Formulation components

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Chapter: Pharmaceutical Drugs and Dosage: Parenteral drug products

Injectable products contain active drugs and inactive ingredients, also called excipients or adjuvants.


Formulation components

Injectable products contain active drugs and inactive ingredients, also called excipients or adjuvants. Adjuvants are excipients that are added to vaccines to help boost body’s immune response. The excipients could be vehicles, cosolvents, buffers, preservatives, antioxidants, inert gases, sur-factants, complexing agents, and chelating agents.

·           Vehicle is the larger continuous phase or the medium in which the formulation is prepared. Water is the most common vehicle, although oil-based injections are formulated in a vegetable oil, such as corn oil, sesame oil, and cottonseed oil or peanut oil.

·           Sesame oil is the preferred oil for most of the official injections in oil. Sesame oil has also been used to obtain slow release of fluphenazine esters given intramuscularly. Examples of injectable products for-mulated with nonaqueous solvents are Diazepam injection USP and Phenytoin Sodium USP.

·           Water for injection is prepared by distillation of deionized water or reverse osmosis, and stored in a manner to ensure that it is pure and free from pyrogens.

·           Sodium chloride injection USP is a sterile solution of 0.9% w/v sodium chloride in water for injection. It is often used as a vehicle in prepar-ing parenteral solutions and suspensions.

·           Cosolvents, such as ethyl alcohol, glycerin, propylene glycol, or PEG, may be used to increase drug solubility in the medium. When cosolvents are used as vehicles, the preparations should not be diluted with water or precipitation may occur.

·           Buffer systems are used to maintain a desired pH of optimum drug solubility and stability.

·           Preservative is used in drug products packaged in multiple-dose vials to prevent the growth of microorganisms that may be intro-duced when the container is pierced for dosing. When preserva-tives are used, their compatibility with drugs should be carefully examined. For example, benzyl alcohol is incompatible with chlor-amphenicol sodium succinate, and the parabens and phenol preser-vatives are incompatible with nitrofurantoin, amphotericin B, and erythromycin.

·           Antioxidants are used to prevent oxidative degradation of sensi-tive drugs. Salts of sulfur dioxide, including bisulfite, metasulfite, and sulfite, are the most common antioxidants used in aqueous parenterals.

·           Chelating agents are added to inactivate metals, such as copper, iron, and zinc that generally catalyze oxidative degradation of drug mol-ecules. Ethylenediaminetetraacetic acid (EDTA) in 0.01–0.05 % w/v concentration is a commonly used chelating agent.

·           Tonicity modifiers, such as dextrose, sodium chloride, or potassium chloride, are commonly used to achieve isotonicity in a parenteral formulation.

·           An isotonic solution has an equal amount of dissolved solute in it compared to the solution it is being introduced into, such as blood for IV injection.

·           Typically in humans and most other mammals, the isotonic solu-tion corresponds to 0.9% w/v sodium chloride or 5% w/v dextrose. An isotonic solution has an osmotic pressure close to that of the body fluids. This minimizes patient discomfort and damage to red blood cells.

·           A hypertonic solution contains a higher concentration of dissolved substances than the red blood cells, which cause the red blood cells to shrink. In contrast, a hypotonic solution contains a lower concentra-tion of dissolved substances than the red blood cells, causing the red blood cells to swell and possibly burst.

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