Third-Generation Beta-Blockers

Third-Generation Beta-Blockers

1. Definition & scope of "third-generation"

• Third-generation β-blockers are β-adrenergic receptor antagonists that, in addition to β-receptor blockade, possess intrinsic vasodilating properties mediated by mechanisms largely unrelated to β-receptor blockade — they are the "vasodilating β-blockers" (G&G 14e Ch.14, pp.272, 281–282).
• G&G classifies the whole β-antagonist family by three "generations" (G&G 14e Ch.14, p.272):
  • First generation — non-subtype-selective (block β₁ = β₂); prototype propranolol; others: nadolol, timolol, pindolol, penbutolol, sotalol.
  • Second generation — β₁-selective ("cardioselective"); metoprolol, atenolol, bisoprolol, acebutolol, betaxolol, esmolol.
  • Third generation — non-selective or subtype-selective antagonists with additional cardiovascular (especially vasodilating) actions: carvedilol, labetalol, carteolol, bucindolol (non-selective vasodilators) and celiprolol, nebivolol, betaxolol (β₁-selective vasodilators) (G&G 14e Ch.14, Table 14–5, pp.279–280).
• KDT explicitly labels nebivolol and celiprolol as "third generation β blocker[s]" — highly selective β₁ blockers that additionally produce vasodilatation (via NO for nebivolol; via NO + weak β₂-agonism for celiprolol) (KDT 8e Ch.10, p.163).
• Katzung frames the same drugs functionally rather than by "generation" — "vasodilating β blockers may be preferred in patients with heart failure or hypertension," and groups carvedilol/labetalol (α-blocking) and nebivolol (NO-promoting) as β-blockers with vasodilating ancillary properties (Katzung 16e Ch.10, pp.169, 1117–1118).
• The defining feature is therefore added peripheral vasodilation, which counteracts the rise in peripheral vascular resistance seen acutely with classical (first/second-generation) β-blockade and confers a more favourable haemodynamic and metabolic profile (G&G 14e Ch.14, pp.273–274).