Chapter 8 • Interpret orders and calculate the volume of oral and parenteral liquid medications necessary to administer ordered doses using either ratio and proportion, formula, or dimensional analysis method • Accomplish conversion of equivalent measurements among metric, household, and apothecary systems as needed for oral or parenteral liquid medication doses • Measure parenteral medications in ordered amounts in the appropriate syringe • Calculate total doses of parenteral medications when two or more medications are ordered to be given together Pretest Interpret the order. __________________________________________________________________ If the drug available is Ceclor 125 mg/5 mL, how many teaspoons of medication should be given to the child for each dose? ____________________ Interpret the order. __________________________________________________________________ How many milliliters should be administered if the drug available is Atarax Syrup 10 mg/5 mL? ____________________ Interpret the order. __________________________________________________________________ How many milliliters of Tylenol should the parent give the child? ____________________ Interpret the order. __________________________________________________________________ What is the volume of medication for the child in the metric system? ____________________ Interpret the order. __________________________________________________________________ How many milliliters would be administered to the patient? ____________________ Interpret the order. __________________________________________________________________ What is the correct volume of medication to be administered to the patient in a dose? ____________________ Interpret the order. __________________________________________________________________ How many milliliters should be given as a weekly dose? ____________________ Interpret the order. __________________________________________________________________ How many milliliters should be administered stat to this patient? ____________________ Interpret the order. __________________________________________________________________ How many mL will be given of the promethazine and how many mL of meperidine? ____________________ What is the total amount of medication in mL if this is prepared in one syringe? ____________________ Volume to be administered in household measurements for a dose: ____________________ What is the metric volume for each dose? ____________________ Interpret the order. __________________________________________________________________ Volume of medication to be administered: ____________________ Interpret the order. __________________________________________________________________ Volume of medication to be administered: ____________________ Interpret the order. __________________________________________________________________ Volume of medication to be administered: ____________________ What volume will be given in household measurements? ____________________ Interpret the order. __________________________________________________________________ Volume of medication to be administered as a dose: ____________________ Interpret the order. __________________________________________________________________ Volume of medication to be administered in household measurements: ____________________ Interpret the order. __________________________________________________________________ What utensil would you tell the patient to use for household administration when person calls and states that the dose spoon is lost? ____________________ Volume of medication to be administered in metric system: ____________________ Volume of medication to be administered in household system: ____________________ Interpret the order. __________________________________________________________________ Volume of medication to be administered in household measurements: ____________________ What metric volume will be given? ____________________ Interpret the order. __________________________________________________________________ Volume of medication to be administered: ____________________ Interpret the order. __________________________________________________________________ *These abbreviations are found on the TJC Do Not Use List and ISMP’s List of Error-Prone Abbreviations, Symbols, and Dose Designations due to medication safety issues. They should not be used. You are being tested on them here because these abbreviations may still appear in the pharmacy setting. For some patients, solid medications such as tablets and capsules are difficult to swallow, and the physician will order oral liquid preparations. These preparations are usually stated in weight or strength/volume such as milligrams/milliliter. Because liquid medications may be dispensed in either drams from the apothecary system or teaspoons in the household measurement system, conversions among all three measurement systems are often required for dispensing or administering the prescription as written. As with solid medications, these conversions may be accomplished by either ratio and proportion or dimensional analysis. If ratio and proportion is used, then the formula method may be used for preparation of the medication for dispensing. If dimensional analysis is used, the conversion among systems may be accomplished by use of additional ratios for conversion in the equation. Thus the entire conversion and calculation may be completed with one elongated proportional step. (Examples are shown later in this chapter.) Some medications for oral administration are prepared in a powder form for reconstitution to a liquid form before dispensing—the subject of Chapter 9. Injectable medications may be given when a person is unable to swallow solid medications or when a quicker effect is necessary. Parenteral medications are given by injection into body tissue and may also be given intravenously or directly into the bloodstream. Because solid medications cannot be injected under the skin except as special intradermal forms such as pellets, most injectable medications must be in liquid form. As with oral liquid medications, some parenteral medications come in powders for injection, requiring reconstitution before administration. These medications usually will not be stable in liquid form for an extended period, so they must be handled for stability at the time of administration (reconstitution of parenteral medications is discussed in Chapter 9). Oral medications are available in solid form as discussed in the previous chapter and in liquid form as discussed in this chapter. When oral medications are given in a liquid form, the absorption is usually faster because solids have to dissolve before absorption. The absorption of a medicine is controlled, in part, by the dosage form administered. Most oral medications are absorbed in the small intestine, although some are absorbed beginning in the mouth or stomach. These medications may be administered with oral syringes that are available in 1-mL, 5-mL, and 10-mL sizes (Figure 8-1), a medication cup (Figure 8-2), a dropper that is available in different measurements and is usually tailored by the manufacturer for a specific drug (Figure 8-3), dosage spoons (Figure 8-4), or by using household devices such as teaspoons and tablespoons. The newest form of administration of oral liquid medications is through a nipple or with a pacifier that will hold a measured amount of medication (Figure 8-5). The choice of administration implement for oral liquid medications depends on the volume of medication to be administered and the availability of supplies. Medication cups are found in institutional settings, whereas droppers and oral syringes may be used either in institutions or at home. Teaspoons and tablespoons are the measurements occasionally used for larger doses in the home setting or when the calibrated utensils are not available. The use of kitchen utensils is usually discouraged, because oral syringes and calibrated cups are more accurate. Liquid drug preparations are labeled with the strength of the drug (such as milligrams) in the total volume (such as milliliters) of the liquid. Remember that liquid medications may be expressed in metric (milliliters, cubic centimeters, and liters), apothecary (drams and minims), and household (teaspoons, tablespoons, pints, and the like) measurement systems. Doses of medication are also calculated based on strength/volume. This fact is then used to prepare liquid medications for administration. For example, a physician may order amoxicillin 500 mg to be given to a child who requires a liquid dosage form. The medication on hand is amoxicillin 250 mg (weight or strength) per 5 mL (volume). In this case the known amounts will be placed into the formula, ratio and proportion, or dimensional analysis equations for preparing the correct amount of medication. If you need to review the formulas for any of these ways of ascertaining the correct dose to be given or if you need to review the safety measures necessary for medication preparation and administration, return to Chapter 7. As with the previous chapter, you will calculate doses for competency. You must remember that dose is the amount of medication to be administered at a specific given time, whereas dosage (to be discussed in Chapter 14) is the total amount of medication that will be administered over a particular length of time. Again, as a reminder, the label on the medication must be in the same system of measurement as that found on the prescription or medication order. If these do not agree, conversion should be accomplished to the system found on the label. Also, be sure the medication names are exactly the same, because many drug names look and sound alike. As you learned in Chapter 7, when using the ratio and proportion method of drug calculation, the dose available (DA) and the dosage form (DF) must be one ratio, and the dose ordered (DO) and dose to be given (DG) must be the other ratio in the proportion. With liquids, DF and DG will be in volume, whereas DA and DO will be in strength or weight of drug. Example 8-1 Remember the formula for using ratio and proportion appears as follows: The DA is 250 mg in the DF of 5 mL. The DO is 500 mg. The proportion is set up as follows: Either multiply the means versus the extremes or cross-multiply if using the fractional components. Example 8-2 Now change this to the household measurement as requested by the physician. Remember that dimensional analysis is really just an elongated form of ratio and proportion using fractional components. To review dimensional analysis as a means of calculating doses, please review Chapter 5. The problem in Example 8-1 would appear as follows for calculation with dimensional analysis:
Calculate Doses of Oral and Parenteral Liquid Medications
1 A physician orders Ceclor 250 mg po tid for a child with otitis media.
2 A physician orders Atarax Syrup 15 mg po qid.
3 A physician orders Tylenol gr v q4h prn fever and aches for a child who has a high fever. The drug available is Tylenol elixir 160 mg/tsp.
4 A physician orders Amoxil 62.5 mg po tid for an infant. The drug available is 125 mg/5 mL.
5 Using the medication order in question No. 4, what amount of medication should be administered in the household measurement? ____________________
6 A physician orders Zofran 2 mg IM to be given 30 minutes before the treatment for a chemotherapy patient. The drug dosage available is Zofran 2 mg/mL.
7 A physician orders Ticar 500 mg IM bid. The reconstituted strength of the medication is 1 gm/2.6 mL.
8 The physician orders vitamin B12 1000 mcg IM qwk. The available drug dosage is 1 mg/mL.
9 A physician orders meperidine 75 mg IM stat for a patient who has had cardiac surgery. The drug dosage available is meperidine 50 mg/mL.
10 A physician orders 50 mg of meperidine and 25 mg of promethazine IM q4-6h prn for a postsurgical patient with pain and nausea. The drug dosage available is meperidine 75 mg/mL and promethazine 25 mg/mL.
11 Ordered medication: amoxicillin 375 mg po tid
12 Ordered medication: streptomycin 750 mg IM
13 Ordered medication: codeine phosphate gr i subcutaneous q4h prn
14 Ordered medication: Mycostatin 500,000 units po tid
15 Ordered medication: erythromycin 0.3 gm po tid
16 Ordered medication: phenobarbital 30 mg po hs*
17 Ordered medication: Prozac 10 mg po qam
18 Ordered medication: Benadryl 25 mg po prn
19 Ordered medication: morphine sulfate gr 1/10 IV q4h
20 Ordered medication: Colace syrup 80 mg po at bedtime
Introduction
Calculation Of Oral Liquid Medications
Calculating Oral Liquid Medications Using Ratio and Proportion
A physician orders Ceftin oral suspension 187 mg. The medication on hand is Ceftin 125 mg/5 mL. Because this prescription will be given at home, the medication order for the label should read the amount to be given in household measurements. Again, review Chapters 4 and 5 as needed.
Calculating Oral Liquid Medications Using Dimensional Analysis
Calculating Oral Liquid Medications Using the Formula Method
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Calculate Doses of Oral and Parenteral Liquid Medications
Tech Alert
A physician orders amoxicillin 500 mg oral suspension. The medication available is amoxicillin 250 mg/5 mL. How much medication would be administered to the patient for a single dose?
tsp. Remember that household measurements are in fractional units rather than decimal units.
A physician orders amoxicillin 500 mg oral suspension. The dosage available is amoxicillin 250 mg/5 mL. How much medication would be administered to the patient for a single dose?
A physician orders Ceftin 187 mg oral suspension. The medication on hand is Ceftin 125 mg/5 mL. Because this prescription will be given at home, the medication order for the label should read the amount to be given in household measurements. With dimensional analysis the problem will have an unknown in teaspoons (x = teaspoons). To obtain the answer in teaspoons, one step of fractional components is added to the calculation, thus eliminating the need for two separate calculations as was necessary with the ratio and proportion or formula methods.
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