What Factors Affect a Digitalis Dosage?

While the herb foxglove, also known as digitalis, had been used by European herbalists to treat heart conditions for centuries, it was not until 1785 that it was first mentioned in English language medical literature. The incorporation of this plant into the medical material was considered to be the beginning of the use of drug therapies in conventional Western medicine. Centuries later, the cardiac glycoside digoxin, or digitoxin, was isolated and determined to be the herb's principle therapeutic constituent and has since remained the most commonly used drug for the treatment of atrial fibrillation in congestive heart failure. Due to the wide variance in individual response to digoxin, it is important to tailor each individual patient's digitalis dosage to ensure that he or she is receiving optimum therapeutic activity and experiencing as few side effects as possible. Other factors that may require adjustments to digitalis dosage are the patient's age, weight, kidney health, diagnosis of associated medical conditions, and drug regimen.

Since digoxin is believed to work through both the inhibition of the enzyme sodium-potassium ATP-ase and the direct action on the vagus nerve, drugs that increase sympathetic nervous system activity or affect the body's ion levels may interact with this drug. If these drugs cannot be discontinued and must be used alongside digitalis, dosage adjustments and direct medical supervision are likely to be required. The drugs dronedarone and amiodarone may increase blood levels of digoxin, making a reduction in digitalis dosage necessary.

Patients undergoing treatment for atrial fibrillation should ideally receive a digitalis dosage carefully adjusted so that they maintain body stores of digoxin greater than the 8 to 12 mcg per kilogram of body weight that is generally recommended for patients with congestive heart failure. Low initial doses may be gradually increased under medical supervision to determine plasma levels of the drug. It is critical that the smallest possible clinically effective digitalis dosage be used to reduce the incidence of dose-dependent side effects.

Pediatric patients are believed to process digoxin differently than adults, making it necessary to use a lower digitalis dosage per kilogram of body weight than is generally recommended. Similarly, patients with moderate to severe reductions in kidney function may not be able to eliminate the drug as rapidly as patients with healthy kidneys. The initial digitalis dosage for these patients should be no greater than 50% of the standard dose. Any increases in dose should be undertaken only under close medical supervision.