Drug Calculations for Nurses

Robert Lapham, BPharm, Clin Dip Pharm, clinical pharmacist, Sunderland, UK

MATHEMATICS
Basics
Introduction
Arithmetic Symbols
Basic Maths
Rules of Arithmetic
Fractions and Decimals
Roman Numerals
Powers or Exponentials

First Principles
Before We Start
Sense of Number and the Use of Calculators or Formulae
Estimation of Answers
The ‘One Unit’ Rule
Checking Your Answer – Does it Seem Reasonable?
Putting it All Together
Minimizing Errors

Percent and Percentages
Introduction
Percent and Percentages
Converting Fractions to Percentages and Vice Versa
Converting decimals to Percentages and Vice Versa
Calculations Involving Percentages
Drug Calculations Involving Percentages
How to Use the Percentage Key on Your Calculator

Units and Equivalences
Introduction
SI Units
Prefixes Used in Clinical Practice
Equivalences
Conversion from One Unit to Another
Guide to Writing Units

Moles and Millimoles
Introduction
What are Moles and Millimoles?
Millimoles and Micromoles

Drug Strengths or Concentrations
Introduction
Percentage Concentration mg/mL concentrations
‘1 In …’ Concentrations or Ratio Strengths
Parts Per Million (ppm)
Drugs Expressed in Units

PERFORMING CALCULATIONS
Dosage Calculations
Introduction
Calculating the Number of Tablets or Capsules Required
Drug Dosages Based on Patient Parameters
Ways of Expressing Doses
Calculating Drug Dosages
Displacement Values or Volumes
Prescriber Calculations

Infusion Rate Calculations
Introduction
Drip Rate Calculations (drops/min)
Conversion of Dosages to mL/hour
Conversion of mL/hour Back to a Dose
Calculating the Length of Time for IV Infusions

ADMINISTERING MEDICINES
Intravenous Therapy and Infusion Devices
IV Infusion Therapy
Answers
Infusion Devices
Infusion Device Classification

Action and Administration of Medicines
Action and Administration of Medicines
Introduction
Pharmacokinetics and Pharmacodynamics
Administration of Medicines
Promoting the Safer use of Injectable Medicines

Children and Medicines
Introduction
Drug Handling in Children
Pharmacodynamics
Routes of Administration of Drugs
Practical Implications
Useful Reference Books
Approximate Values Useful in the Calculation of Doses in Children

The Elderly and Medicines
Introduction
Drug Handling in the Elderly
Specific Problems in the Elderly
General Principles

Sources and Interpretation of Drug Information
Introduction
Sources of Drug Information
The Internet
Summary of Product Characteristics (SPC)
Revision Test
Section One: Basics
Per cent and Percentages
Units and Equivalences
Drug Strengths or Concentrations
Dosage Calculations
Infusion Rate Calculations
Compare Your Scores
Answers to Problems

Answers to Problems Set in Chapters
Per Cent and Percentages
Units and Equivalences
Moles and Millimoles
Drug Strengths or Concentrations
Dosage Calculations
Infusion Rate Calculations
Action and Administration of Medicine

Appendices
Body Surface Area (BSA) Estimates
Weight Conversion Tables
Height Conversion Tables
Calculation of Body Mass Index (BMI)
Estimation of Renal Function
Abbreviations Used in Prescriptions