Oral liquid preparations
According to the monograph of the European Pharmacopoeia (Ph. Eur.), Liquid oral preparations are usually solutions, emulsions or suspensions in which the active ingredient or ingredients are dissolved or dispersed in a suitable vehicle. The preparations are intended for oral use.
Advantages and disadvantages of liquid oral preparations
The advantages of liquid dosage forms are that they are easier to take, especially for older patients or children. While elderly patients often have difficulty swallowing, children are often unable to swallow larger volumes, which makes it difficult to take solid medicinal forms such as capsules or tablets. In addition, liquid dosage forms can be flexibly dosed. A serious disadvantage is the susceptibility to microbial contamination in aqueous systems and the limited storage stability.
Dosage forms of the monograph
In addition to the solutions, emulsions and suspensions, the monograph also lists the drug forms syrups and drops. Furthermore, the solid dosage forms powders and granules are also mentioned, which are converted into the liquid dosage forms solutions, suspensions, drops or syrups immediately before use. For example, certain antibiotics are marketed as a powder (dry juice) due to reasons of stability such as hydrolysis or sedimentation . By filling up with water shortly before ingestion, the liquid form of application is created, in this case a suspension. It is important that the drug is distributed homogeneously. Therefore, the container should be shaken before each use.
Solutions consist of the solvent (vehicle) in which drugs and auxiliary substances are dissolved. Solutions can be divided into real solutions or colloidal solutions depending on the size of the dissolved particles . In real solutions, the particles are <1 nm and are thus distributed in the solvent. They are subject to Brownian molecular motion and are physically stable. Colloidal solutions consist of particles in the size range of 1-1000 nm. Examples of this are solutions of polymers such as starch .
Suspensions and emulsions are coarsely dispersed systems with a particle size> 1000 nm. They are physically unstable. This manifests itself through sedimentation processes and the tendency to phase separation . Suspensions are a disperse system of the solid-in-liquid type. The outer phase represents the solvent, the inner phase the insoluble medicaments and auxiliaries distributed in it. Due to the density difference between the outer and inner phases and the particle size, suspensions show the phenomenon of sedimentation according to Stokes' law . Emulsions, on the other hand, are disperse systems of the liquid-in-liquid type consisting of a hydrophilic phase (water) and a lipophilic phase (oil). Because of the interfacial tension and the presence of a phase boundary, these are immiscible. Therefore, emulsions are stabilized by so-called emulsifiers , which due to their amphiphilic molecular properties attach to the phase boundary and thus mediate between the two phases. Depending on the phase in which water and oil are present, one speaks of an oil-in-water emulsion (O / W; outer phase water) or a water-in-oil emulsion (W / O; outer phase oil). Due to the density difference between water and oil creaming and finally, emulsions show phase separation (Stokes law). Solutions, emulsions or suspensions can also be administered in the form of drops. A prerequisite for this is a suitable device on the container such as a dropper or a pipette . Syrups are watery liquids with a viscous consistency and a sweet taste. Sucrose , polyols or other sweeteners are mostly used.
The auxiliaries that are used in the liquid preparations for ingestion serve on the one hand to stabilize the preparation and on the other hand to improve the taste and appearance. For the latter, the use of approved colorings and flavor corrections applies. For the stability of the preparations, among other things, preservatives, emulsifiers, viscosity-increasing additives, wetting agents , buffers and substances to improve solubility are used.
- Alfred Fahr : Voigt Pharmaceutical Technology for Studies and Work. German Apotheker-Verlag, 12th edition, 2015, ISBN 978-3-769-26194-3 .
- Ursula Schöffling and Silvia Grabs: Dosage Forms Theory - A Galenics Textbook for Theory and Practice . 6th, revised and expanded edition 2015. Deutscher Apotheker Verlag. ISBN 978-3-7692-6085-4 .