Pastes & Gels PDF

Pastes and Gels Learning objectives describe pharmaceutical pastes and gels  types of pastes, and gels discuss the formulation considerations and commonly used excipients for pastes and gels patient counseling points for semisolids, particularly for pastes and gels What is a paste? Pastes are semis...

Pastes and Gels Learning objectives describe pharmaceutical pastes and gels  types of pastes, and gels discuss the formulation considerations and commonly used excipients for pastes and gels patient counseling points for semisolids, particularly for pastes and gels What is a paste? Pastes are semisolid dosage forms that contain a high percentage (often up to 50%) of finely dispersed solids.  stiff consistency (don’t flow at body temp)  stays over the area to which they are applied (don’t spread over healthy skin)  serve as protective coatings (but not occlusive, because pastes are porous)  used in the treatment of oozing lesions (absorb secretions) Types of pastes Single-phase aqueous paste Aqueous gel Triamcinolone acetonide dental paste, USP Fatty paste Hydrocarbon base Zinc oxide paste, USP Aqueous paste (single-phase) Triamcinolone acetonide dental paste (0.1%)  topical corticosteroid (oral lesions, mouth sores, decreases inflammation) Adhesive base (vehicle) suitable for application to the oral cavity (Oromuco-adhesive paste)     gelatin pectin carboxymethylcellulose sodium plasticized hydrocarbon gel (mixture of PEG and mineral oil to form a gel) soft, glossy base Fatty paste Zinc oxide paste (16 - 40%) for diaper rash       Ricinus communis (castor) seed oil Mineral oil Paraffin Balsam tolu resin Petrolatum Preservative free Other brands of zinc oxide paste  Desitin Maximum Strength Original: 40% (contains cod liver oil and lanolin)  GoodSense Diaper Rash [OTC]: 40% (contains methylparaben)  Triple Paste: 12.8%  Z-Guard: 17% (contains petrolatum 57% and soy protein) Zinc oxide is also available as topical aerosol, cream, topical stick, ointment and topical powder (skin protectant) Bases used for pastes Hydrocarbon base  soft paraffin and liquid paraffin Water miscible base  emulsifying ointment  plasticized hydrocarbon (PEG + hydrocarbons) Water soluble bases  PEG bases Preparation of paste Fusion method  Melt all bases & wax with continuous stirring  Add powdered ingredients  Continuous and constant stirring until cool Fusion and trituration method  Melt the base  Take powder (drug) and triturate with melted base (concentrate)  Triturate (mix) the concentrate with the remaining base (heat may be used to facilitate mixing) Commonly used excipients in pastes Additional/alternative hydrophobic solvents  polydimethylsiloxane (liquid silicone)  vegetable oils (canola oil, sunflower oil, corn oil, soybean oil)  organic esters (isopropyl myristate) Preservatives (if necessary) Antioxidants  lipophilic antioxidants (BHA, BHT)  hydrophilic antioxidants (sodium metabisulfite) What is a gel? Gels (sometimes called Jellies) are semisolid systems consisting of colloids as either:  small inorganic particles (colloidal suspension), or  large organic molecules (interpenetrated by a liquid) Based on the external liquid phase, gels can be classified as:  polar/aqueous (hydrogels)  nonpolar/lipids (organogels) Types of gels Nature of the colloids Inorganic gel Organic gels Nature of the solvent Natural polymers Hydrogels Semisynthetic Synthetic Lecithin based Organogels Fatty acids based Sorbitan ester based Like dispersed systems, the particles in gels sediment over time. Like dispersed systems, the particles in gels sediment over time. False The movement of the particles in gels is restricted: due to the three-dimensional network, and the colloidal nature of the particles Inorganic gels two-phase systems (inorganic particles, and the continuous gel phase)  Aluminum hydroxide gel  Bentonite magma colloidal dispersion Pseudoplastic non-Newtonian flow behavior viscosity decreases with increased shear force (shear thinning, thixotropic) due to break down of the structure of the system Common flow behaviors Organic gels single-phase system (no apparent boundaries between particles and gel) contain gelling agents (natural or synthetic polymers)  polyacrylic acid polymers (Carbomer, Carbopol® 980)  tragacanth Adapalene Gel (0.3%) retinoic acid derivative used in the treatment of acne Excipients in Adapalene gel Carbopol 980 (crosslinked polyacrylic acid) EDTA sodium Methylparaben Poloxamer 124 (Polyethylene-Polypropylene Glycol) Propylene glycol Purified water Sodium hydroxide Hydrochloric acid What is the function of these excipients in Adapalene gel. Carbopol 980 EDTA sodium Methylparaben Poloxamer 124 Propylene glycol Purified water Sodium hydroxide Hydrochloric acid Gelling agent What is the function of these excipients in Adapalene gel. Carbopol 980 EDTA sodium Methylparaben Poloxamer 124 Propylene glycol Purified water Sodium hydroxide Hydrochloric acid Gelling agent Chelating agent/Stabilizer What is the function of these excipients in Adapalene gel. Carbopol 980 EDTA sodium Methylparaben Poloxamer 124 Propylene glycol Purified water Sodium hydroxide Hydrochloric acid Gelling agent Chelating agent/Stabilizer Preservative What is the function of these excipients in Adapalene gel. Carbopol 980 EDTA sodium Methylparaben Poloxamer 124 Propylene glycol Purified water Sodium hydroxide Hydrochloric acid Gelling agent Chelating agent/Stabilizer Preservative Surfactant What is the function of these excipients in Adapalene gel. Carbopol 980 EDTA sodium Methylparaben Poloxamer 124 Propylene glycol Purified water Sodium hydroxide Hydrochloric acid Gelling agent Chelating agent/Stabilizer Preservative Surfactant Cosolvent What is the function of these excipients in Adapalene gel. Carbopol 980 EDTA sodium Methylparaben Poloxamer 124 Propylene glycol Purified water Sodium hydroxide Hydrochloric acid Gelling agent Chelating agent/Stabilizer Preservative Surfactant Cosolvent Solvent What is the function of these excipients in Adapalene gel. Carbopol 980 EDTA sodium Methylparaben Poloxamer 124 Propylene glycol Purified water Sodium hydroxide Hydrochloric acid Gelling agent Chelating agent/Stabilizer Preservative Surfactant Cosolvent Solvent pH adjustment pH adjustment Hydrogels Water-swollen structures composed of mainly hydrophilic polymers  natural, synthetic, or semisynthetic Hydrophilic polymers are rendered insoluble due to the presence of crosslinks  entanglements  crystallites  van der Waals interactions  π–π-stackings  hydrogen bonds Physical crosslinking Organogels organic (non-polar) solvents  hexane  isopropyl myristate  sunflower oil, corn oil The gelation process involves the self-assembly of low-molecular-weight gelators (LMWGs) to give polymer-like fibers  acrylic polymers  lecithin  polyethylene Characteristics of gels: Swelling or Imbibition taking up of water (or solvent) by the gel and increase in volume gel-gel interactions are replaced by the gel-solvent interactions Characteristics of gels: Syneresis or weeping of gel opposite of swelling/imbibition many gels often contract spontaneously on standing and exude some fluid medium syneresis becomes more obvious as the concentration of the gelling agent decreases it occurs in both organic and inorganic gels Characteristics of gels: Thixotropy some gels turn into a sol on shaking and reset to the gel on standing. reversible gel-sol transformation time-dependent shear thinning property Characteristics of gels: Structure Inorganic particles can gel a vehicle by the formation of a specific structure  Bentonite or kaolin (clays) forms a lamellar structure that can be extensively hydrated Stimuli-responsive gels most hydrogels show a drastic change in their properties in response to external stimuli (smart hydrogels)  pH  temperature  ionic strength change  biological (enzymes and antigens/antibodies) Xerogel Xerogels are gels in which the vehicle has been removed, leaving a polymer network (films)  Dry gelatin  Tragacanth ribbons  Polystyrene Xerogel has high porosity (15 – 50%) and highsurface area Factors to consider and Patient counseling points 1. Always consider the effect of the vehicle. An occlusive vehicle enhances penetration of the active ingredient. The vehicle itself may have a cooling, drying, emollient, or protective action. It can also cause side effects. 2. Match the type of preparation with the type of lesions, and with the site of application. 3. Clean (and dry) the affected area before applying the drug. If the skin is very dry and flaking, apply the medication while the skin is still damp. 4. The patient should be instructed/trained as to the proper amount of topical agent that is to be used, to ensure the correct dose. Factors to consider and Patient counseling points 5. Wash hands before and after use (using gloves may be recommended). 6. An occlusive dressing, such as a bandage, should not be used unless needed to protect the area from excessive contact or contamination. 7. Greasy ointments can stain clothing. 8. Discuss the effect of applying moisturizers on skin absorption. Explain the order of administration in case of multiple formulations.