How to aspirate and mix regular insulin and NPH insulin in a single syringe?

For example you are ordered to give 20 units of NPH and 10 units of regular insulin. Here’s what you have to do:

1. Instill 20 units of air into the NPH vial and withdraw the needle. The needle used should not touch the insulin.

2. Now, inject 10 units of air into the regular insulin vial and withdraw 10 units of regular insulin.

Always withdraw the regular insulin first to decrease the possibility of the regular insulin becoming contaminated with proteins of the NPH.

3. Reinsert the needle into the NPH insulin vial and withdraw 20 units of NPH insulin.

This time be careful to withdraw only the ordered amount of medication and not to create air bubbles. If excess medication has been drawn, discard the syringe and begin procedure over again. This is because the syringe contains two medications and an excess amount cannot be returned to the vial as the syringe has regular insulin also.


  1. This procedure is not correct. You do not withdraw 30 units of NPH if the order is for 20 units. Also, start with 30 units total of air in the syringe prior to inserting the first 20 units of air into the NPH vial. Then you already have the 10 units of air you need for the vial of regular insulin in the syringe.