00:00
Welcome to pharmacology by Lecturio.
00:03
My name is Dr. Praveen Shukle.
00:05
I am going to cover some topical medications.
00:09
Now, what do I mean by topical medications?
I'm actually not gonna talk about medications per se.
00:14
I'm gonna talk about the vehicles that deliver these medications.
00:18
When I went through medical school, we never got taught about this.
00:21
When I was in pharmacy, well, I learned all about this.
00:24
And it actually is very, very, important for people out in clinical practice.
00:28
Not a lot of this information is going to be on your exams for the USMLE
but it will be very important for you when you get out and practice.
00:36
I promise I'll keep this lecture short so that you're done quickly.
00:40
Let's take a look at an overview of what we're going to talk about.
00:44
We're gonna be talking about various types of mixtures such as topical solutions.
00:48
Now, a topical solution is -- for example; an eye drop.
00:53
Solutions are mixtures with one product dissolved in another.
00:57
A solute is the dissolved product and the base is what the solute is dissolved in.
01:03
Generally speaking, solutions should be clear.
01:07
If they're not dissolved, they will be opaque. Okay. What is a lotion?
Well, there's many definitions of what a lotion is, it's not as simple as one would think.
01:18
Let's start off first with some terms.
01:20
An emollient is a lotion or a cream that forms an occlusive layer on the stratum corneum of the skin.
01:29
A humectant is a lotion or cream that draws water into the stratum corneum of the skin.
01:36
Now a lotion is different from, say other types of mixtures.
01:43
An emulsion for example is a mixture of two unmixable liquids such as oil and water and that generally makes up a lotion.
01:52
The product will often require an emulsifier to keep the emulsion stable.
01:58
Now, the dispersed phase is spread out in the continuous phase.
02:03
So when you look at this example of A, B, C and D, look at A.
02:07
The blue is the continuous phase. The yellow is the dispersed phase.
02:14
When we mix it, it forms a whole bunch of globules like in B.
02:20
but eventually those globules float back up to the top and they separate out
and you're back to the picture in A.
02:27
But if you have an emulsifier, it either coats the yellow portion
or it becomes a nucleus within that yellow portion that keeps it separate and keeps it nice and dispersed.
02:41
A colloid is a mixture of two products, usually a solid and a liquid or a protein in the liquid
and surfactants surrounded the droplets that stabilize the emulsion.
02:55
So there's a lot of components to making a lotion stable.
02:58
What are -- what's a cream and why is it different from a lotion?
A cream is a semisolid emulsion of oil and water.
03:07
Now you can have oil in water so the water is the continuous phase.
03:11
You can have water in oil. Or you can have water in wax.
03:17
An ointment is a little bit different. Ointments are semisolid, so they're much harder.
03:23
They're generally in a viscous base.
03:26
So the base might actually be a wax instead of an oil product.
03:31
We also -- often use melting to fuse the ingredients together with increasing melting points.
03:38
So for example, we might have, say, a wax that we melt to a higher temperature
so eventually the solid that we're dispersing in it melts as well.
03:47
Then we mix it and then we let it solidify.
03:51
Triturated appointments grind the components together
so they're just simply held in place through mechanical forces.
04:00
So that's called trituration.
04:03
Now, we have hydrocarbon bases that really forms the majority of ointments.
04:08
We also can have absorption bases.
04:10
Absorption bases can include wool fat and beeswax.
04:14
We also have water-soluble basis. These are the macrogols.
04:19
We have emulsifying bases.
04:22
These are usually things that are suspended in emulsifying wax like cetrimide.
04:28
And finally we have ointments made out of vegetable oils.
04:32
So, often they're made with things like, say olive oil or sesame oil or almond oil.
04:37
The peanut oils are becoming less and less in favor because of allergy.
04:42
Now, the water number determines the maximum amount of water in an ointment.
04:48
So sometimes you'll have a water number of 25 which represents 25% water.
04:54
Sometimes you'll have a number of three which represents 3% water.