Drug Dosages and Intravenous Calculations Chapter 5 Drug Dosages and Intravenous Calculations

© 2010 Delmar, Cengage Learning. 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.

© 2010 Delmar, Cengage Learning. 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.

Interpreting Drug Orders Physicians use short-hand notations to prescribe drugs © 2010 Delmar, Cengage Learning.

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.

Interpreting Drug Labels (cont’d.) What is the drug? What is the total volume? What is the strength? © 2010 Delmar, Cengage Learning.

Dosage Calculation Methods D = desired dosage H = on-hand dose V = vehicle A = amount to give Dosage formula: . Proportions: Dimensional analysis

Dosage Calculation Methods (cont’d.) An order for 75 mg of phenytoin is given Only 100 mg are available How many tablets should be given? Dosage formula: . Proportions: © 2010 Delmar, Cengage Learning.

Dosage Calculation Methods (cont’d.) Dimensional analysis: . © 2010 Delmar, Cengage Learning.

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.

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.

Parenteral Dosage Calculations (cont’d.) Proportions: . Dimensional Analysis: © 2010 Delmar, Cengage Learning.

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.

Reconstitution of Solutions (cont’d.) Proportions: . © 2010 Delmar, Cengage Learning.

Reconstitution of Solutions (cont’d.) Dimensional analysis: Express: © 2010 Delmar, Cengage Learning.

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.

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.

Intravenous Flow Rates (cont’d.) Dimensional analysis: . © 2010 Delmar, Cengage Learning.

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.

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.

Titration of Intravenous Medications (cont’d.) © 2010 Delmar, Cengage Learning.

Titration of Intravenous Medications (cont’d.) Using dimensional analysis: . © 2010 Delmar, Cengage Learning.

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.

© 2010 Delmar, Cengage Learning. Dosages Based on BSA Formulas: . West Nomogram: common chart used to estimate BSA See Figure 5.3 © 2010 Delmar, Cengage Learning.

© 2010 Delmar, Cengage Learning. 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.