Welcome to pharmacology by Lecturio.
My name is Dr. Praveen Shukle.
I am going to cover some topical medications.
Now, what do I mean by topical medications?
I'm actually not gonna talk about medications per se.
I'm gonna talk about the vehicles that deliver these medications.
When I went through medical school, we never got taught about this.
When I was in pharmacy, well, I learned all about this.
And it actually is very, very, important for people out in clinical practice.
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.
I promise I'll keep this lecture short so that you're done quickly.
Let's take a look at an overview of what we're going to talk about.
We're gonna be talking about various types of mixtures such as topical solutions.
Now, a topical solution is -- for example; an eye drop.
Solutions are mixtures with one product dissolved in another.
A solute is the dissolved product and the base is what the solute is dissolved in.
Generally speaking, solutions should be clear.
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.
Let's start off first with some terms.
An emollient is a lotion or a cream that forms an occlusive layer on the stratum corneum of the skin.
A humectant is a lotion or cream that draws water into the stratum corneum of the skin.
Now a lotion is different from, say other types of mixtures.
An emulsion for example is a mixture of two unmixable liquids such as oil and water and that generally makes up a lotion.
The product will often require an emulsifier to keep the emulsion stable.
Now, the dispersed phase is spread out in the continuous phase.
So when you look at this example of A, B, C and D, look at A.
The blue is the continuous phase. The yellow is the dispersed phase.
When we mix it, it forms a whole bunch of globules like in B.
but eventually those globules float back up to the top and they separate out
and you're back to the picture in A.
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.
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.
So there's a lot of components to making a lotion stable.
What are -- what's a cream and why is it different from a lotion?
A cream is a semisolid emulsion of oil and water.
Now you can have oil in water so the water is the continuous phase.
You can have water in oil. Or you can have water in wax.
An ointment is a little bit different. Ointments are semisolid, so they're much harder.
They're generally in a viscous base.
So the base might actually be a wax instead of an oil product.
We also -- often use melting to fuse the ingredients together with increasing melting points.
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.
Then we mix it and then we let it solidify.
Triturated appointments grind the components together
so they're just simply held in place through mechanical forces.
So that's called trituration.
Now, we have hydrocarbon bases that really forms the majority of ointments.
We also can have absorption bases.
Absorption bases can include wool fat and beeswax.
We also have water-soluble basis. These are the macrogols.
We have emulsifying bases.
These are usually things that are suspended in emulsifying wax like cetrimide.
And finally we have ointments made out of vegetable oils.
So, often they're made with things like, say olive oil or sesame oil or almond oil.
The peanut oils are becoming less and less in favor because of allergy.
Now, the water number determines the maximum amount of water in an ointment.
So sometimes you'll have a water number of 25 which represents 25% water.
Sometimes you'll have a number of three which represents 3% water.