ChemAtlas

Chapter 1

Dosage calculator

Weight-based dosing, tablet and volume counts, infusion rates and concentration conversions — the clinical arithmetic the Chapter 1 objectives ask for.

Frequency codes

QD once a day · BID twice · TID three times · QID four times

20 kgChild · 20 kg200 mg50 kgAdult · 50 kg500 mg90 kgAdult · 90 kg900 mg10 mg/kg/daythen split by frequency:QD ÷ 1 BID ÷ 2TID ÷ 3 QID ÷ 4
Fig. 10An order written in mg per kilogram has to be multiplied by the patient's mass, then divided across the day. Both steps are where the arithmetic goes wrong.
lb
Weight unit
mg/kg/day
mg/kg/day
mg/kg/day

Conversion used

1 kg = 2.20462262 lb. To go from pounds to kilograms, divide.

Each dose

349.266mg

given twice a day

Total per day

698.532mg

patient is 69.8532 kg

Working

  1. 01Convert the weight: 154 lb × (1 kg / 2.20462262 lb)69.8532 kg
  2. 02Daily dose: 69.8532 kg × 10 mg/kg/day698.532 mg/day
  3. 03BID means twice a day, so divide by 2: 698.532 mg ÷ 2349.266 mg per dose

Coursework only

Coursework practice only. Never use this for real dosing — clinical calculations must be verified against the order, the label, and your institution’s protocol.