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Stable Phase Mixtures – Topical Medications

by Pravin Shukle, MD

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    00:01 Now, we just were speaking about mixtures.

    00:03 But we wanna talk about something unique called stable phase mixtures.

    00:07 Stable face mixtures are slightly different than regular mixtures.

    00:10 An example for -- an example are; gels.

    00:14 Now, a gel is a semisolid emulsion that evaporates at body temperature.

    00:19 So an example are of those sterilization gels that we put on our hands after we've seen patients.

    00:25 These are generally gels that are alcohol suspended gels where the continuous phase just rubs on to our hand, the other phase just evaporates, so the alcohol will evaporate.

    00:39 Sometimes you have agents that liquefy at body temperature.

    00:44 An example of that is hair gel.

    00:46 So these are usually suspended in things called ceramides.

    00:50 And finally you have agents that actually solidify at body temperature.

    00:55 So these are the liquid bandages in the suture glues.

    00:58 So these are agents where they're liquid inside the bottle.

    01:02 You put it on a patient's skin and sometimes the heat will activate a chemical or a physiochemical reaction that actually makes it a solid.

    01:11 Sometimes it's the evaporation of the continuous phase leaving back the dispersed phase on the skin that causes healing.

    01:19 A lot of times, the way that we design these products is that when the continuous phase evaporates away, the dispersed phase forms bridges and actually pulls together.

    01:33 So that's why some of these continuous suture sprays will actually pull the edges of skin together if there properly designed.

    01:41 So an example, a chemical example of this are the cyanoacrylates.

    01:46 The next category are foams. So foams -- we all know what foams are.

    01:52 They're emulsions with a surfactant that are lysosysed with air.

    01:56 You probably never defined it that way before.

    01:59 These are ideal with certain types of hair medications where the foam can actually get through the strands of hair that act as barriers to get into the scalp.

    02:09 An example of this is Rogaine foam.

    02:11 Now, the beauty of foams in particular is to get it sensitive tissues.

    02:16 So for example; our burn victims.

    02:19 A lot of our treatments are going to use foams as a treatment vehicle or as a delivery vehicle.

    02:25 Because applying it doesn't cause tearing of the skin.

    02:28 You can actually hover your hand over the skin, apply it very gently without actually disrupting new or growing skin.

    02:36 Another example are proctofoam where you're injecting the foam rectally or vaginal foams.

    02:43 So these are very sensitive tissues particularly when they're inflamed.

    02:46 So you can treat inflammation or an infection in these areas with the foams.

    02:51 A paste is -- from a treatment point of view, the opposite of a foam in the sense that it's very, very, stiff.

    02:59 So these are a stable mixture of a powder; at least 25% powder mixed in oil and a solid.

    03:06 So these are three-phase mixtures; pastes are three-phase mixtures.

    03:10 The most common paste in the world is toothpaste, so you're quite familiar with it.

    03:15 It starts off as a semisolid.

    03:16 You put on your toothbrush and then you start mixing and the different parts of the paste become activated.

    03:22 It is solid until a shear stress is applied.

    03:26 An example are zinc oxide paste that we use in diaper creams, the toothpaste that you see illustrated here and actually, mustard is a paste.

    03:36 Another category of delivery vehicle is the vapor.

    03:41 So vapors often will evaporate on contact with air.

    03:45 So what kind of evaporation are we talking about? Well, there's a process called sublimation.

    03:51 Sublimation is where you take a solid and it turns directly into a vapor without turning into a liquid in between that's called sublimation.

    04:00 So a good example of that is smelling salts.

    04:03 You take the smelling salts, they have a very strong vapor that comes off them.

    04:07 You kinda hold it under the nose of the patient who is passed out.

    04:10 And the noxious nature of that smell will wake them up.

    04:14 Another type of agents are evaporation based vapors like the topical decongestants.

    04:23 So sometimes we'll give a decongestant in the nose or in the -- or through a puffer and then these patients will get them medication after the water phase has evaporated.

    04:34 We also have aerosols.

    04:37 Aerosols are slightly different than vapors in the sense that a vapor is something that's in the gas phase whereas aerosols are tiny little droplets suspended in air.

    04:47 They're so tiny that they're able to be suspended in air for a certain time.

    04:51 Now, the science behind aerosols like you see here, this is a Ventolin puffer.

    04:55 Actually it's my Ventolin puffer.

    04:58 Now, this particular puffer will spray out droplets that are large enough to maintain airborne status until they hit the lung.

    05:10 You -- if you make the droplets too big, they'll have too much momentum and hit the back of the throat.

    05:16 If you make the droplets too small, they will go into the lung and then back out.

    05:22 So you want them to have enough size so that they will impact on to the lung surfaces, but not enough size so that they impact on the back of the throat.

    05:32 So it's actually quite a science designing the proper aerosol.

    05:35 Finally, there's infusion kits.

    05:38 We don't have insufflation or infusion kits anymore.

    05:41 This is a insufflation kit from the 1700s and 1800s.

    05:47 This is a rectal insufflation kit where they used to push cigarette smoke up into a person's bum.

    05:55 I'll just leave it there.

    05:58 All right. Let's move on to sols. What is a sol? Well, the best sol that I can think of that people know about is butter.

    06:05 So sols are used topically when you want extended medication contact.

    06:11 Now a good example of a sol in terms of applying it to a human body is stick deodorant.

    06:18 Another example are the antifungal sols or antifungal sticks.

    06:24 And another example are deodorants and anti-perspirants.

    06:29 Which -- an anti-perspirant is a drug.

    06:31 When you think about it, it's inhibiting the perspiration that's occurring in the armpits.

    06:36 So it's actually a medically active sol.

    06:39 What about powders? Well, powders are kind of self-evident.

    06:43 Powders are often used when moisture is the cause of the problem and yet you still want some kind of a drying agent.

    06:50 So an example are fungal foot powder so you can deliver a drug but maintain the dryness of the area or powdered steroids for example where you want to deliver steroids onto a wet surface and you don't wanna add to the wetness of the surface.


    About the Lecture

    The lecture Stable Phase Mixtures – Topical Medications by Pravin Shukle, MD is from the course Topical Medications.


    Author of lecture Stable Phase Mixtures – Topical Medications

     Pravin Shukle, MD

    Pravin Shukle, MD


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