Urethane is not a recommended anesthetic and its use is discouraged (because it is a mutagen and carcinogen - personnel protection is strictly enforced) - its use is limited to non-survival procedures. 

There are a lot of other anesthetics you can use in combination with ketamine - it would be best to consult your animal facility veterinarian on the matter. 

Hi Ignacia,

I completely know the problems and risks of urethane. I must say that my procedures are non-survival and that I have to use this type of anesthetic mandatory, as ketamine masks my results. So if you have any advise on this topic I would appreciate it, otherwise , I think that any person working with urethane knows this things.

Sorry I did not know your surgery was non-survival... 

I found this article - http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4707145/

Hi again, for those interested in performing experiments with urethane in mice, I have been trying to write a protocol.

Right now I am anesthetizing with 1.5 gr/kilo  and wait 30 minutes until I inject him the ketamine (20 mg/kilo). After the ketamine injection the mouse should loose all the reflexes inmediatly and the surgery can began. Nevertheless, I observed always breathing problems and that it depends on the animal status and the breed, so it would not be strange to see that the anaesthesia causes different effects on different animals of the same breed. With this I am able to perform surgery quickly and achieve the animal's survival.

Hi, María Sáez. I am currently performing non-survival surgeries using 50mg/kg of ketamin followed by 0,7g/kg of urethane. It almost des not influence the cardiovascular system and even Balb/c resist to the anesthesics. I hope I might be useful to you.

Thanks for your feedback Alexandre Santos Bruno , I am sure it will help people.

Hi Maria

We usually use urethane intravenous in rats (1,2 gr/kg) to replace the previous anesthesia with isoflurane. However, my friend is facing some trouble in mice, which is causing death around 30 minutes after. I wonder if you could manage the problem?

Best

Cleyton

Hi Cleyton Sobrinho ,

I ended up using urethane + ketamine for the induction. I used 1.5 gr/kilo of urethane + 20 mg/kg of ketamine in the same syringe. After that the animal lost the reflexes and I could begin the surgery. If the animal had reflexes during the experimental session I used 1/5 of the induction dose. Some animals could not make it but it was a minimal amount. I hope this helps.

Best,

María.

Urethane is a useful anesthetic for preserving cardiorespiratory reflexes, however it is far less effective as a surgical anesthetic than isoflurane and ketamine/xylazine. The main advantage of urethane is that it has a wide therapeutic window and is metabolized slowly giving you a long lasting anesthesia. However, as pointed out by a earlier comment, urethane should not be used for recovery surgeries as it is hepatotoxic.

When adminstering I. P., urethane is generally safe and effective between 1.1-1.8g/kg depending on your preparation (I make a 10% solution in sterile water). Inject a 10% solution in two doses separated by 15-30 minutes to avoid chemical burns in the peritoneum. This applies in mice or rats. In mice it can take over an hour for adequate anesthesia, local anesthetics may be needed regardless. If you are struggling, and want to supplement, I'd always go for isoflurane over ketamine because you can titrate isoflurane easily and withdraw it quickly.

Urethane is much more effective when deliver I.V. and I suggest this is a preferable route of administration. This differences between I.P. and I.V. arises because urethane is absorbed by fat (if I remember correctly). Ideally, start the surgery under isoflurane, implant an i.v. catheter then slowly infuse the urethane (1.1-1.3g/kg in a 20% solution over about 20 minutes is ok for this). I find this gives a stable plane of anesthesia with less drug.

As an aside, working with urethane tends to cause mucus secretion in the airways which can lead to asphyxiation. This can be prevented with 1mg/kg methyl-atropine given with the anesthetic (i.v. or i.p.). However, this might interfere with you experimental goals.

Finally, check the age of your urethane. The salt tends to absorb water and should be stored with Drierite. If your drug is old, the weight of the salt may not be an accurate measure of the drug in solution. If you have doubts, buy fresh, this stuff is cheap.

hi Stephen B Abbott your answer is admirable

hope it will work

Thanks

When it comes to administering medications like urethane and ketamine to mice, it's crucial to follow specific guidelines as these substances are used under strict regulatory standards, especially for research purposes. The doses can vary depending on the specific requirements of the study, the age, weight, and health of the mice, and other factors.

It's important to note that these dosages are general guidelines. The exact dose should be determined by a veterinarian or a researcher trained in laboratory animal medicine, and all procedures involving these substances should comply with institutional and governmental regulations. Always refer to the most recent and relevant guidelines and literature when planning research procedures.

l This list of protocols might help us better address the issue.