To calculate the dose for the patient, the pharmacist must first determine the patient’s body surface area. T he pharmacist elects to use the following equation:
BSA m H t cm W t kg
, 2 ( ) ( )
= 3600×
To use this equation, the patient’s weight and height are converted to metric units:
H eight = 5 feet = 60 inches × 2.54 cm/inch = 152.4 cm Weight = 117 lb ÷ 2.2 lb/kg = 53.2 kg
Solving the equation:
BSA m, . . m
.
( )2 152 4 53 2 2
3600 1 50
= ×
=
T he daily dose is calculated as 150 mg/m2 × 1.50 m2 = 225 mg.
To obtain 225 mg, the patient may take two 100-mg capsules, one 20-mg capsule, and one 5-mg capsule daily.
8 • c al ulation of Doses: Patient Parameters 155
Practice Problems
1. 12.5 mg
2. 12.73 mg gentamicin 3. 30 mg gentamicin 4. Overdose
5. IV: 327.3 to 545.5 mg ciprofloxacin Oral: 363.6 to 727.3 mg
ciprofloxacin
6. (a) ½ tsp. (2.5 mL) erythromycin ethylsuccinate
(b) 10 days
7. 4.4 to 7.5 mL chlorothiazide oral suspension
8. 9.55 mL cyclosporin 9. 2 tsp.
10. Yes, calculations were correct.
11. 30 tablets
12. 0.15 mL digoxin injection 13. 145.5 mcg digoxin
14. 3.41 mL
15. (c) 1.08 mL and 0.65 mL filgras- tim injection
16. 7.58 mL phenytoin suspension 17. 4.8 mcg digoxin
18. 18.33 lb 19. 0.073 mL
20. 93.64 or 94 mg 21. 2 capsules
22. (a) 2.8 mL cefdinir oral suspension 23. 160 clarithromycin capsules
24. 1364 mcg dactinomycin 25. 107.39 mg gentamicin
26. 2.5 mL tobramycin injection 27. 300 mg acyclovir
28. 2 mg tobramycin
29. 101.83 mg/kg aspirin 30. 33 lb
31. (a) 37.5 g vancomycin
(b) 1.875 mL vancomycin injection 32. (a) 0.57 mg indomethacin
(b) 0.28 mL indomethacin injection 33. (a) 150 mg metronidazole
(b) 100 mL
(c) 12 metronidazole tablets 34. (a) 7.5 mL
(b) 10 days
35. 545.5 mg and 630 mg 36. 4.5 mg
37. 35.4 mg mitomycin
38. 2.3 mL (187.5 mg) ritonavir 39. (a) 25 mg
(b) 20.83 mg (c) 21.33 mg (d) 36.57 mg
40. (a) 125 mg diphenhydramine H Cl (b) 120 mg diphenhydramine H Cl 41. 52.7 mg cabazitaxel
42. 196.8 mg etoposide 246 mg leucovorin 820 mg 5-fluorouracil 43. 29.7 mg etoposide
44. 372.96 mg carboplatin
45. 1.15 mg/kg/min methotrexate
46. (a) 75 mg melphalan and 600 mg prednisone
(b) 225 tablets
(c) 120 mL prednisone oral solution 47. 1.6 mg vincristine
59.4 mg doxorubicin 480 mg dexamethasone 48. 42 procarbazine tablets
42 prednisone tablets
49. 26.25 g lapatinib and 20.72 g capecitabine
50. 108.7 mg docetaxel
51. 2.7 mL docetaxel injection 52. 1900 mg 5-fluorouracil
95 mg doxorubicin
950 mg cyclophosphamide 53. 375 mg clarithromycin
54. 7.5 mL clarithromycin suspension 55. 2068.2 mg divalproex sodium, ini-
tial dose
4963.6 mg divalproex sodium, maximum dose
56. Four 500-mg tablets, initial dose 57. 9.4 mg/m2
58. 1 mL ritonavir oral solution 59. 7.2 mL beractant suspension 60. 40 mg/m2
61. Correct
156 Pharma euti al c al ulations
62. A 50-mcg levothyroxine sodium tablet
63. (a) 416 mg nelarabine
(b) 416 mL nelarabine injection 64. Twenty 1-mg topotecan capsules
(4/day) and ten 0.025 mg topote- can capsules (2/day)
65. 81.8 mg/m2
66. O ne hundred five 250-mg lapatinib tablets and ninety-eight 500-mg capecitabine tablets
67. (a) 200 mg cefixime (b) 100 mg/5 mL
(c) 100 mL cefixime suspension 68. 574.5 mg trastuzumab and
130.8 mg docetaxel
References
1. Ferri FF. Practical Guide to the Care of the M edical Patient. 8th Ed. Maryland H eights, MO: Elsevier; 2011.
2. Berkow R, ed. T he M erck M anual. 16th Ed. Rahway, N J: Merck Research Laboratories; 1992.
3. T he Joint Commission. Available at: http://www.jointcommission.org/assets/1/18/SEA_39.PD F. Accessed May 5, 2014.
4. Gomella T L, ed. Neonatology: M anagement, Procedures, On-Call Problems, Diseases, and Drugs. 6th Ed. N ew York, N Y: McGraw-H ill; 2009.
5. Taketomo CK. Pediatric & N eonatal Dosage Handbook. 20th Ed. H udson, O H : Lexicomp/Wolters Kluwer H ealth Clinical Solutions; 2013–2014.
6. Mosteller RD. Simplified calculation of body surface area. T he N ew England Journal of M edicine 1987;317:1098.
7. American C ancer Society. Available at: http:/ / www.cancer.org/ Treatment/ TreatmentsandSideEffects/
TreatmentTypes/index. Accessed February 10, 2011.
8. CancerTreatment.net. Available at: http://regimens.cancertreatment.net/. Accessed May 5, 2014.
9. Chemotherapy Advisor. Available at: http://www.chemotherapyadvisor.com/cancer-treatment-regimens/
section/2412/. Accessed May 5, 2014.
10. N ational Cancer Institute. Available at: http://www.cancer.gov/cancertopics/druginfo/alphalist. Accessed May 5, 2014.
11. MediLexicon. Cancer drugs and oncology drugs. Available at: http://www.medilexicon.com/drugs-list/cancer.
php. Accessed May 5, 2014.
12. Schwarz LR. D elivering cytotoxic chemotherapy safely in a community hospital. Hospital Pharmacy 1996;31:1108–1118.
13. Beach W. College of Pharmacy. Athens GA: T he University of Georgia; 2004.
T he potencies o some antibiotics, endocrine products, vitamins, products derived through biotechnology, and biologics (e.g., vaccines) are based on their activity and are expressed in terms o units of activity, in micrograms per milligram, or in other standardized terms o measurement. T hese measures o potency meet standards approved by the Food and Drug Administration as set orth in the United States Pharmacopeia (U SP).1 In addition, the World H ealth O rganization (W H O ) through the International Pharmacopeia (IP) provides interna- tionally agreed upon standards or biological preparations, which def ne potency or activity, as expressed in international units (I.U. or IU).2
T he activity o a drug or biologic agent is determined by comparison against a cor- responding reference standard—an authenticated specimen used in compendial tests and assays. T he required potencies and respective weight equivalents or some drugs are given in Table 9.1. A USP Unit for one drug has no relation to a USP Unit for another drug.
O the drugs or which potency is expressed in units, insulin is perhaps the most com- mon. Commercially available types o insulin vary according to time or onset o action, peak action, and duration o action; however, all are standardized to contain either 100 or 500 insulin units per milliliter o solution or suspension. T hese products are labeled as
“U -100” (Fig. 9.1) or “U-500.” Insulin is dosed by the administration o a speci ic number o units. Specially calibrated insulin syringes (Fig. 9.2) or pre illed, dial-a-dose insulin pens (KwikPen [Lilly] and FlexPen [N ovo N ordisk]) are employed.
Ob j e c t ive s
Upon successful completion of this chapter, the student will be able to:
P rform al ula on n ol ng un of a y and o h r m a ur of po n y.
9
Ca cu a io I vo vi g U i of Ac ivi y a d O h r
M a ur of Po cy
CAl CUl At IOn s CAPs Ul e Units of Activity
The potency of many pharmaceutical products derived from biological sources is based on units of activity. Units of activity are determined against specific biologic standards and vary between products. Generally, there is an established relationship between a product’s units of activity and a measurable quantity (e.g., units per milligram; units per milliliter).
This relationship may be used in a ratio and proportion to determine either the number of units of activity or the weight or volume containing a specified number of units:
Units of activity given Weight or volume given
Units of activit
( ) ( )
=yy given or desired Weight or volume given or desired
( )
( )
158 Pharma euti al c al ulations
t ab 9 .1 • e xAMPl e s Of Dr Ug POt e n Cy e q UIvAl e n t s
D u U i o m o Po c P W i h e ui a a
Alteplase 580,000 USP Alteplase Units per mg of protein
Bacitracin zinc NLT 65 Bacitracin Units per mg
Cefdinir NLT 960 µg and NMT 1020 µg of cefdinir per mg
Clindamycin hydrochloride NLT 800 µg of clindamycin per mg
Cod liver oil In each gram: NLT 180 µg (600 USP Units) and NMT 750 µg (2500 USP Units) of Vitamin A and NLT 1.5 µg (60 USP Units) and NMT 6.25 µg (250 USP Units) of Vitamin D
Erythromycin estolate NLT 600 µg of erythromycin per mg Gentamicin sulfate NLT 590 µg of gentamicin per mg
Heparin sodium NLT 180 USP Heparin Units per mg
Insulin NLT 26.5 USP Insulin Units per mg
Insulin glargine 27.5 units/mg
Insulin glulisine 28.7 units/mg
Insulin human NLT 27.5 USP Insulin Human Units per mg Insulin lispro NLT 27 USP Insulin Lispro Units per mg Interferon alpha-2b 2.6 × 108 international units per mg Interferon alpha-n3 2 × 108 international units per mg Interferon beta-1b 3.2 × 107 international units per mg Neomycin sulfate NLT 600 µg of neomycin per mg
Nystatin NLT 4400 USP Nystatin Units per mg
Penicillin G benzathine NLT 1090 and NMT 1272 Penicillin G Units per mg Penicillin G potassium NLT 1440 and NMT 1680 Penicillin G Units per mg Penicillin V potassium NLT 1380 and NMT 1610 Penicillin V Units per mg Polymyxin B sulfate NLT 6000 Polymyxin B Units per mg
Somatropin 3 international units per mg
Tobramycin NLT 900 µg of tobramycin per mg
Vancomycin NLT 900 µg vancomycin per mg
Vasopressin NLT 300 Vasopressin Units per mg
Vitamin A 1 USP Vitamin A Unit equals the biologic activity of 0.3 µg of the all-trans isomer of retinol
Vitamin D 40 units per µg
aData taken or derived from various literature sources including the United States Pharmacopeia and the International Pharmacopeia.
As noted previously in this text, medication errors can occur when the term units is abbreviated with a “U.” For example, “100U” could be mistaken or “1000” units. T hus, it is recommended that the term units be spelled out as a matter o practice.
Another e ort to reduce medication errors has been implemented by clari ying the contents o certain packages o multidose injections. Figure 9.3 shows the dual statement o strength in the labeling o a H eparin Sodium Injection in which the drug concentration or the entire contents (30,000 USP Units/30 mL) and the concentration per milliliter (1,000 U SP U nits/mL) are displayed.