Medical Dosage Calculations A Dimensional Analysis Approach Eleventh Edition Chapter 6 Oral Medications

Learning Objectives (1 of 2) 6.1 Calculate simple (one-step) problems for oral medications in solid and liquid form. 6.2 Calculate complex (multi-step) problems for oral medications in solid and liquid form. 6.3 Calculate doses for medications measured in milliequivalents. Slide 2 is list of textbook LO numbers and statements

Learning Objectives (2 of 2) 6.4 Interpret drug labels in order to calculate doses for oral medication. 6.5 Calculate doses based on body weight. 6.6 Calculate body surface area (BSA). 6.7 Calculate doses based on body surface area (BSA). Slide 3 is list of textbook LO numbers and statements

Simple (One-Step) Problems In the calculations you have done in previous chapters, all the equivalents have come from standard tables, for example, 1 t = 5 mL. In this section the equivalent used will come from the strength of the drug that is available, for example, 30 mg/mL.

Medication in Solid Form Example 6.1 (1 of 4) Read the label on the next slide. How many tablets of this narcotic analgesic will be needed for a dose containing 10 mg of hydrocodone bitartrate and 600 milligrams of acetaminophen?

Figure 6.3 Drug label for Vicodin.

Medication in Solid Form Example 6.1 (2 of 4) Vicodin is a combination drug composed of hydrocodone bitartrate and acetaminophen. Therefore, for computational purposes, you need to only address the first listed drug (hydrocodone bitartrate).

Medication in Solid Form Example 6.1 (3 of 4) Because the dose requires 10 mg of hydrocodone bitartrate, convert the 10 mg to the appropriate number of tablets. 10 mg = ? tab

Medication in Solid Form Example 6.1 (4 of 4) The strength of the drug is 5 mg (of hydrocodone bitartrate) per tablet will be used to form the unit fraction.

Medication in Liquid Form Example 6.2 (1 of 2) The prescriber ordered potassium chloride 10 mEq PO daily. The strength of the potassium chloride solution is 20 mEq/15 mL. Determine how many milliliters of this electrolyte supplement you should administer.

Medication in Liquid Form Example 6.2 (2 of 2) You want to change 10 mEq to mL using the strength of 20 mEq per 15 mL to form the unit fraction.

Medications Measured in Milliequivalents Example 6.3 (1 of 3) The order is potassium chloride 30 mEq PO daily in three divided doses. Read the label on the following slide and determine how many tablets should be administered.

Figure 6.11 Drug label for K-Tab.

Medications Measured in Milliequivalents Example 6.3 (2 of 3)

Medications Measured in Milliequivalents Example 6.3 (3 of 3) Because the order indicates “three divided doses,” you would administer 1 tablet of K-Tab every 8 hours.

Multi-Step Problems Example 6.4 (1 of 4) Given quantity 0.4 g Strength 1 tab = 100 mg Quantity you want to find ? tab

Multi-Step Problems Example 6.4 (2 of 4) Read the label below, and calculate the number of tablets of Diflucan that contain 0.4 gram of fluconazole.

Multi-Step Problems Example 6.4 (3 of 4) You want to change 0.4 g to tablets. The strength of the tablets is 100 mg per tab.

Multi-Step Problems Example 6.4 (4 of 4)

Dosages Based on the Size of the Patient Calculating Dosage by Body Weight Sometimes the amount of medication prescribed depends on the patient’s body weight. A patient who weighs more will receive more of the drug, and a patient who weighs less will receive less of the drug.

Dosages Based on the Size of the Patient Example 6.5 (1 of 3) The physician orders Biaxin (clarithromycin) 7.5 milligrams per kilogram PO q12h. If the strength is 250 milligrams per 5 mL, how many mL of this antibiotic drug should be administered to a patient who weighs 70 kilograms? Body weight: 70 kg Order: 7.5 mg/kg Strength: 250 mg/5 mL Find: ? mL

Dosages Based on the Size of the Patient Example 6.5 (2 of 3) Multiply the size of the patient by the order to determine how many milligrams of Biaxin to give the patient.

Dosages Based on the Size of the Patient Example 6.5 (3 of 3) Now convert the 525 mg of Biaxin to milliliters. The strength of the solution is 250 mg/5 mL.

Calculating Dosage by Body Surface Area Body surface area (BSA) is also used in determining appropriate drug dosages. This is particularly true of pediatric drugs and drugs that are used for cancer therapy. A patient’s BSA, which is measured in square meters (m2), can be estimated by using formulas or nomograms.

Calculating BSA Using Formulas

Calculating BSA Using Formulas Example 6.6 (1 of 2) What is the BSA of a man who is 5 feet 6 inches tall and weighs 168 pounds? First, convert 5 feet 6 inches to 66 inches.

Calculating BSA Using Formulas Example 6.6 (2 of 2)

Calculating BSA Using Formulas Example 6.7 (1 of 4) A drug is ordered at 3.3 mg/m2 PO q12h for three doses. How many scored 5-mg tablets of this drug would you administer to a patient with a BSA of 2.29 m2? BSA: 2.29 m2 Order: 3.3 mg/m2 Strength: 1 tab = 5 mg Find: ? tab

Calculating BSA Using Formulas Example 6.7 (2 of 4) The patient’s BSA is 2.29 m2 and the order is for 3.3 mg/m2. First, multiply the size of the patient by the order to determine how many milligrams of the drug to give the patient.

Calculating BSA Using Formulas Example 6.7 (3 of 4) Finally, convert 7.56 mg to tablets.

Calculating BSA Using Formulas Example 6.7 (4 of 4) This example could have been done in one line as follows:

Chapter Summary (1 of 2) It is crucial to ensure that every medication administered is within the recommended safe dose range. Some drugs, such as electrolytes, are measured in milliequivalents (mEq). Calculating doses by body weight Start calculations with the weight of the patient. Multiply the size of the patient (kg) by the order to obtain the dosage.

Chapter Summary (2 of 2) Calculating doses by body surface area Body surface area (BSA) is measured in square meters (m2 ). BSA is determined by using either a formula or a nomogram. Start calculations with the BSA of the patient.