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.
In pharmaceutical solutions both the therapeutic agent and the excipients are legally required to be present in solution over the shelf-life of the formulated product. As a result pharmaceutical solutions are termed homogeneous. One of the major challenges to the pharmaceutical scientist is the attainment of homogeneity in the formulation, due primarily to, in many cases, the limited aqueous solubility of the therapeutic agent. There are three principal types of solution formulations that are administered orally: oral solutions, oral syrups and oral elixirs. In addition, other solution formulations are employed for a local effect, e.g. mouthwashes/gargles and enemas
Oral solutions are administered to the gastrointestinal tract to provide systemic absorption of the therapeutic agent. Due to the resilience of the gastrointestinal environment, oral solutions may be formulated over a broad pH range. However, unless there are issues regarding the solubility or stability of the therapeutic agent, the usual pH of oral solutions is circa 7.0
Syrups are highly concentrated, aqueous solutions of sugar or a sugar substitute that traditionally contain a flavouring agent, e.g. cherry syrup, cocoa syrup, orange syrup, raspberry syrup. An unflavoured syrup is available that is composed of an aqueous solution containing 85% sucrose. Therapeutic agents may either be directly incorporated into these systems or may be added as the syrup is being prepared. If the former method is employed, it is important to ensure that the therapeutic agent is soluble within the syrup base.
Simple syrup: when water is used alone for making syrup.
Medicated syrup: when the aqueous preparation contains some added medicinal substance. E.g. Chlorpheniramine maleate syrup, Ipecac syrup, Chloral hydrate syrup Flavored syrup: which contains aromatic or pleasantly flavored substances and is intended to be used as a vehicle or flavor for prescriptions, e.g. Cherry Syrup, Cocoa Syrup, Orange syrup, Raspberry Syrup.
An elixir is a clear, hydroalcoholic solution that is formulated for oral use. The concentration of alcohol required in the elixir is unique to each formulation and is sufficient to ensure that all of the other components within the formulation remain in solution. For this purpose other polyol co-solvents may be incorporated into the formulation. The presence of alcohol in elixirs presents a possible problem in paediatric formulations and, indeed, for those adults who wish to avoid alcohol.
Linctuses are viscous preparations that contain the therapeutic agent dissolved in a vehicle composed of a high percentage of sucrose and, if required, other sweetening agents. These formulations are administered orally and are primarily employed for the treatment of cough, due to their soothing actions on the inflamed mucous membranes. Linctuses may also be formulated as sugar-free alternatives in which sucrose is replaced by sorbitol and the required concentration of sweetening agent. The dose is small (5ml) and, to ensure prolonged local action, linctuses should be taken undiluted and sipped and swallowed slowly.
Mouthwashes and gargles
Mouthwashes/gargles are designed for the treatment of infection and inflammation of the oral cavity. Formulations designed for this purpose employ water as the vehicle, although a co-solvent, e.g. alcohol, may be employed to solubilize the active agent. The use of alcohol as a co-solvent may act to enhance the antimicrobial properties of the therapeutic agent.
They are dilute, usually saturated, aqueous solutions of volatile oils (e.g. peppermint oil, cinnamon oil) or volatile substances (e.g. camphor). Aromatic waters are also known as medicated waters.