Jason Sparks, Austin Community College
Alligations Podcast
The foundations of medicine and pharmacy are based upon the ancient practices of apothecaries, religious figures and folklore. Those who were entrusted with the well-being of the community took responsibility to prepare the necessary remedies to ensure successful treatment of their patients. In the early 20th century it was the responsibility of the pharmacy to prepare requested medications in specified strength and dosage forms for patient use. It was not until the last half of the 20th century that pharmaceutical companies began to mass produce ready-to-use medications.
Now, while the majority of the pharmaceuticals arrive in the pharmacy already prepared, there are many occasions where a tailored dosage form or strength is required to successfully treat a patient. This process is known as extemporaneous compounding, or the on-demand preparation of a pharmaceutical product for a specific patient at the request of their prescriber. In the practice of compounding many mathematical processes may be used to determine the appropriate amount of ingredient necessary to prepare the new preparation. One such process is known as alligation.
Alligation is used when creating new liquid or new semi-solid preparations from two readily available products. Examples of medical products created using alligation include preparing a new strength of various products, such as ammonia, isopropyl alcohol, dextrose solutions, powders, ointments, lotions or other semi-solids.
While used in pharmacy practice, the process of alligation may also be applied at home. For example, when shopping at the grocery store, many people choose to purchase 2% milk due to its low fat content, however, the same 2% milk may be prepared by combining two existing products in a specific quantity determined by using alligation. As long as one product has a higher concentration of active ingredient and the other product has a lower concentration of active ingredient, in the case of milk it's the fat content, the requested, or desired strength may be prepared.
For example, one may prepare milk in any desired concentration of fat content (such as 1.5%, 1%, 2%, etc) from skim milk (being 0% fat content), and whole milk (being 4% fat content) by combining the two products in a specific quantity which is determined through the alligation process. You may use the process of alligation to adjust the strength or concentration of nearly any product either in the pharmacy or in the home. Alligation is widely used in pharmacy practice in the art of extemporaneous compounding.