[Positive inotropic agents. Generalities and classification]

Abstract

The aim of inotropic therapy is to increase the force of myocardial fibre shortening by improving the availability of calcium to the contractile proteins. Digitalis remains the most widely used drug, but its positive inotropic effects are weak and the therapeutic index is low. Dobutamine is the most useful catecholamine because the most cardioselective and it induces the least increase in myocardial oxygen consumption. There are three groups of new inotropic agents: sympathomimetics: pirbuterol and prenalterol are effective in the short term but tolerance is usually observed within a few weeks. Salbutamol and terbutaline have only been assessed in acute studies, phosphodiesterase inhibitors (MDL 17043, MDL 19025) are powerful inotropic agents in the short and medium term. ARL 115 has mainly been studied by parenteral administration, Amrinone has a largely unknown mode of action, but is a very effective positive inotropic drug; its side-effects limit it as age. However, its derivative, milrinone, seems to be more inotropic and less toxic. The new inotropic drugs currently under assessment are active in the short term but their long-term efficacy and side-effects are still little known. The ideal inotropic agent remains to be discovered.