Dosage Calculations: A Comprehensive Guide with Practice Problems, Study Guides, Projects, Research of Nursing

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6 Steps to Master Dosage Calculations

Dimensional Analysis

LIST OF CONVERSIONS LIST OF CONVERSIONS 1 kg = 2.2 lbs 1 ml = 1 cc IV Flow Rate = ml/hr 30 ml = 1 oz 5 ml = 1 tsp IV Drip Rate = drops(gtts)/min 15 ml = 1 tbsp IV Drop Factor = drops(gtts)/1 ml 1 kg = 1000 gm 1 gm = 1000 mg 1 mg = 1000 mcg 1 L = 1000 ml 1 tbsp = 3 tsp 1 cup = 8 oz 2 cups = 1 pint 2 pints = 1 quart

60 min = 1 hr Step 1 - what do you need? Step 2 - what is the order? Step 3 - what conversions do you need? Step 4 - Solve Step 5 - Round appropriately Step 6 - Check your work

Med Conversions

Ex: Physician ordered 1 liter normal saline to infuse over 8hrs, IV tubing used is 20 drops her mililiter. How many drops her minute will be infused? Order Have Need ______ X _____ = ______ 5 and above you round up to next whole number, 4 and below round down 1L/8hrs x 20gtts/1ml x 1000ml/1L x 1hr/60mins = 20,000/480 = 41.6gtts/min  42 gtts/min Ex: patient had 3 oz of orange juice, how many mililiters is that? 30ml/1oz x 3oz = 90ml Ex: Physician orders Ampicillin 250 mg PO, bottle of liquid ampicillin informs the nurse that every 5 ml contains 100 mg of the drug. How many ml will the patient receive? Order : 250 mg

Ex: Dilantin 11,000mg PO is ordered to be given through NG. It is available as 0.017kg per 13 ml. How much would the nurse administer? Order:11,000mg Available: 0.017kg/13ml 13ml/0.017kg x 1kg/1000g x 1g/1000mg x 11,000mg = 8.4ml Ex: The Nurse is to give Gentamicin 100mg IM. The pharmacy sends a vial labeled 0.5 grams per 5 ml. How many ml will the nurse give? Order: 100mg Available: 0.5g/5ml 5ml/0.5g x 1g/1000mg x 100mg = 1ml

IV Flow Rate ml/hr

Ex: You have an order for 0.23L NS to infuse in 624 minutes by infusion pump. What is the IV flow rate in ml/hr? Order: 0.23L/624min Need:ml/hr 1000ml/1L x 0.23L/624min x 60mins/1hr = 22.1ml/hr Ex: A heparin drip comes premixed from the pharmacy with 25,000 units in 5000ml of NS. The physician orders 1500 units per hr. How many ml will the nurse give per hour? Order: 1500 units/hr Available: 25,000 units/ 500ml

500ml/25,000units x 1500 units/1hr = 30 ml/hr

IV FLOW RATE ML/HR WITH WEIGHT

Ex: Doctor orders patient to start IV heparin drip at 18 units/kg/hr and to administer a loading bolus does of 30 units/kg IV before starting drip. Heparin bag reads 25,000 units per 500ml. Patient weighs 172lbs. What is the IV flow rate in ml/hr and how many units administered for IV bolus?

1. CONVERT WEIGHT FIRST / CALCULATE BOLUS 172lbs /2.2kg = 78.2kg Loading bolus: 30units/kg 30units/1kg x 78.2kg = 2345.5 units for Bolus
2. FIGURE OUT CONVERSION FOR FLOW RATE Ordered: 18 units/kg/hr Available: 25,000 units/ 500 ml 500ml/25,000 units x 18units/1kg x 78.2kg/1hr = 28.2 ml/hr IV flow rate

IV DROP FACTOR drops(gtts)/1ml (DRIP RATE = FLOW RATE)

Ex: Calculate the IV flow rate for 0.22L NS over 14hrs. Infusion set has a drop factor of 4 drops. What is the drip rate? 4drops/1ml x 1000ml/1L x 0.22L/14hrs x 1hr/60mins = 1.047  1 drop/min Ex: Calculate the IV flow rate for 0.86L NS IV over 6.4hrs. Infusion set has a drop factor of 30 drops. What is the IV flow rate in drops/min?

DOSAGE SAFETY CALCULATION

Ex: Provider orders Digoxin 0.92mg daily for child that weighs 16lbs. Safe dosage is 8- 12mcg/kg/day. Is this a safe dosage for this child?

1. CONVERT WEIGHT 16lbs/2.2 kg = 7.3kg Order: 0.92mg/day Safe Dose: 8-12mcg/kg/day 1000mcg/1mg x 0.92mg= 920mcg Is this dose safe? LOW SAFE DOSE 8mcg/1kg x 7.3 kg/ 1day= 58.4mcg HIGH SAFE DOSE 12mcg/1kg x 7.3kg/1day = 87.27mcg NO NOT A SAFE DOSE!

PO/IM PRACTICE PROBLEMS

PO/IM #1 - The doctor orders 122.5mg of ibuprofen to be given PO q6h. The oral suspension available contains 100mg/5ml. How many ml should be administered? PO/IM #2 - The doctor orders 650mg of acetaminophen to be given PO q4h. The pharmacy has 325mg tablets available. How many tablets should be administered?

PO/IM #3 - The doctor orders 62.1mg of acetaminophen to be given PO q4h. Recommended dosage is 15mg/kg/dose. You have 160mg/5ml solution available. How many ml will be administered? PO/IM #4 - 7,500 units of Heparin is ordered to be given SC q12h. The available solution contains 10,000units/mL. How many mL should be injected? PO/IM #5 - 10 units of SC insulin is ordered to be administered every evening. You have a bottle of 100units/mL insulin. How many mL will you administer? PO/IM #6 - 500mg of ciproüoxacin is ordered to be given PO q12h. 250mg tablets are available in the pharmacy. How many tablets will you administer? PO/IM #7 - 500mg of ciproüoxacin is ordered to be given PO q12h. A 250mg/5mL suspension is available. How many mL will be administered per dose? PO/IM #8 - The doctor prescribes 200mg TID of posaconazole to be given PO. A 40mg/mL suspension is available. How many mL will be administered per dose? PO/IM #9 - Lactulose is prescribed with instructions to take 15grams PO daily. A 10g/15mL solution is available. How many mL should be administered? (Round answer to nearest whole number)

Flow #05 - The doctor orders 1,000mL NS to be infused over 8 hours. At how many mL/hr should the IV solution infuse? Flow #06 - The doctor orders 1L NS to be infused over 10 hours. At how many mL/hr should the IV solution infuse? Flow #07 - The doctor orders 1L NS to be infused over 8 hours. At how many mL/hr should the IV solution infuse? Flow #08 - 0.5L of Lactated Ringer is to be infused at a rate of 100mL/hour. At how many hours will it take to infuse? Flow #09 - 1L of Lactated Ringer is to be infused at a rate of 50ml/hour. How many hours will it take to infuse? Flow #10 - The doctor orders 1L D51/2NS with 50mEq K+Cl added to be infused at a rate of 5mEq/hr. At what rate should the IV be set to infuse?

IV DRIP (GTT/MIN) PRACTICE PROBLEMS

Drip #01 - The doctor orders 200mg of erythromycin in 250mL D5W to be infused over 1 hour. The drop factor is 10 gtt/mL. What is the IV rate in gtt/min?

Drip #02 - The doctor orders 150mL of D5W to be infused over 2hr. The drop factor is 20 gtt/mL. What is the üow rate in gtt/min? Drip #03 - The doctor orders D5 LR at 75mL/hr. The drop factor is 10 gtt/mL. At what rate in gtt/min should the IV be regulated? Drip #04 - 1L D5 33% NS has been ordered to be infused over 6 hours. The drop factor is 15 gtt/mL. At what rate in gtt/min should the IV be regulated? Drip #05 - The doctor orders 1,000mL of Lactated Ringer solution to be infused over 16 hours. The drop factor is 15gtt/mL. At what rate in gtt/min should the IV be regulated? Drip #06 - D5 1/2 NS is ordered to be administered at 30mL/hr. At what rate in gtt/min should the IV be regulated when using a microdrip set? Drip #07 - 1L of Lactated Ringer is to be infused at a rate of 100mL/hour. You have a set with drip factor of 20gtt/mL. At how many gtt/min should you regulate the IV? Drip #08 - 250mL of normal saline is to be infused over 2 hours. You have a set with drip factor of 10gtt/mL. At how many gtt/min should you regulate the IV? Drip #09 - 0.5L of normal saline is to be infused at a rate of 30 mL/hour. You have a set with drip factor of 15gtt/mL. At how many gtt/min should you regulate the IV?

Weight #05 - The doctor orders 25mL of acyclovir PO q6h. The patient weighs 120-lbs. The medication comes as 200mg/5mL. The maximum recommended safe dose is 3,200mg/day. Is the ordered dosage safe for this patient? Weight #06 - The pediatrician orders amoxicillin 125mg PO q8h for a 16-pound child. You have available an oral suspension at 125mg/5mL concentration. The safe range is 20-40 mg/kg/day. Is this order in the safe range? Weight #07 - The pediatrician orders amoxicillin 5mL BID for a 22-pound child. You have available an oral suspension at 400mg/5mL concentration. The recommended dosage is 80mg/kg/day. Is this order safe? Weight #08 - The pediatrician orders amoxicillin 2.2mL PO TID for a 12-pound child. You have available an oral suspension at 125mg/5mL concentration. The safe range is 20-40 mg/kg/day. Is this order in the safe range? Weight #09 - A child weighs 15-lb. The recommended dosage of penicillin oral solution for a child is 3.75-12.5 mg/kg q6h. What is the maximum safe daily dosage for this child? (Round to the nearest tenth) Weight #10 - A child weighs 15-lb. The recommended dosage of penicillin oral solution for a child is 3.75-12.5 mg/kg q6h. What is the minimum safe daily dosage for this child? (Round to the nearest hundredth)