Emu Cream Assists Lidocaine: Local Anesthetic Absorption through Human Skin
Lidocaine is probably the most commonly used local anesthetic. For those of you with an organic chemistry or bio-chemistry background, it's an amide. An amide local anesthetic is a much safer agent to use; as it is less likely to cause an allergic reaction. In fact, until a few years ago it was reportable if you got an allergic reaction to an amide local anesthetic.
The other groups are the esters and are much more likely to give you a reaction because they contain para-amino–benzoic-acid (PABA) which a lot of us have been sensitized to in our sunscreens and other products.
Lidocaine is also reasonable in cost and readily available. It's the most understood local anesthetic and a prototype in general.
Most ideas aren't new ideas. The concept of emu oil as being useful for any number of things primarily originated from the people who have used it for many centuries. Actually, some of the oldest people on Earth, as far as the time that they've been here, are the Australoid race, or the Australian Aborigines.
The problem I wanted to address as something to think about is the problem with punctures in the skin or planned-for needle insertion. The obvious one that comes to mind to an anesthesiologist is to start an intravenous for administering drugs. We want to know in a few seconds whether the anesthetic is working or not.
Vaccination is an interesting example. In the last few months, all of the post-secondary students in British Columbia were vaccinated for measles after an outbreak in Vancouver. It's a large group because the hepatitis B and the German measles vaccines, of course, are given to the early pre-teens and that's often a group that we recognize, certainly, as anesthesiologists. It's young people, particularly in the pre-teen and early teen years, that can get very anxious and upset about an injection. If something were available to minimize that trauma, life could be a lot simpler for public health nurses and other personnel.
Suturing of wounds is always a tough consideration – the decision is whether to put the local anesthetic in, and make two or thee holes, or just go straight ahead and suture with a tiny needle. If you had a relatively sterile entity that could numb it either before the injection with the needle, or with regard to the wound itself, then you might be a lot further ahead.
Laser therapy typically is done with injection and can be quite painful in some parts of the body, as most of you are aware, especially the palm of the hand or the base of the foot.
What we need is something that works quickly, that's relatively hypoallergenic, and it also has consistently good absorption. Of course, we need it to be non-toxic and it has to be reasonable in cost. That's why I tested lidocaine, and it's our impression that emu oil is relatively hypoallergenic.
The traditional over-the-counter preparation in both Canada and the U.S. is EMLA cream, which stands for eutectic mixture of local anesthetics. It has lidocaine in it and another agent called prilacaine. It doesn't work as well as I'd like it to. It has a relatively slow action, a minimum of 45 minutes, so that requires pre-planning. If you're going to see somebody in an operating room suite, it literally has to be put on by someone at your suggestion beforehand, or you have to get the parent to purchase it at home and put it on. Do they put it on the right place? Do they put on in the right amount? How does it proceed from there? Unfortunately now, many pediatric institutions are withdrawing or reducing their use of the cream because it's been somewhat erratic as to whether it's actually served a purpose or not. It's often built up impressions and potential feelings, but sometimes those have been very disappointed in the actual use thereof.
The emu oil used in this study was what I call cream - the complete oil verses the separated oil.
What did we test? We created two mixtures that looked, for all intents and purposes to people observing them, the same. Quite honestly, if they would have tasted them, they would have had a considerable difference because all of the local anesthetics are very bitter. It doesn't take a rocket scientist to tell when you've got one in your mouth. As any of you know who have ever had a local anesthetic sprayed in your mouth, for a sore throat or whatever, almost all of them are very bitter.
Anyway, our substance was emu cream and spearmint oil. We use the spearmint oil for two reasons: the relatively positive scent it imparts to most people and; it has the advantage that it may enhance absorption as well. Our second preparation was emu cream of the same batch, Canadian emu oil and spearmint oil again, with lidocaine.
Those were then applied to two sites on six people. The two sites were both chosen as the same and that's in the ventral distal forearm, that is on the part of your wrist which hardly ever has any hair on it. You can start intravenouses there. Usually, they're not large veins, but they work really well and they're exquisitely tender – therefore, a good site to test if you were able to use it. The mixture was applied on both forearms on a two-inch square sites, and then covered with something called Opsite, Tegaderm, or one of the other proprietary units which are a lot like Saran WrapT with a sticky surface around it.
The function of the cover is two-fold. First of all, you increase the warmth and moisture in the area and that might make a difference in penetration. Also, it usually permits an increased concentration crossing across the skin before it's rubbed off or taken away. After twenty minutes, that cover was removed and the residual cream was wiped away. The amount of residual cream left is usually diminished over that time frame.
We then did two major tests on the individuals. The common one we used initially was ice. That's because in my practice in the operating room, I found that if you can check with an ice cube where people can tolerate the ice cube, and not tell the difference whether it's warm or cold, even prior to Cesarean section, you can invariably tell when they're going to have sharpness from the incision with the cold hard steel knife. Then, of course, we used pinpricks because most people were kind of intrigued with the idea that this actually made any difference. Because each individual had the substance A or B on the left or right side, they had some way of observing themselves and determining, on their own basis, if they thought there was a difference from one side to the other.
That's the outline of the methods that we did. Then, the observer who was applying the creams was blinded as to whether it was A or B in each instance, and correspondingly, the observer of the ice and pinpricks was also blinded.
We got fairly simple results in that there was a reduced sensation noted in only one of the two arms, one skin site only. Also, fortunately, the one with the reduced sensation had been treated with mixture B, which was the emu cream, the spearmint and the lidocaine combination.
That's something that might vary – a larger size might make a difference. You might get a difference, too, if you went on other areas which may have more thickened skin.
In the discussion, this has to be done with so-called consistent, proven pain stimulus. The pain and temperature, just for those that aren't as comfortable with the physiology, are virtually tested by the same thing. What I mean is, acute sharp pain, and warm and cold sensations, tend to be affected and carried by the same fibers and the same components of the spinal cord. It's not the same as the burning or dull pain that starts after a few seconds. That is a different type of pain fiber again.
"When we're talking about the next step, the clinical trials, we'll need to start with adults. Where we want to use it is in children, but typically, you can't have much success with the groups within the hospitals discussing the study unless it's been proven on adults.
Of course, the million dollar, multi-national question is "Will emu oils work?" "Which ones will work better?" "Is there a particular feature in emu oil that does work better?" I know that people have tried local anesthetics on their own, and local anesthetics in mineral oil. Whether they've tried it in pure oleic acid, I don't know.
What's the potential use in animals? I feel certainly there is a good possibility in some of the thinner skinned animals. I think of horses, particularly, and probably dogs where you might be able to apply the cream, and not require near as much sedation or other entities.
In general, we need more study with design and data acceptable for publication in a peer-reviewed medical journal.
From the Summer 1997 issue of AEA News, as presented at the American Oil Chemist Society Convention.
