Introduction
Digoxin is a medication sold under the trade name Lanoxin. It is prescribed for patients suffering from mild and moderate heart failure (Concordia Pharmaceuticals Inc., 2016). It is usually used in combination with diuretics or ACE inhibitors (Concordia Pharmaceuticals Inc., 2016). This paper will review the pharmacokinetic properties of digoxin, patient specific factors that change the percentage of free drug, and its hydrophilic and lipophilic properties.
Essence
The absorption of this drug through oral administration is incomplete. Only 60-80% of Lanoxin tablets are absorbed, and the process takes 1 to 3 hours (Concordia Pharmaceuticals Inc., 2016). However, if the medication is taken intravenously, it demonstrates absolute bioavailability (Concordia Pharmaceuticals Inc., 2016). After the drug administration, digoxin is distributed among tissues during 6-9 hours (Concordia Pharmaceuticals Inc., 2016).
Only 13% of the medication is metabolized in healthy volunteers, and the process does not depend on cytochrome P-450 system (Concordia Pharmaceuticals Inc., 2016). Digoxin has first-order elimination kinetics, meaning that the higher dose is consumes, the higher amount of the medication is excreted (Concordia Pharmaceuticals Inc., 2016). Due to the peculiarities of its pharmacokinetics, the dosage of digoxin should be prescribed individually.
The medication has several patient-specific factors that change the percentage of free drug. They include gastrointestinal effects, such as vomiting, anorexia, and nausea, as well as poor renal function and specific central nervous system conditions (Shah, Gandhi, Srivastava, Shah, & Mansukhani, 2017). For example, in some patients, over 40% of the consumed dose may be degraded by colonic bacteria, while the bioavailability of the drug in patients without this factor is usually about 80% (Concordia Pharmaceuticals Inc., 2016). Therefore, it is necessary to adjust the dose according to the patient’s characteristics.
The final thing to be considered about digoxin is its chemical properties. This drug is highly hydrophilic, which means that its dose should depend on lean body mass (MacLeod-Glover, Mink, Yarema, & Chuang, 2016). Since digoxin concentrations do not significantly change in fat tissues, it may be assumed that it is not lipophilic (Concordia Pharmaceuticals Inc., 2016). Lipophilic substances are harder to excrete from the body because they are not excreted directly from kidneys (“Small Molecule Drug,” 2016). To be excreted into urine, they have to be transformed into hydrophilic molecules (“Small Molecule Drug,” 2016). Thus, chemical properties of digoxin facilitate its excretion from the body.
References
Concordia Pharmaceuticals Inc. (2016). Highlights of prescribing information. Web.
MacLeod-Glover, N., Mink, M., Yarema, M., & Chuang, R. (2016). Digoxin toxicity: Case for retiring its use in elderly patients? Canadian Family Physician, 62(3), 223-228.
Shah, A., Gandhi, D., Srivastava, S., Shah, K. J., & Mansukhani, R. (2017). Heart failure: A Class review of pharmacotherapy. Pharmacy & Therapeutics, 42(7), 464-472.
Small Molecule Drug Metabolism. (2016). Web.