Unit 4- Health Science: Medical Math

Dose

Amount of medication given at one time.

Dosage

Amount and frequency of medication given on a schedule.

Initial dose

The first dose given to a patient.

Maintenance dose

Regular amount given to maintain the desired effect.

Maximum dose

Highest recommended dose allowed within specified limits.

Lethal dose

An amount of medication capable of causing death.

Roman numerals: I, V, X

I = 1; V = 5; X = 10.

Roman numerals: L, C, D, M

L = 50; C = 100; D = 500; M = 1,000.

Roman numeral subtraction rule

A smaller numeral before a larger one means subtract, e.g., IV = 4.

Roman numeral addition rule

A smaller numeral after a larger one means add, e.g., VI = 6.

1 tsp and 1 tbsp

1 tsp = 5 mL; 1 tbsp = 15 mL.

1 fluid ounce

Approximately 30 mL.

Metric weight conversions

1 kg = 1,000 g; 1 g = 1,000 mg; 1 mg = 1,000 mcg.

Metric length conversion

1 cm = 10 mm.

Pounds to kilograms formula

kg = lb ÷ 2.2.

Kilograms to pounds formula

lb = kg × 2.2.

Fahrenheit to Celsius formula

°C = (°F − 32) × 5/9.

Celsius to Fahrenheit formula

°F = (°C × 9/5) + 32.

Tablet dosage formula

Tablets = ordered dose ÷ dose per tablet.

Liquid medication dosage formula

mL = ordered dose (mg) ÷ concentration (mg/mL).

Weight-based dose formula

Dose (mg) = weight (kg) × prescribed dose (mg/kg).

Weight-based liquid dose formula

mL = [weight (kg) × dose (mg/kg)] ÷ concentration (mg/mL).

Safe dosage range

Acceptable minimum-to-maximum dose; check before administration.

Macrodrip tubing factors

10, 12, 15, or 20 gtt/mL, depending on the tubing.

Microdrip tubing factor

60 gtt/mL.

What does gtt mean?

Drops; gtt/min means drops per minute.

Gravity IV drip rate formula

gtt/min = [volume (mL) × drop factor (gtt/mL)] ÷ time (min).

IV pump rate formula

mL/hr = total volume (mL) ÷ infusion time (hr).

IV infusion time formula

Time (hr) = total volume (mL) ÷ pump rate (mL/hr).

Medication decimal safety

Use a leading zero (0.5 mg); never a trailing zero (5.0 mg).