FEATURE ARTICLE Digoxin Therapy in the Elderly: Pharmacokinetic Considerations in Nursing Herbert Jelinek P. Warner Q1 Digoxin is effective in controlling ventricular rhythm in atrial fibrillation and is used in heart failure when angiotensin converting enzyme inhibitors and diuretics are ineffective. Be- cause use of more than 1 drug is often required with these conditions, pharmacokinetic con- siderations, including those related to comple- mentary medicine, are important. Increased awareness of drug action in the elderly is im- portant because there is often an increase in body fat and leaner muscle mass as well as changes in organ function, such as that of the kidney, which alters drug activity. Nurses have an important role to play in the safe ad- ministration of digoxin. (Geriatr Nurs 2011;- :---) Introduction C ongestive heart failure is characterized by a complex pathology that combines me- chanical failure, myocardial abnormali- ties, and rhythm disturbance, such as atrial fibrillation (AF). Several clinical trials have indi- cated digoxin for treatment of patients with heart failure that remains symptomatic following first- line use of angiotensin converting enzyme (ACE) inhibitors, beta-blockers, diuretics, and/or aldo- sterone antagonists. 1 Digoxin is also used for per- manent/persistent AF with rapid ventricular rhythm and as first-line treatment in heart failure with coexisting AF. 2 The benefit of digoxin is that it is effective in treating congestive heart failure (CHF) and AF. However, digoxin’s pharmacokinetic profile is af- fected by interactions with other medication used to treat CHF and AF, as well as by aging. 3,4 Nurses’ good understanding of the pharmacokinetics of digoxin in the elderly will ensure that adverse consequences of drug administration are minimized. The problem is that there is no ready algorithm to work out the correct dose as the aging process differs between individuals and occurrence of disease increases, confounded by a narrowing therapeutic window. 5 Pharmacokinetics Pharmacokinetics consists of drug absorption, distribution, metabolism, and elimination, as well as factors affecting these functions. 6 It provides information that enables drug doses and dosing interval to be administered at an appropriate level and ensures optimal plasma concentration and effectiveness. Pharmacokinetic processes differ depending on the route of administration, with oral dosing the most common. Three impor- tant pharmacokinetic parameters are volume of distribution, half-life, and clearance. 6,7 Volume of Distribution The volume of distribution (VD) is determined by the ratio of the amount of drug divided by the plasma concentration. The main determinant of the volume of distribution is the strength of drug binding to tissues. 8 Plasma concentration in turn is determined by many factors such as drug absorption and binding to plasma proteins. Digoxin is absorbed through the intestinal wall via a P-glycoprotein transport molecule and binds to albumin or a 1 -acid glycoprotein (AAG) in the blood. AAG increases in numerous dis- eases such as HIV AIDS, inflammation, thyroid disease, renal and hepatic insufficiency, and AF, which changes the VD of digoxin. 9,10 AAGs also become more prominent in the aged and therefore may change the unbound digoxin drug fraction. 11 Drug Half Life The half-life of a drug is the time taken for the plasma concentration of a drug to be half of its original concentration and depends on the vol- ume of distribution and clearance. Half-life Geriatric Nursing, Volume -, Number - 1 FLA 5.1.0 DTD - YMGN844_proof - 19 April 2011 - 6:23 pm - ce 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109