Roman numerals are often used on prescriptions as they are challenging to alter, whereas decimals are also used elsewhere in pharmacy practices. The following equations can be used to convert degrees Fahrenheit to Celcius and vice versa :ĭegrees C to degrees F: Divide by 5, then multiply by 9, then add 32ĭegrees F to degrees C: Subtract 32, then multiply by 5, then divide by 9 Some commonly used conversions are:Ĭonversion calculations may also occur in other measurements, such as time and temperature. quantity, conversions are required between the US Customary System and the metric unit system. It is important to know units within each system (such as 1 pound = 16 ounces). This issue also impacts patient care as patients may use the household and avoirdupois systems when using their medications (teaspoons and tablespoons), although the medication was dispensed in mL. these factors must be accounted for when computing calculations and consistency when converting units across different measurement systems is important in maintaining accuracy in pharmacy calculations. ĭrugs may be administered through various routes of administration, oral, IV, IM, parenteral, etc. Vitamin D, for instance, is administered in International Units. Powdered substances mixed with a solid or semisolid (ointments) would be calculated as w/w.Īccurate pharmacy calculations prevent medical errors underdosing a patient may lead to inadequate treatment, and overdosing a patient may lead to drug toxicity.Īdditionally, pharmacy calculations require the knowledge of commonly used units certain medications are dispensed in metric system units such as mg or mL, whereas others may be dispensed in other measurement systems.

Percent weight in weight (w/w): Is the number of grams in 100 grams of solution and is expressed as %w/w. A liquid component in a liquid preparation would be calculated on a v/v basis. Percent Volume in Volume (v/v): Is the number of milliliters in 100 mL of solution and is expressed as %v/v. Powdered substances suspended in a liquid vehicle would be calculated as w/v. Percent Weight in Volume (w/v): Is the number of grams in 100 mL of solution and is expressed as %w/v. The following units express percent based on the nature of the ingredient: Percent strength represents the number of grams contained in 100 mL of product and is very useful in pharmacy calculations. Normal saline has a concentration of 0.90% w/v of NaCl in sterile water and therefore is an isotonic crystalloid. It is important to note that when two solutions have equal osmotic pressure and salt concentration, they are said to be isotonic. Thus, if a solution requires a dilution, the active drug in the solution will remain constant, but the volume will increase. The relationship between concentration and volume is inversely proportional. (See Figure 1 for a schematic of the inverse relationship between percent of concentration or ratio strength (decreases), and the total quantity of product (increases)).

Total IV Volume/Time (hour or minute) = mL per hour or minute x Stock Volume = Amount of Solution to be given The following pharmacy calculations are used to determine the dose and dispense drugs in the correct concentrations :ĭesired Dose/Stock Strength = Number of Tablets

If the specific gravity is known, the volume or weight of the desired quantity can be determined. Specific gravity = number of grams of a substance/number of milliliters of a substance.

Specific gravity refers to the ratio of the weight of a substance to the weight of an equal volume of water at the same time. The following definitions can aid in preparing and administering pharmacological drugs.Ĭoncentration is the amount of active ingredient per total weight of a substance.Īlligation involves mixing solutions or solids of varying strengths to obtain another strength of the active ingredient in both. Health care professionals must dispense drugs in the accurate concentrations, calculate correct doses, and compound and prepare medications accurately to ensure that each particular drug is being administered correctly.ĭose refers to the amount of medication taken at a specific time, whereas the dosage of the drug refers to the administration of a frequency, amount, and the number of doses taken over a particular period of time. Utilizing pharmacy calculations to administer therapeutics to patients correctly is vital to patient treatment.

Medication math calculator