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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_5576_Библиотеки_им_академика_М_И_Перельмана
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A physician prescribes tetracycline HCl syrup for a patient who is
to take 2 teaspoonfuls four times per day for 4 days, and then 1
teaspoonful four times per day for 2 days. How many milliliters of
the syrup should be dispensed to provide the quantity for the
prescribed dosage regimen?
Ipecac oral solution has the following formula:
Powdered ipecac contains 2 grams of the combined alkaloids emetine
and cephaeline in each 100 grams of powder. Calculate the quantity of
these alkaloids, in milligrams, in each 5-mL dose of ipecac oral solution.
A loading dose of digoxin for sustained fetal supraventricular
tachyarrhythmia is a total of 1 mg to be administered to the mother
for transplacental transfer to the fetus. One-half of this dose should
be administered initially followed by the remaining one-half of the
dose divided into two doses and administered at intervals of 6 to 8
hours. How many milliliters of digoxin elixir containing 50 μg/mL
would provide the 1-mg dose?
Ciprofloxacin (CIPRO) oral suspension contains 250 mg of
ciprofloxacin per 5 mL. A physician prescribed 125 mg of
ciprofloxacin b.i.d. × 10 days. (a) How many doses are needed? (b)
How many milliliters should be given per dose? (c) How many
milliliters of ciprofloxacin oral suspension containing 250 mg per 5
mL should be dispensed?
A patient has been instructed to take 15 mL of alumina and
magnesium oral suspension four times daily. How many days will
two 12-fl. oz. bottles of the suspension last?
How many grams of dextromethorphan HBr would be needed to
fill the prescription?
The dose of AUGMENTIN oral suspension for a patient is 5 mL
b.i.d. Each 5 mL of suspension contains 400 mg of amoxicillin and
57 mg of clavulanic acid. If the suspension is to be taken for 10
days and is available in 50-mL, 75-mL, and 100-mL containers,
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calculate (a) the least wasteful package size to dispense and (b)
total quantity of amoxicillin taken during the treatment period.
Doses: Injections
A physician ordered 20 mg of meperidine hydrochloride and 0.3
mg of atropine sulfate to be administered preoperatively to a
patient by intravenous injection. Meperidine hydrochloride is
available in a vial containing 25 mg/mL and atropine sulfate is in a
vial containing 0.4 mg/mL. How many milliliters of each should be
used in filling the medication order?
How many milliliters of an injection containing 250 mg of
aminophylline in each 10 mL should be used in filling a medication
order calling for 15 mg of aminophylline?
Pediatric LANOXIN injection contains digoxin, 100 mcg/mL.
What volume must be administered to provide a dose of 0.04 mg?
23
In treating Crohn’s disease, the recommended dose of the
monoclonal antibody adalimumab (HUMIRA) is 160 mg as the
first dose, a second dose of 80 mg 2 weeks later, then a third dose
of 40 mg 2 weeks after the second dose, and followed by a
maintenance dose of 40 mg every 2 weeks. How many prefilled
syringes, each containing adalimumab, 40 mg/0.8 mL, would be
required for the initial 2 months of treatment?
BYETTA injection, as an adjunct for glycemic control in type 2
diabetes mellitus, contains 250 mcg of exenatide in each milliliter
of solution. The injection is available in 1.2-mL prefilled pens. At a
starting dose of 5 mcg b.i.d, (a) how many milliliters are injected
per dose, (b) how many doses are contained in each pen, and (c)
how many days will the dosing pen last the patient?
A patient weighing 77 kg should receive a dose of 1.23 g of
daratumumab (DARZALEX) in treating multiple myeloma. The
drug is available in a 20-mL vial containing 400 mg of
daratumumab. How many milliliters of this solution should be
administered to provide the recommended dose?
Doses: Other Dosage Forms
The initial dose of beclomethasone dipropionate (QVAR
REDIHALER), a breath-activated aerosolized anti-inflammatory
drug for inhalation, is 80 mcg administered twice daily. The
commercial inhaler delivers 40 mcg per metered inhalation and
contains 120 inhalations. How many inhalers should be dispensed
to a patient if a 60-day supply is prescribed?
A 10-week regimen for a brand of a nicotine patch calls for a
patient to wear a 21-mg patch each day for the first 6 weeks,
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followed by a 14-mg patch each day for the next 2 weeks, and then
a 7-mg patch daily for the next 2 weeks to conclude the treatment
regimen. In all, how many milligrams of nicotine are administered?
A transdermal patch contains 6.2 mg of fentanyl and has a drug-
release rate of 50 mcg/hour. The patch is worn for 72 hours.
Calculate (a) the milligrams of fentanyl delivered daily, (b) the
milligrams of fentanyl remaining in the patch when it is removed,
and (c) the percentage of drug remaining in the patch when it is
removed.
VENTOLIN HFA inhaler delivers 75 mg of albuterol sulfate
suspension for inhalation with each actuation dose, and each dose
contains 108 mcg of albuterol sulfate equivalent to 90 mcg of
albuterol. How many doses can be delivered from an inhaler
containing 18 g of albuterol sulfate suspension?
FLONASE nasal spray contains 50 mcg of fluticasone propionate
per actuation spray in each 100 mg of formulation. Each container
provides 120 metered sprays. How many milligrams of fluticasone
propionate are contained in each container?
The dose of diclofenac sodium (VOLTAREN GEL), when applied
to the hands in the treatment of arthritic pain, is 2 g four times a
day. The gel contains diclofenac sodium 1% and is available in
100-g tubes. How many grams of the drug diclofenac sodium
would be administered per day, and how many days of treatment
would be available per tube of gel?
a. 8 g diclofenac sodium per day for 8 days
b. 8 g diclofenac sodium per day for 12.5 days
c. 80 mg diclofenac sodium per day for 8 days
d. 0.08 g diclofenac sodium per day for 12.5 days
SYMBICORT 80/4.5 is an oral inhalation product containing 80
mcg of budesonide and 4.5 mcg of formoterol fumarate per
inhalation. The dose is stated as “two inhalations twice daily.” How
much of each drug would be administered daily?
a. 160 mcg budesonide and 9 mcg formoterol fumarate
b. 0.32 mg budesonide and 0.18 mg formoterol fumarate
c. 320 mcg budesonide and 0.18 mg formoterol fumarate
d. 0.32 mg budesonide and 0.018 mg formoterol fumarate
Each blister on the foil strip of an ADVAIR DISKUS 500/5
contains 12.5 mg of a powder mixture consisting of 500 mcg of
fluticasone propionate and 72.5 mcg of salmeterol xinafoate salt
(equivalent to 50 mcg of salmeterol base) with lactose
monohydrate as a diluent. If a patient inhales the contents of one
blister twice daily, how many milligrams of lactose monohydrate is
he inhaling each day?
CALCQUIZ
7.A. The ophthalmic solution ALPHAGAN P contains 0.15%
brimonidine tartrate in 10-mL containers. The recommended dose is
one drop in the affected eye(s) three times daily. If a glaucoma patient
doses each eye, and the dropper used delivers 20 drops/mL, calculate
the quantity, in milligrams, of brimonidine tartrate administered each
day.
7.B. The starting dose of sodium oxybate oral solution (XYREM) is
4.5 g/night divided into two equal doses and administered 2.5 to 4
hours apart. How many milliliters of the oral solution containing
sodium oxybate, 500 mg/mL, should be administered in each divided
dose?
7.C. A pediatric stool softener contains 393.3 mg of docusate sodium
in each 4-fluid ounce (118-mL) container. If the labeled dose is 2
tablespoonfuls for a 5-year-old child, how many milligrams of
docusate sodium would be contained per dose?
7.D. An oral inhalation (DULERA) to treat asthma provides in each
inhalation 100 mcg of mometasone furoate and 5 mcg of formoterol
fumarate. The recommended dose is “two inhalations twice daily
(morning and evening).” Calculate the quantity, in milligrams, of each
drug inhaled daily.
7.E. In an experiment of tablet-splitting effectiveness, a pharmacist
had a pharmacy student split a previously weighed lisinopril tablet
containing 20 mg of drug. On an electronic balance, the whole tablet
weighed 111.62 mg. After splitting, one “half” tablet weighed 51.21
mg and the other “half,” 58.49 mg. There was residue powder
remaining. Calculate (a) the percent of lost tablet (residue), (b) the
percent accuracy in actual weight (to ideal weight) for each “half
tablet,” and (c) the supposed quantity of drug, in milligrams (not
assayed, of course) in each “half tablet.”
ANSWERS TO “CASE IN POINT” AND
PRACTICE PROBLEMS
Case in Point 7.1
First, calculate the volume of cough syrup containing the child’s dose of
1.5 mg of dextromethorphan HBr:
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Then determine the number of drops of cough syrup that will provide
the 0.75-mL dose:
Practice Problems
Two hundred ten 0.25-mg ropinirole tablets
Thirty-five 25-mg tablets and seventy 5-mg tablets
5.25 mg conjugated estrogen
230 mg amlodipine besylate and 460 mg atorvastatin calcium
a. $17.50
b. 4.17%
70 tablets
32 tablets, 0.5 gallon liquid, 48 g sodium phosphates
11 0.5-mg tablets and 154 1-mg tablets
a. 5 drops ciprofloxacin otic solution
b. 100-μg ciprofloxacin/drop
a. 50 mg acetaminophen
b. 11 drops
14 mcg cyclosporine
6 drops
a. 20 mg simethicone
b. 3.6 mL of infants’ MYLICON drops
c. 240 mg simethicone
50 mg guaifenesin
1 tablespoonful
35 divided doses prednisolone oral solution
1 bottle of posaconazole oral suspension
200 mL tetracycline HCl syrup
7 mg alkaloids
20 mL digoxin elixir
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a. 20 doses
b. 2.5 mL/dose
c. 50 mL ciprofloxacin oral suspension
11 + days
1.2 g dextromethorphan HBr
a. 100-mL package
b. 8000 mg or 8 g of amoxicillin
0.8 mL meperidine hydrochloride and 0.75 mL atropine sulfate
injections
0.6 mL aminophylline injection
0.4 mL LANOXIN injection
9 prefilled syringes, 40 mg/0.8 mL
a. 0.02 mL per dose
b. 60 doses per pen
c. 30 days
61.5 mL daratumumab injection
2 inhalers
1176 mg nicotine
a. 1.2 mg fentanyl
b. 2.6 mg fentanyl
c. 41.94%
240 doses
6 mg fluticasone propionate
0.08 g diclofenac sodium per day for 12.5 days
0.32 mg budesonide and 0.018 mg formoterol fumarate
23.86 mg lactose per day
References
Facts & Comparisons eAnswers [book online]. Baltimore, MD: Wolters Kluwer Clinical
Drug Information Inc.; 2020.
Prescribers’ Digital Reference [book online]. Whippany, NJ: ConnectiveRx; 2020.
Taketomo CK. Pediatric & Neonatal Dosage Handbook. 26th Ed. Hudson, OH:
Lexicomp/Wolters Kluwer Health Clinical Solutions; 2019–2020.
Drug Information Handbook. 28th Ed. Hudson, OH: Lexicomp/Wolters Kluwer Health
Clinical Solutions; 2019–2020.
U.S. Food and Drug Administration. Drugs@FDA: FDA-Approved Drugs. Available at:
https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm. Accessed March 18, 2020.
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The Joint Commission. Sentinel event alert: preventing pediatric medication errors.
Available at: http://www.jointcommission.org/assets/1/18/SEA_39.PDF. Accessed March
18, 2020.
U.S. Food and Drug Administration. Use of over-the-counter cough and cold products in
infants and children. Available at: https://wayback.archive-
it.org/7993/20170406005356/https://www.fda.gov/Drugs/DrugSafety/DrugSafetyPodcasts/
ucm077935.htm. Accessed March 18, 2020.
National Institute of Standards and Technology. Approximate conversions from U.S.
customary measures to metric. Available at: https://www.nist.gov/pml/weights-and-
measures/approximate-conversions-us-customary-measures-metric. Accessed June 4,
2020.
National Institute of Standards and Technology. Appendix C – General Tables of Units of
Measurement. Available at:
https://www.nist.gov/system/files/documents/2019/11/05/appc-20-hb44_final.pdf.
Accessed June 4, 2020.
Allen LV. Ansel’s Pharmaceutical Dosage Forms and Drug Delivery Systems. 11th Ed.
Baltimore, MD: Wolters Kluwer, Inc.; 2018:464.
Actavis Pharma, Inc. LO LOESTRIN FE, product information. Available at:
https://www.loloestrin.com. Accessed March 18, 2020.
Santen RJ, Allred DC, Ardoin SP, et al. Postmenopausal hormone therapy: an endocrine
society scientific statement. Journal of Clinical Endocrinology & Metabolism 2010;95:S1–
S66.
Doheny K. High-dose statins boost survival. Available at: https://www.webmd.com/heart-
disease/news/20161109/high-dose-statins-boost-survival-study#1. Accessed March 18,
2020.
Foster SL, Moore WP. High-dose influenza vaccination in the elderly. Journal of the
American Pharmacists Association 2010;50:546–547.
Rashed SM, Nolly RJ, Robinson L, et al. Weight variability of scored and unscored split
psychotropic drug tablets. Hospital Pharmacy 2003;38:930–934.
Hill SW, Varker AS, Karlage K, et al. Analysis of drug content and weight uniformity for
half-tablets of 6 commonly split medications. Journal of Managed Care Pharmacy
2009;15:253–261.
Verrue C, Mehuys E, Boussery K, et al. Tablet-splitting: a common yet not so innocent
practice. Journal of Advanced Nursing 2010;67:26–32.
Green G, Berg C, Polli JE, et al. Pharmacopeial standards for the subdivision
characteristics of scored tablets. Pharmacopeial Forum 2009;35:1598.
Food and Drug Administration, Department of Health and Human Services. Tablet
splitting. Available at: https://www.fda.gov/drugs/ensuring-safe-use-medicine/tablet-
splitting. Accessed March 18, 2020.
Food and Drug Administration, Department of Health and Human Services. Best practices
for tablet splitting. Available at: https://www.fda.gov/drugs/ensuring-safe-use-
medicine/best-practices-tablet-splitting. Accessed March 18, 2020.
Food and Drug Administration, Center for Drug Evaluation and Research, Department of
Health and Human Services. Guidance for industry: Tablet scoring: Nomenclature,
labeling, and data for evaluation. Available at: https://www.fda.gov/regulatory-
information/search-fda-guidance-documents/tablet-scoringnomenclature-labeling-and-
data-evaluation. Accessed March 18, 2020.
Prince S. Calculations. International Journal of Pharmaceutical Compounding
2003;7:212.
Beach W. College of Pharmacy. Athens, GA: The University of Georgia; 2004.
8
Calculation of Doses: Patient
Parameters
OBJECTIVES
Upon successful completion of this chapter, the student will be able to:
Calculate doses based on factors of age, body weight, and body
surface area.
Utilize dosing tables and nomograms in calculations.
Calculate doses for single and combination chemotherapy
regimens.
Introduction
As noted in Chapter 7, the usual dose of a drug is the amount that
ordinarily produces the desired therapeutic response in the majority of
patients in a general, or otherwise defined, population group. The drug’s
usual dosage range is the range of dosage determined to be safe and
effective in that same population group. This provides the prescriber with
dosing guidelines in initially selecting a drug dose for a particular patient
and the flexibility to change that dose as the patient’s clinical response
warrants. Usual doses and dosage regimens are based on the results of
clinical studies conducted during the drug development process as well as
on clinical information gathered following the initial approval and
marketing of the drug (postmarketing surveillance/postmarketing
studies).
For certain drugs and for certain patients, drug dosage is determined
on the basis of specific patient parameters. These parameters include the
patient’s age, weight, body surface area, and nutritional and functional
status. Drug selection and drug dosage in patients who are pregnant and
in nursing mothers are especially important considerations due to
potential harm to the fetus or child.
Among patients requiring individualized dosage are neonates and
other pediatric patients, elderly patients with diminished biologic
functions, individuals of all age groups with compromised liver and/or
kidney function (and thus reduced ability to metabolize and eliminate
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drug substances), critically ill patients, and patients being treated with
highly toxic chemotherapeutic agents. Certain drugs with a narrow
therapeutic window often require individualized dosing based on blood
level determinations and therapeutic monitoring. Digoxin, for example, at
a blood level of 0.8 to 2 ng/mL is considered therapeutic, but above 2
ng/mL, it is toxic.
1
Because age, body weight, and body surface area are often-used
factors in determining the doses of drugs for pediatric and elderly
patients, these parameters represent the majority of the calculations
presented in this chapter. The dosing of chemotherapeutic agents also is
included because it represents a unique dosing regimen compared with
most other categories of drugs.
Pediatric Patients
Pediatrics is the branch of medicine that deals with disease in children
from birth through adolescence. Because of the range in age and bodily
development in this patient population, the inclusive groups are defined
further as follows: neonate (newborn), from birth to 1 month; infant, 1
month to 1 year; childhood, 1 year through 5 years; late childhood, 6
years to 11 years; and adolescence, 12 years through 17 years of age.2 A
neonate is considered premature if born at <37 weeks’ gestation.
Proper drug dosing of the pediatric patient depends on a number of
factors, including the patient’s age and weight, overall health status, the
condition of such biologic functions as respiration and circulation, and
the stage of development of body systems for drug metabolism (e.g., liver
enzymes) and drug elimination (e.g., renal system). In the neonate, these
biologic functions and systems are underdeveloped. Renal function, for
example, develops over the span of the first 2 years of life. This fact is
particularly important because the most commonly used drugs in
neonates, infants, and young children are antimicrobial agents, which are
eliminated primarily through the kidneys. If the rate of drug elimination
is not properly considered, drug accumulation in the body could occur,
leading to drug overdosage and toxicity. Thus, the use of
pharmacokinetic data (i.e., the rates and extent of drug absorption,
distribution, metabolism, and elimination; see Chapters 10 and 22),
together with individual patient factors and therapeutic response, provides
a rational approach to pediatric drug dosage calculations.
Special considerations in dose determinations for
pediatric patients
The majority of medications commercially available are formulated and
labeled for adult use. When used for the pediatric patient, appropriate
dosage calculations must be made, and often, so must adjustments to the
concentration of the medication. In the absence of a suitable commercial
preparation, pharmacists may be called upon to compound a medication
for a pediatric patient.
Among the special considerations in pediatric dosing are the
following3:
Doses should be based on accepted clinical studies as reported in the
literature.
Doses should be age appropriate and generally based on body
weight or body surface area.
Pediatric patients should be weighed as close as possible to the time
of admittance to a health care facility and that weight recorded in
kilograms.
As available, pediatric formulations rather than those intended for
adults should be administered.
All calculations of dose should be double-checked by a second
health care professional.
All caregivers should be properly advised with regard to dosage,
dose administration, and important clinical signs to observe.
Calibrated oral syringes should be used to measure and administer
oral liquids.
Doses of drugs used in pediatrics, including neonatology, may be found
in individual drug product literature as well as in references, such as those
listed at the conclusion of this chapter.4,
5
CASE IN POINT 8.1
A hospital pharmacist is asked to determine the dose of clindamycin
for a 3-day-old neonate weighing 3 lb 7 oz. In checking the literature,
the pharmacist determines that the dose is listed as follows4:
<1200 g: 10 mg/kg/day divided q12h
<2000 g and 0 to 7 days old: 10 mg/kg/day divided q12h
<2000 g and >7 days old: 15 mg/kg/day divided q8h
>2000 g and 0 to 7 days old: 15 mg/kg/day divided q8h
>2000 g and >7 days old: 20 to 30 mg/kg/day divided q12h
Each divided dose is to be added to an intravenous infusion at the
scheduled hour and infused over a period of 20 minutes.
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