Classification Of Pharmaceutical Suspension

Suspensions are an important class of pharmaceutical dosage form. They are made up of coarse dispersion of insoluble solid particles in a liquid medium. The particle diameter in a suspension is usually greater than 0.5 µm. However, it is difficult and also impractical to impose a sharp boundary between the suspensions and the dispersions having finer particles.

Pharmaceutical suspension

Classification Of Pharmaceutical Suspension

1. Based on General Classes (Route Of Drug Administration)

i. Oral suspension

ii. Externally applied suspension (topical, ophthalmic, otic, nasal)

iii. Parenteral suspension

2. Based On Proportion Of Solid Particles

i. Dilute suspension (2 to 10 % w/v solid)

ii. Concentrated suspension (50 % w/v solid)

iii. Slur-ries (> 50 % w/w solid)

3. Based On Electro Kinetic Nature Of Solid Particles

i. Flocculated suspension

ii. Deflocculated suspension

4. Based On Size Of Solid Particles

i. Colloidal suspension (< 1 micron)

ii. Coarse suspension (>1 micron)

iii. Nano suspension (10 ng)

5. Based On Dispersion Medium

i. Aqueous

ii. Nonaqueous

6. Based On Physical State Of Dispersion Medium

i. Solid-in-liquid

ii. Solid-in-gas (aerosols) suspensions

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Oral Suspension

Solid particles of the active drug are dispersed in a sweetened, flavored, sometimes colored, and usually viscous vehicle for oral administration. Pediatric suspension is formulated in such a way that high concentration of the active pharmaceutical ingredient API) is dispersed in a small volume of suspension to allow a small volume of administration. Antacids and radiopaque suspensions generally contain high concentrations of dispersed solids.

Topical Suspension

They are applied on the skin. They can be semi-solid, liquid or paste. They may be colour with perfume without flavour and sweetener. The diapers phase can exceed 20% w/v. Liquid topical preparations are designed in such a way that the inactive ingredients evaporate leaving the API. Topical suspension formulations need to pay particular attention to the lack of grittiness and smooth feel on the skin. Paste contains a high amount of powder dispersed in a base like liquid paraffin.

Injectable Suspensions

Most parenteral suspensions are designed for intramuscular or subcutaneous administration. This is because they may contain from 0.5% to 30% w/w of solid particles. Antimicrobial preservatives are not recommended for intravenous (IV) suspension. Viscosity and particle size are important factors because they affect ease of administration and release of the drug in depot. Sterility is very important. Sterile API and aseptic techniques are required during manufacture as terminal sterilisation is not possible with suspension. They always come in powder for reconstitution and dispersion before administration.

Otic/Ophthalmic Suspensions

These are intended for administration into the ear or eye respectively. Most otic suspensions are antibiotics, corticosteroids, or analgesics for the treatment of ear infection, inflammation and pain. They are made sterile because they come in contact with the mucosa surface and must be micronised solid phase. Ophthalmic suspensions must never be dispensed if there is evidence of caking or aggregation.

Rectal Suspensions

Local administration through the rectal cavity is used for the treatment or management of local disorders of the colon. Formulation and quality considerations for rectal suspensions are similar to the oral suspensions.

Pulmonary Suspensions/Aerosols

Aerosols are suspensions of drug particles or drug solution in the air and are used for inhalation of drug delivery to the lung. Volatile propellants are frequently used as vehicles for pharmaceutical aerosols.

Flocculated System

In this system, the disperse phase is in the form of large fluffy agglomerates, where individual particles are weakly bonded with each other. As the size of the sedimenting unit is increased, flocculation results in a rapid rate of sedimentation. Here, the sedimentation depends not only on the size of the flocs but also on the porosity of flocs. It can easily be redisoers by shaking the bottle.

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Deflocculated Suspension

Deflocculated suspension is a suspension in which the dispersed particles remain as discrete separated units. Rate of sedimentation is slow, which prevents entrapping of liquid medium which makes it difficult to re-disperse by agitation. This phenomenon is called caking or claying.

Liposomes And Micro-/nanoparticles

Suspensions of liposomes, microspheres, microcapsules, nanospheres, or nanocapsules are used for targeted and controlled delivery of drugs. These are usually intended for parenteral administration.

Vaccines

Vaccines are used for the induction of immunity and are often formulated as suspensions. For example, cholera vaccine and tetanus vaccine are suspensions.