Topical Dosage Forms - Module 6 PDF

**Specific Learning Outcomes** By the end of this module, you will be able to: - Describe types of topical dosage forms. - Describe transdermal drug delivery systems. - Describe advantages and disadvantages of the various types of topical dosage forms. - Identify auxiliary label req...

**Specific Learning Outcomes** By the end of this module, you will be able to: - Describe types of topical dosage forms. - Describe transdermal drug delivery systems. - Describe advantages and disadvantages of the various types of topical dosage forms. - Identify auxiliary label requirements for topical dosage forms. ------- **P** ------- +-----------------------------------------------------------------------+ | **Pluronic Lecithin Organogel (PLO)** | | | | an emulsion used as a base for transdermal drug administration. This | | is a very popular base used in the preparation of manufactured and | | compounded topical medications intended for systemic effect. | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ ------- **A** ------- +-----------------------------------------------------------------------+ | **absorption bases** | | | | ointment bases that have the ability to absorb water. There are 2 | | types of absorption bases: anhydrous and water-in-oil (w/o) emulsions | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **anhydrous absorption bases** | | | | permit incorporation of aqueous solutions to form a W/O emulsion but | | do not contain the aqueous part in its original state. | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **anti-inflammatories** | | | | reduce inflammation of the skin (e.g. hydrocortisone) | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **anti-pruritics** | | | | reduce itchiness of skin (e.g. calamine) | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **astringents** | | | | a drug used topically to shrink tissue and toughen tissue (e.g. zinc | | sulphate) | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ ------- **C** ------- +-----------------------------------------------------------------------+ | **collodions** | | | | syrupy topical emulsion where the thick liquid is dissolved into a | | mixture of alcohol and ether; after application the alcohol and ether | | solvent vaporizes, leaving a medicated film coating on the skin | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ ------- **E** ------- +-----------------------------------------------------------------------+ | **epicutaneous form of administration** | | | | topical use of a drug for local effect | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ ------- **I** ------- +-----------------------------------------------------------------------+ | **inunction** | | | | gently rubbing a cream or ointment into the skin to increase | | absorption | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ ------- **L** ------- +-----------------------------------------------------------------------+ | **liniments** | | | | solutions or mixtures intended for application to the skin via | | massage | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **lotions** | | | | O/W emulsions and their fluid nature makes them quick and easy to | | apply to large areas | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ ------- **O** ------- +-----------------------------------------------------------------------+ | **ointment** | | | | semi-solid emulsion for topical use on the skin. Ointments are broken | | down into four categories according to the USP: oleaginous | | (hydrocarbon) bases, absorption bases, water removable bases and | | water soluble bases. | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **oleaginous bases** | | | | also called hydrocarbon bases and prepared from petrolatum. | | Hydrocarbon bases can only accept very small amounts of water (or | | hydrophilic components) added to them. These bases are greasy and | | hard to wash off with soap and water. | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ ------- **P** ------- +-----------------------------------------------------------------------+ | **pastes** | | | | mixtures with a high concentration of absorbed powders. They are | | stiff and do not soften, therefore they adhere well to the skin | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **plasters** | | | | the drug ingredients are added to a material which sticks to the skin | | (band aid type) | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **protectants and lubricants** | | | | moisturize and protect the skin (e.g. cocoa butter) | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ ------- **R** ------- +-----------------------------------------------------------------------+ | **removable bases** | | | | also called water washable bases and are oil-in-water (o/w) mixtures | | that are easily removed from the skin with water; more commonly | | called creams | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ ------- **S** ------- +-----------------------------------------------------------------------+ | **shampoos** | | | | products used to treat scalp conditions | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **soaps** | | | | cleansing soaps are solid bars which are worked into lather for | | washing the skin. | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **sticks** | | | | an easily transportable and convenient dosage form for administering | | topical medications | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **sun protection factor (SPF)** | | | | provides a relative scale to gauge the exposure time before the skin | | will redden. SPF 15 will provide 15 times longer protection than if | | no sunscreen was applied. | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ ------- **T** ------- +-----------------------------------------------------------------------+ | **tinctures** | | | | an alcoholic or hydroalcoholic solution of extractions from plants; | | often painted on the skin | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **topical aerosols** | | | | sprays that usually contain anti-infectives or local anesthetics and | | are used for injured skin. | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **topical anaesthetics** | | | | cause numbness to the skin (e.g. solarcaine) | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **topical powders** | | | | may be non-medicated and often contain moisture absorbing substances | | to keep skin dry. Other powder products are used to treat athlete's | | foot. | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **topical route of administration** | | | | the administration of a drug on the skin or mucous membrane.The | | topical route may also be referred to as the epicutaneous route (when | | effect is local) or the transdermal route (when the effect is | | systemic) | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **transdermal form of administration** | | | | a formulation designed to deliver a continuous supply of drug into | | the bloodstream for systemic effect by absorption through the skin | | via an ointment, gel, lotion, patch, or disk | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ ------- **W** ------- +-----------------------------------------------------------------------+ | **water soluble bases** | | | | contain only water-soluble compounds and are also are referred to as | | greaseless (due to lack of any lipid component).  Gels or jellies are | | single phase systems and milk or magmas are 2 phase systems | +=======================================================================+ | -- | | -- | +-----------------------------------------------------------------------+ +-----------------------------------------------------------------------+ | **water-in-oil (w/o) emulsion** | | | | already contain an aqueous part and allow the addition of even more | | aqueous solution | +-----------------------------------------------------------------------+ **Introduction to Topical Preparations** Topical dosage forms are used **on the skin and mucous membranes**. The topical route may also be referred to as the epicutaneous route (when effect is local) or the transdermal route (when the effect is systemic). Most topical preparations are used for their local therapeutic effect; however, certain preparations are used for systemic effects. A topical preparation can: - Have a prophylactic effect of keeping the skin in optimal condition (lotion) - Provide a therapeutic effect for a disease condition of the skin - Provide a systemic effect to the body (transdermal patch) With local absorption, products are designed to deliver drug into the skin, with the skin as the target organ. When systemic absorption is desired, drug products are designed to deliver drugs through the skin (percutaneous) to the general circulation for total body effects (the skin is not the target area). The most common topical preparations include ointments, creams, lotions, and transdermal therapeutic systems (patches) applied to the skin. Lesser-used topical dosage forms include solutions, tinctures, pastes, liniments, powders, aerosols, collodions, and soaps.\  \ Topical preparations can be used as: - Protectants and lubricants -- moisturize and protect the skin (e.g., cocoa butter) - Astringents -- drugs used topically to shrink tissue and toughen tissue (e.g., zinc sulphate) - Topical anaesthetics -- to cause numbness to the skin (e.g., Lanacane®) - Anti-pruritics -- to reduce itchiness of skin (e.g., calamine) - Anti-inflammatories -- to reduce inflammation of the skin (e.g., hydrocortisone) **The Skin** - The skin is a human's largest organ. It is an effective protective cover for the body and one of its functions is to prevent microbes, radiation, and chemicals from penetrating the underlying tissue. The skin consists of two main layers, the epidermis (the outer layer) and the dermis (middle layer), plus the underlying subcutaneous tissue (innermost layer). - **The stratum corneum** is the thin layer of cells that covers the **epidermis**. It varies in composition, thickness, and continuity and offers little resistance to drug penetration. The stratum corneum behaves as a semi-permeable membrane and is composed of protein (keratin), water, and lipids. On the surface is a film of material composed of sebum (oil), sweat, and dead epidermal cells. The oily film on the stratum corneum slows evaporation of water to keep the skin supple. Dry, rough, cracked skin is a result of a rapid loss of moisture from the stratum corneum and is usually due to environmental factors such as wind, sun, heat, and dry air. - **The dermis** is the middle layer of skin. The dermis gives skin its strength and elasticity. Hair shafts, sweat glands, and sebaceous glands originate in the dermis. Blood vessels in this layer are able to absorb drugs which are able to penetrate this deep. - **Subcutaneous tissue** in the subcutaneous layer is made mostly of fat, nerves, and blood vessels. Sunscreens ---------- **Promotion of Good Sun Habits** -- The sun produces UV radiation, also known as UV rays. It is important to note that exposure to UV radiation can occur on days that are overcast or cool as well as on hot, sunny, summer days. UV radiation from the sun is harmful to the skin and causes damage to the epidermis. Damage to the epidermis leads to thinning and growth of lesions that can become cancerous. Anyone who spends a great deal of time in the sun is at a higher risk for skin cancer. People with fair skin and blonde or red hair are at a higher risk of developing skin cancer because there is less pigment in the skin. Darker-skinned individuals are at a lower risk because their dark pigmentation offers more protection to the skin. Sunscreens can help reduce sunburn, but they are not as effective against the other harmful effects of UV rays, such as premature aging or depression of the immune system. **Sunscreens** -- A good sunscreen contains a chemical filter, e.g. PABA (para amino benzoic acid), that absorbs, scatters or reflects some of the UV radiation. It should also contain physical filters such as zinc oxide that absorb, scatter, and reflect both UVB and UVA radiation. Sun protection factor (SPF) provides a relative scale to gauge the exposure time before the skin will redden. SPF 15 will provide 15 times longer protection than if no sunscreen was applied. Example: If the skin normally reddens in 20 minutes, and a person applies an SPF 15, the person can stay in the sun for 300 minutes before the skin reddens (compared to no sunscreen). Sunscreens work best if applied 20 to 30 minutes prior to sun exposure to allow time for absorption, and then re-applied 20 minutes after sun exposure begins. Re-application is required after swimming or excessive sweating. Most sunscreen failures are due to inappropriate product use. Some medications cause photosensitivity (heightened sensitivity to sunlight). The patient should wear sunscreen if they are taking medications that cause this. **Common Skin Conditions** There are many common skin conditions that can be treated or controlled with topical drug preparations. Students should be aware that severe infections or other problems may require the use of oral or parenteral drugs. Common skin conditions include: - Acne - Allergic reactions (e.g., hives) - Bacterial infections - Burns - Corns and calluses - Diaper rash - Eczema - Fungal infections - Psoriasis Rosacea - Skin infestations (e.g., lice, scabies) - Ulcers and pressure sores - Viral infections (e.g., warts, cold sores) - Wrinkles **Drug Absorption -- Topical Preparations** A drug must be in contact with and stay within the skin in order to treat the skin condition. Some drugs intended for a local effect may have some absorption from the skin into the bloodstream. It is important then that topical preparations be used sparingly to minimize unwanted systemic effects. Some drugs are administered topically with the intention of achieving systemic effects. Examples include nitroglycerin patches (for angina) and scopolamine patches (for motion sickness) which are absorbed through the skin (percutaneous absorption). **Absorption is influenced by the following:** - **Drug properties**: The greater the concentration of a drug in a vehicle, the greater the amount absorbed into or through the skin. - **Skin condition** (including age): Well hydrated skin absorbs drugs better. If the skin is cracked or cut, the skin barrier is broken allowing drugs to easily be absorbed into the circulation. - **Thickness of the stratum corneum**: This will also influence drug absorption. Infants have thin skin, so absorption occurs more quickly. Absorption from the palms of the hands and soles of the feet is much slower than from other parts of the body. **Factors that affect topical drug absorption include:** - **Application of drug to an area**: The larger the area, the greater the amount of total drug absorption. - **Contact time with the skin**: The longer the drug is left on the skin, the greater the amount absorbed. - **Vehicle**: The vehicle must be suitable for skin interaction. - **Inunction**: Rubbing into the skin will increase absorption. - **Chemicals**: Adding chemicals can increase the absorption of drug. Ointments --------- Ointments are semi-solid preparations intended for application to the skin. In the past, ointment bases were made of vegetable and animal fats and oils. Although some of these natural substances are still used, the majority of ingredients are synthetic or petroleum-based compounds. An ointment may be medicated or non-medicated. Non-medicated ointments are used as lubricants, emollients or the vehicle to which drug ingredients are added. Ointments are broken down into four categories according to the USP: oleaginous (hydrocarbon) bases, absorption bases, water-removable bases, and water-soluble bases. An ointment base is known as the **vehicle** of an ointment. **Oleaginous (Hydrocarbon) Bases Ointments** Oleaginous bases (hydrocarbon bases) are bases prepared from petrolatum. Hydrocarbon bases can only accept very small amounts of water (or hydrophilic components) added to them. These bases are greasy and hard to wash off with soap and water. **Advantages of oleaginous bases:** - Provide a protective barrier and act as an emollient (oil/fat used to soften skin) - Won't dry out (are stable) - Are occlusive and therefore increase drug absorption **Disadvantages of oleaginous bases:** - Greasy and sticky; difficult to wash off - Occlusive barrier does not allow the drainage of fluids from the skin so it may lead to irritation. - Difficult to incorporate aqueous components - May stain fabrics **Common Oleaginous Bases** **Petrolatum USP** -- also known as yellow soft paraffin, petroleum jelly, Vaseline. This may be used in eye ointments. **White Petrolatum USP** -- also known as White Vaseline. This is the same as Petrolatum USP but contains no colour. **Mineral Oil** (liquid paraffin, heavy liquid petrolatum) -- used to levigate powders (make a paste) before adding to a hydrocarbon base; also used internally, plain or in emulsion form (laxative) **Paraffin** (hard and soft paraffin wax) -- used to stiffen hydrocarbon ointment bases and is a purified mixture of solid hydrocarbons **White Ointment USP** and **Yellow Ointment USP** -- wax from the honeycomb of bees is used (White Ointment is bleached); has a faint smell of honey **Absorption Bases -- Ointments** Absorption refers to the water absorbing abilities of the bases, **not** the action on the skin. There are two types of absorption bases -- anhydrous and water in oil (w/o) emulsions. **Anhydrous absorption bases** *permit* incorporation of aqueous solutions to form a W/O emulsion but do not contain the aqueous part in its original state. **W/O emulsions** *already* are emulsions and permit the addition of more aqueous solutions. Both types readily permit the incorporation of water. Absorption bases are greasy but less so than hydrocarbon bases, and they allow the addition of aqueous liquid (e.g., Aquaphor®, Eucerin®). **Advantages of absorption bases:** - Useful as an emollient/protectant without the highly occlusive characteristics of a hydrocarbon base - Useful for incorporating aqueous solutions of drugs - Heat stable and give a better release of the drug (compared to hydrocarbon bases) **Disadvantages of absorption bases:** - Greasy and not readily water-washable; however, they are not as difficult to remove as hydrocarbon bases. - Do not provide the same degree of occlusion as oleaginous bases **Common Absorption Bases** **Hydrophilic Petrolatum USP** -- anhydrous and will absorb large amounts of water or aqueous solutions of drug to form an emulsion. Aquaphor is a commercially prepared absorption base. **Lanolin USP** -- from the wool of sheep and is wax-like. It contains a very small amount of water. **Water-Removable (Water-Washable) Bases -- Ointments (Creams)** Water-removable bases (water-washable bases) are oil in water mixtures (O/W) that are easily removed from the skin with water. **Note:** Although these are USP classified as ointments, they are more commonly (and correctly) called **creams**. **Advantages of water-removable bases:** - Non-greasy feeling; more acceptable to patients - Cream bases are easily washed off - Can be diluted with water or aqueous solutions (bases absorb more water) - Less likely to stain in comparison to other ointments - Good percutaneous absorption of drugs from these bases - Absorb discharge from oozing lesions and are not occlusive **Disadvantages of water-removable bases:** - Can lose water by evaporation - Do not protect the skin and provide little emollient effect - Increased likelihood for interactions between drugs and the ingredients of the base **Common Water-Removable Bases** **Hydrophilic Ointment USP** -- Contains white petrolatum, water, and other ingredients including preservatives **Glaxal Base** -- Commercially available **Water-Soluble Bases (Gels, Jellies, and Magmas)** These bases contain only water-soluble compounds and are also are referred to as greaseless (due to lack of any lipid component). They are produced using polyethylene glycols and other substances. Most often, these bases will be used to incorporate powdered ingredients rather than additional aqueous substances because the final product would become too runny. **[Note]:** Although these bases are USP classified as ointments, they are more commonly (and correctly) called **gels** or **jellies**. These are dispersions similar to suspensions in the oral liquid section except that these are used topically. (Magmas and some jellies are used orally. When used orally, they are referred to as dispersions rather than ointment bases.) Gels can be divided into two categories -- single-phase and two-phase systems. Single-phase systems have solute particles so small that they cannot be distinguished from the solute. This type is often simply called a **gel** or **jelly**. Note that the solute may be hydrophilic, oily or alcoholic. Nasal gels may be used to relieve dry nostrils. Two-phase systems have larger particles of solute although the particles are still extremely small. The solute will settle and will need significant shaking to re-mix thoroughly. These gels are sometimes called **magmas** or **milks**. **Advantages of water-soluble bases:** - Stable, unreactive - Good percutaneous absorption of drug **Disadvantages of water-soluble bases:** - No protective, emollient action for the skin - With addition of water, they soften considerably - Interact with some drugs An example of a water-soluble base is **Polyethylene Glycol Ointment USP**. Selection of Ointment Bases --------------------------- Occlusive hydrocarbon bases are used for dry skin lesions, and the water-washable or water-soluble bases for moist lesions. The bases that are easily removable or greaseless are more convenient for patients. It is not often that an ointment base will be prepared from scratch because commercially prepared bases such as white petrolatum or Glaxal base are available and inexpensive. Other things to consider when choosing an ointment base include the stability of the drug in the base, the extent of release of drug and systemic absorption, and the desired extent of the washability of the product. Pluronic Lethicin Organogel (PLO Gel) ------------------------------------- PLO Gel is an emulsion used as a base for transdermal drug administration. This is a very popular base used in the preparation of manufactured and compounded topical medications intended for systemic effect. There are two phases of PLO -- an oil phase and a water phase. A stable emulsion is prepared by combining the two phases and mixing thoroughly. A commercial kit is available and consists of Diffusamax® A and B. Solvent A is used for organic substances and Solvent B for water soluble substances. The active ingredient (often diclofenac) is levigated with the appropriate solvent to produce a paste. Using a mortar and pestle, the gel is formed by adding one part of Solvent A to three parts of Solvent B. Packaging and Storage of Topical Medications -------------------------------------------- The packaging and storage of topical medications is product-specific. If a topical medication is compounded in a pharmacy, then USP guidelines should be used to determine the expiry date. Certain topical medications are stored in a refrigerator prior to being dispensed, and other topical medications require mixing prior to dispensing. Topical preparations should be kept away from moisture and excess heat. Most manufactured topicals are supplied in metal tubes, plastic or glass jars, or pump bottles. Most compounded topical preparations are dispensed in plastic jars. The size of the ointment jar should be chosen so that the product fills or nearly fills the jar. This helps reduce the possibility of water loss from the product. Water evaporation will cause the product to become more concentrated and unstable. Humectants help to reduce evaporation of the aqueous component of the product while in the container and also after application to the skin. The auxiliary labels **FOR EXTERNAL USE ONLY** and **EXPIRY DATE** must be used. **Application Process for Topical Dosage Forms (Ointments, Creams, and Gels)** 1. Wash hands. 2. Cleanse the affected area with water unless otherwise directed and wash hands again. 3. Remove the ointment or cream from the jar without using fingers; a person does not want to contaminate the product. Use a tongue depressor or applicator. 4. Using firm, yet gentle pressure, apply a small amount of ointment/cream and make sure the area is thoroughly covered. 5. Ensure that clothing is removed from the area to prevent staining. Do not cover the area with tight dressings because this may result in systemic absorption and therefore increase side effects. 6. Always pay close attention to the area when using a product for the first time in the event that an allergic reaction occurs. Symptoms can include rash, swelling, redness, and/or itchiness. If a reaction occurs, stop the medication immediately and contact the physician. 7. Topical corticosteroids must be applied sparingly and it is very important that the area is not occluded. **Other Topical Dosage Forms** **Collodions** Upon application to the skin, the solvents evaporate leaving a transparent film that protects the skin or holds medicinal agents in contact with the skin. The solvents are very flammable and should be stored away from heat and light in a tightly-closed container (e.g., Compound W®). ------------------------------------- ------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------ **Liniments** Solutions or mixtures intended for application to the skin via massage. Products are normally used for relief of muscle pain by promoting blood flow and easing the pain. Liniments should not be applied to broken skin because they contain ingredients such as camphor, menthol, and eucalyptus oil, which would cause a burning sensation. **Lotions** They are often O/W emulsions and their fluid nature makes them quick and easy to apply to large areas. (e.g., Lubriderm®, Moisturel®). **Pastes** Pastes are mixtures with a high concentration of absorbed powders. They are stiff and do not soften; therefore, they adhere well to the skin. Pastes are difficult to apply to the skin, especially hairy parts of the body, and can be removed with vegetable or mineral oil (e.g., zinc oxide paste). **Plasters** The drug ingredients are added to a material which sticks to the skin (band-aid type). Plasters keep medicinal agents in place to treat conditions such as corns. **Shampoos** Products used to treat scalp conditions such as dandruff, seborrhea, and psoriasis. **Soaps** Cleansing soaps are solid bars which are worked into a lather for washing the skin. The basic pH and grease-removing action is harsh on sensitive skin. **Topical Aerosols** Sprays that usually contain anti-infectives or local anesthetics and are used for injured skin. The application process does not involve touching the skin, so applying the medicinal ingredient is convenient. **Topical Powders** Topical use powders may be non-medicated and often contain moisture-absorbing substances to keep skin dry. Other powder products are used to treat athlete's foot. **Topical Solutions and Tinctures** Topical dosage forms painted on the skin or used as a soak (e.g., iodine solution). **Sticks** The most common sticks used today are lip balms and deodorant sticks. **Transdermal Drug Delivery Systems (TDDS)** The transdermal drug delivery system is a transport system designed to facilitate passage of therapeutic quantities of drug substances through the skin and into the circulatory system for systemic effects. The drug is contained in patches that are applied to the skin; the drug is absorbed percutaneously into the circulatory system. **Watch the video [[Transdermal Patches]](https://www.youtube.com/watch?v=xBUCjnSdfNI&list=PLbai4zsgRCOBqnklotJuDJ2YA5pE2C7Qi&index=5).\ ** **Advantages of TDDS:** - They eliminate the problems associated with the oral route such as food-to-drug interactions, GI upset, and liver first-pass metabolism effect. - They are convenient and easy to use (promotes compliance). - Drug can be stopped quickly by removing the patch. - Easily identified - Extends duration of therapy - Non-invasive **Disadvantages of TDDS:** - Not all drugs qualify for TDDS. - Some patients develop contact dermatitis (skin sensitivity) or pruritis (itchiness) with the patch. - Increased cost **Main Components of TDDS** **Occlusive backing membrane or layer** -- This layer prevents the loss of drug and prevents moisture from entering the patch (when showering). **Drug reservoir** -- The drug reservoir stores and releases the drug to the skin. **Control membrane** -- This membrane controls the rate of diffusion. **Adhesive layer** -- The adhesive layer contains the initial dose of the drug and sticks the patch to the skin. **Release liner** -- The release liner protects the adhesive and is removed before application. Some patches, such as Nitro-Dur®, do not have a control membrane and the drug is contained in a matrix. The stratum corneum acts as the control membrane. Some drug matrices have excess drug to ensure continuous saturation and some drug matrices do not contain excess drug so the rate at which the stratum corneum is saturated will decrease over time. **Packaging and Storage** - The TDDS patches are individually wrapped and packaged in a box. - Patches remain in the sealed wrapper until just prior to administration. - Storage is usually at room temperature. **Auxiliary Labels and Patient Advice** An **EXTERNAL USE ONLY **auxiliary label should be affixed to the product. Prior to MRI diagnostic procedures, patients are advised to remove the TDDS to avoid a possible burn. Metal in the outer layer of the TDDS may conduct electrical currents that are produced in the MRI and result in a serious burn. **Do not cut or alter the patches** unless the manufacturer specifies that a patch may be cut in half. **Watch the video [[How to Apply Transdermal Patches]](https://www.youtube.com/watch?v=x8sOrXljT9I&list=PLbai4zsgRCOBqnklotJuDJ2YA5pE2C7Qi&index=6). \ ** **Application Process for TDDS** Since the rate and extent of percutaneous absorption varies with the drug and the site of administration, the TDDS is applied to a site as directed by the manufacturer. - - - - - - - - - - Topical Ointment Topical Cream  Topical Gel Topical Lotion  Topical Paste Topical Shampoo  Topical Solution  Thickest to thinnest Oleaginous: no or little ability to accept water or aqueous ingredients Water-soluble: gel or jelly Absorption: permits incorporation of some aqueous ingredients; somewhat greasy Water-removable: cream What is the purpose of PLO gel? It is a vehicle used to permit systemic absorption of a drug via skin What is a reason that best explains why TDDS products should not be cut? Cutting destroys the rate controlling membrane Paste is a more occlusive topical that an ointment.