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Pastes: What Do They Contain? How Do They Work?
Abstract
Pastes are semisolid stiff preparations containing a high proportion of finely powdered material. Powders such as zinc oxide, titanium dioxide, starch, kaolin or talc are incorporated in high concentrations into a preferably lipophilic, greasy vehicle. A clinically distinctive feature which is generally attributed to pastes is the quality to absorb exudates by nature of the powder or other absorptive components. Reviewing the various pharmacopoeias serious doubts arise from the various formulas of pastes and their absorptive features. The zinc oxide pastes of the USP XXII, the DAB 10 and BP 88 (US, German and British pharmacopoeias). are composed of petrolatum, zinc oxide and starch. Petrolatum, a highly lipophilic, water-immiscible vehicle surrounds the powder particles preventing any absorption of water or exudates.
The goal of our investigation was to test a simple experimental setting to characterize the clinically important absorptive feature of powders and pastes.
The absorptive features of the powders were determined by the method of Enslin. The absorptive features of the paste preparations were calculated from the weight difference between the paste preparation before and after incubation with water using a simple standardized procedure.
The absorptive features of titanium dioxide, zinc oxide, kaolin, corn starch and methylcellulose powder in pharmacopoeia quality were determined. Zinc oxide and kaolin powder showed the highest absorption of 1,000 mg water/g powder (100%). The water absorption of corn starch and titanium dioxide was 700 and 450 mg/g powder, respectively. The absorptive features of a series of paste preparations were studied in a simple experimental setting. The data show that two-phase pastes consisting of two immiscible components, one (the dispersed or inner phase; powder) being suspended in the other (the continuous or outer phase; lipophilic vehicle), have no absorptive features. In contrast, three-phase pastes consisting of a hydrophilic two-phase emulsion with high concentrations of incorporated powder (cream pastes) show considerable water uptake.
We conclude that the classical two-phase pastes such as the zinc oxide pastes have no absorptive features. On the contrary, these formulations are highly occlusive. Therefore lipophilic pastes are only indicated when protection of intact skin against aggressive body exudates and humidity is required. The hydrophilic three-phase pastes or cream pastes show considerable water uptake and fulfil common expectations of pastes to dry the skin.
... respectively) (mindat.org/min-1719.html). Sun screening by clays is also influenced by their small particle sizes [Juch RD, et al 1994]. Most of the clayey soils used for sunscreen had majority of their particle sizes in the 2 to 50 µm range. ...
... Most of the clayey soils used for sunscreen had majority of their particle sizes in the 2 to 50 µm range. Given their small particle sizes, their specific surface area may provide a platform for the absorption or scattering of radiant energy [Juch RD,et al 1994]. and thereby reduce the intensity of UV radiation that reaches the skin. ...
Clayey soils used traditionally for therapeutic and cosmetic purposes in Edo state, Nigeria were studied and characterized for their Geochemical, Physico-chemical and Mineralogical properties. Five clayey soil samples were collected from selected communities-Uzalla, Aforwa and Ohordua within Edo state and standard laboratory methods were used to determine their colour, particle size distribution, pH, specific surface area (SSA) and cation exchange capacity (CEC). Atomic Absorption spectrometry (AAS) were used to characterized the major and minor elemental composition. X-ray Diffractometry (XRD) was used to identify the mineralogical component of the soils samples. Results show that the pH values range from 5.22 to 6.46. The CEC range from 30.8 to 25.6meq, The SSA values were between 0.5 and 2.4 m 2 /g. From the colours of the samples, they are inferred to contain hematite and goethite which are present in many skin sunscreen and beauty products. Results of the AAS analysis show that major and minor elements range from 1.0 mg to the limit of delectability 0.0001mg/g. SiO 2 values range between 54.85 and 63.1wt%, whereas Al 2 O 3 values range from 12.63 to 26.78%. Results of XRD analysis for mineralogical investigation reveal that the samples are dominantly composed of quartz, kaolinite, halloysite, illite, mica and feldspar.. Samples with the highest concentration of iron oxide showed also the highest UV protection ability.
... In pharmacopoeia quality, the 1:1 kaolin-water system exhibits the highest clinical absorptive feature amongst other common pharmaceutical materials used in hydrophilic paste preparations (Juch et al., 1994). Technologically, the 1.0 solid/liquid ratio of the kaolin aqueous dispersions showed the optimal water content 50% in the preparations of easily molded, consistent, and desirable adhesive pastes (Ramasamy et al., 2015). ...
The present study aims to evaluate the potentiality of 7 selected structural highly ordered kaolinite-rich samples from Egyptian Carboniferous sedimentary deposits (located at Abu Zenima district, west central Sinai peninsula) to use them in medicinal semisolid formulations as peloids. The effect of particle geometry and kaolinite crystallite size are studied to check their influence on thermal dosage performance.
The studied samples exhibit a variable mineralogy. Kaolinite is the main constituent (ranging from 81 to 94%), followed by quartz (up to 14%), lesser amounts of anatase and halite, and traces of hematite, magnetite, alunite and gypsum. The kaolinite order “Hinckley Index” varies from 1.28 to 1.50. 1:1 (w/w) kaolin mud pastes were prepared with purified water in Eppendorf tubes using a touch vibration vortex mixer for 2 min. The cooling kinetics of pastes were measured by using a differential scanning calorimetry equipment (Shimadzu DSC-50Q). Specific heats were calculated, following Cara et al. (2000). The granulometry and geometric surface area were measured by laser diffraction (Mastersizer 2000LF, Malvern Instruments) in the range 0.02 and 1500 μm.
All analyzed samples showed a clear predominance of particles under 4 μm (ranging from 82 to 94%), with median size (D50) ranging from 0.93 to 1.35 μm. The heat retention time during cooling from 50 °C to 32 °C reached up to 30.82 min, oscillating around an average of 28.72 min, and the temperature corresponding to the minimal dosage time (T20) was not exceed below 34.7 °C. A good correlation (R2 = 0.875) was found between heat retention time and specific heats. There is no correlation between kaolinite content and thermal properties, but R2 values around 0.6 are found with granulometry (finer the particles, greater the heat retention time t32 and the specific heat). Even if sample H5 (Gabal Hazbar deposit) is not the richest in kaolinite, it exhibits the best thermal dosage performance, in accordance with the granulometry (D50 = 0.93 μm), and geometric surface area (3.73 m2/g).
Preparations for cutaneous (or dermal) application may be used for local treatment as well as for transdermal administration with a systemic effect. The chapter focuses on preparations with a local effect and on design of formulation and method of preparation of those prepared in pharmacies. The interaction between skin, active substance and base, the anatomy of the skin and biopharmaceutical aspects of cutaneous preparations are discussed. Due to the important role of pharmacists in prescription assessment some recommendations for communications with the physician are provided. One aspect is how to proceed with a request for the mixing of two licensed medicines or for the addition of an active substance or an excipient to a licensed product. The formulation design is generally following the several phases of the multicomponent preparations. Based on the classification of the European Pharmacopoeia the typical types of cutaneous dosage forms are discussed further, with regard to formulation and processing. Extemporaneous preparation mostly involves the addition of active substances to base preparations. Preparations standardised in European formularies are used to illustrate special properties, design of formulation and preparation methods. Preparation processes for large scale may require different techniques than small scale preparations.KeywordsFormulationPreparationBaseSemisolidCutaneous liquidCreamOintmentCutaneous gelPasteSkinCutaneous emulsionCutaneous powderCutaneous solutionCutaneous suspension
Il farmaco galenico è un medicinale tradizionale preparato dal farmacista secondo le indicazioni della farmacopea ufficiale della Repubblica Italiana. In Italia è anche possibile preparare farmaci galenici tratti dalle farmacopee degli altri Paesi dell’Unione Europea.
Preparations for cutaneous (or dermal) application may be used for local treatment as well as for transdermal administration with a systemic effect. The chapter focuses on preparations with a local effect and on design of formulation and method of preparation of those prepared in pharmacies. The interaction between skin, active substance and base, the anatomy of the skin and biopharmaceutical aspects of cutaneous preparations are discussed as well as the therapeutic effect of the base. Because of the important role of the pharmacist in prescription assessment some recommendations for the communication with the physician are given. One aspect is how to proceed with a request for the mixing of two licensed medicines or for the addition of an active substance or an excipient to a licensed product. The formulation design is generally following the several phases of the multicomponent preparations. Based on the classification of the European Pharmacopoeia additionally the typical types of cutaneous dosage forms are discussed further, with regard to formulation as well as the way of processing. Extemporaneous preparation mostly involves the addition of active substances to base preparations. Preparations standardised in European formularies are used to illustrate special properties, design of formulation and preparation methods. Preparation processes for large scale require some other methods than small scale preparations.
Die Struktur der einphasigen flüssigen Systeme bedarf keiner weiteren Erörterungen. Bezüglich der mehrphasigen flüssigen Systeme vom Typ der Emulsionen ergeben sich ebenfalls keine wesentlichen neuen Gesichtspunkte. Bei der flüssigen O/W-Emulsion ist die äußere Phase Wasser, in der die Lipidphase in Tröpfchenform emulgiert ist. Die Emulgierung wird durch dominierend hydrophile Emulgatoren ermöglicht, die sich mit ihrem lipophilen Anteil an die dispersen Lipidpartikel anlagern (Abb. 3.1). Umgekehrt findet sich bei flüssigen W/O-Systemen eine äußere lipophile Phase. In dieser sind Wassertröpfchen emulgiert, wobei dominierend lipophile Emulgatoren sich mit ihrem hydrophilen Anteil an das Wassertröpfchen anlagern (s. Abb. 3.1). Bei W/O/W-Systemen sind zusätzlich innerhalb der emulgierten Lipidtröpfchen hydrophile Komponenten emulgiert, bei O/W/O-Systemen analog innerhalb der emulgierten Wassertröpfchen lipophile Komponenten (Abb. 3.2).
Pharmacopeias contain a large number of formulations for all topical dermatological vehicles. The New German Formulary (NRF) has been expanded considerably in recent years, mainly as a result of the inclusion of numerous formulas from the former German Democratic Republic's Standard Formulary (SR). Topical dermatological vehicles have important intrinsic effects. Dermatological vehicles that are particularly appreciated for their pronounced cooling effect include wet dressings, vehicles where the continuous phase is an aqueous solution (such as O/W lotions), and, above all, bases that contain alcohol. Many vehicles have lubricating effects, providing significant dry skin relief to atopic dermatitis sufferers. W/O- and O/W emulsions differ greatly in the amount of lipids they contain. Occlusive effects are achieved mainly by fatty bases, two-phase-pastes, W/O emulsions with a low water content as well as O/W emulsions and spreading, tenside-free oil baths. The most important intrinsic effects of topical dermatological vehicles are their hydrating and barrier-stabilizing effects. Glycerol is particularly useful in this regard because it has both hydrating and regenerative protective effects on the skin. While no pharmacopeial base has been found to produce significant dehydration of the skin, three-phase pastes appear to have a mild dehydrating effect that can be used therapeutically. Dermatological vehicles may also produce skin irritation. This is a particular problem with microemulsions. Merely a few pharmacopeial bases are still noted for significant sensitizing potential. Many pharmacopeial vehicles have been modified or have been newly introduced to avoid sensitizations.
Occlusion of the skin is used in clinical dermatology to promote wound healing and to increase the transcutaneous penetration of topically applied drugs. These effects are related to the degree of occlusion exerted and depend on the physicochemical nature of the dressing. We have evaluated the effects of four different materials on the skin barrier and the stratum corneum water holding capacity (WHC) using the Plastic Occlusion Stress Test (POST). The following materials were compared: hydrocolloid dressing, polyurethane film, polyethylene film, and a plastic chamber. These devices were applied on the volar forearm for 24 hours in 10 healthy volunteers (mean age 32 ± 4 years). Upon their removal, the stratum corneum WHC, measured as skin surface water loss (SSWL), was recorded continuously for 25 minutes using an Evaporimeter.
SSWL decay curves showed significant differences between the occlusive materials (analysis of variance, p < 0.01). Higher SSWL values were recorded in sites occluded with the plastic chamber, whereas the polyurethane film resulted in poor occlusive capacity. Hydrocolloid dressing and polyethylene gave similar responses with higher WHC values compared to polyurethane (p < 0.05). The relevance of these findings to clinical dermatology in terms of wound healing and drug absorption is discussed.