Insuln syringe

My cat is diabetic and I am injecting him with 4.5 units of ProZinc insulin twice a day. The ProZinc syringes are quite expensive (both from the vet and online) so I was planning on using cheaper syringes made by a different manufacturer.  However, I have been told that I should use only ProZinc syringes. I would much appreciate the opinion of someone who is a) qualified and b) independent as to whether this is correct. The ProZinc syringes are: U40 / 0.3ml / 29G / 12.7mm The cheaper ones I was looking at are made by SOL-M are for use with insulin and are the same spec: U40 / 0.3ml  / 29G / 12.5mm Both syringes have 0.5 unit markings. Thanks so much in advance - and massive kudos for setting up and maintaining your site.

Hello. I'm glad that you checked because this is a complicated concept and can lead to serious mistakes.   The key information is not with the syringes but the number of mg of insulin (the number of thousands-of-a-gramme of insulin) dissolved in each ml of liquid, which can differ between manufacturers.   So 1ml of manufacturer A's insulin will not necessary contain the same number of units of insulin as 1ml of manufacturer Bs insulin.   A 'unit' will therefore need to be a different volume of liquid and, since the syringes measure in units, will need a solution-specific syringe to pull it up. I happen to be a human diabetic; I always receive insulin that is concentrated such that 1ml of fluid contains 100 units of insulin.  My understanding is that this is mostly standard in human medicine (perhaps there are exceptions in paediatrics?);  that whichever insulin syringe one takes 0.01mls of, there should always be the same number of units within that 0.01 ml of liquid.   Im sure that this has prevented accidents over the years. However, animal insulin has historically not followed that pattern.  Therefore, if your vet asks you to stick to one make of syringe and tells you that they are different, this is probably correct.

For example, a quick google search brought up 100 mg / ml and 40 mg / ml solutions of insulin, which would each require the same syringe to have different marks in order to measure out a Unit.