Foundations: Medication Calculation and Conversions

Vocabulary terms, metric/apothecary/household conversion equivalencies, and dosage calculation formulas covered in the medication calculation lecture.

Microgram (mcg)

A metric unit of weight equal to $0.001\,mg$ ($1{,}000\,mcg = 1\,mg$) or $0.000001\,g$ ($1{,}000{,}000\,mcg = 1\,g$).

Milligram (mg)

A metric unit of weight equal to $1{,}000\,mcg$ and where $1{,}000\,mg = 1\,g$.

Gram (g)

A metric unit of weight equal to $1{,}000\,mg$, $1{,}000{,}000\,mcg$, and where $1{,}000\,g = 1\,kg$.

Grain (gr)

An apothecary unit of weight equal to $60\,mg$.

Cubic centimeter (cc)

A metric unit of volume that is equivalent to $1\,mL$.

Fluid ounce (fl oz)

A household and apothecary unit of liquid volume equal to $30\,mL$.

Standard cup

A household unit of volume equal to $8\,fl\,oz$ or $240\,mL$.

Teaspoon (tsp)

A household unit of volume equal to $5\,mL$.

Tablespoon (tbsp.)

A household unit of volume equal to $3\text{ teaspoons}$ or $15\,mL$.

Pound (lb) to Kilogram (kg) Conversion Factor

The equivalence where $2.2\,lb = 1\,kg$ ($1{,}000\,g$).

Lbs. to Kg Conversion Formula

$$\text{Lbs.} / 2.2 = \text{Kg}$$

Kg to Lbs. Conversion Formula

$$\text{Kg} \times 2.2 = \text{Lbs.}$$

Desired (D)

The amount of medication ordered by the provider to be administered.

Available (A)

The dosage strength of the medication currently on hand or supplied by the pharmacy.

Quantity (Q)

The amount of medication or physical vehicle (such as $1\text{ tablet}$ or a specific volume of liquid) that contains the available dosage strength.

Formula for PO Meds & Injections

$$\frac{\text{Desired}}{\text{Available}} \times \text{Quantity} = X$$

Gravity IV Infusion

The manual method of infusing intravenous medication without an electronic pump, regulated by adjusting a roller clamp and counting drops in the drip chamber per minute.

Formula for Drops per Minute (IV gtt/min)

$$\frac{\text{Total Volume to be Infused}}{\text{Total Amount of Time in Minutes}} \times \text{Drop Factor} = X$$

Macrodrip Tubing Set

An intravenous tubing set that delivers large drops, commonly calibrated to drop factors such as $10\,drops/mL$ or $15\,drops/mL$.

Microdrip Tubing Set

An intravenous tubing set that delivers very small drops with a drop factor of $60\,drops/mL$.