Suspensions

What is Suspension?

Suspension is a composition that contains minute drug particles spread evenly in vehicles where drugs have a low degree of solubility. Suspensions are biphasic liquid dose forms of medicament containing small solid particles with a particle size range of 0.5-5.0 micron. Suspensions are consumed orally and administered intravenously and topically. Chemically, they seem to be more stable than solutions.

Classification and Functions of Suspensions

Suspensions are classified as follows based on the particle size of the dispersed phase: A coarse suspension consists of dispersed particles with a diameter of more than one micrometre. A colloidal suspension is a distribution of particles having a diameter of less than 1µm.

If the patient has difficulty swallowing solid dosage forms, a liquid dosage form of suspension is used. Solid dosage forms dissolve and absorb more quickly, but liquids dissolve and absorb more slowly. Suspensions are a way of creating drugs with low solubility. Drugs in their soluble form taste bad.

The suspension should subside slowly and be easily redispersed when the container is agitated. In suspension, the particles are tiny and homogenous in size, due to which the finished product does not have a rough texture.

Medicinal Applications of Suspensions:

• Aqueous pharmaceutical suspensions are used as drug products
• Suspensions are also used as in-process materials during the manufacturing of industrial pharmaceutical products
• Medicinal tablets are also coated with a suspension of insoluble coating material

Particle Nature 

• The suspension particles exist as independent entities in a deflocculated environment
• Sedimentation rate is negligible and sediment is compact, due to which it is difficult to redisperse and form a cake-like structure when shaken
• The  deflocculated suspensions are smooth, because the component is suspended for a long time, giving them a pleasing appearance
• The creation of non-redispersible sediments in a suspended system can be described by crystal bridging.  Crystal bridging and locked aggregation in the formulation are the causes. Crystal bridging happens when multiple particles simultaneously produce crystals on their surfaces in an ongoing formation
• Sedimentation pertains to settling particles (or) floccules in liquified form caused by the gravitational force. Brownian particle movement prevents settling by having scattered material in dynamic equilibrium. Brownian movement depends on the dispersed phase’s density and the dispersed medium’s bulk modulus
• Brownian movement is noticed when particles are 2 and 5 µm long and particle density and medium viscosity are favourable
• Potential Zeta: The differences in the surface of a firmly bonded layer and the electroneutral portion of the solution are characterised as the zeta potential

Function of Suspension :

• Pharmaceutical suspensions can be formulated to cover the unpleasant smell and taste of drugs
• Pharmaceutical suspensions may also serve the purpose of being an alternative means to give or administer drugs to small children or older patients who have difficulty in solving solid dosage forms
• Bioavailability of drugs in suspensions have the highest rates than any other dosage form
• Pharmaceutical suspensions also give resistance to the process of degradation of drugs by oxidation or microbial activity or by hydrolysis
• Usage of pharmaceutical suspension duration and concert of action of drugs can be controlled
• If we compare it with solution dosage form, we will find that a higher concentration of drug can be incorporated by suspension products
• The Zeta potential, rather than the Nernst potential, determines the degree of repulsion between neighbouring particles. The attractive forces overcome the repulsive forces when the Zeta potential is decreased below a particular threshold and the particles come around
• Structured transporters, also known as thickening agents, increase the viscosity of the continuous phase, allowing the particles to remain suspended for an extended period. In addition, these constructed vehicles trap the particle, reducing particle sedimentation
• Acacia, Tragacanth and sodium alginate are not widely used. Instead, semi-synthetic structural vehicles are extremely popular. Variations include methylcellulose, CMC, hydroxypropyl methylcellulose, and others. Thickening agents include clays such as hydrated aluminium silicate. A hydrating agent or substance reduces the interfacial tension. It is adsorbed to increase particle affinity for the surrounding medium while reducing intra articular forces
• Even high-density particles float on the liquid’s surface until the air layer is entirely displaced. The addition of a wetting agent, such as alcohol in tragacanth mucilage, glycerin or glycerol in sodium alginate, provides the removal of air on the surface and the simple entry of transporters into pores. However, an excessive wetting agent causes foaming or an objectionable taste or odour in the suspension

Conclusion

Suspensions are an easy way of curating pharmaceutical products other than the regular forms involved. Flocculating chemicals or surfactants diminish interfacial tension by acting as a surfactant with a negative charge that is adsorbed on the particle. They also inhibit flocculation in the effects of appropriate ions due to the natural repulsion of opposite charges. Sodium lauryl sulphate, sodium dioctyl sulphocyanate, and other negatively – charged surfactants are also present in non-ionic surfactants. Tweens and carbowaxes are often used.