(BOOK) DRUG CALCULATIONS FOR NURSES A STEPBY-STEP APPROACH 3RD Edition By ROBERT LAPHAM.

(BOOK) DRUG CALCULATIONS FOR NURSES A STEPBY-STEP APPROACH 3RD Edition By ROBERT LAPHAM. Drug treatments given to patients in hospital are becoming increasingly complex. Sometimes, these treatment regimes involve potent and, at times, new and novel drugs. Many of these drugs are toxic or possibly fatal if administered incorrectly or in overdose. It is therefore very important to be able to carry out drug calculations correctly so as not to put the patient at risk. In current nursing practice,the need to calculate drug dosages is not uncommon. These calculationshave to be performed competently and accurately, so as not to put not only the nurse but, more importantly, the patient at risk. This book aims to provide an aid to the basics of mathematics and drug calculations. It is intended to be of use to nurses of all grades and specialities, and to be a handy reference for use on the ward. The concept of this book arose from nurses themselves; a frequently asked question was: ‘Can you help me with drug calculations?’ Consequently, a small booklet was written to help nurses with their drug calculations, particularly those studying for their IV certificate. This was very well received, and copies were being produced from original copies, indicating the need for such help and a book like this. The content of the book was determined by means of a questionnaire, sent to nurses asking them what they would like to see featured in a drug calculations book. As a result, this book was written and, hopefully, covers the topics that nurses would like to see. Although this book was primarily written with nurses in mind, others who use drug calculations in their work will also find it useful. Some topics have been dealt with in greater detail for this reason, e.g. moles and millimoles. This book can be used by anyone who wishes to improve their skills in drug calculations or to use it as a refresher course. This book is designed to be used for self-study. Before you start, you should attempt the pre-test to assess your current ability in carrying out drug calculations. After completing the book, repeat the same test and compare the two scores to measure your improvement. To attain maximum benefit from the book, start at the beginning and work through one chapter at a time, as subsequent chapters increase in difficulty. For each chapter attempted, you should understand it a fully and be able to answer the problems confidently before moving on to the next chapter. Alternatively, if you wish to quickly skip through any chapter, you can refer to the ‘Key Points’ found at the start of each chapter. A note about drug names In the past, the British Approved Name (BAN) was used for drugs in the UK. European law now requires use of the Recommended International Non-proprietary Name (rINN) for medicinal substances.In most cases, the old BAN and the new rINN are identical. Where the two differ, the BAN has been modified to the new rINN; for example: amoxicillin instead of amoxycillin. Adrenaline and noradrenaline have two names (BAN and rINN). However, adrenaline and noradrenaline are the terms used in the titles of monographs in the European Pharmacopoeia and are thus the official names in the member states. The British Pharmacopoeia 2008 shows the European Pharmacopoeia names first followed by the rINN at the head of its monographs (adrenaline/epinephrine); the British National Formulary (BNF) has adopted a similar style. For a full list of all the name changes, see the current edition of the BNF. Affected drugs that appear in this book will be referred to by their new name (rINN) followed by their old name (BAN) in brackets; for adrenaline, this book will follow the convention used by the British Pharmacopoeia. Case reports The journal Pharmacy in Practice highlights real-life medication errors to act as learning points for practitioners. Some of these have been used as Case Reports in this book to illustrate important points to remember. How to use this book To obtain the maximum benefit from this book, it is a good idea to attempt the pre-test before you start working through the chapters. The aim of this pre-test is to assess your ability at various calculations. The pre-test is divided into several sections that correspond to each chapter in the book, and the questions try to reflect the topics covered by each chapter. You don’t have to attempt questions for every chapter, only the ones that you feel are relevant to you. Answering the questions will help you identify particular calculations you have difficulty with. You can use calculators or anything else you find helpful to answer the questions, but it is best to complete the pre-test on your own, as it is your ability that is being assessed and not someone else’s. Don’t worry if you can’t answer all of the questions. As stated before, the aim is to help you to identify areas of weakness. Once again, you don’t have to complete every section of the pre-test, just the ones you want to test your ability on. Once you have completed the pre-test and checked your answers, you can then start working through the chapters. Concentrate particularly on the areas you were weak on and miss out the chapters you were confident with if you wish. It is up to you as how you use this book, but hopefully the pre-test will help you to identify areas you need to concentrate on. The pre-test consists of 50 questions and covers all the topics and types of questions in the book. Mark your score out of 50, then double it to find your percentage result. BASICS The aim of this section is to test your ability on basic principles such as multiplication, division, fractions, decimals, powers and using calculators, before you start any drug calculations. Long multiplication Solve the following: 1 678 × 465 2 308 × 1.28 Long division Solve the following: 3 3143 ÷ 28 4 37.5 ÷ 1.25 PRE-TEST Fractions Solve the following, leaving your answer as a fraction: 5 6 7 8 Convert to a decimal (give answers to 2 decimal places): 9 10 Decimals Solve the following: 11 25 × 0.45 12 5 ÷ 0.2 13 1.38 × 100 14 25.64 ÷ 1,000 Convert the following to a fraction: 15 1.2 16 0.375 Roman numerals Write the following as ordinary numbers: 17 VII 18 IX Powers Convert the following to a proper number: 19 3 × 104 Convert the following number to a power of 10: 20 5,000,000 9 16 2 5 5 6 3 8 ÷ 3 4 9 16 ÷ 3 4 12 16 × 5 9 3 7 × Basicsxiii PER CENT AND PERCENTAGES This section is designed to see if you understand the concept of per cent and percentages. 21 How much is 28% of 250 g? 22 What percentage is 160 g of 400 g? UNITS AND EQUIVALENCES This section is designed to test your knowledge of units normally used in clinical medicine, and how to convert from one unit to another. It is important that you can convert between units easily, as this is the basis for most drug calculations. Convert the following. Units of weight 23 0.0625 milligrams (mg) to micrograms (mcg) 24 600 grams (g) to kilograms (kg) 25 50 nanograms (ng) to micrograms (mcg) Units of volume 26 0.15 litres (L) to millilitres (mL) Units of amount of substance Usually describes the amount of electrolytes, as in an infusion (see Chapter 7 ‘Moles and millimoles’ for a full explanation). 27 0.36 moles (mol) to millimoles (mmol) DRUG STRENGTHS OR CONCENTRATIONS This section is designed to see if you understand the various ways in which drug strengths can be expressed. Percentage concentration 28 How much sodium (in grams) is there in a 500 mL infusion of sodium chloride 0.9%? mg/mL concentrations 29 You have a 5 mL ampoule of dopexamine 1%. How many milligrams of dopexamine are there in the ampoule? xiv Pre-test ‘1 in ...’ concentrations or ratio strengths 30 You have a 10 mL ampoule of adrenaline/epinephrine 1 in 10,000. How much adrenaline/epinephrine – in milligrams – does the ampoule contain? Parts per million (ppm) strengths 31 If drinking water contains 0.7 ppm of fluoride, how much fluoride (in milligrams) would be present in 1 litre of water? DOSAGE CALCULATIONS These are the types of calculation you will be doing every day on the ward. They include dosages based on patient parameters and paediatric calculations. Calculating the number of tablets or capsules required The strength of the tablets or capsules you have available does not always correspond to the dose required. Therefore you have to calculate the number of tablets or capsules needed. 32 The dose prescribed is furosemide (frusemide) 120 mg. You have 40 mg tablets available. How many tablets do you need? Drug dosage Sometimes the dose is given on a body weight basis or in terms of body surface area. The following questions test your ability at calculating doses based on these parameters. Work out the dose required for the following: 33 Dose = 0.5 mg/kg Weight = 64 kg 34 Dose = 3 mcg/kg/min Weight = 73 kg 35 Dose = 1.5 mg/m2 Surface area = 1.55 m2 (give answer to 3 decimal places) Calculating dosages Calculate how much you need for the following dosages: 36 You have aminophylline injection 250 mg in 10 mL. Amount required = 350 mg 37 You have digoxin injection 500 mcg/2 mL. Amount required = 0.75 mg 38 You have morphine sulphate elixir 10 mg in 5 mL. Amount required = 15 mg 39 You have gentamicin injection 40 mg/mL, 2 mL ampoules. Amount required = 4 mg/kg for a 74 kg patient: how many ampoules will you need? Dosage calculations xv Paediatric calculations 40 You need to give trimethoprim to a 7-year-old child weighing 23 kg at a dose of 4 mg/kg twice a day. Trimethoprim suspension comes as a 50 mg in 5 mL suspension. How much do you need for each dose? Other factors to take into account are displacement volumes for antibiotic injections. 41 You need to give benzylpenicillin at a dose of 200 mg to a 6-month-old baby. The displacement volume for benzylpenicillin is 0.4 mL per 600 mg vial. How much water for injections do you need to add to ensure a strength of 600 mg per 5 mL? MOLES AND MILLIMOLES This section is designed to see if you understand the concept of millimoles. Millimoles are used to describe the ‘amount of substance’, and are usually the units for body electrolytes (e.g. sodium 138 mmol/L). Moles and millimoles 42 Approximately how many millimoles of sodium are there in a 10 mL ampoule of sodium chloride 30% injection? (Molecular mass of sodium chloride = 58.5) Molarity 43 How many grams of sodium chloride is required to make 200 ml of a 0.5 M solution? (Molecular mass of sodium chloride = 58.5) INFUSION RATE CALCULATIONS This section tests your knowledge of various infusion rate calculations. It is designed to see if you know the different drop factors for different giving sets and fluids, as well as being able to convert volumes to drops and vice versa. Calculation of drip rates 44 What is the rate required to give 500 mL of sodium chloride 0.9% infusion over 6 hours using a standard giving set? 45 What is the rate required to give 1 unit of blood (500 mL) over 8 hours using a standard giving set? xvi Pre-test Answersxvii Conversion of dosages to mL/hour Sometimes it may be necessary to convert a dose (mg/min) to an infusion rate (mL/hour). 46 You have an infusion of dopamine 800 mg in 500 mL. The dose required is 2 mcg/kg/min for a patient weighing 60 kg. What is the rate in mL/hour? 47 You are asked to give 500 mL of doxapram 0.2% infusion at a rate of 3 mg/min using an infusion pump. What is the rate in mL/hour? Conversion of mL/hour back to a dose 48 You have dopexamine 50 mg in 50 mL and the rate at which the pump is running is 21 mL/hour. What dose – in mcg/kg/min – is the pump delivering? (Patient’s weight = 88 kg) Calculating the length of time for IV infusions 49 A 500 mL infusion of sodium chloride 0.9% is being given at a rate of 21 drops/min (standard giving set). How long will the infusion run at the specified rate? 50 A 250 mL infusion of sodium chloride 0.9% is being given at a rate of 42 mL/hour. How long will the infusion run at the specified rate?