Copyright © 2021 The Author(s): This is an open-access article distributed under the terms of the CC BY-NC 4.0 which permits unrestricted use, distribution, and reproduction in any medium for non-commercial use provided the original author and source are credited

Yogesh Sahu¹, Arvind Singh Jadon², Prateek Jain¹, Bhupendra Singh Thakur¹, Basant Khare¹, Anushree Jain¹*

²Amity Institute of Pharmacy, Amity University, Gwalior, Madhya Pradesh, India-474001

Article Info:

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Article History:

Received 02 Jan 2021

Reviewed 13 Feb 2021

Accepted 27 Feb 2021

Published 15 March 2021

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Cite this article as:

Sahu Y, Jadon AS, Jain P, Thakur PS, Khare B, Jain A, An Overview on Recent Advances in Pharmaceutical Suspensions, International Journal of Medical Sciences & Pharma Research, 2021; 7(1):1-3

DOI: http://dx.doi.org/10.22270/ijmspr.v7i1.54 ____________________________________________

*Address for Correspondence:

Anushree Jain, Adina College of Pharmacy, Sagar, Madhya Pradesh, India-470001.

Abstract

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The suspension is a biphasic liquid or semi-solid dosage form where the finely divided insoluble solid drug particles are homogeneously dispersed in a liquid or semi-solid medium. The solid drug particles act here as the dispersed phase and the liquid or the semi-solid as the dispersion 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. Suspensions are an important class of pharmaceutical dosage forms. The advantages of suspension dosage forms include effective dispensing of hydrophobic drugs; avoidance of the use of cosolvents; masking of unpleasant taste of certain ingredients; offering resistance to degradation of drugs due to hydrolysis, oxidation or microbial activity; easy swallowing for young or elderly patients; and efficient intramuscular depot therapy. In addition, when compared to solution dosage forms, relatively higher concentration of drugs can be incorporated into suspension products. The present review provides an overview of various aspects of suspensions such as classification of suspensions, theories of suspensions, various suspending agents, formulations aspects of suspensions, stability of suspensions and recent research work that is being carried on suspensions.

Keywords:Suspensions, suspending agents, flocculated, Stability.

The pharmaceutical suspension is a biphasic liquid or semi-solid dosage form where the finely divided insoluble solid drug particles are homogeneously dispersed in particles act as the dispersed phase or internal phase. The internal phase consisting of insoluble solid particles having a range of size(0.5 to 5 microns) which is maintained uniformly throughout the suspending vehicle with aid of single or combination of suspending agent. The external phase (suspending medium) is generally aqueous in some instance, may be an organic or oily liquid for non-oral use. A pharmaceutical suspension defined as a coarse dispersion containingfinely divided insoluble material suspended in a liquid medium. The physical chemist defines the word "suspension" as two-phase system consisting of an un dissolved or immisciblematerial dispersed in a vehicle (solid, liquid, or gas).¹

Suspension can improve chemical stabilityof certain drug. For example, Procaine penicillin G. Drug in suspension exhibits higher rate of bioavailability than other dosageforms. Solution > Suspension > Capsule > Compressed Tablet > Coated tablet

Duration and onset of action can be Controlled. For example, ProtamineZinc-Insulin suspension. Suspension can mask the unpleasant/bitter taste of drug. For example,Chloramphenicol.

Physical stability, sedimentation and Compaction can cause problems.It is bulky. Sufficient care must be taken during handling and transport.It is difficult to formulate.Uniform and accurate dose may not be achieved.

(1)Oral suspension: Oral suspension is biphasic liquid dosage form contains one or more active ingredients suspended in a suitable vehicle.These kinds of suspensions are formulated to administer drugs like antibiotics which may contain a dose in the range of 125-500 mg/ml of the suspension.In pediatric drops, the concentration of suspended drugs may be relatively higher.

It is easy to swallow suspended insoluble powdered drugs especially by the pediatric andgeriatric patient than the tablets and capsules.The suspension ensures faster dissolution needed for absorption compared to the tablets and capsules.

Injectable suspensions are heterogeneous systems consisting of the drug dispersed in a liquid medium. They are sterile, pyrogen free and physically and chemically stabile over the intended shelf-life. They are administered through the subcutaneous and intramuscular routes. They are not administered intravenously as it may lead to vaso-occlusion. They may usually contain a drug concentration in between 0.5-5.0% which passes easily through the hypodermic needle. Procaine benzyl penicillin, known as Procaine penicillin G and Benzathinebenzylpenicillin were also known as benzathine penicillin G are the examples of antibiotics which are injected intramuscularly

(a) Therapeutic use of drugs those are insoluble in conventional solvents (i.e. water, water miscible and water immiscible).

Externally applied suspensions are used topically and designed for dermatological, cosmetic and protective purposes. Such kind of suspension should spread easily and must not be too fluidic to run off the skin surface.Calamine lotion is a classic example of such suspension applied for protective rationale but it also possesses a cosmetic feel.

Suspension can be classified as flocculated suspension and deflocculated suspension,

Flocculation is an architecture which results from the lowering of the electrical forces of repulsion between the dispersed particles of suspension along with dominant attraction force. Under this condition, the particles with reduced repulsive force approach each other resulting into a loosely aggregated structure popularly known as floc. As the floc or floccule is composed of many individual particles resulting in a large network of individual particles, the rate of sedimentation is always rapid. The floccules have loose porous structure and the dispersion medium can flow through them during SedimentationThe floccules also entrap a large amount of the liquid phase. Therefore, the volume of the final sediment will still be large and facilitate re-dispersion with ease by moderate shaking.

In a deflocculated suspension, the individual particles remain as discrete separated units and settle slowly. The slow rate of settling of particles prevents the individual particles of this suspension to entrap any liquid medium and becomes compacted leading to cake formation. This phenomenon of caking is a very serious physical stability issue encountered in suspension. Another characteristic feature of this suspension is that the supernatant remains cloudy for sufficient time after shaking. Particles exist as separate entities and do not form floccules.The rate of sedimentation is high. The rate of sedimentation is slow.Sediment is easy to re-disperse.

1. Suspension is usually applicable for drug which is insoluble (or) poorly soluble.

5. Insoluble drug or poorly soluble drugs which required to be given orally in liquid dosage forms.

(in case of children, elderly, and patients have difficulty in swallowing solids dosage forms)

6. To overcome the instability of certain drug in aqueous solutionInsoluble derivative formulated as suspension. An example is oxytetracycline HCL (instable) calcium salt (stable)

The major rate-limiting step in the absorption of drugs from suspension dosage form is drug dissolution which is generally rapid due to the large surface area of the particles. Suspensions are expected to demonstrate improved bioavailability compared to the same drug formulated as a tablet or capsule. This is because the suspension already contains discrete drug particles whereas tablet dosage from must undergo disintegration in order to maximize the necessary dissolution process. Frequently antacid suspensions are perceived as being more rapid in action and therefore more effective than an equivalent dose in the form of tablets.

The particle size of the active pharmaceutical ingredient (API) and inert excipients is a very important parameter that has the surface area increases inversely with the particles size.

Polymorphism of pharmaceuticals is the ability of the molecule to assemble into multiple crystal structures. Different polymorphs have different arrangements of atoms within the unit cell, and this can quite often have a remarkable impact affect the pharmacokinetics and Pharmacodynamics increased rate and extent of oral absorption compared to crystalline drugs.

It is a prerequisite that the hydrophobic drug particles must be wetted properly for the uniformdispersion in the continuous medium. The wetting is very important irrespective of the physical nature of the drug, diffusible or in-diffusible. The finely distributed hydrophobic drug particles are coated with a film of air preventing its dispersion in the external medium.

If the drug particles are not wetted properly, the suspension may exhibit poor physicalstability and poor dissolution properties. As a result, the drugs bioavailability and invivo performances can greatly be at stake.

Formulation of suspensions may seem to be simple. After encountering numerous technical problems during pharmaceutical suspension development, the formulator (pharmacist) makes it simple. Some pharmaceutical suspensions are marketed as either prepared form or granular mixtures or dry powders called PFS (powder for suspension) intended for reconstitution.Pharmaceutical suspension may be formulated for different routes of administration for example oral, topical, ophthalmic, inhalation, otic, rectal, and injection. Examples of some pharmaceutical suspensions: Amoxicillin Oral Suspension, Mebendazole Oral Suspension, Albendazole Oral Suspension, Natamycin Ophthalmic Suspension etc.

The various components, which are used in suspension formulation, are as follows.

Buffers and pH adjusting agents: They are added to stabilize the suspension to a desired pH range.

Osmotic agents: They are added to adjust osmotic pressure comparable to biological fluid.

Coloring agents: They are added to impart desired color to suspension and improve elegance.

Taste masked pharmaceutical suspensions.Sustained release suspensions.Nano suspensions are the biphasic colloidal dispersions of nanosizeddrug particles stabilized by surfactants without the matrix materials.They can also be defined as a biphasic system consisting of pure drug particles dispersed in an aqueous vehicle in which the diameter of the/suspended particle is less than 1 pm in size.They have average diameter of particle 200-600nm.

Today pharmaceutical suspension has occupied a vast space among the dosage forms. It can administer through different routes like oral, external and injectable. Hence, the optimization of formulation parameters of this dosage form is a very challenging task. The rationale of optimized formulation for a particular therapeutic target would only be achieved if the bio-availability issues are addressed properly.

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