# Drug Dosages and Intravenous Calculations Objectives

Chapter 5 Drug Dosages and Intravenous Calculations Objectives ▪ ▪ ▪ ▪ Interpret drug orders and labels Calculate drug orders Identify and calculate medication volumes Calculate the volume of reconstituted medication in powdered form ▪ Perform intravenous and intramuscular calculations © 2010 Delmar, Cengage Learning. 2 Objectives (cont’d.) ▪ Perform titration calculations ▪ Calculate drug dosages based on body weight ▪ Calculate drug dosages based on BSA using formulas and the West Nomogram chart © 2010 Delmar, Cengage Learning. 3 Interpreting Drug Orders ▪ Physicians use short-hand notations to prescribe drugs © 2010 Delmar, Cengage Learning. 4 Interpreting Drug Labels ▪ Labels give information such as: • • • • Dosage strength Brand name (or generic name) Manufacturer How to administer (orally, sublingually, injection, or other) • Drug form (e.g., tablet, capsule, liquid) • Expiration date © 2010 Delmar, Cengage Learning. 5 Interpreting Drug Labels (cont’d.) ▪ What is the drug? ▪ What is the total volume? ▪ What is the strength? © 2010 Delmar, Cengage Learning. 6 Dosage Calculation Methods ▪ Dosage formula: • . ▪ Proportions: • . ▪ Dimensional analysis © 2010 Delmar, Cengage Learning. 7 Dosage Calculation Methods (cont’d.) ▪ An order for 75 mg of phenytoin is given • Only 100 mg are available • How many tables should be given? ▪ Dosage formula: • . ▪ Proportions: • . © 2010 Delmar, Cengage Learning. 8 Dosage Calculation Methods (cont’d.) ▪ Dimensional analysis: • . © 2010 Delmar, Cengage Learning. 9 Parenteral Dosage Calculations ▪ Administered through a non-gastrointestinal route (e.g. syringe) Figure 5.1 A 3-mL syringe Figure 5.2 A 1-mL syringe © 2010 Delmar, Cengage Learning. 10 Parenteral Dosage Calculations (cont’d.) ▪ 0.25 mg of a medication by IM injection is ordered • In stock is a vial labeled 0.5 mg in 2 mL • What volume should be administered? ▪ Dosage formula: • . © 2010 Delmar, Cengage Learning. 11 Parenteral Dosage Calculations (cont’d.) ▪ Proportions: • . ▪ Dimensional Analysis: • . © 2010 Delmar, Cengage Learning. 12 Reconstitution of Solutions ▪ 300 mg Zithromax IV is ordered • In stock is a vial of powdered Zithromax that states: – “Constitute to 100 mg/mL with 4.8 mL of Sterile Water for Injection” – Single-dose vial contains 500 mg ▪ Dosage formula: • . © 2010 Delmar, Cengage Learning. 13 Reconstitution of Solutions (cont’d.) ▪ Proportions: • . © 2010 Delmar, Cengage Learning. 14 Reconstitution of Solutions (cont’d.) ▪ Dimensional analysis: • Express: © 2010 Delmar, Cengage Learning. 15 Intravenous Flow Rates ▪ Rate of flow: number of drops (gtt) that flow into patient per minute • . • Drop factor: number of drops it takes to produce 1 cc • Amount of solution: total amount of solution administered • Time: time it takes for solution administration © 2010 Delmar, Cengage Learning. 16 Intravenous Flow Rates (cont’d.) ▪ An IV bag contains 1,000 mL solution • Drop factor is 90 gtt/mL • Flow rate is 125 gtt/min • Find infusion time: © 2010 Delmar, Cengage Learning. 17 Intravenous Flow Rates (cont’d.) ▪ Dimensional analysis: • . © 2010 Delmar, Cengage Learning. 18 Titration of Intravenous Medications ▪ Four-step process: • • • • If order has different units than strength of solution, convert the strength Determine lower limit by using lower range given together with patient’s weight Use step 1 result to convert lower limit in step 2 into units of milliliters per hour Use step 3 result together with ratio of upper titration range to lower titration range, to find upper limit © 2010 Delmar, Cengage Learning. 19 Titration of Intravenous Medications (cont’d.) ▪ IV line was ordered to titrate between 2 and 4 mcg/kg/min • Patient weighs 60 kg • IV solution contains 60 mg of drug in 300 mL solution • Determine rate of flow in milliliters per hour © 2010 Delmar, Cengage Learning. 20 Titration of Intravenous Medications (cont’d.) ▪. © 2010 Delmar, Cengage Learning. 21 Titration of Intravenous Medications (cont’d.) ▪ Using dimensional analysis: • . © 2010 Delmar, Cengage Learning. 22 Dosages Based on Weight ▪ Convert patient’s weight to kilograms ▪ Find dose (range) for body weight • Example: 400 mg/kg/day for 99 lbs – How many milligrams a day? – How many every 6 hours? © 2010 Delmar, Cengage Learning. 23 Dosages Based on BSA ▪ Formulas: • . • West Nomogram: common chart used to estimate BSA – See Figure 5.3 © 2010 Delmar, Cengage Learning. 24 Summary ▪ Physicians use short-hand notations ▪ Drug labels contain a lot of information ▪ Dosages can be calculated using formulas, proportions and dimensional analysis ▪ Many parenteral dosages and reconstitution of solutions can be determined by using: © 2010 Delmar, Cengage Learning. 25

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