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PSACalculations Seungmin HanContents • 1. Calculations Section Structure • 2. Practice Questions • Dose calculations • Rate calculations • Concentration calculationsCalculationsSection • 8Qs • Each 2 marks • Calculator on the same screen • Do not need to use all info providedTypesofQuestions • Dose calculations for prescriptions (adjusting for patient’s age/weight/surface area, number of tablets) • Concentration calculations • Infusion rate calculations (infusion pumps) Concentrations(1:x,x%) • Concentration (%) = mass of solute (g(x 100) volume of solution (mL) • Default = g in mLConcentrations(1:x,x%) • 1:100 = 1g in 100mL = 1000mg in 100mL = 10mg in 1mL = 1% • 1:1000 = 1g in 1000mL = 1000mg in 1000mL = 1mg in 1mL = 0.1% • 1:10,000 = 1g in 10,000mL = 1000mg in 10,000mL = 0.1mg in 1mL = 0.01%Convertingunits • Change to unit they are asking for – e.g. mcg / mg / mL / L How much morphine is 20mL of oramorph 10mg/5mL? Calculate the dose in mg. • Keep units in your calculations/equations Mass = concentration x volume 10𝑚𝑔 4 × 20𝑚𝐿 = 40mg 5𝑚𝐿Convertingunits ÷60 mL/hour → mL/min ×60OpioidConversionTableOpioidConversionTablePracticeQuestions 1minDosecalculations • Units • Duration • Concentrations Calculation What volume (mL) of benzylpenicillin sodium solution should the patient be given for 24 hours? (Write your answer in the box provided). 1.8 Solution • One dose = 3.6kg * 25mg/kg = 90 mg • For 24 hours, he needs 90mg x2 = 180 mg • 600mg in 6mL • 180mg in 1.8mLA 12 year old child (Body Surface Area = 1.5 m ) is How many 5mg tablets will you need to being discharged from your ward. He has been prescribe for a one week supply? 2 prescribed Drug X at a dose of 20 mg/m orally daily. Drug X is available in 5mg tablets. 42 Solution •Dose for 1 day = 1.5 x 20mg = 30mg •30mg is 6 x 5mg tablets •Number of tablets for 1 week supply = 6 x 7 = 42A 6-month-old child (Body surface area = 0.4 m ) has How many 250 mg vials of acyclovir been admitted to the paediatric ward. He requires will he require over the period of his 500 mg/m acyclovir intravenously three times a day treatment, given that acyclovir must be for 10 days. used immediately after reconstitution? 30 vials Solution •Dose = 500mg x 0.4m = 200mg TDS for 10 days •1 vial for each dose (1 vial TDS for 10 days) • = 30 vialsA patient on the ward has been prescribed 30mg Calculate the appropriate strength of Zomorph tablets BD and 10ml Oramorph (10mg/5ml fentanyl patch. morphine) oral solution PRN for malignancy- associated bone pain. Over the past week he has been taking 10mls Oramorph three times a day in Fentanyl 50 patch addition to his regular Zomorph tablets. He now has difficulty swallowing and the pain team suggested switching to a fentanyl patch. Solution REGULAR Zomorph 30mg BD = 60mg morphine per day PRN Oramorph oral solution = 10mg/5ml morphine 10mL = 20mg TDS = 60mg per day BNF – palliative care section So, Total (regular + PRN) Daily Dose = 120mg morphine per day Equivalent dose is Fentanyl 50 patchBNF – Morphine, Medicinal formsConcentrationcalculations • Concentration (%) = mass of solute(x 100) volume of solution • Default = g in mL • 1% = 1:100 = 1g in 100mL Mr X is a 54 year-old man weighing 80kg. He has so far Calculation been given 12ml of 1% lidocaine hydrochloride as local How much more volume (in ml) can Mr X be anaesthesia for lancing of an abscess. The maximum dose given. allowed in 200mg. 8mL Solution Recall that 1% = 1g/100ml = 1000mg/100ml = 10mg/ml Already given 12mL - 120mg 80mg more can be given 8mL more can be givenA 24-year-old man requires sutures for extensive How much adrenaline (in micrograms) has lacerations to the face and chest. Lidocaine been administered? hydrochloride 1% with adrenaline (epinephrine) 1:200,000 is used to provide local anaesthesia 65mcg before suturing, and a total of 13 mL is injected SC around the wound. Solution 1:200,000 = 1g in 200,000mL = 1000mg in 200,000mL = 1mg in 200mL = 1000mcg per 200mL 5mcg per mL In 13mL = 5 x 13 = 65mcg 65mcgA 79-year-old man is admitted to hospital from a What volume of elixir should he be given nursing home with congestive cardiac failure. each day according to the information in He is taking several medicines, including digoxin the referral letter? (dose 0.125 mg daily according to the referral letter). 2.5mL He is struggling to take his medicines and, where possible, prefers to take these in liquid form. Digoxin is provided as an elixir of strength 50 micrograms/mL. Solution 0.125mg = 125mcg daily Strength of digoxin elixir = 50 micrograms/mL. Volume of elixir to be administered = mass / conc = 125mcg / 50mcg/mL = 2.5 mLRatecalculations • Default = g in mL • 1% = 1:100 = 1g in 100mL • Mg → mL or mL → mg • /hour → /minute 125 Solution Dose over 4 hrs: 0.75mg = 750mcg Digoxin infusion concentration: 1.5mcg/mL Conc = mass / vol 1.5mcg/mL = 750mcg / vol Vol = 750mcg / 1.5mcg/mL = 500 mL 500mL over 4 hrs 500/4 = 125 mL/hrA syringe pump is set at 6 ml/hour, and it contains a What dose of the drug is the patient drug at a concentration of 250 mg in 5 ml of 5% receiving in micrograms/kg/min? dextrose. The patient weighs 80 kg. 62.5mcg/kg/min Solution 250mg in 5mL In 6mL – 300mg 6mL/hour = 300mg/hour =5mg/min =5000mcg/min 5000mcg/min / 80kg 62.5mcg/kg/minA patient with an acute coronary syndrome is What is the correct rate of infusion, prescribed an infusion of glyceryl trinitrate, which in ml/hour? is supplied in a 0.1 % solution, at an initial dose of 60 micrograms/minute. 0.001mL/hour Solution 60mcg = 0.06mg so 0.06mg/min = 3.6mg/hour 0.1% = 0.1g in 100mL = 100mg in 100mL = 1mg in 1mL 3.6mg in 3.6mL 3.6mL/hourFinaltips • 3 sections still left after Calculations, 2 marker x 22 Qs • If your answer has >3 decimal places & Q does not say ‘rounded to 2dp’ …Thankyou! • Seungmin.han1@nhs.netAminophylline infusion is prescribed for a patient with What should be the rate of infusion in severe asthma at a dose of 500 micrograms/kg/hr. ml/min? The patient weighs 60 kg and the concentration of aminophylline in the infusion bag is 5 mg/100 ml. 10mL/minute Solution Dose of aminophylline: 500mcg/kg/hr x 60kg = 30,000mcg/hour = 30mg / hour = 0.5mg / minute 5mg / 100mL = 0.5mg / 10mL = 10mL/minuteA patient is prescribed dopamine at a dose of 5 At what rate should the infusion be set in micrograms/kg/min. He weighs 80 kg. The infusion ml/hour? vials contain 200mg/ 5ml of the drug. •0.6mL/hour Solution •Dose required = 5mcg/kg/min x 80kg = 400 mcg/min •0.4mg/min •24mg/hour •200mg per 5mL = 40 mg per mL •=24mg in 0.6mL •Infusion volume = 0.6mL •Infusion rate = 0.6mL/hour
