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.
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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.
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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.
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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.
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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.
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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.
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Buffer systems are used to maintain a desired pH of optimum
drug solubility and stability.
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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.
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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.
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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.
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Tonicity modifiers, such as dextrose, sodium chloride, or
potassium chloride, are commonly used to achieve isotonicity in a parenteral
formulation.
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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.
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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.
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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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