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 Gels1.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 Gels2. 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 Use1. Acetic acid Aci-jel Tragacanth, acacia Vaginal: restoration and

maintenance of acidity

2. Becaplermin Regranex Gel Na CMC Dermatologic3. Benzoly peroxide Desquam-X Gel Carbomer 940 Acne vulgaris4. Clindamycin Cleocin T Gel Carbomer 934P Acne vulgaris5. Clobetasol Termovate Gel Carbomer 934 Antipruritic6. Cyanocobalamin Nascobal Methylcellulose Nasal: hematologic7. Desoximetasone Topicort Gel Carbomer 940 Anti-inflammatory;

antipruritic8. Metronidazole Metro-Gel Carbomer 934P Vaginal-bacterial9. 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)