Types of Topical Medications

00:01 Welcome to pharmacology by Lecturio.

00:04 My name is Dr. Praveen Shukle.

00:06 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.

00:49 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.

01:37 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.

03:27 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.

03:48 Then we mix it and then we let it solidify.

03:51 Triturated ointments grind the components together so they're just simply held in place through mechanical forces.

03:57 So that's called trituration.

04:00 Now, we have hydrocarbon bases that really forms the majority of ointments.

04:05 We also can have absorption bases.

04:08 Absorption bases can include wool fat and beeswax.

04:11 We also have water-soluble basis. These are the macrogols.

04:17 We have emulsifying bases.

04:19 These are usually things that are suspended in emulsifying wax like cetrimide.

04:26 And finally we have ointments made out of vegetable oils.

04:30 So, often they're made with things like, say olive oil or sesame oil or almond oil.

04:35 The peanut oils are becoming less and less in favor because of allergy.

04:40 Now, the water number determines the maximum amount of water in an ointment.

04:46 So sometimes you'll have a water number of 25 which represents 25% water.

04:51 Sometimes you'll have a number of three which represents 3% water.