[Underdosing and overdosing with digitalis].

Incorrect dosage of digitalis occurs frequently and is due in most cases to relative over- or underdosage. The narrow therapeutic range of all cardiac glycosides and the lack of an ideal preparation form the basis, and noncompliance of the ill-informed patient as well as the changing digitalis requirement from patient to patient, and even in the same patient, are the most frequent causes of dosage errors. Important guidelines for the dosage of digoxin and digitoxin (renal failure, diseases of the liver and gastrointestinal tract, body weight, age, electrolyte disorders, hypoxia, thyroid dysfunction and drug interactions) are discussed. Symptoms, signs and treatment of underdigitalization and digitalis intoxication, a frequent and often lethal complication, are reviewed.