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MAGMAS AND GELS
Dr. Mehwish QayyumPharm.dMs.Drug design and discovery (University of Surrey)Senior lecturer
Gels
Are semisolid systems consisting of either suspensions made up of small inorganic particles or large organic molecules in a liquid vehicle rendered jelly like by the addition of a GELLING AGENT.
Sometimes called JELLIES
High degree of physical/chemical cross linking may be involved
interlacing/ internal friction
Resulting into high viscosity
Responsible for semi-solid state
Terminologies related to gel Imbibition: Taking up of a certain amount of liquid without a
measureable increase in volume Swelling: Taking up of a liquid by gel with an increase in volume Syneresis Form of instability in which separation of solvent phase
occurs coz of elastic contraction of polymeric molecules Thixotropy A phenomenon in which if gel is agitated it may become
fluid and remain in solid state only after remaining undisturbed for a period of time i.e sol gel transfer
Examples of Gelling Agents 1. Carbomers 910; 934; 934P; 940;
941;1342
2. Carboxymethylcellulose; natural gums
*0.5 to 2.0% concentration in water
Classes of Gel
2 phase systems - separation between the insoluble matter and liquid vehicle is observed. This type contains inorganic materials also small particles distribute them in liquid in the form of floccules(inorganic)(magma)Example: Al(OH)3 Gel
Single phase gel - consist of organic macromolecules uniformly distributed throughout the liquid where no apparent boundary is seen(organic)Example: Na CMC and Tragacanth Gel(twisted mated strands wound together by stronger vander waals forces to form crystalline and amorphous regions)
Continuous phase - commonly aqueous where alcohol and gels may be use as continuous phase (organogels)Example: Mineral oil + polyethylene resin = oleaginous ointment base
Hydrogels Include ing that are dispersible as colloidals they include organic
hydrogels natural and synthetic gums e.g silica and methyle cellulose
Types of Gel
Type 1-Heterogels Irreversible system 3-dim structure Held by covalent bonds Show synerisis Type 2-Commonly used gels Heat reversible Held by h-bonds Gelling is influenced by pH additives Show synerisis
Characteristics of Gels Gels may be thicken on standing,
forming a THIXOTROPE, and must be shaken before use to liquefy the gel and enable pouring – Aluminum Hydroxide Gel
Because of high degree of attraction between the dispersed phase and water medium, the gels remain fairly uniform upon standing and does not readily settle
Preparation of gels and magmas:
Prpeared by freshly precipitating the dispersed phase in order to achieve a fine degree of subdivision of the particles and gelatinous character to those particles
Desired gelatinous ppt results when solutions of inorganic
agents react to form an insoluble chemical having a
high attraction for water.
As the microcrystalline particles of ppt develop
they strongly attract water to yield gelatinous particles which for gel ppt
Preparation of gels and magmas
Other magma and gels may be prepared by +ion in water
of inorganic chemical and hydrated form constitutes the dispersed phase of dispersion
In addition to water vehicle other agents such as
propylene glycol, hydroxy propyl cellulose etc may be
used tto enhance gel formation
Coz of high degree of attraction b/w disperse phase and the aq medium in both magmas and gels these prep remain fairly
uniform on standing with little settling of disperse phase
On long standind synerisis may be seen but
on little shaking uniformity is re
established
Label should have statement shake well before use freezing
must be avoided
Preparation of Gels
1.By freshly precipitating the disperse phase upon reacting an inorganic agents, a gelatinous precipitate results
Example: Preparation of Al(OH)3 gel is by reacting Al(Cl)3 + Na2CO3
NaHCO3
Preparation of Gels
2. By direct hydrating the inorganic material in water
Al2O3 + H2O Al(OH)3
Examples: Aluminum Hydroxide Gel; Alugel; Amphogel; Ce-lu-gel; Cremalin; Hydroxal; Vanogel; Aluminum Phosphate Gel (Phosphagel) - Antacid
Polyvinyl alcohols are used for gel preparation in skin formulations when they are applied these alcohol evaporate leaving a thin layer on skin
Examples of Gel
Clobetasol propionate- Termovate GelDermatologic: Antipruritic
Example of Gel
Acetic acid- Aci-jelVaginal: Restoration and maintenance of acidity
Example of Gel
Progesterone- Crinone GelVaginal: Bioadhesive gel; Progesterone supplement and replacement
Uses of gel
Lubricant for catheters Bases for patch testing NaCl gel for electrocardiography Floucinonide Gel for anti-
inflammatory corticosteriod Na Fluoride & Phosphoric acid gel –
dental care prophylactic Tretionoin Gel for treatment of acne Prostaglandin Gel – intravaginal
Gels and Magmas Are considered colloidal dispersion since
they contain particles of colloidal dimensions
APPROPRIATE NAMES (COLLOIDAL DISPERSION)
SOLS – term to designate a dispersion of solid in either a liquid, solid or gas dispersion medium
A. Prefix HYDRO – water as dispersion medium so called HYDROSOL
B. Prefix ALCO – alcohol as the dispersion medium so called ALCOSOL
C. AEROSOL – dispersion of solid or liquid in gaseous phase
Examples Of Topical Gels
1. Erythromycin and benzoyl peroxide topical gel - Benzamycin
2. Clindamycin Topical gel - Cleocin T Topical Gel
3. Benzoyl Peroxide Gel - Desquam-X 10 Gel - acne vulgaris
4. Hydroquinone Gel - Solaquin Forte Gel - bleach for hyperpigmented skin
5. Salicylic Acid Gel - Compound W Gel - keratolytic
6. Desoximetasone Gel - Topicort - anti-Inflammatory, antipruritic agent
Examples of Topical Gel
Active Ingredient Proprietary Gelling agent Route and Use
1. Acetic acid Aci-jel Tragacanth, acacia Vaginal: restoration and maintenance of acidity
2. Becaplermin Regranex Gel Na CMC Dermatologic
3. Benzoly peroxide Desquam-X Gel Carbomer 940 Acne vulgaris
4. Clindamycin Cleocin T Gel Carbomer 934P Acne vulgaris
5. Clobetasol Termovate Gel Carbomer 934 Antipruritic
6. Cyanocobalamin Nascobal Methylcellulose Nasal: hematologic
7. Desoximetasone Topicort Gel Carbomer 940 Anti-inflammatory; antipruritic
8. Metronidazole Metro-Gel Carbomer 934P Vaginal-bacterial
9. Progesteron Crinone Gel Carbomer 934P Progesterone supplement
10.Tretinoin Retin –A Hydroxypropyl Acne vulgaris cellulose
TRANSDERMAL PREPARATIONS Ointments, creams, gels designed to deliver a
drug systematically by addition of PENETRATION ENHANCERS to the topical vehicle
Examples of Penetration Enhancers Dimethyl sulfoxide (DMSO), ethanol,
propylene glycol, glycerin, polyethylene glycol, urea, dimethyl acetamide, sodium lauryl sulfate, poloxamers, Spans, Tweens, lecithin, and terpenes
Example: PLURONIC lecithin organogel (PLO) – Pluronic (Poloxamer) F127 gel (usually 20% to 30% concentration)