Yea I used it previously for the rat perfusion purpose. the concentration of the urathane was 1.25g/kg/5ml in saline. The volume of IP injection is about 600~800 microliter. It works very nicely. but the precaution to be consider is you should close the cover of urethane anesthesia tube tightly since it evaporates continuously and efficacy will be gradually decreased.

I have been using Sodium pentobarbitone at 50-60mg/kg IP for in vivo cardiovascular experiment on rat.

No. I have used thiopentone sodium 40 mg/Kg body weight IP for in vivo diabetes experiments on rodents

Yes, i use urethane for anesthesia on rats IP and it works fine. Maybe the urethane you are using is quite old and if that is the case, then it will be less effective and therefore u will have to increase the dosage ( perhaps to 1.4g/kg). Also ensure that u fast your animals for at least 7-12 hr before anesthetizing and avoid injecting into intergumentary organs of the animal.

The urethane is fresh and I make fresh solution of it every day, so that should be not the problem. Im gonna ensure the fasting period and hope it will get better, because it really take too long to induce a good level of anesthesia for surgery. Thank you

WE are routinely using uretanne anaesthesia at dose level of 1.25 gram/kg (i.p.) in two divided dose. Difference in both dose is around 1 - 3 minutes. Do not give complete dose in single administration. Use fresh solution.

Yes, Urethane can be used for induction of anesthesia in rats for long time (7- 8 hrs) considering the factors like fasting of rats which should be 12- 14 hrs, secondly use of freshly prepared urethane solution (1.5 g/kg i.p.), and finally injecting the dose intraperitoneally slowly for faster effect. Another thing to be taken into consideration is that; after the urethane is been injected intraperitoneally, keep the animal in a dark and silent place for faster induction of anesthesia.

I've had the same problem at 1.5 g/kg (IP) for anesthetized recordings in rats -- I usually have to wait 1-2 hrs for the induction of deep anesthesia. I think I will try fasting them in the future. Thanks for the advice,

I also have some induction problems at 1.5 g/kg (IP), even when freshly prepped. Probably not, but does dissolving urethane in water or saline make a difference?

I have the same problem ,when i inject urethane 1.5g/kg via  IP i must wait for about 30-45 min for recording eEPSP and i have to repeat additional  dose and finally after 2-3 hour the rat would be die  unfortunately !!!! any comment please .

Hello Geisson Marcos Nardi,

                                 But we can't use ti ketamine/xylazine for stress related studies in animals because which has antidepressant activity.. so what would be the better choice of anesthesia for this kind of study..

Thanks in advance for your suggestion.. 

Before anesthatize the animals should keep the animals for fasting atleast for 4-8hrs. then you may not face these kind of problems... 

Use freshly prepared one.  U can increase the dose till 1.5g/kg. Yes it takes a bit long time to get anesthetized. You can try other alternatives one as well.

I am using 1.25g/kg of urethane it is working very nicely.. use freshly prepared urethane..

I too am having issues with my rats dying approximately 4 hours after I administer urethane (1.5mg/kg, ip). I haven't had issues in the past, but recently all of my rats die before I am even able to record. Has anyone had this problem? I use a stock of urethane, not fresh, but my rats are going down fine. Any help would be great as I am beginning to get very frustrated!

I have used urethane in rats (1.5g/kg, ip) and the rats fell asleep in about 15 to 30 minutes. It's very important to correctly manipulate the animal and reduce the strees levels. In addition, it's advisable to put the animals in their cage after the injection and leave it in a dark place.

A ketamine injection (20 mg/kg, ip) would be a good inductor (if it's not incompatible with your experiment) of the urethane anesthesia and a tracheotomy helps to regulate the respiratory acticity of the animals.

Hope it helps.

Do any of you use a syringe filter on the urethane solution?

Is a PTFE syringe filter compatible? We also have MCE filters.

Thank you!

hello, now that you are talking about it, i would like to ask about the fast usefulness, what´s the outcome for those of you who tried it, and about urethane dilution, has anybody else notice an incresed volume after diluting it with just water, and in what ratio, how can i minimize the stress while handling the rat, is it better if a induce the animal on the same room where they are held, or to apply it on the procedure room (which is in an upper floor)

Are you diluting in ethanol or saline? Since urethane can be dissolved to a higher concentration in alcohol. I just wondered if using ethanol may shorten the time until the rats die? This will be a non-survival surgery, using a different method for euthanasia. The rats will have temperature measured under urethane, no painful procedures. I do realize that ethanol will be hypothermic. Thank you for any answers!

Best way to give Urethane is IV with slow infusion!

Hi, i am using the urethane 50% solutions in dist. water in 1.2-1.5 g/kg dose. It works really good if rat did not eat before the IP. I prefer the rat stay 1-2 h with water but no food before the injection. If no opportunity to wait - it could require more of urethane or multi injections - so, we cant calculate a real dose of urethane. I did my own statistics and found that rats with "no food" before IP need the recommended doses of 1.2 - 1.3 g/kg, and, when they were fed before the injection the dose in most cases increased up to 1.6 g/kg with no animal lost from overdose....

We used it in non-survival surgeries, when we euthanise animal after measurements.

If you are doing survival procedures, it is better to use IP K/X mixture for long procedure or isoflurane inhalation for short procedures .

We used it in non-survival surgeries, when we euthanise animal after measurements.

If you are doing survival procedures, it is better to use IP K/X mixture for long procedure or isoflurane inhalation for short procedures .

I used it for non survival experiments but it is forbitten from 2013 in France :(  

Actually the veterinarians bloked 

I am doing circuit mapping experiments with optogenetics and cyclic voltammetry in urethane-anesthetized Long-Evans rats. I've also been having both induction problems as well as problems with the rats dying when I start recording (usually 2-4 hours after the final IP injection). Our technician suggested that I may have accidentally injected into the intestine rather than the peritoneal cavity. I've also had trouble effectively monitoring the depth of anesthesia. Sometimes when rats have completely lost their toe-pinch reflex, they still display whisking and eyeblink reflexes. I found a reference (attached) in which they show that eyeblink reflexes are transiently or not suppressed by urethane, so those do not seem to be good indicators. Is whisking similarly not a good indicator of anesthetic depth?

While I only use urethane on mice, I think the respiratory distress from mucus production is likely an issue for those experiencing death in the 2-4 hour range.  My surgeries have always required tracheotomies due to the nature of the experiments but the the paper below suggests that tracheotomy can decrease anaesthesia associated morbidity when using urethane.  I also split the dosage and give in 2 i.p. injections ~20 minutes apart.  

Article Moldestad O, Karlsen P, Molden S, Storm JFTracheotomy improv...

You should induce with ketamine or tiletamine if you use urethane for long-term anesthesia.

Avoid urethane if you can and use gas anestesia or a TIVA-pump (propofol, alphaxalone or ketamine) instead. In a rat you can infuse into the lateral tail vein or into tibia. The latter is often the easier route. 

Does the Anesthetic Urethane Influence the Pharmacokinetics of Drugs?

This discussion has provided me with some helpful tips, so I thought I would contribute some notes on my experience with urethane anesthesia (I use both rats and mice, but mostly mice).

- I agree that urethane should be relatively fresh. I don't use anything older than 2 weeks. Within this time frame I have not noticed any diminished effects.

- Strains can make a big difference. I've noticed that DBA mice have a much narrower dose that they tolerate than C57, for example, and also tend to require a higher dose.

- I have never been able to achieve full anesthesia with the commonly reported 1.2 g/kg. Typically, my mice require 1.4-1.6 g/kg (even when urethane is made the same day) in a saline solution of 0.1 g/ml (dissolving in distilled water does not seem to make a difference). But this is also because I wait until toe pinch and eye blink reflexes are gone. If urethane does maintain spinal reflexes as previously mentioned, then what test is done to ensure the animal is anesthetized?

- In my DBA mice, which as I mentioned are more sensitive to urethane, I have noticed that the dose does not linearly scale with body weight. Smaller animals require a higher dose. So for example, for a 25 g mouse I would give 1.6 g/kg, whereas for a 35 g mouse I would give 1.4 g/kg. The 35 g mouse still gets a larger volume, but the range of urethane given is narrower than the range of body weight. This is just my personal observation in DBA mice, I have not seen anything like this reported elsewhere.

- I have tried food-depriving animals as was suggested here, but have not noticed that this helps in my animals for some reason. It might make them more prone to overdose, but it did not seem to reduce the dose required for anesthesia.

- One very important thing that may be obvious to most people but is not always taught directly is to massage the site of i.p. injection! I do this for about 5 seconds to make sure the urethane is rapidly and completely absorbed. When I had not done this in the past, I used to have to give upwards of 2 g/kg and then once the animal was under, it would continue to decline rapidly (presumably because urethane is still in the periphery and being absorbed slowly). Massaging the area of injection will reduce the time it takes for the animal to go under, and reduce the dose you need if you have not been doing this. This is also a good habit for any i.p. injection. Having said that, urethane anesthesia still requires a lot of time and I still often wait about 2h.

Hope some of this is useful,

Mina

Beate,

the foot withdrawal reflex is not really a good indication of anesthesia. It is commonly (ab)used because it is easily accessible. Unfortunately, it does not disappair before the level of anesthesia is very deep. This contributes to the rather high fatality rate associated with anestesia of rodents. What is commonly used to monitor anesthesia in other species is the location and shape of the pupilla, in combination with the palpebral or corneal reflex.

Assessment of anesthetic depth is particularly complicated when using dissociative agents like urethane, ketamine or tiletamine. A patient might appear to be awake while under influence of these drugs, but nevertheless be under full surgical grade anesthesia. What this means, paradoxically, is that you should not worry to much about oberved movement in the patient while using these drugs. Movement is a poor indication of wakefulness when using dissociative agents to achieve anesthesia.

You can monitor the patient's pain responses if you have equipment to measure the heart and respiration rates. They will increase if you do something the patient perceives as painful. A pulse oximeter will give you the heart rate and in addition monitor the blood oxygenation level. Mind you, the fast heart rate in small rodents means you must use special equipment, e.g. the small rodent pulseoximeter produced by Kent Scientific. Over-the-counter veterinary pulse oximeters are not applicable.

Further, you can use bupivacaine with epinephrine (marketed as Marcain-Adrenalin in Europe) to induce a local nerve block, typically by injecting above the eyes if you plan to do surgery on the top of the skull. Use an insulin or Hamilton syringe to deposit the local anesthetic. Lidocaine is rather toxic to rodents and should be avoided, but in my expericence bupivacaine with epinephrine is well tolerated. With successful local anesthesia, you do not need more than moderate to heavy sedation to perform surgery on a patient.

Beate, have you tried making an incision in the cisterna magna and draining some CSF? This could help with the mechanical heart beat artifacts because it reduces the physical pulsations at the brain level. This is particularly true if you are trying to record near a ventricle.

I have been using 1.25g/kg urethane for rats and it works well for me. Moreover, I am not making it fresh everytime.