The document discusses various drugs that can increase the force of myocardial contraction, known as positive inotropic drugs, including cardiac glycosides like digoxin, beta-adrenergic agonists, and phosphodiesterase inhibitors. It provides details on the mechanisms of action and effects of these drugs, such as how cardiac glycosides inhibit the sodium-potassium ATPase pump to increase intracellular calcium levels. A variety of conditions are also listed where these positive inotropic drugs may be used, including congestive heart failure, shock, and cardiac emergencies.

1. Dr. RAGHU PRASADA M S
MBBS,MD
ASSISTANT PROFESSOR
DEPT. OF PHARMACOLOGY
SSIMS & RC.
1

2. Force of myocardial contraction
An ideal cardiotonic agent should not increase
heart rate & should be devoid of toxic effects.
Positive inotropic drug: increases force of
contractions
Increase force of myocardial contraction
Causes improved heart’s pumping ability
Negative inotropic drug: decreases force of
contraction

3.  Cardiac glycosides: Digitoxin, Digoxin
 β-adrenergic agonists (New dopamine receptor
agonist): dopamine, Dobutamine, Dopexamine
Phosphodiesterase inhibitors : Amrinone
Milrinone

4. SOURCE GLYCOSIDES
1.D.PURPUREA - Digitoxin, Gitoxin,
Gitalin
2.D.Lanata - Digitoxin, Gitoxin
Aglycon consist of cyclopentanoperhydrophenanthrene
(steroid) ring 5 or 6 membered unsaturated lactones
ring.

5.  Digitalis increase force of cardiac contraction by a
direct action independent of innervations.
 It selectively binds to extra cellular face of
membrane associated NA+K+ ATPase of myocardial
fibres & inhibits this enzyme.
 Inhibition of this cation pump results in progressive
accumulation of NA+ intracellularly.
 This indirectly results in intracellular Ca+
accumulation.

6. CHF
Cardiac Arrhythmias :
Atrial fibrillation,
Atrial flutter (AFL)
Proxysmal supraventricular tachycardia (PSVT
Precaution & contraindications :-
Hypokalemia
Thyrotoxicosis

7.  Extra cardiac –
anorexia, nausea, vomiting, abdominal pain are usually
reported first , are due to gastric irritation, mesenteric
vasoconstriction & CTZ stimulation.
 Cardiac --
almost every type of arrhythmia can be produced by
digitalis ; pulses big minus , nodal & ventricular extra
systoles, ventricular tachycardia & terminally
fibrillation.

8.  They are used intravenously in CHF emergencies
 Example of β -Adrenoceptor agonists
 Dobutamine
• Exciting β1 Adrenoceptor → positive inotropic
action →the volume of output↑
• Exciting β2 Adrenoceptor→dilate the vascular →
afterload↓
 have benefits within short time

9. Phosphodiesterase-Ⅲ inhibitors
Inodilator / inodilating drugs
Inhibiting the activity of PDE Ⅲ → cAMP↑→ causes an
increase in myocardial contractility and vasodilatation
→total peripheral resistance →cardiac output ↑
Examples:
Amrininone: Inhibits the excess product of NO, TNF and
affects the neurohormone, anti-the forming of thrombus
Milrinone: stronger 20 time

10.  Congestive heart failure
 Shock conditions-hypovolumic, septic,
cardiogenic
 Cardiac emergencies

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