Drug dosage form: An introduction, principle, classification, with its factor.

What is the drug dosage form?

Dosage form

The drug dosage form is known as the active pharmaceutical ingredients (API) that are combined with the excipients or additives and act at the site of action with their action in different forms.

In the form of dosage forms, the drug molecules are delivered at the site of action within the body to produce optimum desired effects and minimum adverse effects.


The most common dosage forms are generally administered orally, and it is the most convenient method to deliver medication, which leads to mass production and ultimately lower manufacturing costs. Some medications are not available in oral form because they cannot be properly absorbed in the G.I tract.

For instance, heparin is only available as an injectable formulation because it is ineffective when administered orally.

The route of administration and dosage form is also determined by other factors, including the age of the patient, the disease being treated, the area of the body that the drug needs the reach, ease of administration, and the characteristics of the drug.


Drug– The substances which meant for treatment, mitigation, or prevention of diseases or disorders in human beings or animals, intended to affect any function or any structure of the human body are termed as Drugs. For example- Paracetamol, Aspirin, salbutamol.

The dosage form is a transformation of a pure chemical compound into a predetermined form by admixing drug compounds with different kinds of non-drug components collectively known as Adjuvants each having a specific function. For example- tablets, capsules, syrups, suppositories, creams.


These are the means by which drug molecules are delivered at the site of action within the body. Drugs are probably administered as pure chemical substances alone and almost always given as formulated preparations or medicines.

These can vary from relatively simple solutions to complex drug delivery systems via the use of appropriate additives or excipients in the formulations. The excipients provided varied and specialized pharmaceutical functions.

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The need for dosage forms-

-Dosage form for safe and convenient delivery of accurate dosage. For example- Tablets, capsules, syrups.

With the protection of a drug substance from the exterminatory influence of oxygen or moisture present in the atmosphere. For example- coated tablets, sealed ampules.

-For the protection of a drug substance from the exterminatory influence of gastric juice(acid) after oral administration. For example- Enteric-coated tablets.

-To mask the bitter taste, salty obnoxious and odor of a drug substance. For example- Capsules, coated tablets, flavored syrups.

-For liquid preparations of compounds that are either insoluble or unstable in the desired vehicle. For example- Suspension.

– For a liquid dosage form of substances soluble in the desired vehicle. For example- Solutions.

-For extended drug action through controlled release mechanisms. For example- Controlled release tablets, capsules, suspension.

-For optional drug action from topical administration sites. For example- Ointments, creams, ophthalmic, ear, and nasal preparations.

-To provide the insertion of drugs into the body cavities. For example- rectal, vaginal suppositories.

-To provide the placement of the drug within body tissues. For example- implants.

-To provide optimal drug action through inhalation therapy. For example- Inhalants, inhalations.

In general, many dosage forms are permit ease of drug identification through distinctiveness of color, shape, or identifying markings, etc.

Classification of dosage form-

Dosage form of a drug substance are classified on there physical form and route of administration through which that are act at site of administration are-

Classifications based on physical form of dosage form-

Dosage forms may be classified based on the physical form of the final product which is as under-

Solid dosage form

These are also allowed for accurate dosing. The complete dose is contained within the contents of the solid dosage form, which minimizes measuring errors. These may, however, be difficult to swallow, have a slow onset of action, and maybe degraded by the acidic contents in the stomach.

These are including tablets, capsules, caplets, lozenges, troches, pastilles, powders, and granules.

-Increased stability

-Ease of packaging, storage, and dispensing


-Little or no taste or small

Semi-solid Dosage Forms-

These are different in their composition from liquid and solids. They are usually intended for topical application. These are applied to the skin or to the mucous membrane to achieve the local or systemic effects.

These are too thick to be considered a liquid dosage form and not solid enough to be considered a solid dosage form.

Examples include emulsion, ointments, pastes, creams, lotion, gels, pastes, etc.

These have many characteristics in common like- consistency, presentation, preservation requirement, and also the route of administration which is mainly topical.


Liquid Dosage Forms-

These are containing one or more active ingredients in a liquid vehicle such as a syrup, elixir, solutions, suspensions, collodions, emulsions, mouthwash, etc.

The drug may be dissolved in the vehicle or suspended as a very fine particle. These can be administered by many routes, but often less stable than medications in the solid dosage form.

The liquid dosage form can be sterile or non-sterile depending on the route of administration.

-Easy dosage adjustment, particularly for pediatric patients.

-Easy to swallow, particularly for pediatric and geriatric patients.

-The onset action is faster than that of solid dosage forms.

Gaseous Dosage Forms-

This class comprises drug products that are packaged under pressure in a holder with a ceaseless or restricted conveyance valve framework.  The gas contains inside restoratively dynamic medications that are released upon activation of an appropriate valve system.

Examples include aerosols, nebulizer, sprays, inhalers, etc.

Classifications based on the route of administration of dosage form-

The pattern of absorption in drugs changes considerably between individual drug substance as well as between the different administration routes.  Dosage forms are designed to endow the drug in a suitable form for absorption from each selected route of administration.

The route of administration for a drug product is generally determined by the physicochemical characteristics of the drug molecules.

1.Oral route-

Through the oral route, dosage forms are comprised of pharmaceutical formulations taken orally by mouth for systemic effects. These are absorbed through the various epithelia and mucosa of the gastrointestinal tract at varying rates except for drugs that are absorbed in the buccal cavity. For example- tablets, capsules, suspensions, lozenges, pills, granules, powders, emulsions, etc.

2. Topical route-

Through the topical route, dosage form includes in drug molecules that are in a suitable solid base like- powders and aerosols, semi-solid base like- ointments, creams, foams, gels, poultice, and pastes, or in liquid form like- solutions, suspension of solids in aqueous solutions or emulsions which possesses either hydrophobic or hydrophilic properties.

These are applied to the skin or other topical surfaces like- the eye, ear, and nose mainly for local action. Systemic drug delivery can also be achieved using topical preparations like- transdermal patches, though absorption is often poor and erratic.

3. Rectal route-

Through the rectal route, the solutions, suppositories, or emulsions administered rectally for local rather than systemic effects. This route can also be used to deliver drugs that are inactivated by gastrointestinal fluids when administered orally or when the oral route of the patient is precluded.

4. Parenteral route-

Through the parental route, usually sterile, particulate-free, and non-pyrogenic solutions or suspensions (of drugs in water or other suitable physiological acceptable vehicles) are injected into the body using syringe and needle, infusion set, etc.

5. Inhaled/ Respiratory route-

Through this route, the dosage form where drugs are delivered in gaseous, aerosol mist, or ultrafine solid particle form into the lungs. These classes of the dosage form are mainly for direct treatment and management of respiratory diseases. Examples include nebulizers, powder aerosols, and pressurized metered-dose aerosols.

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6.Vaginal route-

Through the vaginal route, dosage forms are intended to be used in the vaginal cavity for either contraception, induction of labor, treatment of vaginal infections, or local menopausal symptoms. Commonly the vaginal dosage forms like creams, tablets, vaginal gels, and pessaries, suppositories, foams, ointments, tampons, inserts, and others include vaginal rings, vaginal films, etc.

7. Ophthalmic route-

Through the ophthalmic route, principally sterile solutions, ointments, and suspensions, essentially free from particles or substances that might irritate the eye. These are meant to be gently applied to the eyelids or placed in the pocket between the eyelids and the eyeball. Ophthalmic dosage forms are commonly used for the treatment of local ocular disorders, For example- infection and inflammation or intraocular disorders such as glaucoma.

8. Nasal route-

Through the route, non-sterile aqueous-based systems are instilled within or sprayed into the nasal cavity from a dropper or a plastic squeeze bottle. These are predominantly employed for the treatment of local disorders like- infections, congestion, and allergic rhinitis. Nasal preparations when absorbed through the nasal mucosa to achieve the systemic effect.

9.Otic route

Through the otic route, non-sterile aqueous solutions, or solutions prepared with glycerin or other solvents and dispersing agents that are instilled into the ear canal for the treatment of local disorders.

Administration route of the dosage form with components-

Oral route– Solutions, syrups, suspensions, emulsions, gel, powders, granules, capsules, tablets

Rectal route– Suppositories, ointments, creams, powders, solutions.

Topical route– Creams, ointments, pastes, gels, lotions, solutions, topical aerosols, transdermal patches

Parenteral route– Injections in the form of solutions, suspensions, emulsion, implants, irrigation, and dialysis solutions.

Respiratory/inhalation route– Aerosols in the form of solutions, suspension, or powder form, inhalations, sprays, and gases.

Nasal route– Solutions, inhalations, aerosols

Ophthalmic route- For Eyes- Solutions, ointments, solutions

For Ears– Solution

Factors affecting drug dosage form-

Particle size and surface area-

It results in an increase in the specific surface like- surface area per unit weight of powders. It affects the process of drug dissolution rate, absorption rate, dosage form content uniformity, and stability. These are all dependent to varying degrees on particle size, size distribution, and interactions of solid surface.

In many cases, for both drugs and additives, particle size reduction is requiring achieving the desired physiochemical characteristics.

Surface area-

The fine material, that commonly in the micrometer or submicrometer (nanometer) form with a large specific surface, which dissolves at faster rates that can lead to improved drug absorption by passive diffusion.

On the other hand, the formulated nitrofurantoin preparations with an optimal particle size of 150 mm that reduced the gastrointestinal distress. While it still allowing the enough urinary excretion of urinary antibacterial agents.


The relatively insoluble compounds that can exhibit abnormal or incomplete absorption. It might be suitable for use more soluble salt or other chemical derivatives. Alternatively, micronizing, complexation or solid dispersion techniques are might be deputed.

Solubility, and especially the degree of saturation in the vehicle, can also be important in the absorption of drugs already in solution in liquid dosage forms since precipitation in the gastrointestinal tract can occur, modifying bioavailability.


During the process of dissolution, the drug molecules in the surface layer dissolve and leading to a saturated solution around the particles in the form of the diffusion layer. The dissolved drug molecules then pass throughout the dissolving fluid for contact with absorbing mucosa and are then absorbed.

Replenishment of expended drug molecules in the diffusion layers is achieved by further drug dissolutions and the absorption process continued.

Partition coefficient pKa-

One of the first properties of a molecule that should be predicted or measured is its partition coefficient between an oil and a water phase or log P. That gives a measurement of the lipophilicity of a molecule, which can be used as a prediction for how it will be able to cross a biological membrane.

One of the most common ways of measuring the partition coefficient is to use the shake flask method.


Practically all drug compounds are handled in powder form at the stage during the manufacturing of dosage forms. Many drug substances may exist in more than one form in different with molecular packing arrangements in the crystal lattice.

This property is termed polymorphism and different polymorphs may be prepared by manipulation of conditions of particle formation during crystallization such as solvent, temperature, and rate of cooling.

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The chemical phase of drug compounds is generally centered on the chemical stability of the drug and compatibility with the other formulation ingredients. It should be emphasized that the packaging of the dosage form is an important factor contributing to product stability and must be an integral part of stability testing programs.

Chemical changes involving additives and any physical modifications to the product must be carefully monitored to optimize formulation stability.

Organoleptic properties

Modern medicines demand that the pharmaceutical dosage forms are acceptable to the patient. Unfortunately, many drug substances that are used today are unpalatable and unattractive in their natural state. The dosage forms containing such drugs, particularly oral preparations, may require the addition of approved flavors and colors.

The use of flavors applies primarily to liquid dosage forms intended for oral administration. Colors are deputed to improve or standardize an existing drug color, to mask a color change, or complement a flavor.

Other drug properties-

At the same time as ensuring that dosage forms are chemically and physically stable and therapeutically effective. These also relevant to establish that the selected formulation is capable of efficient and, in most cases, large-scale manufacture.

Hygroscopic drugs may require low moisture in manufacturing environments and need to avoid water during their preparation. Poorly flowing formulations may require the addition of flow agents, For example-fumed silica, suspensions, ointments, creams.

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