How to Dilute and Store Cortrosyn for ACTH Stimulation Testing

Can you please review how you recommend diluting Cortrosyn for low-dose ACTH stimulation testing? 

It's expensive and I don't want to give a whole vial to every dog, since most of my patients weigh les than 30 pounds.

My Response:

Yes, Cortrosyn is expensive. And once reconstituted, it has a limited shelf-life. However, by following the protocol outlined below, you can easily dilute, aliquot and store Cortrosyn after reconstitution for up to 6 months. This makes each ACTH stimulation test much less expensive, because each vial of Cortrosyn can be used to perform as many as five ACTH stimulation tests.

Cortrosyn is supplied in vials each containing 0.25 mg (250 μg) of synthetic ACTH (cosyntropin) in powder form. Because the dose of Cortrosyn used to perform an ACTH stimulation test is only 5 μg/kg, small to medium sized dogs require only a fraction of the ACTH contained in each vial.

How to Aliquot and Store Each Vial of Cortrosyn for Subsequent Use

1. Reconstitute the Cortrosyn power by adding exactly 2.5-ml of sterile saline solution to the vial. With this dilution, the resulting concentration of the Cortrosyn solution in the vial would be 100 μg/ml.
2. Once Cortrosyn is reconstituted, aspirate 50-μg doses (0.5 ml) into 5 plastic syringes. Or, if smaller ACTH doses are desired, aspirate 25-μg doses (0.25 ml) into 10 syringes. (For more accurate dosing, I use insulin or tuberculin syringes).
3. DO NOT store reconstituted Cortrosyn in glass containers or vials. The reason that the Cortrosyn needs to be stored in plastic is that ACTH will stick to glass, thereby lowering the available amount of Cortrosyn that would be injected at time of testing.
4. The syringes containing the reconstituted, diluted Cortrosyn should be labeled with the product, dose in each syringe, and the date the Cortrosyn was reconstituted.
5. Freeze each of the syringes at -20C. Avoid storing these syringes in a frost-free freezer, which must periodically warm up to defrost. Repeated freezing and thawing cycles would compromise the integrity of the Cortrosyn.
6. When frozen properly, aliquots can be stored for up to 6 months without loss of efficacy.
7. Alternatively, the Cortrosyn solution can be stored refrigerated (4C) where it has been shown to be bioactive and stable for at least 4 weeks.

Diluting the Cortrosyn and using a low-dose ACTH stimulation test protocol is very cost-effective. In this way, 1 vial of Cortrosyn can be used to test multiple patients without compromising the quality of the test results.

As an example, at the 5-µg/kg dose, 5 dogs weighing 10 kg (22 lbs) can be tested using a single vial, reducing the cost of the drug by 80%. By looking at the cost benefit, it is clear that the savings could be significant by using this testing protocol.

For more information on how to perform an ACTH stimulation test, see my post entitled, What's the Best Protocol for ACTH Stimulation Testing in Dogs and Cats?