31. T he recommended maintenance dose of beclomethasone dipropionate (BECLO VEN T ), an aerosolized inhalant, is 100 mcg administered twice daily.
T he commercial inhaler delivers 50 mcg per metered inhalation and contains 200 inhalations. H ow many inhalers should be dispensed to a patient if a 60-day supply is prescribed?
32. A 16-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, followed by a 14-mg patch each day for the next 2 weeks, and then a 7-mg patch for the next 2 weeks to conclude the treatment regimen. In all, how many milligrams of nicotine are administered?
33. A transdermal patch contains 5 mg of fentanyl and has a drug-release rate of 50 mcg/hour. T he patch is worn for 72 hours. Calculate (a) the milligrams of fen- tanyl 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.
34. If a VEN T OLIN inhaler contains 20 mg of albuterol, how many inhalation doses can be delivered if each inhalation dose contains 90 mcg?
35. FLON ASE nasal spray contains 50 mcg of fluticasone propionate per actuation spray in each 100 mg of formulation. Each container provides 120 metered sprays.
H ow many milligrams of fluticasone propionate are contained in each container?
36. T he dose of diclofenac sodium (VOLTAREN GEL), when applied to the hands in the treatment of arthritic pain, is 2 g four times a day. T he gel contains diclof- enac sodium 1% and is available in 100-g tubes. H ow many grams of the drug diclofenac sodium would be administered per day, and how many days of treat- ment 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
37. SYMBICORT 80/4.5 is an oral inhalation product containing 80 mcg of budesonide and 4.5 mcg of formoterol fumarate per inhalation. T he dose is stated as “two inha- lations twice daily.” H ow 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
38. An aerosol oral inhaler delivers, per actuation, 40 mcg of beclomethasone dipro- pionate. T he recommended starting dose is 40 to 80 mcg twice daily. T he highest recommended dose is 320 mcg twice daily. Compare the number of daily inhaler actuations to deliver the lowest starting dose and the highest recommended dose.
126 Pharma euti al c al ulations
CAl Cq UIz
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 adminis- tered 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 four fluid ounce (118 mL) container. If the labeled dose is 2 tablespoonful 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 µg of mometasone furoate and 5 µg of formoterol fumarate. The recommended dose is
“two inhalations twice daily (morning and evening).” Calculate the quantity, in mil- ligrams, 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 resi- due 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.”
An Sw ERS To “CASE In p o In T” An D p RACTICE p Ro b l EmS Case in Point 7.1
First, calculate the volume of cough syrup containing the child’s dose of 1.5 mg of dextromethorphan H Br:
30 15
1 5 0 75
mg mL
mg
x mL x mL
= . =
; .
T hen determine the number of drops of cough syrup that will provide the 0.75-mL dose:
1 20
0 75 15 mL
drops
mL x drops
x drops of cough syrup
=
=
. ;
7 • c al ulation of Doses: General c onsiderations 127
Practice Problems
1. Two hundred ten 0.25-mg rop- inirole tablets
2. T hirty-five 25-mg tablets and seventy 5-mg tablets
3. 5.25 mg conjugated estrogen
4. 230 mg amlodipine besylate and 460 mg atorvastatin calcium
5. (a) $17.50 (b) 4.2%
6. 70 tablets
7. (d) 32 tablets, 0.5 gallon liquid, 48 g sodium phosphates
8. (d) 11 0.5-mg tablets and 154 1-mg tablets
9. (a) 5 drops ciprofloxacin otic solution
(b) 100-mg ciprofloxacin/drop 10. (a) 50 mg acetaminophen
(b) 11 drops
11. 14 mcg cyclosporine 12. 6 drops
13. (a) 20 mg simethicone
(b) 3.6 mL of infants’ MYLICO N drops
(c) 240 mg simethicone 14. 25 mg rimantadine H Cl 15. 1 tablespoonful
16. 40 divided doses sodium oxybate oral solution
17. 1 bottle of posaconazole oral suspension
18. 200 mL tetracycline H Cl syrup 19. 7 mg alkaloids
20. 20 mL digoxin elixir 21. (a) 40 doses
(b) 2.5 mL/dose
(c) 100 mL ciprofloxacin oral suspension
22. 11 + days
23. 1.2 g dextromethorphan H Br 24. (a) 100-mL package
(b) 8000 mg or 8 g of amoxicillin 25. 0.8 mL MEPERG AN and 0.375
mL atropine sulfate injections 26. 0.6 mL aminophylline injection 27. 0.4 mL LAN O XIN injection
28. 9 prefilled syringes, 40 mg/0.8 mL 29. (a) 0.02 mL per dose
(b) 60 doses per pen (c) 30 days
30. 60 mcg/0.1 mL 31. 2 inhalers
32. 1176 mg nicotine 33. (a) 1.2 mg fentanyl
(b) 1.4 mg fentanyl (c) 28%
34. 222 doses
35. 6 mg fluticasone propionate
36. (d) 0.08 g diclofenac sodium per day for 12.5 days
37. (d) 0.32 mg budesonide and
0.018 mg formoterol fumarate 38. 2 actuations (lowest daily starting
dose) and 16 actuations (highest daily recommended dose)
References
1. Drug Facts and Comparisons. St. Louis, MO: Wolters Kluwer H ealth; 2014.
2. Physicians’ Desk Reference. Montvale, N J: Medical Economics; 2014:68.
3. Taketomo CK. Pediatric & N eonatal Dosage Handbook. 20th Ed. H udson, O H : Lexicomp/Wolters Kluwer H ealth Clinical Solutions; 2013–2014.
4. Semla T P. Geriatric Dosage Handbook. 19th Ed. H udson, O H : Lexicomp/Wolters Kluwer H ealth Clinical Solutions; 2013–2014.
5. Drug Information Handbook. 23rd Ed. H udson, O H : Lexicomp/Wolters Kluwer H ealth Clinical Solutions;
2014–2015.
6. T he Joint Commission. Available at: http://www.jointcommission.org/assets/1/18/SEA_39.PD F. Accessed May 1, 2014.
128 Pharma euti al c al ulations
7. U.S. Food and Drug Administration. Use of over-the-counter cough and cold products in infants and children.
Available at: http://www.fda.gov/D rugs/D rugSafety/D rugSafetyPodcasts/ucm077935.htm. Accessed July 24, 2014.
8. U nited States Pharmacopeial Convention. United States Pharmacopeia 32 N ational Formulary 27. Vol. 1.
Rockville, MD: United States Pharmacopeial Convention; 2009:728.
9. U nited States Pharmacopeial Convention. United States Pharmacopeia 32 N ational Formulary 27. Vol. 1.
Rockville, MD: United States Pharmacopeial Convention; 2009:604.
10. Actavis Pharma, Inc. LO LO EST RIN FE, product information. Available at: http://www.loloestrin.com/
Accessed July 24, 2014.
11. Santen RJ, Allred D C, Ardoin SP, et al. Postmenopausal hormone therapy: an endocrine society scientific statement. J Clin Endocrinol M etab 2010;95:S1–S66.
12. Available at: http://www.women.webmd.com/endometriosis/high-dose-progestin-for-endometriosis. Accessed July 25, 2014.
13. Foster SL, Moore W P. H igh-dose influenza vaccination in the elderly. J Am Pharm Assoc 2010;50:546–547.
14. Rashed SM, N olly RJ, Robinson L, et al. Weight variability of scored and unscored split psychotropic drug tablets. Hosp Pharm 2003;38:930–934.
15. H ill SW, Varker AS, Karlage K, et al. Analysis of drug content and weight uniformity for half-tablets of 6 com- monly split medications. J M anag Care Pharm 2009;15:253–261.
16. Verrue C, Mehuys E, Boussery K, et al. Tablet-splitting: a common yet not so innocent practice. J Adv Nurs 2010;67:26–32.
17. Green G, Berg C, Polli JE, et al. Pharmacopeial standards for the subdivision characteristics of scored tablets.
Pharmacopeial Forum 2009;35:1598.
18. Food and D rug Administration, D epartment of H ealth and H uman Services. Tablet splitting.
Available at: http:/ / www.fda.gov/ D rugs/ ResourcesForYou/ C onsumers/ BuyingU singM edicineSafely/
EnsuringSafeU seofMedicine/ucm265754.htm. Accessed May 1, 2014.
19. Food and Drug Administration, D epartment of H ealth and H uman Services. Best Practices for Tablet Splitting.
Available at: http:/ / www.fda.gov/ D rugs/ ResourcesForYou/ C onsumers/ BuyingU singM edicineSafely/
EnsuringSafeU seofMedicine/ucm184666.htm. Accessed May 1, 2014.
20. Food and D rug Administration, Center for D rug Evaluation and Research, D epartment of H ealth and H uman Services. Guidance for Industry: Tablet Scoring: N omenclature, Labeling, and Data for Evaluation.
Available at: http://www.fda.gov/downloads/Drugs/GuidanceComplianceRegulatoryInformation/G uidances/
UCM269921.pdf. Accessed May 1, 2014.
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22. Beach W. College of Pharmacy. Athens, G A: T he University of G eorgia; 2004.
As noted in the previous chapter, the usual dose o a drug is the amount that ordinarily pro- duces the desired therapeutic response in the majority o patients in a general, or otherwise de ned, population group. T he drug’s usual dosage r ange is the range o dosage determined to be sa e and e ective in that same population group. T his provides the prescriber with dosing guidelines in initially selecting a drug dose or a particular patient and the f exibil- ity to change that dose as the patient’s clinical response warrants. U sual doses and dosage regimens are based on the results o clinical studies conducted during the drug development process as well as on clinical in ormation gathered ollowing the initial approval and market- ing o the drug (postmarketing surveillance/postmarketing studies).
For certain drugs and or certain patients, drug dosage is determined on the basis o speci ic patient parameters. T hese parameters include the patient’s age, weight, body sur- ace area, and nutritional and unctional status. D rug selection and drug dosage in patients who are pregnant and in nursing mothers are especially important considerations due to potential harm to the etus or child.
Among patients requiring individualized dosage are neonates and other pediatric patients, elderly patients with diminished biologic unctions, individuals o all age groups with compro- mised liver and/or kidney unction (and thus reduced ability to metabolize and eliminate drug substances), critically ill patients, and patients being treated with highly toxic chemotherapeutic agents. Certain drugs with a narrow therapeutic window o ten require individualized dosing based on blood level determinations and therapeutic monitoring. Digoxin, or example, at a blood level o 0.9 to 2 ng/mL is considered therapeutic, but above 2 ng/mL, it is toxic.1
Since age, body weight, and body sur ace area are o ten-used actors in determining the doses o drugs or pediatric and elderly patients, these parameters represent the major- ity o the calculations presented in this chapter. T he dosing o chemotherapeutic agents also is included because it represents a unique dosing regimen compared with most other categories o drugs.