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PHARMACEUTICAL LIQUID DOSAGE FORM

The liquid dosage forms, whether for internal, parenteral or external use may be either monophasic or biphasic products.
Monophasic products are represented by true or colloidal solutions and solubilised preparations. They are appeared to be similar in physical appearance and consists of only one phase. They may have water as the solvent or may be occasionally based on some other liquids.
The biphasic products are exemplified by emulsions or suspensions and consists of two phases. In emulsions generally both the phases are liquids, while in suspensions the continuous phase is liquid and the dispersed phase is finely divided solids.
Liquid preparations are easy to swallow and thus more useful for pediatrics and geriatrics.
On the other hand drug in soluble state is chemically less stable than its insoluble state.
Monophasic dosage forms are available as:

Liquid for internal use, Eg: Syrups, Elixirs, Linctus, drops and draughts.
Liquids for external use, which are of two types:

Liquid to be applied to the skin, eg: liniments and lotions.
Liquids for body cavities. Eg: Gargles, throat paints, mouth washes, eye drops, eye lotions, ear drops, nasal drops, spray and inhalations.

What Are Pharmaceutical Liquid Dosage Forms?

Pharmaceutical liquid dosage forms are drug formulations that are in a liquid state, ready for consumption. These include solutions, suspensions, and emulsions. They offer a versatile approach to delivering medications to patients of all ages.

Advantages of Pharmaceutical Liquid Dosage Forms

Convenience and Precision

Liquid medications are easy to measure and administer accurately, making them a preferred choice for patients with specific dosage requirements. The risk of underdosing or overdosing is significantly reduced.

Rapid Absorption

Liquid dosage forms are quickly absorbed by the body, ensuring a faster onset of action. This is especially crucial for medications that require immediate relief or for patients with difficulty swallowing solid forms.

Liquid for internal use:

The largest proportion of the liquid formulations are liquid for internal use. Drug should have sufficient solubility in commonly used solvent, like water.

Syrups:

Syrups are sweet and viscous aqueous preparations. Simple syrup is a saturated solution of sucrose in purified water. The concentration of sucrose used is 66.7 % w/w (as per Indian Pharmacopoeia, IP). They are either flavoring syrups (syrups containing aromatic or flavored substances) and medicated syrups (Syrup containing medicinal substances).
Syrups are used for formulating antibiotics, antitussives, antihistaminic, sedatives, vitamins etc.
Most syrups are aqueous solutions of sucrose or dextrose. Artificial syrups are also in the market, where artificial sweetening agents (Eg: saccharine and sodium cyclamate) are used.
The artificial syrups are having two points in their favour

They are free from carbohydrates and suitable for diabetics.
They have lesser stability problems as compared to sugar based syrups.

Syrups are commonly used for the following reasons:

They are palatable
Syrups have high osmotic pressure which prevents growth of bacteria, fungi and prevent decomposition of many vegetable substances. Due to this syrups have the self-preservative activity.
Syrups retards oxidation because it is partly hydrolysed into reducing sugars, such as lavulose and dextrose.

Elixirs:

Elixirs are clear sweetened and flavoured hydroalcoholic solutions for oral use. Non medicated elixiers such as aromatic elixir are mainly used as flavoured vehicle. Medicated elixiers have their own therapeutic value.
Alcohol content in elixiers varies from 3 to 40%. Due to high alcohol content, elixirs are not the choice of dosage forms for pediatrics.
The main ingredients of elixirs are ethyl alcohol, water, glycerin, propylene glycol, flavouring agent, colouring agent and some preservative. The medicated elixirs usually contain a potent drug such as, antibiotics, antihistamines or sedatives.

Eg: Piperazine Citrate Elixirs I.P (Piperazine Citrate)

Linctuses:

Linctuses are viscous liquid and oral preparations that are generally prescribed for the relief of cough. Mostly it contains ingredient with sedative action and some contains expectorants. Simple syrup is generally used as a vehicle for most of the linctuses. This give soothing to the sore mucous membrane of the throat.
To obtain and prolong local action, linctuses should be taken undiluted and sipped and swallowed slowly.

Eg: Codeine Linctus B.P.C (API: Codeine Phosphate)

Drops:

These are small dose liquids administered without dilution with the help of dropper.
The oil soluble vitamins, such as vitamin A and D concentrates in fish liver oil are presented as drops for administration.
Since these preparations contain potent medicaments, the dose must be measured accurately.
Droppers is either graduated in fractions of a milliliters or pre calibrated.

Liquid Formulations for External Use:

Monophasic liquids for external use may be categorised into following classes

Liquids for application to the intact skin, such as liniments, lotions etc
Liquids for the use in one or the other body cavities such as gargles, throat paints, eye drops, eye lotions, ear drops, ear douches, nasal drops, enemas etc.
Liquids meant to be inhaled into or sprayed in nasal or respiratory tracts.

Liniments:

The liniments are liquid or semi-liquid preparations meant for application to the skin. The liniments are usually applied to the skin with friction and rubbing of the skin. They are solutions or emulsions in an aqueous or oily vehicles.
They are used as counter irritant, rubefacient and soothing.
Alcohols are also used in the preparation of liniments. Alcohol in the liniments helps in the penetration of medicaments into the skin and also increases its counter irritant and rubefacient action.
In oily liniments arachis oil is used commonly, which spread more easily on the skin.
A liniment should not be applied to the broken skin because it may causes excessive irritation.

Eg: Liniment of Camphor.

Lotions:

Lotions are suspensions, emulsions, combination of emulsion-suspension or aqueous or non-aqueous solutions designed to be applied to the unbroken skin without friction.
They are used for their epidermic effect, such as local cooling, soothing, protective, drying or moisturizing properties depending upon the ingredients used.
They are directly applied to the skin with the help of some adsorbent material, such as, cotton wool.

Eg: Calamine Lotion I.P

Collodions:

Collodions are liquid preparations for external use. It contains pyroxylin (nitrocellulose) in a mixture of ethyl ether and alcohol.
They are applied to the skin by means of a soft brush or suitable applicator. After application ether and alcohol get evaporated and leaves a film of pyroxylin on the surface of the skin. As the preparation contains the volatile substances collodions are highly inflammable.

Gargles:

Gargles are clear aqueous solutions used in the posterior region of mouth by agitating the solution with exhaled air to produce local effect in throat and these are not to be swallowed in large amount.
They are usually available in concentrated form with direction for dilution with warm water before use. They are brought into intimate contact with the mucous membrane of the throat and are allowed to remain in contact with it for a few seconds before they are thrown out of the mouth.
They are used to relieve soreness in mild throat infection. Phenol or thymol is generally present in small concentration for its antibacterial activity. Potassium chlorate is also included in gargles for its weak astringent effect to tone up a relaxed throat. It also stimulates secretion of saliva which relieves dryness, eg: Phenol gargles, Potassium chloride and phenol gargles.

Mouth Washes:

These are aqueous solutions with a pleasant taste and odour used to make clean and deodorise the buccal cavity.
Generally they contain antibacterial agents, alcohol, glycerin, sweetening agents, flavouring agents and colouring agents.

Eg: Sodium Chloride Mouth Wash, Compound B.P.C.

Throat Paints:

Throat paints are viscous preparations of medicaments for local action in the pharynx. Glycerin is commonly used as a base because, being viscous, it adheres to mucous membrane for a long period and it possesses sweet taste.
They are applied to the throat with a brush. Throat paints are used in treatment of inflammations of various areas of the mouth and throat.

Douches:

Douches are aqueous solutions intended to clean, deodorise, soothe or medicate body cavities.
Eye douches, often termed as eyewashes, are used to remove foreign particles and discharges from the eyes.
Douches are generally dispensed in the form of a powder or tablet with a specific directions for dissolving it in a specific quantity of warm water. Vaginal douches must be sterile.
They are used for:

Cleansing agents: Isotonic sodium chloride solution
Antiseptics. Eg: Mercuric chloride (0.001%)
Astringent, Eg: Alum (1%)

Enemas:

Enemas are aqueous or oily solutions, suspension or emulsions of medicaments intended for rectal administration, to cause bowel evacuation, to bring about local or systemic therapeutic action etc.
Enemas meant for cleaning purpose are used to evacuate faeces in constipation or before an operation. They act by any one of the following methods:

By stimulating peristalsis.
By lubricating impacted faeces.

Ear Drops:

Ear drops are solutions, suspensions or emulsions of drugs in water, glycerin or propylene glycol intended for instillation into the ear.
These are used for removal of excessive cerumen, to treat infection, inflammation or pain and for cleaning and drying of ear.

Eye Drops:

These are sterile solutions or suspensions of drugs that are instilled into the eye with a dropper. The eye drops are usually made in aqueous vehicle. It should be sterile, isotonic with lachrymal secretions and free from foreign particles to avoid irritation to the eye.
A suitable preservative like phenyl mercuric nitrate (0.002%), Benzalkonium chloride (0.01%) may be used to prevent bacterial or fungal growth.
Eye drops usually contain substances having antiseptic, anti-inflammatory, anesthetic and miotic properties.

Nasal Drops:

These are aqueous solutions of drops that are instilled into the nose with a dropper.
Nasal drops should be isotonic with 0.9% sodium chloride having neutral pH and viscosity similar to nasal secretions by using0.5% methyl cellulose.

Biphasic Liquid Dosage form:

Liquids which consist of two phases are known biphasic liquids. Eg: Emulsions and suspensions.

Emulsions:

Emulsions are thermodynamically unstable heterogeneous biphasic system consisting of two immiscible liquids, one of which is dispersed as minute globules into the others.
This type of formulations are stabilized by using emulsifying agent. Internal phase droplets are generally ranged in diameter of 0.1 µm to 100 µm.
Emulsions are mostly classified as oil in water (o/w) emulsions and water in oil (w/o) emulsions.
Emulsions are used for

Oral administration, Eg: Liquid Paraffin Emulsion IP
Intravenous administration, Eg: Emulsion of vitamin A,D and K and
For external use, Eg: Emulsions for topical administration.

Suspensions:

Suspensions are heterogeneous biphasic, thermodynamically unstable liquid dosage form of medicaments in which insoluble solid particles (as internal, discontinuous or dispersed phase) is uniformly distributed in liquid phase (External, continuous or dispersion phase).
In suspensions finely divided particles ranging from 0.5 to 5 microns are dispersed in a liquid vehicle.
Suspensions are used for oral, parenteral and external applications. Suspensions which are meant for external applications should have small particle size to avoid gritty feeling to the skin and to cover a larger area of the skin. Smaller particles also helps in the penetration of drug through the skin.

Pharmaceutical Liquid Dosage Form FAQs

1. What are the main advantages of Pharmaceutical liquid dosage forms?

Pharmaceutical Liquid dosage forms offer precise dosing, rapid absorption, and ease of administration, making them suitable for patients with specific dosage requirements or those who have difficulty swallowing solid forms.

2. Can liquid dosage forms be used for pediatric patients?

Yes, liquid dosage forms are often the preferred choice for pediatric patients as they allow for accurate dosing, making it easier to administer medications to children.

3. How do manufacturers ensure the stability of liquid formulations?

Manufacturers use various techniques, including proper storage conditions, container selection, and preservatives, to maintain the stability of liquid formulations and extend their shelf life.

4. Are there any specific storage conditions for liquid dosage forms?

Storage conditions may vary depending on the formulation. It is essential to follow the manufacturer’s instructions to maintain the product’s integrity and effectiveness.

5. What regulatory bodies oversee the production of liquid dosage forms?

Regulatory bodies like the FDA (Food and Drug Administration) play a crucial role in overseeing and regulating the production of pharmaceutical liquid dosage forms to ensure quality, safety, and efficacy.