The main difference between solutions and suspensions is that a solution is homogeneous mixture formed when two or more soluble chemical moieties are dissolved in dissolving medium while suspensions are heterogeneous mixtures when finely divided solid moieties are dispersed in dispersing medium.
Solutions vs. Suspensions
A solution is a one-phase system in which solute is dissolved in vehicle completely on the other hand suspension is a two-phase system in which solid particles are not dissolved in the vehicle and remain suspended evenly throughout the vehicle. Solutions are simple mixtures of the solute and solvent while suspensions are mixtures of finely divided solid particles and vehicle requiring a suspending agent to suspend the solid particles in the vehicle. Solutions support the water-soluble chemical moieties whereas suspensions can support the water-soluble and insoluble chemical moieties. In solutions, the dissolved particles do not settle down at the bottom of the container even if kept for the long period on the other hand in suspensions the suspended particles settle down at the bottom of the container if kept for some time. There is no need to shake the container of solutions before use while in case of suspensions shaking of the container is the basic requirement before use to ensure even distribution of the solid particles. Although solutions require preservatives, some solutions do not require preservatives like concentrated sugar solutions (syrups) and high content alcoholic solutions while all suspensions need preservatives depending upon chemical degradation pathway of suspended solid particles. In solutions, the solubility of solute can be enhanced through the pH adjustment while pH has no such role in suspensions.
What are Solutions?
Solutions are liquid preparations prepared by dissolving one or more than one active chemical moieties (solute) into a suitable solvent. The solute is the chemical moiety which is dissolved while the solvent is the vehicle in which solute is dissolved. The solvents used can be aqueous (water-based) or non-aqueous. Aqueous solvents are used because most of the chemical moieties are soluble in water. Sometimes the co-solvents are used when water alone is not sufficient to dissolve chemical moieties. Nonaqueous solvents are used when chemical moieties are not stable in water or dissolve in water. Solutions can be saturated or unsaturated depending upon the concentration of solute. If the concentration of the solute is below the solubility limit, then the solution is termed as the unsaturated solution, and if the concentration of solute is above the solubility limit, then the solution is termed as the saturated solution.
When sugar or salt is dissolved in water, it forms the sugar or salt solution.
What are Suspensions?
A suspension is a liquid or semi-liquid preparation prepared by uniformly dispersing un-dissolved chemical moieties into a dispersion medium. The basic ingredients in suspensions are the drug, functional excipients and external medium. The main role of functional excipients is wetting of drug, influencing flocculation, controlling viscosity, adjusting ph. The other ingredients are flavoring, sweetening, coloring, and preservative agents. Without wetting agents(suspending agent), a suspension cannot be prepared as suspending agents do not allow suspending particles to settle down. Suspensions are formulated pharmaceutically to mask the bitter taste of the drug. In suspensions, the solid particles are mono-dispersed spheres evenly suspended in 3 dimensions throughout the dispersion medium. Suspensions can be classified according to disperse and dispersion medium e.g. the suspension of liquid droplets is called Aerosols.
Example of suspensions is paracetamol suspension.
- Solutions are homogeneous mixtures whereas suspensions are heterogeneous mixtures.
- Solutions are single phase system on the other hand Suspensions are a biphasic system
- Particles do not settle down in solutions as components of solutions are completely miscible while Particles settle down in suspensions because particles are suspended in the vehicle
- The strength of the solutions is measured in w/v,v/v,v/w but the strength of suspensions is measured as mg/ml.
- Solutions are effective for the hydrophilic drugs on the other hand Suspensions are effective for hydrophobic drugs.
- Those chemical moieties which are not stable in water cannot be formulated in solution form Those chemical moieties which are unstable in water can be formulated in suspension form.
The conclusion of the above discussion is that solutions are simple preparations as compared to suspensions. Suspensions are preferred when solutions cannot be the best option to be formulated. Pharmaceutically both are important because both have their own advantages as drug formulations.