Active Pharmaceutical Ingredient

An active pharmaceutical ingredient (API) is the active drug substance in a solid pharmaceutical formulation, typically combined with excipients such as binders, disintegrants, and preservatives, whose concentration can be expressed on an as-is, dried, anhydrous, or potency basis depending on the analytical approach used.

Microbial Assay Testing

The active drug in a solid formulation is known as active pharmaceutical ingredient or API. It is very rare that an ingredient is prescribed in pure state for consumption. The ingredient is mixed with other excipients to improve dosagae properties. Some of the commonly used excipients added to tablets and capsules are:

• Emulsifying agents
• Stabilizing agents
• Binders
• Tablet disintegrants
• Viscosity increasing agents
• Sweeteners
• Antioxidants
• Lubricants
• Antimicrobial preservatives
• Colouring agents
• Anti cracking agents

Such additives help achieve the desired properties of the medicinal formulations.

Concentration expression of active ingredient in the formulation

Concentration of the active ingredient termed assay is expressed in four commonly used terms:

As is basis

The expression denotes analysis of the product as it is received. The sample is analysed directly without any drying. For example, if 100 milligram of material is found to contain 98% of API then its assay on’ as is basis’ is reported as 98%

Dried basis

The sample received is pulverized to a fine powder is and dried before being weighed out to prepare the sample solution. This process is performed by heating to 105° to 120°C for specified time and drying in a desiccator to constant weight. Heat sensitive materials can be dried in vacuum over a desiccant such as P2 O5. The water removed is that which is absorbed from the environment and is not chemically bound to the material. Drying in the oven does not necessarily remove bound water or water of hydration.

Anhydrous basis

Anhydrous basis implies that there is no water present in the material before analysis is performed. It means that the sample does not have any absorbed water or bound water such as hydrates.

The sample is weighed as received and residual moisture content, if any, is measured independently by methods such as Karl Fischer titration or Loss on drying. At time of calculation of assay value the water content is subtracted from the sample weight

Potency

Assay and potency are not necessarily the same. Potency has specific reference to the ingredient which has biological activity. It refers to molecules such as biologically active antibiotics, vitamins or optical isomers where one isomer is biologically active and the other optical isomers shows no such activity. For this reason potency can be different from chemical assay and refers to the actual label claim of the active pharmaceutical ingredient in the formulation. Microbial assays are performed to estimate the potency of the drug.

Hope this brief article has served to clear some of your lingering doubts. Please share your views and offer your comments.