Solid and Liquid Oral Dose Calculations



Solid and Liquid Oral Dose Calculations



OBJECTIVES



• Estimate, calculate, and evaluate a variety of solid and liquid medication doses.


• Calculate dosages for liquid medications to the nearest tenth of a milliliter.


• Measure oral liquids in a calibrated measuring cup.


• Measure syringe volumes in 3- and 5-mL syringes.


• Calculate and evaluate safe dose ranges (SDRs) for medication doses.





Essential Prior Knowledge






Essential Equipment






Estimated Time To Complete Chapter






Introduction


This chapter builds on prior knowledge to solve many basic and complex medication dose problems using DA, with an emphasis on estimation and evaluation of the answer. Calculations based on weight are included.


Assessments and safety checks are critical before, during, and after medication administration.


It is always helpful to have a simple example in mind to build on for more complex equations. This chapter covers situations involving a variety of orders, medications, and metric units of measurement. Analysis, repetition, and practice are the keys to ease of problem solving.



ESSENTIAL Vocabulary




Calibration Set of graduations that indicate capacity or size in standard units of measure. Measuring devices for precise doses of medications have calibrations, such as the lines on a measuring cup or a syringe.


Concentration, Liquid Ratio of a specific amount of drug in a specified amount of solution; for example, 10 mg per mL or 5 mg per 5 mL.


Concentration, Solid Ratio of a specific amount of drug contained in the solid drug form supplied; for example, 50 mg per cap. The concentration of a medication, solid or liquid, is always found on the label.


Divided Doses Total dose for the day divided by a frequency schedule.


Precise Having sharply defined, accurate limits based on a standard. For example, syringes, special medication droppers, and teaspoons have precise capacities. Household equipment does not.


Ratio The relationship between two quantities.


Safe Dose Range (SDR) Manufacturer’s dosage guidelines for minimum and maximum safe medication doses based on laboratory and clinical trials of therapeutic effectiveness. For example, the SDR for aspirin for adults is 325 to 650 mg q4h.




RAPID PRACTICE 5-1   Vocabulary Review


Estimated completion time: 5-10 minutes Answers on page 500


Directions: Indicate whether the statement is true or false.






RAPID PRACTICE 5-2   Metric Solid Oral Dose Calculations and Review


Estimated completion time 10-20 minutes Answers on page 500


Directions: Convert the dose ordered to the desired dose using estimation and mental arithmetic. Verify your answer with calculations.





























































Ordered Dose Concentration Supplied Amount to Give
1 0.25 mg 0.125 mg per tab scored ____________________
2 150 mg 0.1 g per tab scored ____________________
3 0.5 mg 0.25 mg per cap ____________________
4 125 mg 250 mg per tab scored ____________________
5 350 mcg 0.175 mg per tab scored ____________________
6 0.5 mg 0.25 mg per tab scored ____________________
7 0.1 mg 0.2 mg per tab scored ____________________
8 1 g 500 mg per cap ____________________
9 2.5 g 1000 mg per tab scored ____________________
10 250 mg 0.5 g per tab scored ____________________


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Only cut scored tablets. Cutting unscored tablets can result in uneven distribution of drug amounts. (In Brown M, Mulholland J: Drug calculations: process and problems for clinical practice, ed. 8, St. Louis, 2008, Mosby. Courtesy Amanda Politte, St. Louis, MO.)





EXAMPLES


Ordered: 250 mg.


Available: dose concentration 125 mg per cap.


The nurse can see at a glance that the order is about twice the amount on hand. If the numbers do not divide evenly, an approximate amount of the unit dose is estimated.



RAPID PRACTICE 5-3   Metric Oral Solid Dose Calculations Using Estimation and DA Equations


Estimated completion time: 30-60 minutes Answers on page 500


Directions: Review the metric equivalents in Chapter 4. Study worked-out problem 1, and solve problems 2-5. Estimate answers by moving decimals for needed conversions, and verify with a DA equation. Evaluate answers: Is the equation balanced? Does the estimate support the answer? It would be helpful to write out the four steps of the DA equation before proceeding to problem 2.






1. Ordered: 0.5 g tab PO daily. Label: dose concentration 250 mg per tab.



2. Ordered: 0.25 g tab PO daily. Label: dose concentration 125 mg per tab scored.



3. Ordered: 0.1 g tab PO daily. Label: dose concentration 0.05 g per tab.



4. Ordered: 75 mcg tab PO daily. Label: dose concentration 50 mcg per tab scored.



5. Ordered: 20 mEq tab PO bid. Label: dose concentration 10 mEq per tab.



6. Ordered: 0.2 g cap PO at bedtime. Label: dose concentration 100 mg per cap.



7. Ordered: 250 mg cap PO at bedtime. Label: dose concentration 0.25 g per cap.



8. Ordered: 0.25 g cap PO tid. Label: dose concentration 125 mg per cap.



9. Ordered: 0.175 mg tab PO daily. Label: dose concentration 350 mcg per tab scored.



10. Ordered: 0.1 mg tab PO daily. Label: dose concentration 50 mcg per tab.



Q: Ask Yourself




A: My Answer



Converting Grams to Micrograms and Micrograms to Grams by Moving Decimal Places


When a problem calls for converting micrograms to grams or grams to micrograms, beginners enter two conversion factors in a DA equation: micrograms to milligrams and milligrams to grams, or grams to milligrams and milligrams to micrograms.


Microgram-milligram conversions are frequently encountered in dose calculations. Microgram-gram conversions are occasionally needed in calculations of intravenous doses. Medication errors can occur when the prescriber writes an order in micrograms and the nurse mistakes it for milligrams or vice versa.


Microgram-gram conversions can be reduced to one step if desired by using the conversion factor 1,000,000 mcg = 1 g, since micro- means one millionth of the base unit.



EXAMPLES


Conversion factor: 1,000,000 mcg = 1 g.





























Ordered   Equivalent Decimal Movement
0.5 g = 500,000 mcg decimal moved six places to the right
250,000 mcg = 0.250000 g implied decimal moved six places to the left
0.004 g = 4000 mcg decimal moved six places to the right


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TEST TIP:


If you are comfortable with milligram conversions (milligrams to micrograms and milligrams to grams), use a stepped approach for microgram-gram conversions. First, change the ordered amount to milligrams and then to micrograms.






RAPID PRACTICE 5-4   Moving Decimal Places for Microgram-Gram Conversions


Estimated completion time: 5-10 minutes Answers on page 501


Directions: Convert the units ordered to milligrams and then micrograms (mental arithmetic).



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RAPID PRACTICE 5-5   Decimal Conversions Using One or Two Conversion Factors


Estimated completion time: 10-15 minutes Answers on page 502


Directions: Make the units equivalent.




























































Needed Conversion Number of Decimal Places to Be Moved Answer
1 0.3 g = ? mg __________ __________
2 200 mcg = ? mg __________ __________
3 0.5 mg = ? mcg __________ __________
4 15,000 mcg = ? g __________ __________
5 0.004 g = ? mcg __________ __________
6 2200 mg = ? g __________ __________
7 350 mcg = ? mg __________ __________
8 50,000 mcg = ? g __________ __________
9 0.05 g = ? mg __________ __________
10 500 mg = ? g __________ __________


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RAPID PRACTICE 5-6   Metric Oral Medication Calculation Practice


Estimated completion time: 30 minutes Answers on page 502


Directions: Study the medication order and the unit dose supplied. Estimate the answer and verify it with a DA equation. Evaluate the answer. Is the equation balanced? Does the estimate support the answer?






1. Ordered: codeine sulfate 60 mg stat for a patient in pain.


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2. Ordered: Ativan 1 mg PO prn at bedtime for a patient with anxiety.


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3. Ordered: Biaxin 0.25 g PO daily for a patient with an infection.


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4. Ordered: Lopressor 0.1 g PO daily at bedtime for a patient with hypertension (ATN).


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image Communication


Nurse: “Mr. Jones, I have your blood pressure medication, lopressor, __ mg. “Do you take this at home?”


Mr. Jones: “I take blood pressure medication but I can’t remember the name or how much.”


Nurse: “It has another name, metoprolol.”


Mr. Jones: “That’s what I take at home, but it’s a different color.”


The nurse holds the medication and rechecks the order because a different color of the same medication indicates a different dose. If there is nothing on the record to indicate why the dose would be changed, the prescriber needs to be contacted promptly.








RAPID PRACTICE 5-7   Metric Oral Medication Calculation Practice


Estimated completion time: 20 minutes Answers on page 503


Directions: Estimate answer and verify with DA equation. Evaluate the answer. Supply needed conversion factors.




1. Ordered: alprazolam 0.5 mg PO q12h for a patient with anxiety.


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2. Ordered: sulfisoxazole 1000 mg PO tid for a patient with a recurrent urinary tract infection.


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3. Ordered: vasotec 5 mg daily at bedtime for a patient with hypertension.


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4. Ordered: zidovudine capsules 0.3 g PO bid for a patient who is HIV positive.


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5. Ordered: diltiazem HCl 0.12 g PO daily for a patient with hypertension (HTN).


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Analyzing Liquid Dose Orders


Liquids may be supplied in a variety of containers. As with all dose calculations, the ordered dose and the drug concentration noted on the label must be included in the calculation. Liquid medications ordered and supplied in milligrams may require a calculation if the dose is supplied in more than 1 mL of solution. The estimate of the answer can be made right away if the metric units are matched. Compare the result with your estimate.





Rounding numbers to simplify estimated liquid dose






EXAMPLES


Ordered: 300 mg.


Available: 75 mg in 1 mL of liquid


It is obvious that the order calls for much more than the unit dose per milliliter supplied. The nurse might approximate the dose by rounding the 75 up to 100 for easier division, giving a rough estimate of around 3 or more unit doses. The exact calculation requires a DA equation.



EXAMPLES


Examine the following order:


Ordered: 200 mg liquid.


Available: 80 mg per 5 mL concentration.


The terms are the same: milligrams. It is obvious that the order for 200 mg exceeds two times the dose (80 mg) per volume on hand. Thus, the estimate is that more than 10 mL will be given. Follow the estimate with an exact calculation in a DA equation. Compare the result with the estimate.






RAPID PRACTICE 5-8   Metric Conversions and Estimating Answers for Liquid Medications


Estimated completion time: 10 minutes Answers on page 503


Directions: Examine the order and the label concentration. Follow the example in problem 1 to estimate the dose to be administered to the nearest milliliter or number of tablets.




































Dose Ordered Concentration Available Conversion Give Same, More, or Less of Available Dose per Volume Estimated Amount
1 0.25 g 250 mg per mL 0.25 g = 250 mg Same 1 mL
2 5000 mcg 2.5 mg per mL
3 0.1 g 300 mg per mL
4 750 mg 0.5 g per mL
5 200 mg 0.1 g per mL


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CLINICAL RELEVANCE


Liquid unit dose concentrations are often written with a slash (e.g., 100 mg/5 mL). The slash mark (/) appears in printed drug literature for drug concentrations. It should not be handwritten in a patient’s medical record. The slash can be misinterpreted as the number 1 if it occurs next to a number. For example, 100 mg/5 mL could be read as 100 mg per 15 mL instead of 5 mL. Write per instead of using the slash: 100 mg per 5 mL. The slash is clearly seen in printed materials.






Setting Up DA-Style Equations for Liquid Dose Calculations


Review: The process required is to multiply a given quantity by one or more conversion factors to solve an equation. The process is the same for a liquid as for a solid.



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Mar 1, 2017 | Posted by in NURSING | Comments Off on Solid and Liquid Oral Dose Calculations

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