Archer Pharmacology – Dosage Calculation and Medication Administration Practice Test

The main idea is to convert a given volume of fluid into a rate of drops per minute by using the drop factor. To get drops per minute, combine how much fluid you’re delivering (in mL), how quickly (in minutes), and how many drops come per mL (the drop factor, gtt/mL). The rate in gtt/min is (V × D) / T because mL × (gtt/mL) gives gtt, and dividing by minutes gives gtt/min.

With V as mL, T as minutes, and D as gtt/mL, the correct expression is (V × D) / T, which is mathematically the same as (V/T) × D. For example, if V = 100 mL, T = 60 min, and D = 20 gtt/mL, then rate = (100 × 20) / 60 = 2000/60 ≈ 33.3 gtt/min.

Why the other forms don’t fit: placing time in the numerator or the drop factor in the denominator yields incorrect units (for instance, gtt/min^2 or mL^2/min) and does not represent drops per minute.