Injections are sterile, pyrogen-free liquid preparations intended for parenteral administration.
They can be solutions, suspensions, or emulsions, depending on the drug's properties.
Components of Injectable Formulations:
Active Pharmaceutical Ingredient (API):
The drug substance is formulated to ensure stability, efficacy, and safety.
Example: Antibiotics, analgesics, or hormones.
Vehicle:
A medium in which the API is dissolved or suspended.
Aqueous Vehicles: Water for Injection (WFI) is the most commonly used.
Non-Aqueous Vehicles: Fixed oils (e.g., sesame oil), water-miscible solvents (e.g., polyethylene glycol) for drugs insoluble in water.
Additives:
Buffers: Maintain a stable pH (e.g., phosphate or citrate buffers).
Antioxidants: Prevent oxidation (e.g., ascorbic acid, sodium bisulfite).
Preservatives: In multi-dose vials to inhibit microbial growth (e.g., benzyl alcohol, phenol).
Chelating Agents: Improve stability by binding metal ions (e.g., EDTA).
Tonicity Adjusters: Ensure isotonicity with body fluids (e.g., sodium chloride, dextrose).
Types of Injections:
Intravenous (IV): Directly into the bloodstream; requires isotonicity and high sterility.
Intramuscular (IM): Administered into muscle tissue; can use oily or aqueous vehicles.
Subcutaneous (SC): Injected into the fat layer beneath the skin; requires small volumes.
Intradermal (ID): Administered into the dermis layer of skin; typically for vaccines or diagnostic purposes.