A synthetic catecholamine used in acute heart failure increases stroke volume with minimal increase in heart rate, allowing higher doses without marked tachycardia. Its commercial preparation is a racemic mixture of two enantiomers with opposing chronotropic actions. Which drug is described?
- A Dobutamine ✓
- B Isoproterenol
- C Dopamine
- D Norepinephrine
Correct answer: A. Dobutamine
Explanation
Dobutamine is supplied as a racemate. The l-isomer is a potent beta-1 agonist with some alpha-1 activity, while the d-isomer is a weak beta-1 and beta-2 agonist but also an alpha-1 antagonist. Their combined effect favours strong positive inotropy with relatively modest chronotropy. Isoproterenol produces intense tachycardia and dopamine at inotropic doses causes appreciable chronotropy, so neither fits. Norepinephrine raises afterload through vasoconstriction and reflexively slows the heart.
Reference: Goodman and Gilman's The Pharmacological Basis of Therapeutics, 14th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.