Editorial: Quality Assurance in Compounding, Part X

United States Pharmacopeia (USP) Chapter <785> Osmolality and Osmolarity

Osmotic pressure plays a critical role in physiological processes and is a factor that must be considered in most parenteral as well as some oral liquid preparations. The osmotic pressure of a solution depends upon the number of "particles" (molecules or ions) in solution and is a colligative property like melting point, freezing point, vapor pressure, etc. Osmolality is expressed in osmoles or milliosmoles per kilogram of solvent (Osmol per kg or mOsmol per kg), and osmolarity is expressed in osmoles or milliOsmoles per liter of solution. (Note that osmolality is based on a kilogram of solvent and osmolarity is based on a liter of solution.)

Apart from the goal of preparing solutions with a desired osmolality in the range of 285 to 310 mOsmol per kg (corresponding to 0.9% sodium chloride solution), this test method can also be used as a quality check for solutions. When the same solution is prepared repeatedly, its osmolality can be quickly checked to confirm it is within the range it should be. This quality check for some preparations may result in an osmolality outside the physiological range of 285 to 310, but it can still be used. For example, if an oral solution is prepared quite often, and it has an osmolality of about 750 mOsm/kg, then as batches are prepared, they can be quickly tested to confirm they are in this range. This does not give information regarding the concentration of a specific ingredient but is an overall check of the preparation, for information such as pH, viscosity, specific gravity, etc. When working with single-ingredient solutions, however, osmolality can be correlated with concentration of the ingredient for additional quality-assurance applications in the pharmacy.

Osmometers are generally of the vapor pressure or freezing point depression types. These instruments have a small footprint (1 sq ft), require minimal maintenance, and a sample size of about 50 �L (so there is no real loss in the amount of preparation compounded). It takes less than 2 to 5 minutes to perform a test with minimal set up and clean up required.

Osmolality and osmolarity are two characteristics that are directly applicable to a quality-assurance program in some compounding pharmacies.


Loyd V. Allen, Jr., PhD, RPh
Editor-in-Chief

As many of you are aware, Spectrum is conducting a voluntary recall of certain lots of Caffeine, Citrated Powder, Purified. We received one request to verify the assay of this material and determined that the lots in question meet labeled specifications. Due to the fragile nature of patients for which this is used, Spectrum elected to conduct this voluntary recall. If you have any questions regarding this recall, please feel free to contact Spectrum at 800-791-3210, extension 349, and ask for Steve Newton.

Regards,

Erik Tosh, RPh, FACA
Director
Spectrum Pharmacy Products
800-791-3210 Extension 247

USP is conducting a survey regarding compounded medications used in pediatric and geriatric patients to determine the most frequently compounded medications and how often these medications are requested. USP is interested in providing quality standards for compounded medications in order to assist those practitioners who provide this service to patients, and to ensure that the medications compounded are safe for patients and consumers. For more information see http://www.usp.org/hqi/pharmInfo/compoundingPharmSurvey.html

This week 43 citations and abstracts on the topic of androgen replacement in men have been added to CompoundingToday.com's literature search database. See the complete list at www.compoundingtoday.com/Articles/SearchResult.cfm?Batch=122

Easier Pouring
When pouring liquid from a large beaker into a small orifice container, place a glass rod (hold in place with tape or the finger) over the top of the beaker such that it rests in the middle of the spout and bisects the top of the beaker. The rod should extend out over the spout about one or two inches. When pouring, the glass rod will guide the liquid to the end of the rod that should be placed over the container opening. With a little practice, low-viscosity liquids (alcohol, etc.) can be easily poured with little or no loss.