The cardiovascular effects of xamoterol, a beta 1‐adrenoceptor partial agonist, in healthy volunteers at rest.

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Abstract
The cardiovascular effects of three single intravenous doses of a beta 1‐adrenoceptor partial agonist, xamoterol (0.025, 0.05 and 0.1 mg kg‐1) and placebo were studied in six healthy volunteers at rest using a single‐blind design. In addition to heart rate and blood pressure measurements, cardiac contractility was measured by means of M‐mode echocardiography and systolic time intervals. Ambulatory 24 h Holter‐ monitoring of the electrocardiogram was performed. Plasma concentrations of xamoterol were measured. Compared to baseline, xamoterol (0.025 mg kg‐1) increased heart rate (61 +/‐ 3‐68 +/‐ 3 beats min‐1, means and SEM) and systolic blood pressure (119 +/‐ 3‐138 +/‐ 5 mm Hg) but decreased pre‐ejection period (100 +/‐ 4‐76 +/‐ 5 msec). Stroke volume (88 +/‐ 6‐104 +/‐ 10 ml), cardiac output (4.8 +/‐ 0.4‐6.6 +/‐ 0.61 min‐1), velocity of circumferential fibre shortening (1.15 +/‐ 0.06‐1.50 +/‐ 0.06 circ s‐1) were increased by xamoterol. No significant changes were produced by placebo. No dose‐dependent effects were seen and maximum effects were produced by 0.025 mg kg‐1 xamoterol. Significant effects were observed for 2 h. The areas under the plasma concentration curves (AUC0‐12) showed a linear dose response. No adverse effects attributable to xamoterol were seen in haematological, biochemical, urinalysis or electrocardiographic tests. Four volunteers were aware of a more forceful heart beat after xamoterol, but this was mild and transient. It is concluded that xamoterol has a positive inotropic action.