Eye drops are sterile liquid preparations containing the drug in a solution or suspension form.
They are the most commonly used ophthalmic formulations.
Components:
Active Ingredient: The drug, e.g., antibiotics, anti-inflammatory agents, or antihistamines.
Vehicle: Aqueous or non-aqueous solution (e.g., purified water or oils like castor oil).
Preservatives: Benzalkonium chloride, phenylmercuric nitrate.
Buffering Agents: Maintain pH (e.g., boric acid, phosphate buffers).
Tonicity Adjusters: Sodium chloride, dextrose.
Viscosity Enhancers: Methylcellulose, hydroxypropyl methylcellulose.
Antioxidants and Stabilizers: Protect drug from degradation.
Formulation Considerations:
pH Adjustment: Must match the tear fluid to minimize irritation.
Preservation: Balancing antimicrobial efficacy with ocular tolerance.
Viscosity Enhancement: Using agents like hydroxypropyl methylcellulose to increase residence time.
Clarity: Ensuring the solution is free from turbidity or particulate matter.
Examples:
Antibiotic Drops: Ciprofloxacin ophthalmic solution.
Glaucoma Drops: Timolol maleate ophthalmic solution.
Preparation Steps for Eye Drop Solutions
Dissolve drug and excipients in the vehicle (water or water-cosolvent mixture).
Adjust pH and tonicity.
Filter through a 0.22 μm (or finer) filter to remove particulates and achieve sterility if performing aseptic filtration.
Fill into sterile containers under aseptic conditions (if not performing a terminal sterilization).
Terminal Sterilization (e.g., autoclave at 121 °C for 15–20 min) if the formulation and container are heat-stable.