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What Are The Different Oral Liquid Dosage Form

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Oral liquid dosage forms are better than tablets or other solid drugs for patients that have difficulty in swallowing. They are a good choice for children and elderly patients. Liquids absorb faster than solids in the body fluids and have more flexibility in achieving the proper dosage of medication. Moreover, liquids are usually more palatable than solids.

There are some shortcomings of liquid dosage forms, however, compared with solid forms. These include: lower stability and often a shorter life, harder to measure dosage accuracy (measuring dose is required), more easily contaminated by micro-organisms, bulky to carry around and easily lost if the container is broken.

Oral liquid dosage forms are commonly divided into two forms – monophasic and biphasic. Each type contains one or more active ingredients within a liquid vehicle, creating a homogenous liquid that can be administered orally either in neat form, or after dilution. The liquid dosage form may contain other substances such as emulsifying, dispersing, solubilizing, stabilizing, suspending, wetting, thickening agents and antimicrobial agents for preservation. The liquids may also contain sweetening agents, flavouring and allowable colouring agents. For paediatric preparation, the concentration of sweetening such as sodium or potassium saccharin should not be more than 5mg/kg of the body weight.

Monophasic liquid forms are essentially homogenous solutions of active ingredient dissolved in water or non-aqueous solvent (e.g., alcohol, glycerine or ether). The most common monophasic forms are:

  • Syrup. The syrup is a viscous oral solution that contains one or more active ingredients. The base contains large amounts of sugar such as sucrose or sorbitol, which can inhibit crystallization, or change the taste, base properties and/or modify solubilization. Syrups that are labelled as sugarless may contain other sweetening agents such as saccharin as well as thickening agents.

Syrups may contain some 95 v/v% ethanol or other solvents to assist with preservation or imparting flavour. Some antimicrobial agent(s) may also be added to the syrup to maintain the quality of the preparation.

Syrups have the following advantages:

  • Ability to disguise the bad taste of medication
  • The thick character of the syrup has a soothing action on irritated tissues of the throat
  • Syrups may contain little or no alcohol
  • Easy to adjust the dose for children

A common form of syrup is the Linctus which is defined as a syrupy or sticky

preparation containing medicaments exerting a local action on the mucous membrane of the throat.

  • Spirit/Essence. This class of dosage forms are alcoholic or hydro-alcoholic solutions of volatile substances. The substance may be solid liquid or gas but when in solution form can be used as flavouring agent or for the therapeutic value of the aromatic solute.
  • Elixir. Elixirs are clear sweetened or flavoured liquid, which contains active ingredients dissolved in suitable base. Elixirs often contain a high percentage of sucrose, and may contain 95% ethanol or diluted ethanol. They are less viscous and sweet than syrups. They are more able to maintain water or alcohol soluble materials in solution than syrups are more stable and easily prepared by simple solution. Conversely they are less able to mask the taste of medicated substances than syrups.
  • Fluid extracts. Fluid extracts are solutions of drugs or therapeutic or nutritional materials usually made by solvent extraction from plant material. Examples are extracts of celery or oats.
  • Mouth wash, Gargles. These liquids are usually aqueous or water-alcohol solutions that are mildly medicated to help address problems with teeth and gums, or with antiseptic to help heal throats.

Biphasic liquid forms are encountered when dissolution of the active ingredient(s) do not dissolve in common solvents. The most commonly encountered are suspensions, emulsions or mixtures.

  • Oral Suspension. The oral suspension is a liquid form that contains active ingredients suspended in a suitable base. Over time, the solid particles may separate but shaking will re-disperse on shaking.
  • Oral Emulsion. This oral liquid contains active ingredients that are unstable in the water phase and but can be stabilized in an oil-in-water dispersions. Either or both of the phases may contain dissolved solids. Both liquid phases may separate but can be mixed by shaking. The preparation is fully stable and can provide a homogenous dose after proper shaking.
  • Mixtures. The oral liquid contains one or more active ingredients that are either suspended or dispersed in suitable base. As with the suspensions or emulsions, the suspended solids may separate but are easily re-suspended on shaking.

Linctus. This viscous oral liquid contains active ingredients that are dissolved in a suitable base and contains high concentration of sugar. This treatment is used for cough treatment and can be taken without water.

The oral liquids are homogenous liquid preparations, which contain an emulsion, solution or suspension of one or more active ingredients that are suitable as liquid base. These preparations are administered either as is or after dilution. The preparations contain other substances such as The oral liquids also contain sweetening agents, flavoring and allowable coloring agents. For paediatric preparation, concentration of sweetening such as sodium or potassium saccharin should not be more than 5mg/kg of the body weight.

During the manufacturing, packing, distribution and storage processes, the microbial quality should be checked as well as the microbial count to make sure that these are at acceptable criteria. The oral liquid should not be diluted or stored after the dilution unless the monograph directs for dilution. The diluted oral liquid might become unstable after a long period physically or chemically; as such, it should be diluted freshly or used as stated on the label.

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