Sunday 18 August 2013

DRUG DOSAGE FORMS; Solutions

SOLUTIONS
A solution is a homogeneous mixture that is prepared by dissolving a solid, liquid, or a gas, in another liquid and represent a group of preparation in which the molecule of the solute or a dissolved substance are dispersed among those of the solvent. Most solution are unsaturated with the solute, in other words, the concentration of the solute in the solution is below its solubility limit. The strength of the pharmaceutical solutions is usually expressed in the terms of % strength, although for very dilute preparations, expression of ratio strength is some time used. The term % when used without qualification (as with w/v, v/v, or w/w) means % weight-in-volume for solutions or suspensions of solids in liquids; % weight-in-volume for solution of gases in the liquid; % volume-in-volume for solutions of liquids in liquids; and weight-in-weight for mixture of solids and semisolids. Solutions are of following types

Aqueous solutions:
These are the solutions in water. For example Aromatic Water, Aqueous Acids, Solutions, Douches, Enemas, Gargles, Mouthwashes, Juices, Nasal Solutions, and Irrigation Solutions.
(a)  Aromatic waters: The USP defines the aromatic water as clear, saturated aqueous solution of volatile oils or other aromatic or volatile substances. The odors and tastes are similar, respectively, to those of the drugs or volatile substances from which they are prepared. They are used principally as flavored or perfumed vehicles.
(b)  Aqueous acids: Inorganic acids and certain organic acids, although of minor significance as therapeutic agents, are of great importance in pharmaceutical manufacturing and analysis. This is especially true for acetic, hydrochloric, and nitric acids. Many of the more inorganic acids are available commercially in the form of concentrated aqueous solutions. The %age of the strength varies from one acid to the other and depends on the solubility and stability of the solute in water and on the manufacturing processes.
(c)  Diluted acids: Diluted acids in USP are aqueous solutions of acids of a suitable strength (usually 10%w/v but diluted Acetic Acid is 6% w/v) for internal administration or for the manufacturing of other preparations. The strength of the official undiluted acids is expressed in %age in w/w, where as the strength of the official diluted acids are expressed in % in volume (w/v).
(d)  Douches: The douches are aqueous solutions directed against a part or into the cavity of the body. It functions as a cleansing or antiseptic agent. E.g., an eye douche, used to remove the foreign particles and discharges from the eyes. Douches are often dispensed in the form of powders with direction for dissolving in a specified quantity of water or the solution may be prepared by the pharmacist. Douches are not official class of preparations but several substances in the compendia frequently are employed as such in weak solutions. Vaginal douche are common example and used for cleansing and hygienic purpose.
(e)  Enemas: Enema preparations are rectal injections employed to evacuate the bowl, influencing the general system by the absorption, or to affect a local disease. The latter two are called retention enemas. They may posses’ anthelmentic, nutritive, sedative, or simulative properties or they may contain radiopaque substances for roentgen graphic examination of the lower bowel. Sodium chloride, Sodium bicarbonate, Sodium monohydrate phosphate, Glycerin, Docusate Potassium, and light Mineral oil are used in enemas to evacuate the bowel. Evacuation enemas are generally given at body temperature in quantities of 1 to 2 pt injected slowly with an injection. Retention enemas are to be retained in the intestine and should not be used in larger quantities than 150 ml for an adult. Usually the volume is considered smaller such as a few ml and the term used for these enemas is microenemas. Valporic acid, Metronidazole and Endomethacin have been formulated as microenemas for the purpose of absorption.
(f)   Gargles: These are aqueous solutions frequently containing antiseptic, antibiotics, and/or anesthetics used for treating the pharynx and nasophyrynx by forcing air from the lungs through the gargles that is held in the throat; subsequently, the gargle is expectorated. Many gargles must be diluted before the use.
(g)  Mouthwashes: Mouthwashes are aqueous solutions often in concentrated form containing one or more active ingredients and excipients. They are used by swishing the liquids in the mouth cavity. Mouthwashes are used for two purposes, therapeutic (plaque, gingivitis, dental caries, and stomatitis) and cosmetic (bad breath by adding antimicrobial and/or flavoring agents) purposes.
(h)  Juices: A juice is made from the freshly ripe fruit, is aqueous in character, and is used in making syrups that are employed as vehicles.  The freshly expressed juices is preserved in Benzoic acid and allow to stand in room temperature for several days, until the pectin that naturally are present are destroyed by enzymatic action, as indicated by the filtered juices yielding a clear solution with alcohol
(i)    Nasal solutions: Nasal solutions are usually aqueous solutions designed to be administered to the nasal passage in the drops or sprays.
(j)    Otic solutions: These solutions are occasionally are referred as ear or aural preparations. Other oral preparation includes suspension and ointments for topical application in the ear. Ear preparations are usually placed in the ear canals by drops or in small amounts for the removal of excessive cerumen (ear wax) or for the treatment of ear infections, inflammations or pain.
(k)  Irrigation solutions: Irrigation solutions are sterile, non pyrogenic solutions used to wash or bath surgical incisions, wounds, or body tissues. Because they come in contact with the exposed tissues, they must meet the astringent USP requirements for sterility, total solids, and bacterial endotoxins.
(l)    Syrups: Syrups are concentrated, viscous, aqueous solutions of sugar or a sugar substituted with or without flavors and medical substances. When purified water alone is used in making the solution of sucrose, the preparation is known as syrup or simple syrup if the sucrose concentration is 85 %. In addition to sucrose, certain other polyols, such as Glycerin or Sorbitol, may be added to retard the crystallization of sucrose or to increase the solubility of added ingredients.  Alcohol often is included as a preservative and also as a solvent for flavors; further resistance to microbial attack can be enhanced by incorporating antimicrobial agents. When the aqueous preparation contains some additional medicinal substances, the syrup is called medicated syrup. Flavored syrups are usually not medicated, but rather contain some aromatic or pleasantly flavored substances and are intended to be used as a vehicle or flavor for prescription, such as Acacia, Cherry, Cocoa, Orange, and Raspberry.
Nonaqueous solutions:
Pharmaceutical preparations, and, in particular, those intended for internal use, rarely contain more than one minor quantities of the organic solvents that are common to the manufacturing or the analytical operations. Products of commerce for internal use may contain solvents such as ethanol, glycerin, propylene glycol, certain oils, and liquid paraffin. Preparation intended for external use may contain solvent in addition to those just mentioned, namely isopropyl alcohol, polyethylene glycol, various others, and certain esters. The various types of non aqueous solution are mentioned below.
(a)  Collodions:  These are liquid preparations containing pyroxylin, partially nitrated cellulose, in a mixture of ethyl ethers and ethanol. They are applied to the skin by mean of a soft brush or other suitable applicator and, when the ether and ethanol have evaporated, leave a film of pyroxylin on the surface. Salicylic acid collodion USP, contain 10% w/v of salicylic acid in flexible collodion USP and use as a keratolytic agent in the treatment of corn and warts.
(b)  Elixirs: Elixirs are clear, pleasantly flavored, sweetened hydro alcoholic liquids intended for oral use. The main ingredients in elixirs are ethanol and water but glycerin, sorbitol, polypropylene glycol, flavoring agents, preservatives, and syrups often are used in the preparation of the final products. The solvents are often used to increase the solubility of the drug in the dosage form. Elixirs are more fluid than syrups, due to the use of less viscous ingredients such as alcohol and the minimal use of viscosity improving agents such as sucrose.
(c)  Glycerins: Glycerin’s or glycerites are solutions are mixtures of medicinal substances in not less than 50% by weight of glycerin.  Most of the glycerins are mostly viscous and some have jelly like consistency. Glycerin is suitable pharmaceutical solvent forming permanent and concentrated not otherwise obtainable. Glycerins are hygroscopic and should be stored in tightly closed containers.
(d)  Inhalations: Inhalation preparations are so used or designed that the drug is carried to the respiratory tract of the patient. The vapors or mist reaches the affected area and give prompt relieve from the symptoms of bronchial nasal congestion. Another group of products, also known as meter-dose-inhalers (MDIs) are propellant–driving drug suspension or solutions in liquefied gas propellant with or without a co-solvent and are intending for delivering meter dose of the drugs to the respiratory tract.
(e)  Liniments:  Liniments are alcoholic or oil based solutions or emulsions containing therapeutic agents intended for external use. These preparations may be liquids or semisolids that are rubbed onto the affected area; because of this, they were once called embrocations. These are usually applied with fractions and rubbing of the skin, the oil or soap base for ease of the application and massage. Alcoholic liniments are generally used for their rubefacient, counterirritant, mildly astringent, and penetrating effects. Depending on their ingredients liniments works solely as a protective coating. Other liniments contain antipruritics, astringents, emollients, or analgesics and are classified on the basis of their active ingredients.
(f)   Oleovitamins: Oleovitamins are fish liver oils diluted with edible vegetable oils or emulsions of the indicated vitamins or vitamin concentrates (usually vitamin A and D) in the fish liver oil. These vitamins are unstable in the presence of rancid oil; therefore these preparations should be stored in small, tight containers, preferably under vacuum or under the atmosphere of an inert gas, protected from light and air.
(g)  Spiritis: Spirits are sometime called essences, are alcoholic or hydro alcoholic solutions of volatile substances. Like the aromatic water, the active ingredient in the spiritis may be the solid, liquid, or gas. Generally the alcoholic concentration of spiritis is rather high, usually over 65%. Because of the greater solubility of the aromatic or volatile substances in alcohol than in water, spiritis can contain a greater concentration of this material than the corresponding aromatic water. When mix with water or aqueous preparation, the volatile substances generally separates and form a milky preparation. Salts may be precipitated from aqueous solution by the addition of spiritis. Spiritis may be used pharmaceutically as a flavoring agent and medicinally for the therapeutic value of the aromatic solutes. The spiritis still listed in the USP/NF are aromatic ammonia spirit, camphor spirit, compound orange spirit and peppermint spirit.

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