DOSAGE CALCULATIONS
I.
Systems of Measurement with Conversion A. B. C. D. Metric System Apothecary System Household System Avoirdupois System
Commonly accepted conversions: _______________________________________________________________________ Metric Apothecary Household ______________ Solid measures: 1 kg 2.2 lb 454 g 1.0 lb 1 g = 1000 mg 15 gr (gr xv) 60 mg 1 gr (gr i ) 30 mg ½ gr (gr ss) Liquid measures: 1 L = 1000 mL 240 mL 30 mL 15 – 16 mL 8 mL 4 – 5 mL 1 mL 0.0 6 mL II. Calculating Dosage: I. Oral Drugs A. Basic formula: Desired dose ( D) On- hand dose (H) X V = Amount to be given (A)
8 f oz (f oz viii) 1 f oz ( f oz i) 4 f dr (f dr iv) 2 f dr ( f dr ii) 1 f dr (f dr ii) 15 -16 min 1 min ( min i)
about 1 quart 1c 2 tbsp 1 tbsp = 3 tsp 2 tsp 1 tsp = 60 gtt
Ex. Order: amoxicillin 100mg PO qid Available: amoxicillin 250 mg / 5 mL D H B. Ratio & Proportion H : V= D :x 250 mg : 5 mL = 100 mg : x 250 x = 500 x = 2 mL x V = A 100 mg x 5 mL 250 mg = 2 mL
C. Fractional Equation (FE) H= D V x 250 mg = 100 mg 5 mL x 250 mg x = 500 mg/mL X = 2 mL
2. Parenteral Drugs Same with oral liquids Ex. Order: oxacillin 250 mg IM q 6H Available: oxacillin 500 mg vial to be reconstituted with 2.7 mL sterile water. D x V = A H 250 mg x 3 mL = 750 mL = 1.5 mL 500 mg 500 3. Intravenous fluids: Method II: Two - step 1. Amount of solution = Hours to administer 2. mL per hour 60 minutes X mL
drop factor ( gtt/ mL) = drops/ minute (gtt/ min)
Ex.
Order: 1000 mL of D5LR to infuse over 12 hours Available: macrodrip set with 10 gtt/ mL & microdrip set with 60 gtt/ mL 1. 1000 mL 12 h = 83.33 mL/h
2. 83.33 mL/ h X 60 minutes
60 gtt/mL = 83 gtt/ min
10% solution = __________grams per mL 5% dextrose in water =
Practice Problems: 1. Ordered: 250 mg tablet
Available: 100 mg scored tablet:
2. Ordered: 6.5 mg 3. Ordered:.2 g
Available : 10 mg / mL Available: 3 gr capsule Available: 600 mg/ 1 f oz
4. Ordered: Robitussin cough syrup 225 mg PO 5 Ordered: Penicillin G 400,000 U IM
Available: Penicillin G 1, 000,000 U in 5 mL
6 You want to administer 0.8 grams of a 10% solution. How many mL should the client receive? 7. Ordered: 500 mL of D5 water in 5 hours. Macrodrip set.
Practice Problems: 1. Ordered:Morphine 10 mg Available Morphine 16 mg/mL 2 Ordered: 150,000 U 3. Ordered: 2 g Available: 400,000 U / 5 mL Available: 1 gr capsule
4. Ordered: Infuse 1000ml in 5 hours. 5. Ordered 1500 mL of D5LR in 24 hours. 6. Ordered: 250 mL of D5W to KVO.