calculation of oral medication

Calculate with ConfidenceCalculate with Confidence55thth edition edition

Gray MorrisGray Morris

Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Calculation of Oral MedicationsCalculation of Oral Medications

Unit Four: Chapter 17Unit Four: Chapter 17

Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

3Mosby items and derived items © 2010 by Mosby, Inc., an affiliate of Elsevier Inc.

Calculation of Oral Medications: Calculation of Oral Medications: ObjectivesObjectives

After reviewing this chapter, you should be able to:After reviewing this chapter, you should be able to:

1.1. Identify forms of oral medicationsIdentify forms of oral medications

2.2. Identify terms on labels used in calculationIdentify terms on labels used in calculation

3.3. Calculate dosages for oral medications using Calculate dosages for oral medications using ratio and proportion, the formula method, and ratio and proportion, the formula method, and dimensional analysisdimensional analysis

4.4. Apply principles to obtain rational answersApply principles to obtain rational answers


Background: Oral MedicationsBackground: Oral Medications

Most economicalMost economical Easiest to administerEasiest to administer Most common type of medication givenMost common type of medication given Available as solids and liquidsAvailable as solids and liquids


Forms of Solid MedicationsForms of Solid Medications

Tablets Tablets Powdered medications molded in shapesPowdered medications molded in shapes

Caplets Caplets Elongated tablets coated to ease swallowingElongated tablets coated to ease swallowing

Scored tablets—use pill cutterScored tablets—use pill cutter Tablets with indented markings designed to cut Tablets with indented markings designed to cut

and deliver ½ to ¼ what is in a whole tabletand deliver ½ to ¼ what is in a whole tablet

Note: Breaking an unscored tablet is dangerous Note: Breaking an unscored tablet is dangerous

and can result in an unintended doseand can result in an unintended dose


Forms of Solid Medications Forms of Solid Medications (cont’d)(cont’d)

Enteric-Coated TabletsEnteric-Coated Tablets Special coating protects against gastric secretionsSpecial coating protects against gastric secretions NEVER crush EC tablets—defeats the purposeNEVER crush EC tablets—defeats the purpose

Sublingual TabletsSublingual Tablets Placed under tongue for direct absorption Placed under tongue for direct absorption NEVER swallow SL tablets—prevents desired NEVER swallow SL tablets—prevents desired

effecteffect Layered TabletsLayered Tablets

Layers or cores of two meds with different Layers or cores of two meds with different compatibilities or absorption componentscompatibilities or absorption components


Forms of Solid Medications Forms of Solid Medications (cont’d)(cont’d)

Time-Release and Extended-Release TabletsTime-Release and Extended-Release Tablets Labeled SA, LA, XL, SR, or ERLabeled SA, LA, XL, SR, or ER Released over a period of timeReleased over a period of time NEVER crush, chew, or breakNEVER crush, chew, or break

CapsulesCapsules Contains powder, liquid, or oil with hard/soft Contains powder, liquid, or oil with hard/soft

gelatin coatinggelatin coating NEVER crush, chew, or break without consulting a NEVER crush, chew, or break without consulting a

pharmacistpharmacist Others: Troches, Lozenges, PulvulesOthers: Troches, Lozenges, Pulvules


Figure 17-1 A,Figure 17-1 A, Various shapes of tablets. B,Various shapes of tablets. B, Tablets scored in halves and fourths. (From KeeTablets scored in halves and fourths. (From KeeJL, Marshall SM: JL, Marshall SM: Clinical calculations: with applications to general and specialty areas, Clinical calculations: with applications to general and specialty areas, ed. 6, St. Louis, 2009, Saunders.)ed. 6, St. Louis, 2009, Saunders.)

Figure 17-3Figure 17-3 Pill/tablet cutter. (From Kee JL, Marshall SM: Pill/tablet cutter. (From Kee JL, Marshall SM: Clinical calculations: with applications to Clinical calculations: with applications to general and specialty areas, general and specialty areas, ed. 6, St. Louis, 2009, Saunders.)ed. 6, St. Louis, 2009, Saunders.)


Figure 17-4Figure 17-4 Layered tablet. (From Clayton BD,Layered tablet. (From Clayton BD,Stock YN, Harroun RD: Stock YN, Harroun RD: Basic pharmacology for nurses, Basic pharmacology for nurses, ed. 14, St. ed. 14, St.

Louis, 2007, Mosby.)Louis, 2007, Mosby.)

Figure 17-5Figure 17-5 Timed-release capsule. (From Clayton BD, Stock YN,Timed-release capsule. (From Clayton BD, Stock YN,Harroun RD: Harroun RD: Basic pharmacology for nurses, Basic pharmacology for nurses, ed. 14, St. Louis, 2007, ed. 14, St. Louis, 2007,

Mosby.)Mosby.)


Figure 17-6Figure 17-6 Various types of capsules. A,Various types of capsules. A, Lanoxicap. B,Lanoxicap. B, Different types of Different types of capsules. (Acapsules. (A from from Mosby’s drug consult 2003, Mosby’s drug consult 2003, St. Louis, 2003, Mosby. BSt. Louis, 2003, Mosby. B courtesy courtesy

Amanda Politte, St. Louis.)Amanda Politte, St. Louis.)

Figure 17-7Figure 17-7 Forms of solid oral medications. Forms of solid oral medications. Top row, Top row, Uniquely shaped Uniquely shaped tablet, capsule, scored tablet; tablet, capsule, scored tablet; bottom row, bottom row, gelatin-coated liquid capsule, gelatin-coated liquid capsule, extended-release capsule, enteric-coated tablet. (From Potter PA, Perry extended-release capsule, enteric-coated tablet. (From Potter PA, Perry

AG: AG: Fundamentals of nursing, Fundamentals of nursing, ed. 7, St. Louis, 2009, Mosby.)ed. 7, St. Louis, 2009, Mosby.)

Figure 17-8Figure 17-8 Various sizes of gelatin capsules. (Courtesy Various sizes of gelatin capsules. (Courtesy Oscar H Allison. From Clayton BD, Stock YN, Harroun RD: Oscar H Allison. From Clayton BD, Stock YN, Harroun RD:

Basic pharmacology for nurses, Basic pharmacology for nurses, ed. 14, St. Louis, 2007, ed. 14, St. Louis, 2007, Mosby.)Mosby.)


Points to RememberPoints to Remember

Converting dosages from apothecary to Converting dosages from apothecary to metric can result in discrepanciesmetric can result in discrepancies ASA (CF: gr i = 60 to 65 mg)ASA (CF: gr i = 60 to 65 mg)

10% rule—no more than 10% variance 10% rule—no more than 10% variance should exist between dose ordered and dose should exist between dose ordered and dose administeredadministered

Capsules are administered wholeCapsules are administered whole Tablets are available in different strengthsTablets are available in different strengths


Points to Remember (cont’d)Points to Remember (cont’d)

It is safer to give whole tablets equal to the It is safer to give whole tablets equal to the dose than to cut tabletsdose than to cut tablets

Maximum number of tablets or capsules used Maximum number of tablets or capsules used to deliver a dose is usually three (3)to deliver a dose is usually three (3) Exceptions exist, such as some HIV meds—Exceptions exist, such as some HIV meds—

always double-check dosagealways double-check dosage Some measures and units such as mEq do Some measures and units such as mEq do

not convert between metric and apothecarynot convert between metric and apothecary


ExamplesExamples

The following three examples are based on The following three examples are based on

this order:this order:

Give: Digoxin 0.375 mg p.o. dailyGive: Digoxin 0.375 mg p.o. daily

Available: Digoxin in scored tablets of 0.25 mgAvailable: Digoxin in scored tablets of 0.25 mg


0.25 mg : 1 tab = 0.375 mg : tab (known) (unknown)(available) (ordered)

0.25 mg 0.375 mg1 tab tab0.25 = 0.375 (1)0.25 0.3750.25 0.25

11.5 tabs = 1 tabs

2

x

xx

x

x

Ratio and Proportion MethodRatio and Proportion Method


Formula MethodFormula Method

(D) 0.375 mg (Q) 1 tab = x tab

(H) 0.25 mg0.375

= 0.25

1 1 tabs

2

x

x


1 tab 0.375 mg

tab = 0.25 mg 1

0.375 tab =

0.251

= 1 tabs2

x

x

x

Dimensional Analysis MethodDimensional Analysis Method


Additional ExampleAdditional Example

The following example is a dimensional The following example is a dimensional analysis item that incorporates a conversion analysis item that incorporates a conversion and is based on this order:and is based on this order:

Give: Nitroglycerin gr 1/150 sublingual p.r.n. Give: Nitroglycerin gr 1/150 sublingual p.r.n. chest painchest pain

Available: Sublingual nitroglycerin tabs labeled Available: Sublingual nitroglycerin tabs labeled 0.4 mg0.4 mg


Dimensional Analysis Dimensional Analysis with Conversionwith Conversion

1gr 1 tab 60 mg 150 tab =

0.4 mg gr i 11

60 150 tab =

0.460

150 = 0.4

0.40.4 1 tab

x

x

x

x

x


Variations of Tablet/Capsule Variations of Tablet/Capsule ProblemsProblems

To determine the number of tablets needed To determine the number of tablets needed over a period of days, multiply doses per over a period of days, multiply doses per day by the number of daysday by the number of days

Example: Valium 10 mg p.o. q.i.d for 7 days. Tablets Example: Valium 10 mg p.o. q.i.d for 7 days. Tablets available are 5 mg tablets.available are 5 mg tablets.

1.1. Multiply 5 mg Multiply 5 mg 2 for each dose = 2 tablets per 2 for each dose = 2 tablets per dosedose

2.2. Multiply 2 tablets Multiply 2 tablets 4 for 4 doses/day = 8 4 for 4 doses/day = 8 tablets/daytablets/day

3.3. Multiply 8 tablets per day Multiply 8 tablets per day 7 to find number 7 to find number needed for 7 days = 56 tabletsneeded for 7 days = 56 tablets


Variations of Tablet/Capsule Variations of Tablet/Capsule Problems (cont’d)Problems (cont’d)

Determining dosage to be given each timeDetermining dosage to be given each timeExample: A client is to receive 1 g of a drug daily in Example: A client is to receive 1 g of a drug daily in

four divided dosesfour divided doses

Total daily allowance Dosage to be delivered

Number of doses per day1 g or (1,000 mg)

= 250 mg each time the medication is given4


Calculating Oral LiquidsCalculating Oral Liquids For clients with dysphagia (difficulty swallowing) For clients with dysphagia (difficulty swallowing)

or a nasogastric, jejunostomy, or gastrostomy or a nasogastric, jejunostomy, or gastrostomy tubetube

For infants and young childrenFor infants and young children Types—may contain multiple medsTypes—may contain multiple meds

Elixir—meds dissolved in alcohol and water—Elixir—meds dissolved in alcohol and water—aromaticaromatic

Suspension—meds dissolved in waterSuspension—meds dissolved in water Syrup—one or more meds dissolved in sugar and Syrup—one or more meds dissolved in sugar and

waterwater

Note: NEVER give oral liquids by IV–FATAL!Note: NEVER give oral liquids by IV–FATAL!


Measuring Oral LiquidsMeasuring Oral Liquids

1.1. Standard calibrated measuring cupStandard calibrated measuring cup Metric, apothecary, or household measureMetric, apothecary, or household measure Place on flat surface and view at eye levelPlace on flat surface and view at eye level Pour with label facing you so it can be readPour with label facing you so it can be read

2.2. Calibrated droppersCalibrated droppers Use only dropper supplied with medicationUse only dropper supplied with medication

3.3. Calibrated oral syringes (tsp/mL marks)Calibrated oral syringes (tsp/mL marks) Used for accuracy of liquid doses (e.g., 6.4 mL)Used for accuracy of liquid doses (e.g., 6.4 mL) Pour medication in cup and draw up into syringePour medication in cup and draw up into syringe NEVER use oral syringes for parenteral medsNEVER use oral syringes for parenteral meds


Figure 17-9Figure 17-9 Reading meniscus. The meniscus is caused byReading meniscus. The meniscus is caused bythe surface tension of the solution against the walls of the container.the surface tension of the solution against the walls of the container.

The surface tension causes the formation of a concave orThe surface tension causes the formation of a concave orhollowed curvature on the surface of the solution. Read the levelhollowed curvature on the surface of the solution. Read the level

at the lowest point of the concave curve. (From Clayton BD,at the lowest point of the concave curve. (From Clayton BD,Stock YN, Harroun RD: Stock YN, Harroun RD: Basic pharmacology for nurses, Basic pharmacology for nurses, ed. 14,ed. 14,

St. Louis, 2007, Mosby.)St. Louis, 2007, Mosby.)

Figure 17-11Figure 17-11 Oral syringes. (Courtesy Chuck Dresner. From Clayton BD, Stock YN,Oral syringes. (Courtesy Chuck Dresner. From Clayton BD, Stock YN,Harroun RD: Harroun RD: Basic pharmacology for nurses, Basic pharmacology for nurses, ed. 14, St. Louis, 2007, Mosby.)ed. 14, St. Louis, 2007, Mosby.)

Figure 17-10Figure 17-10 Medicine dropper. (Modified fromMedicine dropper. (Modified fromClayton BN, Stock YN, Harroun RD: Clayton BN, Stock YN, Harroun RD: Basic Basic

pharmacology for nurses, pharmacology for nurses, ed. 14,ed. 14,St. Louis, 2007 Mosby.)St. Louis, 2007 Mosby.)

Figure 17-12Figure 17-12 Filling a syringe directly from medicineFilling a syringe directly from medicinecup. (Modified from Clayton BD, Stock YN, Harroun RD:cup. (Modified from Clayton BD, Stock YN, Harroun RD:Basic pharmacology for nurses, Basic pharmacology for nurses, ed. 14, St. Louis, 2007,ed. 14, St. Louis, 2007,

Mosby.)Mosby.)


Measuring Oral Liquids (cont’d)Measuring Oral Liquids (cont’d)

Do NOT confuse dosage strength with total Do NOT confuse dosage strength with total volume in containervolume in containerExample: May contain 100 mL in bottle, but strength Example: May contain 100 mL in bottle, but strength

will be something like 125 mg in 5 mLwill be something like 125 mg in 5 mL Calculations are performed in the same Calculations are performed in the same

manner as for solid forms of medicinesmanner as for solid forms of medicines


Order: Dilantin 200 mg p.o. t.i.d.Order: Dilantin 200 mg p.o. t.i.d.Available: Dilantin suspension 125 mg in 5 mLAvailable: Dilantin suspension 125 mg in 5 mL

125 mg : 5 mL = 200 mg : mL(known) (unknown)

125 = 200 5125 1,000125 125

1,000125

8 mL

x

x

x

x

x

calculation of oral medication

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