Follow
Consistency of contents (dose to dose and bottle to bottle within the same bottle) :All doses dispensed from a given multidose container should have acceptable uniformity of drug content. In addition, the drug content must be identical between different bottles of a given batch of emulsion.
Separation volume or creaming :Once an emulsion is left undisturbed for some time, it may show separation of the dispersed phase from the dispersion medium. For example, in the case of an o/w emulsion, creaming of an emulsion is sometimes observed, indicating a higher concentration of the dispersed oil phase in the upper layer of the emulsion. This upper layer is visually distinguishable from the lower layer due to greater light opacity and scattering by the higher concentration of dispersed phase globules. The higher the concentration of the dispersed phase, the greater the light blurring and the greater the instability in a small thickness of the creamy layer. Thus, the ratio of the volume occupied by the separated phase is an indicator of the physical instability of the emulsion. The larger this volume, the more stable the emulsion.
Dispersed phase size distribution :The size distribution of the dispersed phase should remain fairly constant during the shelf life of the emulsion. Brownian motion, movement during handling, and gravitational motion of the dispersed phase lead to collisions of the globules with each other, which can cause aggregation or agglomeration as the dispersed phase increases in size. Changes in the size of dispersed phase globules on storage are indicative of the inherently low physical stability of emulsions.
Drug concentration :In cases where the concentration of the drug in the emulsion is close to the solubility of the drug, temperature fluctuations during storage, preferential evaporation loss of one phase, incompatibility with packaging materials, or
Inadvertent nucleation. Crystal growth can be inhibited by using appropriate solvents and surfactants and by forming an emulsion at a concentration lower than the thermodynamic solubility of the drug. Changes such as drug crystallization or evaporative loss of the continuous phase may reflect changes in drug concentration during storage stability or shelf life.
Amplitude :The use of an emulsion dosage form can improve taste, especially by dissolving bitter drugs in the dispersed phase. However, inclusion of drugs in the dispersed phase may not be sufficient because some drugs inadvertently partition into the continuous phase depending on the partition coefficient (logP) of the compound.
The palatability of emulsions can be increased by using sweeteners, flavors and colorants. In some cases, special taste-masking methods may be required, such as complications. These considerations are, of course, not relevant for parenteral emulsions. In the case of parenteral emulsions, tissue irritation and osmotic pressure are important considerations.
Redispersibility :pA separate or creamy emulsion should redisperse easily with gentle shaking of the container.
Absence of phase separation :Coherence leading to phase separation is irreversible. Although creaming of emulsions is inevitable to some extent, the dispersed phase should not be aggregated and separated from the dispersion medium. It needs to be designed into the formulation using the right surfactant at the right concentration.
Deliverability :The labeled number of doses and the labeled amount of emulsion should be dispensable from a bottle under normal dispensing conditions by the patient. This is usually done by pouring out the labeled dose number from the container and making sure that
The remaining dose can be poured completely over a reasonable period of time.
Flow :The emulsion should not be too viscous to pour freely from the bottle or flow through a needle syringe or IV infusion set (for parenteral emulsion).
Lack of bacterial growth :The use of antimicrobial preservatives may be sufficient for oral and topical emulsions, whereas parenteral, nasal and ophthalmic suspensions must be sterile.
