Digoxin blood level in dogs and cats
Digoxin is a heart medicine from the digitalis group; in dogs it is used, for example, to slow the heart rate in atrial fibrillation. The space between a level that helps and a level that harms is narrow, so vets measure how much of it is in the blood. The number is read together with the time of the last tablet, potassium, kidney values and how the animal feels.
What it shows
Digoxin has a narrow therapeutic window: the amount that works and the amount that poisons are close to each other, and the same tablets can give different levels in different animals. The drug leaves the body mainly unchanged through the kidneys, so kidney function strongly affects how long it stays in the blood.
The level settles after about five half-lives. In dogs the half-life is roughly 23–39 hours; in cats it is extremely variable. A commonly described schedule for dogs and cats is a first test 2–7 days after the start, with blood drawn 8–12 hours after the last tablet, and then about every 6 months, or sooner if signs of poisoning appear. In a small 2022 study of dogs on long-term digoxin, levels sometimes jumped well above the target after the first year without any change in what was given, and the authors advise checking more often.
Higher than reference — what it may be a sign of
- Above the target window. Signs of too much digoxin include loss of appetite, nausea, vomiting, diarrhea, drowsiness and weakness. Digoxin can also cause almost any kind of heart rhythm disturbance, so an ECG is part of the picture.
- Kidney problems. When the kidneys clear less, the level rises; azotemia (raised kidney values) increases the risk of toxic effects.
- Other medicines. Some medicines raise the level of digoxin in the blood; the vet checks the full list.
- Timing of the sample. Blood taken soon after a tablet gives a higher number than a sample at the usual time.
Toxic effects can appear even when the level is inside the target window; low potassium and raised kidney values make them more likely. A result is not a signal to change anything at home: the vet decides what to do with it.
Lower than reference
A level below the window may mean the medicine is not reaching the effect the vet expects. Common practical reasons are a sample taken too early after the start, missed tablets and the time of the last tablet. Long-term phenobarbital can lower digoxin levels by speeding up its removal (see phenobarbital).
Look at together with
- Potassium — low potassium makes toxic effects of digoxin more likely; some medicines given alongside it lower body potassium.
- Creatinine and urea — kidney function decides how fast digoxin is cleared.
- Calcium — high calcium is listed among the conditions where the vet has to be extra careful with digoxin.
- ECG and heart rate — the main way to see whether the medicine helps and whether the rhythm shows signs of excess.
Units and conversion
Digoxin is reported in ng/mL or nmol/L. One ng/mL is about 1.28 nmol/L, so 1.0 ng/mL is about 1.3 nmol/L. In the app each row keeps the unit printed on the form; the chart converts to ng/mL so forms from different labs line up.
Reference range
The therapeutic range is on your lab’s form. For digoxin it is not a range of healthy animals but a target window in which the medicine usually helps without poisoning, and the target is set by the vet for each animal. The Merck Veterinary Manual gives a target of 0.8–1.2 ng/mL (about 1.0–1.5 nmol/L) and calls 2.5 ng/mL (about 3.2 nmol/L) or more toxic. Published targets for dogs differ: the 2022 study lists 0.8–1.5 and 0.6–1.0 ng/mL measured about 8 hours after the tablet and notes that there is no single agreed range.
Cats and dogs
Cats are more sensitive to digoxin than dogs, and it is rarely, if ever, given to cats. The half-life in cats is extremely variable, so the level in a cat is harder to predict from the number of tablets alone. If a cat does receive it, the vet reads the level together with kidney values and potassium.
In dogs digoxin is used, for example, to control the heart rate in atrial fibrillation, often together with other heart medicines. The half-life in dogs is about 23–39 hours and depends strongly on kidney function. In the 2022 study, dogs with levels far above the target had weakness, depression, a poor appetite and a very slow heart rate, and these settled after the vet changed the plan.
Add a lab form — Pet Tracker Space recognises the lines, keeps the form’s units and draws each indicator over time with your lab’s reference band.
Sources
- Gordon SG, Saunders AB, Malcolm E. Positive Inotropes for Use in Animals (digoxin). Merck Veterinary Manual, professional version, full review June 2023, last updated September 2024.
- Colella A, Digiaro S, Fiorentino M, Greco B, Sasanelli M, Paradies P. Serum digoxin concentrations in dogs with atrial fibrillation on long-term digoxin (title shortened). Open Veterinary Journal, 2022;12(3):360–369.
- VCA Animal Hospitals. Digoxin (medication information for pet owners).
This page explains what a lab value means. It is not a diagnosis and not a substitute for your veterinarian — only they can interpret results for your pet.