The effect of oral dosing of xamoterol on systolic time intervals in man and xamoterol plasma concentrations in heart failure patients.

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Abstract
1. Six healthy male human volunteers of mean age 30.8 years (range 23‐ 37) were given single oral doses of xamoterol (20, 50, 100 or 250 mg) and placebo with a 1 week interval between each dose. Xamoterol produced a significant decrease in systolic time intervals (QS2I, LVETI and PEPI) and a significant increase in systolic blood pressure indicating a positive inotropic effect on the heart at rest. The changes in QS2I were dose‐related. Maximum decreases in QS2I were noted 1 to 2 h after dosing and were achieved with a dose of 100 mg. 2. In a second study, oral administration of xamoterol at 3 doses (100, 200 or 300 mg) and placebo were studied in 12 patients of mean age 60.4 years (range 52‐73) with mild to moderate heart failure. Each dose was given twice daily for 7 days in a random order. Each dose of xamoterol produced a significant decrease in systolic time intervals indicating a positive inotropic effect on the heart at rest in patients with heart failure. It was not possible to distinguish between the effects of the three doses of xamoterol. 3. In heart failure patients, peak plasma concentrations of xamoterol occurred 1 to 2 h after dosing at all dosage levels and there was a linear relationship between dose and plasma concentration. 4. In both studies xamoterol was well tolerated and only minor adverse experiences were reported. 5. We conclude that, at rest, xamoterol has a positive inotropic effect on the heart when given orally to healthy volunteers or patients with mild to moderate heart failure.