INTRODUCTION:

A dry emulsion comprising a matrix comprising a water-soluble or water-dispersible polymer and having dispersed there in a liquid hydrophobic phase. Dry emulsions are of interest because of their stability and sustained release effect. Dry emulsions present a potential oral drug delivery system for lipophilic and low soluble drug substances and for drug substances needing protection against light or oxidation.

For the preparation of dry emulsions we use drug, solid carrier, aqueous phase and lipophilic solvent. The solid carriers used to prepare dry emulsions are gelatin, lactose, maltodextrin, mannitol, povidone, sucrose etc. Insoluble carrier like colloidal silica can also be used. To avoid stability problems water soluble polymers like hydroxyl propyl methyl cellulose, methyl cellulose and povidone are used as solid carriers. Commonly used co-solvents are Polyethylene glycol, Propylene glycol, Glycerol etc. The thickening agents used are Natural and synthetic gums, Cellulose derivatives, colloidal silica. The sweetening agents used are Glucose, Aspartame, and Sucrose etc.

Properties of the dry emulsions:²

· The type of rotary atomizer and the rotation rate had no noticeable effect on the technical properties of the dry emulsions containing 40% lipid.

· The reconstitution properties of the dry emulsions are affected by both the type of rotary atomizer and by the rotation rate of the atomizer.

· This is probably due to a particle size effect caused by the reduction of particle size with increased rotation rate of atomizer.

· The dry emulsions are cohesive powders having poor flow ability due to low density, the size and shape of the particles. The technical properties have to be improved for example by melt our wet granulation. The droplet size distribution of the liquid O/W emulsions before spray drying and after reconstitution

· Dry emulsions having lipid content below 50% reformed the original emulsion. With increasing the lipid content from 30 to 80% the droplet size of dry emulsions is reduced. It is possible to encapsulate up to 80% lipid with pharmacoat 603 as a solid carrier.

· Dry emulsions having lipid content up to 40% dry powder mass reformed the original O/W emulsion upon reconstitution. Higher the liquid viscosity, the atomized droplet size increases resulting in a bigger particle size of the powder.

Advantages of dry emulsion

· They improve the bio availability of drug substances.

· Reduced Side effects .

· Dry emulsions are attractive because they are physically and microbiologically stable formulations.

· They represent a potential oral drug delivery system for lipophilic and low soluble drug substances.

· Used for drug substances needing protection against light or oxidation.

· Dry emulsions provide most constant possible effective blood levels over prolonged durations of therapy.

Disadvantages of dry emulsion:

· Preparation needs to be shaken well before use.

· A measuring device is needed for administration.

· A degree of technical accuracy is needed to measure a dose.

· Storage conditions may affect stability.

Method of preparations:

Dry emulsions are prepared by using

1. Spray drying

2. Lyophilization

3. Rotary evaporation

Spray drying: ^3,4

Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals. A consistent particle size distribution is a reason for spray drying some industrial products such as catalysts. Air is the heated drying medium; however, if the liquid is a flammable solvent such as ethanol or the product is oxygen-sensitive then nitrogen is used.

Fig. no.1-Spray Dryer

Lyophilization or freeze-drying:^5,6

Lyophilization, or freeze drying, is a process that removes water from a liquid drug creating a solid powder, or cake. The lyophilized product is stable for extended periods of time and could allow storage at higher temperatures. In protein formulations, stabilizers are added to replace the water and preserve the structure of the molecule.

Before administration, a lyophilized drug is reconstituted as a liquid before being administered. This is done by combining a liquid diluent with the freeze-dried powder, mixing, and then injecting. Reconstitution usually requires a reconstitution and delivery system to ensure that the drug is correctly mixed and administered

Fig. no.2-Lyophilization, or freeze drying

Rotary evaporation

Rotary evaporators are typically used to remove solvents following chemical reactions. Combined with gentle heat from the evaporator bath.

Fig. no.3- Rotary evaporators

Evaluation test for dry emulsions:¹⁰

Determination of melting point-

Melting point determined by capillary method.

Solubility:

The solubility determined by adding excess but measured amount of drug in 100ml volumetric flask containing 7.2 phosphate buffer and kept under agitated conditions at 37⁰ c± 0.5 in water bath shaker for 2hrs. The dispersions are filtered through Whatman filter paper and analyzed for the quantity of drug dissolved.

Drug content analysis:

Dry emulsion equivalent to 10 mg of drug is weighed accurately and dissolved in suitable solvent. Filter through Whatman filter paper no. 41. The stock solutions are diluted suitably. The drug content is analyzed by U V spectrophotometer

Scanning electron microscopy:

SEM photomicrographs are taken by analytical scanning electron microscope for studying surface morphology.

Density:

The density of the dry emulsions is determined by helium pycnometry. For one determination each sample was measured seven times. A Pascal 140 equipped with a dilatometer type CD3P was applied to determine the density of the dry emulsions by mercury porosimetry.

Moisture content:

Moisture content are determined by Thermo Gravimetric Analysis. Approximately 15.00 – 20.00 mg. samples were placed in the sample pan and the effluent gas was dry nitrogen. The scanning rate was 100 C / min in the scan range 50-2000 C. The moisture content can be determined as the weight loss between 50 and 1200 C.

In-vitro dissolution studies:

Dissolution profiles of pure drug, dry emulsion and dry suspension and tablet are compared on the basis of time required to release maximum drug. Cumulative percent drug release at 15, 30, 45, 60, 120, 180, 240, 300, 360, 420, 480 minutes are observed.

Applications of dry emulsions:¹¹

1. Oral drug delivery

2. Transdermal drug delivery

3. Parentral drug delivery

4. In the formulation of antifoams.

5. In cosmetic formulations

6. In household care wipes, in skin care wipes, in baby care wipes and in makeup removing wipes.

7. In bath salt formulations.

8. In surface coating formulations for e.g.: in paints

REFERENCES:

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Received on 03.12.2015 Accepted on 18.12.2015

Asian J. Pharm. Res. 5(4): October- December, 2015; Page 208-210

DOI: 10.5958/2231-5691.2015.00032.5