Digoxin: Hyper or Hypo Kalaemia

• cardiac glycoside manufactured and derived from the Foxglove plant.
• It inhibits the Sodium-Potassium ATPase, similarly known as the Sodium-Potassium Pump.
• Sodium and Potassium are moved across the cell membrane via active transport.
• inhibits this action, thereby inhibiting the electrical impulses in the atrioventricular node in the upper portion of the heart.
• In turn, the medication is utilized to control the rate in RVR (Rapid Ventricular Rate) Atrial Fibrillation, most commonly

Hyperkalaemia

• decreases the use of K+ ions in the sodium-potassium pump by decreasing the NA-K ATPase activity. This reduction leads to a build-up of potassium in the body.
• Dehydration and various illnesses often are also contributing factors to the change to K+ levels and hyperkalemia.
• Creatinine, urine K+, and Osmolarity labs would be the first step in determination of the reason for the hyperkalemia.

Hypokalaemia

• Not caused by Digoxin
• most frequently caused prior to the digoxin toxicity and is many times a key element to causing the digoxin toxicity.
• patient has an underlying need for K+ secondary to a reduction of intake and or excess excretion.
• Diuretics commonly used in associated illnesses such as the first-line treatment of HTN (hypertension) & CHF (congestive heart failure), will result in increased secretion of K+ through the renal system (kidneys).
• This reduction of K+ from the diuretic will enhance and speed the toxic serum levels of the digitalis/digoxin

Mechanism of Toxicity in Hypokalaemia

• In hypokalemia the original concerntration of K across the membrane get decreased thereby decreasing the Resting Membrane Potential which deteremines refractiveness of the cell and the cell itself becomes more responsive to slight ionic changes.
• digoxin delays the K influx in the cardiac muscle rendering it more excitable to AP thus causing extrasystoles or Premature beats which are due to enhanced presence of calcium inside the cells

References:

1. American Academy of Family Physicians On-Line Journal Reference(s); National Institute of Health On-Line Library: Case Studies.
2. http://www.cvpharmacology.com/cardiostimulatory/digitalis
3. Mechanisms, manifestations, and management of digoxin toxicity
4. http://www.drugguide.com/ddo/view/Davis-Drug-Guide/51218/all/digoxin