# Calculation of Solid Oral Doses and Dosages

• Calculate solid oral doses using metric and apothecary measurement systems

• Accomplish conversion of equivalent measurements of oral solid doses between the metric and apothecary systems

• Interpret medical orders and accurately calculate the solid oral dose to be administered using either ratio and proportion, the formula system, or dimensional analysis

• Calculate total dosages of solid oral medication necessary for dispensing a physician’s order

## Introduction

Using the oral route for medication administration is the safest and most frequently used means of administering medicines. **Oral medications** come in solid forms (such as tablets and capsules) and liquid forms. Variations of these solid forms, such as powders and granules, are dissolved in liquids for administration (see Chapters 8 and 9). Other advantages of administering medications orally include convenience for the patient, absence of damage to skin, and reduced cost of manufacturing the medication because the drug does not require the use of sterile technique, allowing the drug to be more economical.

## Calculating Solid Oral Medication Doses

More rules that should be considered when calculating medication dosage follow:

• Capsules are not made to be opened or divided, although in some special circumstances this may occur with permission from the physician.

• Scored tablets may be divided, but tablets not scored are not intended to be divided or broken.

• **Enteric-coated, buccal,** and **sublingual** tablets are not intended for crushing.

• Buccal and sublingual tablets should not be swallowed whole but should be dissolved within the oral cavity in the designated location.

• If a part of a tablet is the answer to the dose problem, be sure that altering the tablet by breaking or crushing will not alter the pharmaceutical action or purpose of the medication and that the calculations have been correctly made and the correct medication strength has been chosen.

Drug calculations may be obtained by using one of three methods. The method that you feel the most comfortable using is the correct method for you to use. One method is using ratio and proportion (discussed in Chapter 2). Dimensional analysis is an extended form of ratio and proportion and may also be used for calculating a dose of medication. Finally, the following formula may be used for calculations:

### Calculating Medications Using Ratio and Proportion

Also remember that when part of the ratio is missing, the unknown number is represented by “*x*”. If a calculation is necessary and one of the components of the proportion is missing, the missing part or *x* can be found by filling in the known parts of the proportion and then completing the problem as with any proportional problem. To use proportion, the dosage available (DA) and the dose ordered (DO) must be in the same measurement system. If the systems differ, conversion must be done to bring these components into the same system. (See Chapter 4 for help in remembering the measurement systems and Chapter 5 for help in converting among systems.) Later in this chapter you will calculate problems requiring conversion. Now you can begin performing calculations with medications in the same system.

### Calculating Medications Using Dimensional Analysis

Dimensional analysis is actually just an elongated form of ratio and proportion using multiple fractional units. To use dimensional analysis, ratios must allow for the cancellation of measurements from one ratio into the next. (See Chapter 5 for a review of dimensional analysis basics.)