PF1011 Calculations 2 & 3 Notes PDF

PF1011 – Calculations 2 Dr Kevin Murphy [email protected] Sessions 2/3 Overview Introduction to the Session 2 Practice questions on Socrative Demonstration of answers Short 10-minute break Repeat for Session 3 Medicine dispensing Principles Interpreting dosage i...

PF1011 – Calculations 2 Dr Kevin Murphy [email protected] Sessions 2/3 Overview Introduction to the Session 2 Practice questions on Socrative Demonstration of answers Short 10-minute break Repeat for Session 3 Medicine dispensing Principles Interpreting dosage instructions No calculations for the patient Simple measurement Children & dosage forms Dispensing calculations Session 2 Dispensing solid dosage forms Dispensing liquid dosage forms Weight-based dosing Corticosteroid dispensing Dimensional analysis A method for expressing the same quantity in different units Convert 5 in to cm Convert 1 week (wk) to hrs 1) 2.54 𝑐𝑚 = 1 𝑖𝑛 1) 1 𝑤𝑘 = 7𝑑 & 1𝑑 = 24 ℎ𝑟 2.54 𝑐𝑚 7𝑑 24 ℎ𝑟 2) =1 2) =1& =1 1 𝑖𝑛 1 𝑤𝑘 1𝑑 7𝑑 24 ℎ𝑟 2.54 𝑐𝑚 3) 1 𝑤𝑘 ∗ 1 𝑤𝑘 ∗ 1𝑑 = 168 ℎ𝑟 3) 5 𝑖𝑛 ∗ = 12.7 𝑐𝑚 1 𝑖𝑛 Use the method that works for you! (which may not be this one) Dispensing solid dosage forms A prescriptions contains the following: Metformin 1 g tab BD You have a stock of 500 mg. How many tablets will the patient take each day? Correct unit Dose Frequency 𝑡𝑎𝑏𝑠 1 𝑡𝑎𝑏 1,000 𝑚𝑔 1 𝑔 2 𝑑𝑜𝑠𝑒𝑠 4 𝑡𝑎𝑏𝑠 = ∗ ∗ ∗ = 𝑑 500 𝑚𝑔 1𝑔 𝑑𝑜𝑠𝑒 𝑑 𝑑 Dispensing liquid dosage forms A prescriptions contains the following: Ranitidine syrup 150 mg BD You have a stock of ranitidine syrup 15 mg/mL. How many mL will the patient take each day? Correct Dose Frequency unit 𝑚𝐿 1 𝑚𝐿 150 𝑚𝑔 2 𝑑𝑜𝑠𝑒𝑠 20 𝑚𝐿 = ∗ ∗ = 𝑑 15 𝑚𝑔 1 𝑑𝑜𝑠𝑒 𝑑 𝑑 Weight-based dosing A prescriptions for a 10-year old child contains the following: Paracetamol susp 15 mg/kg QDS x 5/7 The susp is available as 200 mg/mL and the child weighs 30 kg. How many mL will be needed for the prescription? Correct unit Dose Frequency Duration 𝑚𝐿 1 𝑚𝐿 15 𝑚𝑔 30 𝑘𝑔 𝐵𝑊 4 𝑑𝑜𝑠𝑒𝑠 5 𝑑 45 𝑚𝐿 = ∗ ∗ ∗ ∗ = 𝑅𝑥 200 𝑚𝑔 1 𝑘𝑔 𝐵𝑊 1 𝑑𝑜𝑠𝑒 1𝑑 𝑅𝑥 𝑅𝑥 Corticosteroid dispensing A prescription contains the following instructions: Prednisolone 30 mg x 6/7. Reduce by 5 mg every 6 days until 0. Q. Calculate how many Prednisolone 5 mg tablets should be supplied to fill the prescription? Day Day Day Day Day Day 1 2 3 4 5 6 Opt 1: Add individually 6 6 6 6 6 6 Opt 2: Add rows 5 5 5 5 5 5 Opt 3: Add columns 4 4 4 4 4 4 Opt 4: Sum of consecutive integers 3 3 3 3 3 3 2 2 2 2 2 2 𝑛 ∗ 𝑛+1 ∗ # days 1 1 1 1 1 1 2 Where n= max # of tablets Session 2 Calculations Type vevox.com into your browser Enter the following room number: 162-924-833 Or Click the link below: https://vevox.app/#/m/162924833 Question 1 Paracetamol has a recommended dose for a 10-year-old child of 15mg/kg body-weight four times a day. The child weights 30kg. A suspension is available at a concentration of 200mg/5ml. Calculate the volume of suspension (in mL) to be administered in each dose. Question 2 A patient buys a 400 mL bottle of lactulose for constipation. The dosage regimen is 3 x 5 mL spoonfuls three times a day. If the patient takes the lactulose according to the dosage regimen, for how many days will the mixture last? (round to one decimal place) Question 3 The dose of codeine for a child (15 kg) is 200 mcg/kg. How much (in mL) do you need to draw up for a single dose if codeine is available as a 5 mg/mL ampoule? Question 4 A prescription contains the following instructions: Prednisolone 40 mg x 5/7. Reduce by 5 mg every 5 days until 0. The above prescription is for a patient on a reducing regimen of Prednisolone tablets. Calculate how many Prednisolone 5 mg tablets should be supplied to fill the prescription? PF1011 – Calculations 3 Dr Kevin Murphy [email protected] Compounding Becoming less and less common Compounding from prefabricated forms more common Compounding calculations Session 3 Calculations with ratios and proportions Dilutions, mixtures, and compounding Calculations with ratios and proportions How many mL of D5W (5% dextrose) should be administered to a hygoglycaemic patient to provide 150 mg of dextrose? Concentration stays constant 𝐴𝑃𝐼(𝑔) 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 (% 𝑤/𝑣) = 𝑇𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 (𝑚𝐿) 5𝑔 150 𝑚𝑔 1𝑔 = ∗ 100 𝑚𝐿 ? 𝑚𝐿 1,000 𝑚𝐿 1𝑔 100 𝑚𝐿 ? 𝑚𝐿 = 150 𝑚𝑔 ∗ ∗ = 3 mL 1,000 𝑚𝑔 5𝑔 Dilution of stock solution (liquids) A GP orders 250 mL of 15% (v/v) solution to prepared from a stock supply of 80% (v/v) solution. How many mL of stock solution are needed? Active Pharmaceutical Ingredient quantity stays constant 𝐴𝑃𝐼(𝑚𝐿) 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 (% 𝑣/𝑣) = 𝑇𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 (𝑚𝐿) 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 % 𝑣/𝑣 ∗ 𝑇𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 𝑚𝐿 = 𝐴𝑃𝐼 (𝑚𝐿) 15 𝑚𝐿 𝐴 80 𝑚𝐿 𝐴 ∗ 250 𝑚𝐿 𝑇 = ∗ ? 𝑚𝐿 (𝑇) 100 𝑚𝐿 (𝑇) 100 𝑚𝐿 𝑇 15 𝑚𝐿 𝐴 100 𝑚𝐿 (𝑇) ∗ 250 𝑚𝐿 𝑇 ∗ = 46.875 mL (T) 100 𝑚𝐿 (𝑇) 80 𝑚𝐿 (𝐴) Following a formula The formula for B.M.X. is: Benylin 110 mL Maalox 110 mL Lidocaine 2% 20mL How much Maalox liquid would be required to make 500 mL of BMX? Round answer to nearest whole number Concentration quantity stays constant 𝐴𝑃𝐼(𝑚𝐿) 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 (% 𝑣/𝑣) = 𝑇𝑜𝑡𝑎𝑙 𝑣𝑜𝑙𝑢𝑚𝑒 (𝑚𝐿) 110 𝑚𝐿 (𝐴) ? 𝑚𝐿 (𝐴) = 240 𝑚𝐿 (𝑇) 500 𝑚𝐿 (𝑇) 110 𝑚𝐿 (𝐴) ∗ 500 𝑚𝐿 𝑇 = ? 𝑚𝐿 𝐴 = 229.16ጻ 𝑚𝐿 = 229 𝑚𝐿 240 𝑚𝐿 (𝑇) Dilution of solids You are supplied with 50g of 2% sulphur ointment. How many grams of yellow soft paraffin must be added to produce 0.5% w/w sulphur ointment? 𝐴𝑃𝐼 𝑔 𝐴𝑃𝐼(𝑔) 𝐶𝑜𝑛𝑐. % 𝑤/𝑤 = = 𝑇𝑜𝑡𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 𝑔 𝐴𝑃𝐼 𝑔 + 𝐸𝑥𝑐𝑖𝑝𝑖𝑒𝑛𝑡𝑠(𝑔) 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 % 𝑤/𝑤 ∗ 𝑇𝑜𝑡𝑎𝑙 𝑤𝑒𝑖𝑔ℎ𝑡 𝑔 = 𝐴𝑃𝐼 (𝑔) 2𝑔 ∗ 50 𝑔 = 1 𝑔 100 𝑔 0.5 𝑔 (1 𝑔) = 100 𝑔 (1 𝑔) + 49 𝑔 + 𝑋 𝑔 100𝑔(1 𝑔) 𝑋𝑔= − 50 𝑔 = 200 𝑔 − 50 𝑔 = 150 𝑔 0.5𝑔 Increasing concentration How much salicylic acid (in grams) should be added to 500g of 10% salicylic acid ointment to prepare 25% salicylic acid ointment? (Round to the nearest gram) 𝐶𝑜𝑛𝑐𝑒𝑛𝑡𝑟𝑎𝑡𝑖𝑜𝑛 (% 𝑤/𝑤) 𝐴𝑃𝐼(𝑔) = 100 𝑔 𝐴𝑃𝐼 𝑔 + 𝐸𝑥𝑐𝑖𝑝𝑖𝑒𝑛𝑡𝑠(𝑔) 25 𝑔 (50 𝑔+𝑋 𝑔) = 100 𝑔 50 𝑔+𝑋 𝑔 +(450 𝑔) 25 𝑔 50 𝑔 + 𝑋 𝑔 + 25 𝑔(450 𝑔) = 100 𝑔(50 𝑔 + 𝑋 𝑔) 1,250 𝑔 + 25𝑋 𝑔 + 11,250 𝑔 = 5,000 𝑔 + 100𝑋 𝑔 1,250 𝑔 + 11,250 𝑔 − 5,000 𝑔 = 100𝑋 𝑔 − 25𝑋 𝑔 7,500 𝑔 = 75𝑋 𝑔 X = 100 𝑔 Session 3 Calculations Type vevox.com into your browser Enter the following room number: 136-528-347 Or Click the link below: https://vevox.app/#/m/136528347 Question 1 How many milligrams of Drug X are required to make 5 mL of an 8 % w/v solution? Question 2 If 5 g of solid ingredient is added to 45 g of a base, what is the % w/w strength? Question 3 A concentrated antiseptic solution contains Chlorhexidine Gluconate and Cetrimide in the ratio 20:1. If a 25 mL sachet contains 0.015 % w/v Chlorhexidine, what quantity of Cetrimide will it contain? Question 4 How many millilitres of a 1-in-400 stock solution should be used to make 4L of a 1-in-2,000 solution? 187.5 mg 75 mg 7.5 mg 187.5 mcg Question 5 How much salicylic acid (in grams) should be added to 680g of 10% salicylic acid ointment to prepare 15% salicylic acid ointment?