A patient in septic shock has a resting heart rate of 128 beats per minute. The intensivist wants an inotrope that increases stroke volume with relatively little additional tachycardia compared with isoproterenol. The appropriate choice and its rationale are:
- A Epinephrine, because it spares the sinoatrial node at low doses
- B Norepinephrine, because it is a pure beta-1 agonist
- C Dobutamine, because its isomers combine weak alpha-1 antagonism and beta-1 agonism, limiting chronotropy ✓
- D Isoproterenol, because pure beta-2 stimulation avoids cardiac side effects
Correct answer: C. Dobutamine, because its isomers combine weak alpha-1 antagonism and beta-1 agonism, limiting chronotropy
Explanation
Dobutamine is a racemic mixture: the plus-isomer is a potent beta-1 agonist and alpha-1 antagonist, while the minus-isomer is a weaker beta-1 and beta-2 agonist with alpha-1 agonist activity. The combined profile yields strong inotropic effects with modest chronotropic drive, making it preferable when tachycardia is undesirable. Norepinephrine is predominantly an alpha-1 agonist, and isoproterenol produces marked tachycardia through nonselective beta stimulation.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
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