Pharmaceutical suspensions are biphasic dosage forms consisting of solid particles (usually a drug) dispersed in a liquid vehicle (usually water or a suitable aqueous or non-aqueous medium). They are used for oral, topical, or parenteral administration when other dosage forms (e.g., tablets, capsules) are not suitable. Suspensions can be used for drugs that are poorly soluble or unstable in solution form.
Classification of Pharmaceutical Suspensions:
1. Based on Particle Size:
- Coarse Suspensions: Particle size > 50 μm
- Fine Suspensions: Particle size 0.5-50 μm
- Colloidal Suspensions: Particle size < 0.5 μm
2. Based on Route of Administration:
- Oral Suspensions
- Topical Suspensions
- Parenteral Suspensions
Composition of Pharmaceutical Suspensions:
1. Active Pharmaceutical Ingredient (API): The drug to be delivered.
2. Vehicle or Base: The liquid portion of the suspension, typically water or a suitable non-aqueous solvent.
3. Stabilizers and Surfactants: These prevent particle aggregation, improve stability, and ensure uniform distribution of particles.
4. Preservatives: Used to prevent microbial growth and maintain shelf life.
5. Flavoring Agents and Sweeteners: Added for taste enhancement in oral suspensions.
Theory of Pharmaceutical Suspensions:
Suspensions are heterogeneous systems in which solid particles are dispersed in a liquid medium. The stability of a suspension depends on factors like particle size, particle charge, and the viscosity of the vehicle. Proper formulation and storage conditions are essential to prevent sedimentation or caking of particles.
Formulation of Pharmaceutical Suspensions:
Formulation involves selecting the appropriate ingredients and determining their proportions to achieve a stable and effective suspension. The formulation process considers the drug&39;s solubility, particle size, and compatibility with the vehicle and excipients.
Evaluation of Pharmaceutical Suspensions:
1. Particle Size and Distribution: Measured using techniques like laser diffraction or microscopy.
2. Physical Stability: Check for signs of settling, caking, or changes in appearance.
3. Redispersibility: Assess the ability of the suspension to redisperse upon shaking.
4. Viscosity: Determine the viscosity of the suspension, which affects ease of administration and flow properties.
5. pH: Measure the pH to ensure it is within an acceptable range for stability.
6. Microbial Content: Test for the presence of microorganisms, and ensure the use of effective preservatives.
7. Drug Content: Quantify the drug concentration to ensure it matches the label claim.
Advantages of Pharmaceutical Suspensions:
1. Suitable for Poorly Soluble Drugs: Suspensions are used for drugs with limited solubility.
2. Flexibility: Can be formulated for various routes of administration.
3. Dose Flexibility: Allows for dose adjustment by altering the volume or concentration.
4. Taste Masking: Useful for pediatric or geriatric patients due to flavoring options.
Disadvantages of Pharmaceutical Suspensions:
1. Uneven Dosage: Without proper shaking or mixing, patients may receive non-uniform doses.
2. Stability Issues: Suspensions can be prone to settling, and stability may be a concern.
3. Storage Requirements: Some suspensions require refrigeration or specific storage conditions.
4. Palatability: Taste and texture can be unpleasant for some patients.
5. Administration Difficulty: Some patients may have difficulty swallowing or measuring doses accurately.
Pharmaceutical suspensions offer a valuable dosage form for certain drugs, especially when solubility or other factors limit the use of traditional formulations. However, careful formulation, evaluation, and storage are essential to ensure their safety, efficacy, and patient acceptance.