Cardiovascular drugs

Cardiovascular drugs

1. Drugs that alter contraction forces (inotropes)

   • Glycosides
     • They cause intracellular calcium to build up to make a more forceful contraction. They have a narrow safety margin and high doses can cause fatal arrhythmias! FOXGLOVE PLANT. E.g. Digoxin
   • Calcium sensitizers
     • They enhance the affinity of myocardial troponin C to existing intracellular calcium. They also act as a vasodilator! E.g. Vetmedin
   • Xanthine derivatives
     • They are caffeine derivatives and produce a mild positive inotropic effect. They also stimulate the heart rate!

2. Drugs that alter heart rate (chronotropes)

   • Xanthine derivatives
     • Because of their caffeine-like effects they cause a mild increase of the heart rate (positive chronotrope)
   • Beta blockers
     • This is a negative chronotrope and works by antagonising the beta adrenergic receptors of the heart and prevent it from becoming too fast in a sympathetic stimulation. They have potent hypotensive effects in surgery, diuretics and CCB's. They increase bradycardia with Digoxin and an overdose would lead to blood pressure collapse!
   • Glycosides
     • Acts on the nerve cells of the heart causing a decrease in the heart rate (negative chronotrope)
   • Calcium channel blockers
     • Inhibit the uptake of calcium in three cells: 1. Heart muscle cells - causing a mild negative inotropic effect 2. Vascular smooth muscle - mild vasodilation 3. Heart nerve cells - mild negative chronotropic effect

3. Drugs that alter peripheral circulation

   • ACE Inhibitors
     • They block Angiotensin Converting Enzyme = vasodilation = decrease in BP so Angiotensin I cannot convert to Angiotensin II. E.g. Fortekor
   • Diuretics
     • A loop diuretic - Inhibits sodium reabsorption in the ascending Loop of Henle. This produces a more dilute urine and reduces oedema and resp. distress. Hypokalaemia is a potential side effect - it replaces extra Na that returns into circulation but spirondactones are K absorbers so they work well together.
   • Vasodilators
     • Absorbed through the skin causing vasodilation. They cause a marked decrease in BP in emergency CHF