DWR Diagnostics

Therapeutic Drug Monitoring

Test name

Test details

Sample requirement

Test code

Turnaround time


After a minimum of 3-5 day’s treatment

Sample 8 hrs post-pill

Serum (Not gel)


2 days


After a minimum of 2-3 weeks’ treatment

Sample at any time of day

Serum *


Same day

Potassium bromide

After a minimum of 120 days treatment, unless loading dose given.

Sample at any time of day

Serum *


2 days

Therapeutic drug monitoring

**NB: Drug assays are affected by marked haemolysis. Take a sample into a serum tube, allow to clot thoroughly and then spin to separate the

serum. Ensure serum is not significantly haemolysed before sending. Serum gel tubes should not be used for digoxin, although can be

accepted for bromide and phenobarbitone. Ideally the serum should be removed from the gel and placed into a plain tube before dispatch.


Digoxin levels should be measured in serum without a gel separator 5-7 days after initiation or dose-adjustment. The timing of the sample depends

on the requirement to either detect a minimum effective level (trough sample, 8-12 hours post-pill) or toxicity (peak level, 2 – 5 hours post-pill).


Phenobarbitone takes up to 3 weeks to reach a steady state, at which time there is minimal variation in serum levels throughout the day, assuming

animals are on twice daily treatment. Hence samples can be taken at any time of the day. If the dose has been changed, allow at least 2 weeks,

preferably 3 weeks before re-testing.

Potassium bromide

Serum KBr levels take 125 days to stabilise. After this, the sample can be taken at any time of day.

Test and Profiles

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