Cardiotonics are medications used to increase the tonus of cardiac muscle. They help in strengthening the cardiac muscle and increase cardiac output. Most commonly used categories are CARDIAC GLYCOSIDES, SYMPATHOMIMETICS etc. They are given in cases of CARDIAC SHOCK, MYOCARDIAL INFARCTION, CONGESTIVE HEART FAILURE, CARDIAC SURGICAL PROCEDURES. Very widely used cardiotonic is DIGITALIS. The main chemical constituent of foxglove plant is DIGITOXIN, DIGOXIN both enhancing the strength of cardiac muscle. DIGITOXIN: Characteristic features: Color: white to pale colored Odour: Odourless Taste: Bitter Nature: Exists as microcrystalline powder. Proposed biochemical mechanism of action of these cardiac glycosides is their ability to inhibit Na+ K+ ATPase pump responsible for Sodium -Potassium exchange. In general, the membrane depolarization/repolarization effects are brought about by 3 ions- Na+,K+ and Ca2+. 1.During resting phase, concentration of Na+ is very high outside. 2. On membrane depolarization, Na+ enters the cell-->elevating action potential 3. Elevated Na+ levels drives in Ca2+ that enters the cell slowly. 4. Increased levels of Ca2+ triggers the movement of K+ out of the cell. 5. The action potential is established by Na+ K+ exchange. The energy required for this exchange is provided by Na+ K+ ATPase pump. Cardiac glycosides act by inhibiting this enzyme. As a result, Ca2+ retains withing the cell increasing the contraction of cardiac muscle. DIGOXIN acts similar to Digitoxin. It differs in GI absorption, halflife, Onset of action etc. Another drug in this class is DOBUTAMINE commonly sold under brand name DOBUTREX. It is useful in patients with cardiac decompensation. Ref: 1. http://www.people.vcu.edu/~urdesai/car.htm accessed on Dec 1st 2011. 2. http://www.drugs.com/mtm/dobutrex.html accessed on Dec 1st 2011. THIS BLOG IS FREE OF PLAGIARISM.