Drug Calculations

IV DRUG ADMINISTRATION Drug Calculations November 2007 Drug Calculation Assessment SECTION 1: Units & Equivalences SECTION 2: Calculating dose as volume SECTION 3: Drug Strengths & Stated Concentrations SECTION 4: Duration of Infusion – Stated rate (dose per min) & Infusion rate (mL/hr) SECTION 5: Infusion Rate Calculations SECTION 1: Units & Equivalences 1 Kg = 1,000 g 1 g = 1,000 mg 1 mg = 1,000 micrograms 1 L = 1,000 mL Converting from One Unit to Another To convert from a larger unit to a smaller unit, multiply by 1000 or move the decimal point three places to the right To convert from a smaller unit to a larger unit, divide by 1000 or move the decimal point three places to the left Units & Equivalences Convert 0.25 mg into micrograms Convert 600 micrograms to mg Answers 0.25 × 1000 or move decimal point three places to the RIGHT = 250 micrograms 600 ÷ 1000 or move the decimal point three places to the LEFT = 0.6 mg SECTION 2: Calculating Dose as Volume What you WANT X what it is IN What you have GOT = the volume you want to administer What we WANT Furosemide 250mg/10mL Furosemide Time 0700-0900 ? 1200-1400 Dose 200mg Route IV Start Date 18.05.07 End Date 1600-1800 2200-2400 Other Time Signature of Doctor P.Rescriber What we have GOT What it is IN A patient is prescribed 200mg of Furosemide I.V. The ampoules available contain 250mg in 10mL. What volume containing the drug do you need to administer? Answer What you WANT X what it is IN What you have GOT 200 mg 250 mg × 10 mL = 8 mL SECTION 3: Drug Strengths & Stated Concentrations What you HAVE (mg) CONCENTRATION (mg/mL) = How much fluid is required (Volume) Aciclovir Time 0700-0900 ? 1200-1400 ? Dose 250mg Route IV Start Date 18.05.07 End Date 1600-1800 2200-2400 ? Other Time Signature of Doctor Additional Comments P.Rescriber Final Concentration 5mg/mL A patient is prescribed 250mg of Aciclovir I.V. Aciclovir has to be initially reconstituted with water for injection, then added to a bag of compatible infusion fluid, giving a final concentration of 5mg/mL. How much infusion fluid should be used dilute the reconstituted Aciclovir to achieve this final concentration? What we HAVE CONCENTRATION Answer What you HAVE (mg) CONCENTRATION (mg/mL) 250mg 5mg/mL = 50 mL A 1% (w/v) solution means that in every 100mL of solution you will find 1g of drug. Therefore, how many g of Glucose would there be in 500mL of 5% Glucose? Glucose 5% 500ml Answer A 1% (w/v) solution means that in every 100mL of solution you will find 1g of drug. 100mL = 1g Therefore a 5% w/v must mean that 100mL = 5g Multiply each side by 5 500mL = 25g 1:10,000 strength means that in every 10,000ml of solution you will find 1g of Adrenaline. Therefore, how many mg of Adrenaline would there be in 10mL of 1:10,000 Adrenaline? Answer 1:10,000 means that 1g of adrenaline is dissolved in 10,000mL. 1g = 10,000mL 1000mg = 10,000mL Divide both sides by 1000 1mg = 10mL SECTION 4: Duration of Infusion Stated rate (dose per min) Infusion rate (mL/hr) Stated Rate – dose per min Dose (mg) = Time Rate (mg/min) Furosemide must be administered at a rate no faster than 4mg/minute. How many minutes would it take to give 200mg of this drug? Furosemide Time 0700-0900 ? 1200-1400 Dose 200mg Route IV Start Date 18.05.07 End Date 1600-1800 2200-2400 Other Time Signature of Doctor Additional Comments P.Rescriber Rate of 4mg/minute Furosemide 250mg/10mL Rate (mg/min) DOSE(mg) Answer Dose (mg) = Time Rate (mg/min) 200mg 4mg/min = 50 minutes Infusion rate – mL/hr Volume (mL) = Rate (mL/min) Time (Min) X 60 = Rate (mL/Hr) * Tip if rate is in hours omit “X 60” Omeprazole 40mg/100mL Omeprazole (Losec ®) 40mg is diluted in 100mL of compatible infusion fluid. This infusion has to be given over 20 minutes. What rate should you set the infusion pump at, in ml/hr, to deliver this dose? Answer Volume (mL) = Time (mL/hr) x 60 Rate (hr) 100ml 20 mins x 60 = 300mL/hr Acetylcysteine 7.5g/1000mL Acetylcysteine (Parvolex ®) 7.5g is diluted in 1000mL of compatible infusion fluid. This infusion has to be given over 16 hours. What rate should you set the infusion pump at, in ml/hr, to deliver this dose? Answer Dose (mL) = Time (mL/hr) Rate (hr) 1000 16 = 62.5 mL/hr SECTION 5: Infusion Rate Calculations What you WANT x 60 (60 mins per hr) What you have GOT X what it is IN = the volume you want to administer Glyceryl Trinitrate Time 0700-0900 1200-1400 Dose 25 micrograms/ minute Route IV Start Date 18.05.07 End Date 1600-1800 2200-2400 Other Time Signature of Doctor Additional Comments P.Rescriber Continuous Infusion You are required to give a patient Glyceryl Trinitrate as a continuous I.V infusion at 25 micrograms/minute. You have prepared a 50mg in 50mL infusion. What rate should you set the infusion pump at, in ml/hr, to deliver this dose? What we WANT Glyceryl Trinitrate 50mg/50mL What we have GOT What its IN 60 mins per hr Answer What you WANT x 60 (60 mins per hr) What you have GOT X what it is IN 25 micrograms x 60 = 1500 micrograms/hr 1500 ÷ 1000 = 1.5 mg 1.5 mg x 50mL 50 mg = 1.5 mL/hr