Here is your short essay on Parenteral Products

1. Vehicle:

Water for injection (WFI) is the vehicle of first choice. It should be free from ions and pyrogens. Medicaments like barbiturates and sulphonamides need water free from carbon dioxide.

Oxygen-sensitive drugs call for oxygen-free water. Water of suitable quality must be prepared by distillation or reverse osmosis. It can also be rendered free from ions by passing through an ion-exchanger. Sterile Water for Injection.

SWFI is water for injection sterilized and suitably packaged in single dose containers not exceeding 100 ml capacity and contains no bacteriostatic agent.

Bacteriostatic Water for Injection (BWFI) is sterile water for injection containing one or more suitable bacteriostatic agents. Boiling of water makes it free from atmospheric gases and such water should be stored suitably so that the re-absorption of oxygen and carbon dioxide is not possible.

In addition to water, some cosolvents are sometimes used to replace a portion of water in certain formulations. Thus cosolvents may be used either to increase the stability of the drug or to reduce its hydrolytic degradation. Commonly used water-miscible co-solvents include ethyl alcohol, glycerin, propylene glycol, polyethylene glycol and dimethylacetamide. Limited solubility and poor stability of some drugs either in water or in aqueous solvents may necessitate the use of non-aqueous hydrophobic solvents like fixed oils. Such vehicles must meet the requirements of degree of saturation, saponification value, iodine number, free fatty acids and unsaponifiable matter. Most commonly used oils include peanut, sesame, corn and cottonseed. Non-aqueous vehicles should be disposable by the body and should be non-irritant to the tissues. Mineral oils are rarely used as vehicles for parenteral preparations as these are not metabolisable. Primary considerations involved in the selection of a vehicle are solubility, stability and safety.

2. Additives:

Apart from the vehicle, parenteral products contain many solutes as stabilizers of additive substances. All the solutes employed in the preparation of parenterals should be of highest purity. In addition, solutes should be free from microbial contamination and pyrogens. They should be free from microbial contamination and pyrogens. They should also conform to the solubility characteristics as desired by the physical form for the compound and should be free from gross dirt.

(a) Stabilizers:

Stabilizers ensure the stability of the drug compound in the preparation. Drugs in the form of their solutions are more liable to degradation through oxidation and hydrolysis and hence the stability of parenteral products against such degradation should be ensured.

Oxidative degradation can be minimized by the use of antioxidants and when this course is not feasible, the products may be sealed in an inert atmosphere of nitrogen or carbon dioxide Hydrolytic degradation can be minimized by adjustment of pH or by replacing water with other vehicles, partially or wholly. Some degradations are catalyzed by stray metallic ions and such a problem can be overcome by the use of sequestering or chelating agents like EDTA.

(b) Buffering agents:

Formulations must maintain the intended pH. Changes in the pH of a product may occur during storage because of degradative reactions taking place in the product, interaction of the product with the components of the containers and loss or dissolution of gases and vapors.

Such problems are avoided by the use of buffering agents to suppress the changes in pH. Commonly used buffering systems include acetates, citrates, phosphates etc.

(c) Antioxidants:

Antioxidants are needed in the parenteral products containing oxygen-sensitive drugs so as to avoid oxidative degradation. Sodium bisulphite (0.1%) is the most commonly used antioxidant. Other antioxidants include acetone sodium formaldehyde sulphoxylate and thiourea.

Activity of certain antioxidants may be enhanced by the sodium salt of EDTA because it can chelate the metallic ions which otherwise catalyze the oxidative degradation reactions.

(d) Antimicrobial agents:

These agents are to be essentially included in multiple dose packagings to prevent multiplication of any accidentally introduced microbes in the products during the withdrawal of doses. Such agents should always be used with full recognition of their potential toxicity.

Frequently used antimicrobial agents include phenol or cresol (0.5%), cholorocresol (0.2%), phenylmercuric nitrate (0.002%), chlorobutanol (0.5%), benzethionioum chloride and benzalkonium chloride (0.001%).

(e) Tonicity Contributors:

Some parenteral solutions are required to be isotonic with blood serum or other body fluids. The overall tonicity of a solution can be calculated by computing the molecular concentration of the solute or by determining the freezing point of the solution. Tonicity of a solution is a function of the quality and quantity of sum total of the solutes present. If necessary, the tonicity of a solution may be increased by the addition of calculated amounts of substances like sodium chloride, borax etc. The materials used for tonicity adjustment must be compatible with other ingredients of the solution.

(f) Wetting, Suspending & Emulsifying agents:

Wetting agents are used in injectable suspensions to maintain the particle size and to counteract caking. Commonly used wetting agents include tween-80, sorbitan trioleate, Pluronic F-68 etc. Commonly used suspending agents in parenteral suspensions are sodium CMC methylcellulose, acacia, gelatin, polyvinylpyrrolidone etc. Sodium citrate may K included to prevent flocculation of suspended particles. Lecithin is the most commonly employed emulsifying agent for parenteral emulsions.