Introduction to Clinical Pharmacology Chapter 3 Making Drug Dosing Safer

Multiple Check System 1 in 10,000 hospital deaths each year are a result of mistakes made calculating drug dosages. Order entry, bar coding, and technological checks Best method: manual redundancy system and the “5 rights and 3 checks” method Nurses are the last line of defense for patients when it comes to drug calculation errors

Drug Label Information Need drug, form, and dosage strength on the drug label Review the MAR Trade name = brand name; generic name = official drug name Unit dose method

Use of Zero Always use a zero before decimal points in drug dosages so the dosage is not incorrectly read .25 mg could be misread as 25 mg, rather than 0.25 mg

Review of Arithmetic: Fractions Fractions: consist of a numerator and a denominator Adding proper fraction with like denominators and unlike denominators

Review of Arithmetic: Fractions (cont.) Comparing fractions Multiplying fractions Multiplying whole numbers and fractions Multiplying mixed numbers Multiplying whole numbers and mixed numbers Dividing fractions Dividing fractions and mixed numbers

Review of Arithmetic: Ratios Ratio: a way of expressing a part of a whole or the relation of one number to another

Review of Arithmetic: Percentages A percent means a part per hundred It can also be expressed as a fraction Changing a fraction to a percentage Changing a ratio to a percentage Changing a percentage to a ratio

Review of Arithmetic: Proportions A proportion is a method of expressing equality between two ratios Used to find an unknown quantity The first and last terms of the proportion are called the extremes The second and third terms of the proportion are called the means

Review of Arithmetic: Decimals A decimal is a fraction in which the denominator is 10 or some power of 10 Parts of a decimal: number(s) to the left of the decimal, decimal, number(s) to the right of the decimal Types of decimals Reading decimals Adding decimals Subtracting decimals

Review of Arithmetic: Decimals (cont.) Multiplying a whole number by a decimal Multiplying a decimal by a decimal Dividing decimals Changing a fraction to a decimal Changing a decimal to a fraction

Calculations of Drug Dosages: Systems of Measurement Nurse must be familiar with calculations of all forms of drug dosages Systems of measurement: The metric system The apothecary system Household measurements Conversion between systems Conversion within a system

Calculations of Drug Dosages: Solutions Solute is a substance dissolved in a solvent Solutions are prepared by using a solid and a liquid, or a liquid and a liquid

Calculations of Drug Dosages: Reading Drug Labels Drug labels give important information the nurse must use to obtain the correct dosage Unit dose: a method of dispensing drugs in which each capsule or tablet is packaged separately Drug labels contain two names: trade name, generic name Dosage strength: the average strength given to a patient as one dose

Calculations of Drug Dosages: Oral Dosages of Drugs Computed: physician not available, written in apothecary system and label in metric system Tablets and capsules (dose desired)/(dose in hand) = (dose administered)

Calculations of Drug Dosages: Parenteral Drug Dosage Must be in liquid form before administered Available in three forms Parenteral drugs in disposable syringes or cartridges Parenteral drugs in ampules and vials Parenteral drugs in dry form

Calculations of Drug Dosages: Parenteral Drug Dosage (cont.) Calculating intravenous flow rates To allow IV fluid to infuse over a specified period, the IV flow rate must be determined Methods of calculating intravenous flow rates Method 1 Method 2 Method 3

Calculations of Drug Dosages: Parenteral Drug Dosage (cont.) Oral or parenteral drug dosages based on weight The dosage may be based on the patient’s weight In many instances, references give the dosage based on the weight in kilograms rather than pounds

Dosage Calculations Using Dimensional Analysis Procedure of calculating dosage using dimensional analysis: Step 1: identify the unit of measure to be calculated Step 2: write the identified unit of measure to be calculated, followed by an equal sign Step 3: dosage strength is written, with the numerator always expressed in the same unit that was identified before the equal sign

Dosage Calculations Using Dimensional Analysis (cont.) Procedure of calculating dosage using dimensional analysis (cont.): Step 4: write the next fraction with the numerator having the same unit of measure as the denominator in the previous fraction Step 5: the problem is solved by multiplication of the two fractions

Dosage Calculations Using Dimensional Analysis (cont.) Procedure of metric conversion using dimensional analysis: Step 1: write the unit of measure to be calculated, followed by an equal sign Step 2: express the dosage strength as a fraction with the numerator having the same unit of measure as the number before the equal sign

Dosage Calculations Using Dimensional Analysis (cont.) Procedure of metric conversion using dimensional analysis (cont.): Step 3: write the next fraction with the numerator having the same unit of measure as the denominator in the previous fraction Step 4: expand the equation by filling in the missing numbers using the appropriate equivalent Step 5: solve the problem by multiplication

Dosage Calculations Using Dimensional Analysis: Temperatures Two scales used: Fahrenheit Celsius