sympathetic activation during tilt. This mechanism of action might explain the pronounced sympathomimetic effects of the drug, especially during orthostatic stress.

Comparison of impedance cardiography and echocardiography for measurement of stroke volume.

The relationship between stroke volume (SV) measured simultaneously by impedance cardiography (SVI) and echocardiography (SVE) has been analyzed. Change in stroke volume in 6 healthy volunteers was induced by passive head-up tilting (80 degrees) and by oral administration of the sympathomimetic drug amezinium. A correlation of r = 0.83 (p much less than 0.01) was found between SVI and SVE calculated by the equation: SVE = 16.0 + (0.528 x SVI). Though stroke volume is overestimated by impedance cardiography, the method may be useful for the clinical pharmacologist interested in a simple non-invasive tool to estimate stroke volume and change in it.

[Threshold of action of meproscillarin following intravenous administration]. / Wirkungseintritt von Meproscillarin nach intravenöser Applikation.

A placebo-controlled double-blind trial was conducted, to determine the onset of effect of Meproscillarin (injected intravenously). 28 days apart six healthy volunteers were given double-blind 1,0 mg Meproscillarin or placebo and 60 days later 0,6 mg Digoxin, each drug as short infusion over four minutes. The total electromechanical systole corrected for heart rate (QS2c), was used as criterion of the inotropic effect of the glycoside. After placebo there no changes were observed over a period of two hours. Both glycosides shortened QS2c for about--16 ms. From Meproscillarin a 40% higher dosis was required, to achieve the same effect as with digoxin. After use of Meproscillarin the peak effect was reached after ten minutes; after digoxin a period of 60--120 minutes were required. The results show that intravenously given Meproscillarin is a fast acting glycoside.