|
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. |
Shop online!
