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Beta blockers


  • block beta-adrenergic receptors
  • some have selectivity for beta-1 or beta-2 receptors
  • b-blockers are used to reduce cardiac work and myocardial oxygen consumption.
  • They bind to b1 adrenoreceptors within the sino-atrial node and the myocardium,
  • act to reduce the increase in heart rate and force of contraction
    • during exercise
    • times of anxiety
  • they also improve myocardial perfusion by prolonging diastole

Affects

  • slow heart rate

  • depress myocardium

Drugs

  • intrinsic sympathomimetic activity (less cold extremities)
    • oxprenolol
    • pindolol
    • acebutolol
    • celiprolol
  • water-soluble (less psychiatric disturbance, more problems in renal impairment)
    • atenolol
    • celiprolol
    • nadolol
    • sotalol (may prolong QT - avoid Hypokalaemia)
  • vasodilating
    • labetalol
    • celiprolol
    • carvedilol
    • nebivolol
  • cardioselective (beta-1 antagonism > beta-2)
    • atenolol
    • betaxolol
    • bisoprolol
    • metoprolol
    • acebutolol
  • short acting
    • esmolol

Contra-indications

Side Effects

  • heart
    • fatigue, loss of joie de vivre
    • subtle changes in exercise tolerance
    • hypotension
    • bradycardia
    • heart failure
    • conduction disorders
  • peripheral CVS
    • peripheral vasoconstriction
    • coldness of extremities
  • respiratory
    • bronchospasm
    • Use with caution in asthma & heart failure
  • neuro
    • sleep disturbance
  • GI disturbance
  • metabolic
    • reduction in glucose tolerance
    • impaired response to hypoglycaemia
  • Other
    • exacerbations of Psoriasis
    • Dry eyes
    • corneal anaesthesia
    • allergy

Side effects

  • Intolerance
    • fatigue
    • cold extremities
    • sexual dysfunction
    • loss of motivation
  • Bronchospasm: regardless of whether the drug used is cardioselective or not
  • CNS effects
    • more common with lipid soluble drugs and include
    • malaise
    • vivid dreams
    • nightmares
    • hallucinations
  • Masking of hypoglycaemia
  • Metabolic disturbances
    • increase plasma triglyceride
    • decrease high density lipoprotein

Use

Pharmacokinetics

  • well absorbed orally
  • lipid soluble drugs e.g. metoprolol
    • absorbed more rapidly by the gut, than the lipid insoluble drugs
    • experience higher presystemic metabolism in the gut wall and the liver
    • once in the circulation these drugs tend to be protein bound
  • Polar b blockers
    • excreted by the kidney without metabolism
    • have longer half-lives
    • not protein bound
    • accumulate in renal failure
  • Half-life of most b blockers is short such that multiple daily dosing may be required
  • b1 selective blockers are preferred because there are less side effects

Dose

  • Atenolol 50-200 mg daily
  • Metoprolol 100-400 mg daily
  • Bisprolol 5-20 mg daily

Interactions

  • Anti-arhymthmics
  • Antidepressants
  • Antihypertensives
  • Ca++ channel blockers