Digoxin is the primary cardiac glycoside in clinical use. Because of the narrow therapeutic index and risk of toxicity, therapeutic drug monitoring is highly recommended. In Egypt, most cardiologists give digoxin holiday for both atrial fibrillation and heart failure, it is not clear if the interrupted digoxin regimens are effective since serum digoxin concentrations might fall below the therapeutic range.

Objective: To evaluate and compare the digoxin serum concentration and patient's quality of life in the continuous versus interrupted digoxin dosing regimens.

Digoxin is a cardiac glycoside prescribed in heart failure and certain supraventricular tachyarrhythmias. It exerts a positive inotropic, neurohormonal, and electro physiologic actions on the heart . For heart failure patients, the targeted steady state serum digoxin level is between 0.5 and 0.8 ng/ml . Ventricular rate control in atrial fibrillation patients will usually require higher digoxin steady state serum concentrations . However, serum digoxin level higher than 2 ng/ml is associated with increased incidence of adverse drug reactions and should be avoided . Because of inter and intra-patient variability, narrow therapeutic index, and risk of toxicity, digoxin doses are calculated based on the patient weight, renal status, indications and drug interactions. Due to substantial overlap between therapeutic and toxic levels of digoxin, therapeutic drug monitoring is a must especially in patients with deteriorating renal function and electrolyte disturbance. In Egypt, most cardiologists give a digoxin holiday for patients with atrial fibrillation and /or heart failure where patients skip the drug doses on Thursday and Friday or Friday only every week to avoid possible drug accumulation and toxicity. It is not clear if these interrupted digoxin regimens really offer safer alternative over the continuous dosing regimens without compromising the effectiveness. It is anticipated that plasma digoxin levels may fall below the therapeutic range during the holiday which may affect patient clinical status and quality of life.

Inclusion Criteria:

• Patients with atrial fibrillation (AF)
• with or without congestive heart failure (CHF)
• taking digoxin tablets with or without holiday regimens

Exclusion Criteria:

• taking the following drugs concurrently: amiodarone, verapamil, quinidine and propafenone.
• diagnosed with thyroid disorders (hyperthyroidism & hypothyroidism).
• diagnosed with renal failure
• pregnant