Formulation of Suspensions
Biphasic liquids such as suspensions and emulsions are unique dosage forms because many of their properties are due to the presence of a boundary region between two phases. In suspensions, a liquid and an insoluble solid meet to form an interface. In the case of emulsions, two immiscible liquids, usually oil and water, form an interface.
Formulation of Suspensions
1Wetting agents: They are added to disperse solids in continuous liquid phase . Example: Polysorbate 80, 20, span etc.
2. Suspending agents: They are added to flocs the drug particles.
3. Thickeners: They are added to increase the viscosity of suspension. Example: gaur gum, xanthan gum.
4. Buffers and pH adjusting agents: They are added to stabilize the suspension to a desired pH range.
5. Colouring agents: They are added to impart desired colour to suspension and improve elegance.
6. Preservatives: They are added to prevent microbial growth.
Preparation of Suspensions
Step 1: Suspensions are prepared by grinding the insoluble materials in the mortar to a smooth paste with a vehicle containing the wetting agent.
Step 2: All soluble ingredients are dissolved in same portion of the vehicle and added to the smooth paste to step 1 to get slurry.
Step 3: The slurry is transformed to a graduated cylinder, the mortar is rinsed with successive portion of the vehicle.
Step 4: Decide whether the solids are
• Suspended in a structured vehicle
• Flocculated and then suspended
Add the vehicle containing the suspending agent (or) flocculating agent.
Step 5: Make up the dispersion to the final volume .Thus suspension is prepared.
Stability of Suspension
Factors that contribute to appreciable stability of a suspension include:
1. Small Particle Size:
• Reduced size of the dispersed particle increases the total surface area of the solid.
• The greater the degree of subdivision of a given solid the larger the surface area.
• The increase in surface area means also an increase in interface between the solids and liquids leading to an increase in viscosity of a system.
2. Increasing the Viscosity:
• Increased viscosity of the continuous phase can lead to the stability of suspensions.
• This is so because the rate of sedimentation can be reduced by increase in viscosity.
Viscosity increase is brought about by addition of thickening agents to the external phase.
• It is important to note that the rate of release of a drug from a suspension is also dependent on viscosity.
• Another factor which negatively affects the stability and usefulness of pharmaceutical suspensions is fluctuation of temperature. Temperature fluctuations can lead to caking and claying.
Mr. Shiv Kumar is the Author and founder of pharmaceutical guidance, he is a pharmaceutical Professional from India having more than 14 years of rich experience in pharmaceutical field.
During his career, he work in quality assurance department with multinational company’s i.e Zydus Cadila Ltd, Unichem Laboratories Ltd, Indoco remedies Ltd, Panacea Biotec Ltd, Nectar life Science Ltd. During his experience, he face may regulatory Audit i.e. USFDA, MHRA, ANVISA, MCC, TGA, EU –GMP, WHO –Geneva, ISO 9001-2008 and many ROW Regularities Audit i.e.Uganda,Kenya, Tanzania, Zimbabwe. He is currently leading a regulatory pharmaceutical company as a head Quality. You can join him by Email, Facebook, Google+, Twitter and YouTube