Liquid dosage form: An introduction, classification, excipients, with its advantage.

What is a liquid dosage form?

iquid-dosage-forms
Liquid dosage forms

The liquid dosage form is pourable pharmaceutical preparations, which contain a mixture of active drug components and non-drug components (excipients) that dissolved or suspended in a suitable solvent or mixtures of solvents. These are pharmaceutical formulations, those designed to provide a maximum therapeutic response in a target population when difficulty in swallowing solid dosage forms and produce a rapid therapeutic effect.

These are may supply as ready-to-use in the form of liquid or powder for reconstitution. These are administered by both oral and parenteral routes in the form of injectable, inhalation, ophthalmic, otic, nasal, and topical. Oral liquids are nonsterile, whereas liquids administered by the parenteral route are available as sterile and nonsterile formulations.

Introduction

Liquid dosage forms are one of the oldest dosage forms which are used for the treatment of patients with rapid and high absorption of medicinal products. Therefore, the compounding of liquid dosage retains a particularly useful for individuals who have difficulty in swallowing solid dosage forms like-pediatric, geriatric, intensive care, and psychiatric patients, and in the case where precise or individualized dosages are required.

These are prepared by dissolving the active ingredients in an aqueous or non -aqueous solvents which are includes solutions, suspensions, and emulsions, etc. These forms are needed various excipients including vehicle, stabilizer and viscosity builders, preservatives, sweeteners, color, and flavor. In addition, solubilizes are required in case of clear liquids, suspending agents are needed for suspensions and emulsifying agents for emulsions.

Classification of Liquid Dosage Forms

Liquid dosage forms are classified into two groups are-

-Monophasic liquid dosage forms

-Biphasic liquid dosage forms

Monophasic liquid dosage forms

Monophasic liquid dosage forms are the simplest form of presenting medication for rapid and high absorption of medicinal drugs. These are in a one-phase system consisting of two components-solute (that gets dissolved) and the solvent (where solute dissolves).

The monophasic liquid dosage forms are classified as-

-Liquids for oral use

-Liquids for external use

-Liquids for special use

-Parenteral solutions for Injection use

Liquids for oral use-

 Monophasic liquid dosage form for oral use comprises one phase pourable pharmaceutical formulations intended for oral administration. For examples include mixtures, linctus, draughts, elixirs, syrups, and drops.

Mixtures– Pharmaceutical mixtures for liquid oral preparation are consist of one or more medicaments that dissolved, suspended, or diffused in an aqueous vehicle. These are generally freshly or recently prepared and used fairly quickly, usually within a month for short term therapy like cough, diarrhea, constipation, etc.

Mixtures are classified into five groups are-

-Simple mixtures containing soluble substances

-Mixtures containing diffusible solids which do not dissolve in water, but maybe mixed when shaking. As a result, these are evenly distributed throughout the liquid for sufficient time.

-Mixtures containing in-diffusible solids are not dissolved in water and do not remain uniformly distributed in the solvent for a sufficiently long time.

-Mixtures containing precipitate forming liquids.

-Mixtures containing slightly soluble liquids.

Linctus-as-liquid-dosage-forms
Source-internet

Linctus– Linctuses are viscous oral liquid dosage form which contains one or more medicaments that dissolved in a vehicle, usually contains a high proportion of sucrose or other sugars. These are chiefly used as demulcent, expectorant, or sedative principally in the treatment or relief from cough. As such, linctuses are intended to be sipped slowly in small doses and that allowed to trickle down the throat in an undiluted form. That gives a maximum and prolonged effect of medicament in the throat.

Draughts– A draught is an older term used to describe oral liquid dosage form which contains only one or two large doses. The volume of the formulation is generally larger than that usually utilized in a traditional mixture of formulations and each dose is supplied in separate bottles.

Elixirs-in-liquid-dosage-forms
Source-internet

Elixirs– Elixirs are clear, flavored, sweetened, hydroalcoholic liquid oral dosage forms that usually contain either potent or unpleasant-tasting drugs. These may be medicated or unmedicated. Compared to syrups, elixirs are usually less sweet and less viscous because these are containing a lesser amount of sugar. Because of their hydroalcoholic character, these are better to able than are syrups to maintain both water-soluble and alcohol-soluble components in solution.

Syrups-as-liquid-dosage-forms
Source-internet

Syrups– Syrups are concentrated aqueous solutions which are containing one or more sugar components, highly sucrose, or sugar substitute. The concentration of sugar in syrup is 66.7 % in w/w. These are maybe medicated or unmedicated.

The unmedicated often referred to as simple syrups and used as vehicles for medicinal substances that to be added later, either in the extemporaneous compounding of prescriptions or in the preparation.

pediatric-drops-as-liquid-dosage-form
Source=internet

Drops (Pediatric drops)- Drops are liquid preparations of potent drugs which are usually in a solution that is intended to be administered in small volumes with the aid of a suitable measuring device or calibrated dropper to pediatric patients.

Monophasic liquid dosage forms for external use

These include monophasic liquid preparation for external use such as lotions, liniments, and collodions.

Lotion-as-liquid-dosage-form

Lotions– Lotions are solutions, but may also be in form of suspensions or emulsions, which intended for external application to the skin.

These are rubbed on the skin without friction with the help of some absorbent material such as cotton, wool or gauze soaked in it.

In some cases, these are applied to the scalp, where the vehicle for the medication is alcohol-based, that allowing for rapid drying of the hair and thus making the product more acceptable to the patient like-Salicylic Acid Lotion 2% BPC. In these cases, problems of flammability are addressed by suitable labeling on it.

Liniments– Liniments are liquid preparation which intended to be rubbed with friction and massaged onto unbroken skin to obtain analgesia, rubefacient, or generally stimulating effects at the site. These are usually solutions of oils, alcohols, or soaps, but maybe formulated as in the form of emulsions.

Collodions-as-liquid-dosage-form
Source-internet

Collodions– Collodions are principally solutions of pyroxylin in a vehicle of ether and alcohol that are intended to be painted onto the skin using a brush or rod and left to dry. When dry, the collodion leaves a protective film covering the site. These are highly volatile and flammable, and care should be taken to label any preparation properly.

Monophasic liquid dosage forms for special use

gargles-as-liquid-dosage-form
Source-internet

These include monophasic liquid preparation for special use such as gargles, mouthwashes, throat paints, eye drops, eye lotions, ear drops, nasal drops and sprays, douches, and enemas.

Gargles– Gargles are aqueous solutions that contain antiseptics, antibiotics, and anesthetics that are intended for the prevention or treatment of throat infections. These are generally formulated in a concentrated form.

Mouthwash-as-liquid-dosage-form

Mouthwashes– Mouthwashes are aqueous solutions which are in pleasant taste and odor intended for local treatment of the membranous lining of the mouth and gums. These are generally containing antibacterial agents, alcohol, glycerin, sweetening agents, flavoring agents, and coloring agents.

Throat paints- Throat paints are viscous liquid preparations that are applied with the help of a brush to the mucosa of the mouth or throat. Glycerin is commonly used base in throat paints because it possesses a sweet taste and it adheres to the mucous membrane for a long period.

Eye-drops-as-liquid-dosage-form

Eye drops– Eye drops are sterile solution or suspensions of drugs which are instilled into the eye with the help of a dropper. These are usually made in an aqueous vehicle. These should be isotonic with lachrymal secretions, buffered and free from foreign particles to avoid irritation to the eye.

Eye lotions– Eye lotions are sterile aqueous solutions which are used for washing the eye. These are supplied in concentrated form and are required to be diluted with warm water immediately before use. These are generally used to remove foreign substances from the eye.

Ear-drops-as-liquid-dosage-form
Source-internet

Ear drops– Ear drops are medicated solutions of drugs that are instilled into the ear with the help of a dropper. These are usually used for cleaning the ear, softening the wax, and for treating the mild infections in ears.

Nasal-drops-as-liquid-dosage-form
Source-internet

Nasal drops and sprays– Nasal drops are solutions of drugs which are instilled into the nostrils with the help of a dropper. These are the same preparations as nasal drops but instilled into the nostrils in the form of a spray. Both formulations intended for administration to the nasal cavities to obtain a systemic or local effect.

Douches– Douches are liquid preparations that are used to cleanse deodorize, soothe or medicate wounds, body orifices, or cavities.

enema bag with douche syringe
Enema-bag-with-douche-syringe

Enemas– Enemas are liquid preparations which often formulated as solutions though they may be presented as an emulsion or suspension and intended for rectal administration. These are used for cleansing, therapeutic or diagnostic purposes.

Parenteral Solutions for Injection use-

Parenteral solutions are sterile drug solutions which are intended for administration through needle or pressure syringe. Through injection drugs may be injected into most any vessel or tissue of the body, but the most common routes are intravenous (IV), intramuscular (IM), and subcutaneous (SC).

Parenteral Solutions for Injection use-

These may be in small-volume injections, and packaged in ampules for single-dose administration, vials for multiple-dose injections. In large-volume parenteral containing 100 ml to 1 liter of fluid, which are intended for the slow intravenous administration or infusion of medications and nutrients in the hospitalized or home care setting.

Biphasic liquid dosage forms

Biphasic liquid dosage forms are those ones which contain two phases. A good example of biphasic liquid dosage forms is suspensions and emulsions.

Suspensions– Suspensions are biphasic liquid dosage forms which are containing essentially insoluble finely divided solid particles or drugs that suspended with the help of a suspending agent in a liquid medium. These forms of medicament are in finely divided solid particles that dispersed in a liquid or semisolid vehicle. The solid particles act as a disperse phase whereas liquid vehicle acts as the continuous phase.

These are generally taken both orally or parental route. These are used for external applications also. Many forms of suspensions are supplied as dry powders which are converted into suspensions by adding a specified amount of vehicle before use. This process is done to ensure the stability of the suspension.

For example- Ampicillin for oral suspensions, Barium sulfate suspensions, Insulin zinc suspension, etc.

Emulsions– Emulsions are biphasic liquid preparation that containing two immiscible liquids usually oil and water, where one of which is dispersed as minute globules into the other and rendered homogeneous by the addition of an emulsifying agent. The liquid which is converted into minute globules is called the disperse phase and the liquid in which the globules are dispersed is called the continuous phase.

Generally, two immiscible liquids are cannot be dispersed for a long period, so an emulsifying agent is added into the system. These are forming the film around the globules in order to scatter them indefinitely in the continuous phase so that a stable emulsion is formed.

Emulsions are of two types-

-Oil in water type (o/w)- The forms of emulsions in which oil is in the dispersed phase and water is in the continuous phase.  These emulsions are preferred for internal use. In o/w emulsions gum acacia, tragacanth, methylcellulose, saponins synthetic substances, and soaps are formed from monovalent bases such as sodium, potassium which are used as an emulsifying agent.

-Water in oil type (w/o)- The forms of emulsions in which water is in the dispersed phase and oil is in the continuous phase. Wool wax, resins, beeswax, and soaps formed from divalent bases such as calcium, magnesium, and zinc which are used as an emulsifying agent. The w/o emulsions are mainly used externally in the form of lotions or creams.

Excipients in liquid dosage forms-

Excipients are the components of a formulation other than the active ingredients. These may be the natural or synthetic substance that is combined with the drug for the purpose of long-term stability, making up a formulation that contains a drug or to confer a therapeutic enhancement on the drug in the final dosage form.

Oral liquid formulations are prepared by combining different ingredients to perform functions like wetting and solubilization, stabilization, and to impart suitable color, taste, and viscosity. The formulations are should be compatible, non-reactive, and stable. The common excipients that are required for any liquid formulation are-

-Vehicles

-Solubilizers

-Preservatives

-Stabilizers

-Organoleptic agents

Vehicles

Solvents– In liquid dosage formulations, vehicles or solvents are major components that are used as a base in which drugs and other excipients are dissolved or dispersed. These function by breaking of bond and reducing the effective charge on ions thus increasing solute-solvent forces of attraction which are eventually greater than solute-solute and solvent-solvent forces of attraction. For example- water, hydro-alcoholic liquid systems, polyhydric alcohols, acetic acid, ethyl acetate, and buffers.

Co-solvent- Co-solvents are water-miscible organic solvents that are used in liquid drug formulations to increase the solubility of poorly water-soluble substances or to enhance the chemical stability of a drug. Co-solvent increases the solubility of a drug. Other co-solvents are sorbitol, glycerol, propylene glycol, and syrup.

Solubilizers

Solubilizers are used to increase the solubility of the drug. In solubilizer wetting agents and surfactants are used. In solubilizer, wetting agents are used to creates a homogenous dispersion of solid particles in a liquid vehicle. Wetting agents are surfactants that when dissolved in water, that lower the contact angle and aid in spreading water on the particle surface to displace the air at the surface and helps in wetting and solubilization. For-

-pH adjustment

-Co-solvency

-Complexation

-Preservatives

Preservatives are added to prevent microbial growth and necessary due to the chance of microbial growth. The majorities of Liquid Dosage For preservatives are of both acid and non-acid types and are bacteriostatic rather than bactericidal. Preservatives must have the following criteria-

Effective against a broad spectrum of microorganisms.

Preservatives are used for physically, chemically, and microbiologically stable for the lifetime of the product.

These are non-toxic, non-sensitizing, soluble, compatible, and with acceptable taste and odor.

Acidic– phenol, benzoic acid, sorbic acid

Neutral preservatives– chlorobutanol, benzyl alcohol

Quaternary ammonium compounds– Benzalkonium chloride

Stabilizers-

Oxidation, photolysis, solvolysis, and dehydration are common transformations taking place in liquid dosage forms. Amongst them for oxidation and photodecomposition of drugs are very common pathways of drug decomposition and are very difficult to control due to low activation energies. Trace amounts of impurities, which are invariably present in the drug or excipient initiate the oxidation reaction. Drugs that exist in reduced form show increased susceptibility when it is consistently exposed to an open environment. The pH of the solution may contribute to the oxidation of drugs because ionized forms of these drugs at particular pH are very prone oxidation.

Antioxidants

Antifoaming agents

Suspending and Viscosity Enhancing Agents

Humectants

Flocculating agents

Chelating agents

-Organoleptic properties-

Flavoring agents– Flavoring agents are an agent in liquid pharmaceutical products which is added to the solvent or vehicle component of the formulation in which it is most soluble or miscible. In liquid Dosage Form, the flavor in natural origins such as peppermint, lemon, herbs, and spices are also available as oils, extracts, spirits, or aqueous solutions.

Sweetening agent– Sucrose enhances the viscosity of liquids and also gives a pleasant texture in the mouth. The term sugar-free solution includes sweetening agents such as sorbitol, mannitol, saccharin, and aspartame as an alternative to sugar such as sucrose, fructose. Sugar in the form of sucrose and sugar substitutes in artificial sweeteners. There are one of the most popular is the sorbitol solution, which contains 64% w/w sorbitol.

Coloring agent– Coloring agents are generally natural or synthetic water-soluble, photo-stable ingredients that are selected according to the flavor of the preparations. For example- mint-flavored formulations are commonly a green color, whereas in banana-floured solutions a yellow color is commonly employed.

You may read- Drug dosage form.

Advantages of liquid dosage form

-The active agent in liquid dosage forms is homogeneously dispersed throughout the product.

-The active agent of liquid dosage forms is in solution and does not need to undergo dissolution. Therefore, the therapeutic response is generally faster than solid dosage forms.

-The dose of the active agent in liquid dosage forms is easily and conveniently adjusted by measuring a different volume.

-Liquid dosage forms in solution may be swallowed by patients, who have difficulty taking tablets or capsules, as might be the case with pediatric or geriatric patients.

-Such drugs like-potassium chloride may cause ulceration to the mucosa in the form of a tablet which avoids this side effect when present in solution form.

-Drugs in the bitter and unpleasant taste can be given in sweetened, colored, and flavored vehicles.

-Drugs in the form of hygroscopic and deliquescent medicaments that are not suitably dispensed in solid dosage form they may easily be given in liquid dosage form.

-Drugs like adsorbents and antacids are more effective in the form of the liquid dosage form.

-The liquid dosage form is expected for certain types of products like-cough medicaments and others.

Disadvantages of liquid dosage form-

-The active ingredients in liquid dosage forms, when present in solution, are usually more susceptible to chemical degradation which particularly hydrolysis, and then when they are in a solid dosage form.

-The shelf-life of a liquid formulation is often much shorter than that of the corresponding solid formulations.

-In liquid formulation solutions often provide a suitable media for the growth of microorganisms and may, therefore, require the incorporation of a preservative.

-Liquid formulations are bulky and therefore they are inconvenient to transport and store.

-Liquid formulations may require special storage facilities such as antibiotic suspension.

-The taste of a drug, which is usually unpleasant, is always more prominent when in solution than in a solid form.

-The delivery of the liquid formulation in dose depends upon the patient measuring the proper volume. This can be a significant issue for vision-impaired patients, patients with arthritis, or patients unable to read the numbers on an oral dosing syringe or medicine cup.

-The solution is often susceptible to microorganisms, and therefore preservative is frequently incorporated into the formulation. Some patients may be allergic to certain preservatives.

-Two incompatible drugs cannot be dispensed together as it is possible in case of solid dosage forms.


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