Factors affecting tolerance to digitalis.

A review of factors altering the safety margin between a therapeutic and a toxic dose of digitalis includes the consideration of: clinical conditions to which digitalis action may be undesirable, allergy and hypersensitivity to digitalis, physiologic factors modifying tolerance to digitalis, factors that change the amount of digitalis in the body, nervous and metabolic factors modifying tolerance to digitalis, modifications of digitalis tolerance produced by the status of the myocardium, and modifications of digitalis tolerance produced by diseases of other organs. The problems related to digitalis toxicity are more common than those of resistance to treatment. The most important factors contributing to decreased tolerance and risk of toxicity are: heart disease, poor renal function, hypokalemia and hypothyroidism. The roles of impaired liver function, chronic lung disease, acid-base disturbances, anesthesia, autonomic imbalance, calcium and magnesium are less important and less well established.