Pharmaceutical solutions may be generally defined as liquid preparations in which the therapeutic agent and the various excipients are ...
Pharmaceutical solutions may be generally defined as liquid preparations in which the therapeutic agent and the various excipients are dissolved in the chosen solvent system. Pharmaceutical solutions may contain a range of excipients, each with a defined pharmaceutical purpose. Examples of these include
- the vehicle, usually purified water
- co-solvents, e.g. propylene glycol,
glycerin, alcohol
- agents specifically to enhance the solubility of the therapeutic
agent in the vehicle, e.g. surface-active agents
- preservatives, e.g. parahydroxybenzoate esters (methylhydrox-
ybenzoate and propylhydroxybenzoate), boric acid and borate
salts, sorbic acid and sorbate salts, phenolics
- sweeteners, e.g. glucose, saccharin, aspartame
- rheology (viscosity) modifiers, e.g. hydrophilic polymers
(cellulose derivatives, alginic acid, polyvinylpyrrolidone)
- antioxidants, e.g. sodium formaldehyde sulphoxylate,
butylated hydroxyanisole, butylated hydroxytoluene
- buffers to regulate the pH of the formulation, e.g. citrate
buffer
Advantages and disadvantages of pharmaceutical solutions
Advantages
- Therapeutic agents can easily be administered orally to
individuals who have difficulty in swallowing, e.g. elderly
patients, infants.
- The therapeutic agent is dissolved in the formulation and is
therefore immediately available for absorption. Providing the
drug does not precipitate within the gastrointestinal tract, the
bioavailability of pharmaceutical solutions is greater than that
of oral solid-dosage forms.
- Taste-masking of bitter therapeutic agents may be readily
achieved.
- Easy to swallow than solid dosage forms, which are particularly acceptable to pediatric and geriatric use.
- A drug solution is now available for absorption. Therefore, the therapeutic response is faster than a solid dosage form that require dissolution step before drug absorption takes place.
- A solution is a homogeneous system with uniform drug distribution throughout the preparation. In the suspension or emulsion formulations of unequal dosing can occur due to phase separation during storage and agitation is needed before use.
- gastric contents diluted by reducing irritation of the gastric mucosa caused by high local concentration of some drugs (aspirin, KCl) when administered as a solid dosage form
Disadvantages
- Pharmaceutical solutions for oral administration are
unsuitable for therapeutic agents that are chemically unstable
in the presence of water.
- The poor solubility of certain therapeutic agents may prohibit
their formulation as pharmaceutical solutions. The reader
should note that certain techniques are available to enhance
the solubility of poorly soluble drugs. These will be
highlighted later in this chapter.
- Pharmaceutical solutions are expensive to ship and are bulky
for the patient to carry due to the associated mass of the
product
- Liquids are bulky and are therefore inconvenient to transport and store. Moreover, immediate lose of the whole product occurs in case of breakage of the container.
- Poor stability of the ingredients in aqueous environment of solutions compared to that formulated as a tablet or capsule, which is particularly important for drugs susceptible to hydrolysis.
- Solutions often provide suitable media for the growth of microorganisms and may therefore require the incorporation of a preservative.
- Accurate dosage will depend on the ability of the patients to use a 5 ml spoon or, more rarely, a volumetric dropper. Inaccurate dosing may lead to loss of the therapeutic efficiency.
- The unpleasant taste of drugs is more pronounced in solutions than when in a solid form. Sweetening agents & flavors can be used to make solutions more palatable.
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