53. T he literature states the pediatric dose of the antibiotic clarithromycin as “7.5 mg/kg q12h.” Calculate the daily dose in milligrams for a child weighing 55 lb.
54. If, in the previous problem, the medication is administered as a suspension con- taining 125 mg clarithromycin/5 mL, what volume should be administered for each single dose?
55. T he recommended initial once-a-day dose of the neurologic drug divalproex sodium is 25 mg/kg/day, to be increased as indicated to an absolute maximum dose of 60 mg/kg/day. Calculate these quantities for a 182-lb patient.
56. Diproex sodium is available in 250 mg and 500 mg strength tablets. From the information in the previous problem, what strength tablet and quantity could a pharmacist recommend for an initial dose?
8 • c al ulation of Doses: Patient Parameters 151 57. T he recommended pediatric dose of leuprolide acetate suspension for intramus-
cular injection is 7.5 mg, once per month, for a child weighing 25 kg. W hat is the equivalent dose, based on mg/m2, for this child measuring 36 inches in height?
U se the BSA equation as needed.
58. T he starting pediatric dose of ritonavir is 250 mg/m2 twice daily. Calculate the single dose, in milliliters, of an oral solution containing 600 mg of ritonavir in 7.5 mL of solution, for a child with a body surface area of 0.64 m2.
59. Beractant intratracheal sterile suspension may be administered to premature neo- nates within 15 minutes of birth, as indicated, for the prevention and treatment of respiratory distress syndrome. T he suspension is available in 4-mL and 8-mL vials containing 25 mg of drug per milliliter. T he dose is 100 mg/kg of birth weight. Calculate the dose of the suspension for a newborn weighing 1800 g.
60. T he dose of the drug ixabepilone is 40 mg/m2, but if a patient’s BSA is above 2.2 m2, the dose is calculated based on 2.2 m2. U sing Figure 8.3, determine which dose parameter should be used for a patient who is 6 feet tall and weighs 200 lb.
61. T he pediatric dose of levothyroxine sodium is based on both age and body weight, according to the following:
0 to 3 months, 10 to 15 mcg/kg/day 3 to 6 months, 8 to 10 mcg/kg/day 6 to 12 months, 6 to 8 mcg/kg/day 1 to 5 years, 5 to 6 mcg/kg/day 6 to 12 years, 4 to 5 mcg/kg/day
Verify the correctness of a physician’s order for the dispensing of 100-mcg tablets to be taken once a day by a 6-year-old child weighing 48 lb.
62. Levothyroxine sodium tablets may be crushed and suspended in water and administered by spoon or drop to infants and children who cannot swallow intact tablets. From the information in the previous problem, should a 25-mcg tablet, a 50-mcg tablet, or a 75-mcg tablet be crushed and suspended for administration to a 10-month-old infant weighing 17 lb?
63. T he pediatric dose of nelarabine is 650 mg/m2 administered intravenously over a period of 1 hour daily for 5 consecutive days. T he drug is available in vials containing nelarabine, 250 mg/50 mL. U sing Figure 8.2, calculate (a) the daily dose of drug, in milligrams, for a child weighing 15 kg and measuring 100 cm in height, and (b) the total volume of injection to infuse per treatment period.
64. T he oral dose of topotecan in the treatment of small cell lung cancer is 2.3 mg/
m2/day once daily for 5 consecutive days, repeated every 21 days. T he medication is available in 0.25 mg and 1 mg capsules. Recommend the strength and number of capsules to dispense for the initial course of treatment of a patient who weighs 165 lb and measures 5 feet 11 inches in height. U se the BSA equation.
65. A patient who is 6 feet tall and weighs 187 lb has been given 170 mg of a medica- tion based on a 2 mg/kg basis. Calculate the same dose, based on mg/m2. Use the BSA equation as needed.
66. T he recommended dosage of lapatinib for metastatic breast cancer is 1250 mg given orally once daily on days 1 to 21, in combination with capecitabine 2000 mg/m2/day given orally on days 1 to 14 of a 21-day cycle. H ow many 250-mg tablets of lapatinib and 150-mg or 500-mg tablets of capecitabine should be dis- pensed for each cycle of therapy for a patient with a calculated BSA of 1.75 m2? (Also, refer to the package inserts online and think about the possible prescription- labeling instructions for the patient.).
152 Pharma euti al c al ulations
CAl Cq UIz
8.A. The drug eribulin mesylate is used in late-stage metastatic breast cancer at an intra- venous dose of 1.4 mg/m2. It is administered on days 1 and 8 of a 21-day cycle.
The dose is reduced by 20% for patients with moderate renal impairment. Calculate the reduced dose, in (a) mg/m2, (b) mg/kg, and (c) the treatment-day dose, in mil- ligrams, for a 110-lb patient measuring 5 feet 2 inches in height.
8.B. A parent takes her 5- and 7-year-old boys to the pediatrician, both with pharyngitis.
The boys weigh 40 and 50 lb, respectively. The doctor prescribes an oral suspension of cefuroxime axetil (CEFTIN) at a dose of 20 mg/kg/day divided b.i.d. × 10 days.
The suspension has a cefuroxime axetil concentration of 125 mg/mL. How many milliliters of suspension will be needed during the course of treatment?
8.C. The first-day loading dose of a drug is 70 mg/m2 followed by a dose of 50 mg/m2 daily thereafter. Irrespective of the patient’s BSA, a dose is not to exceed 70 mg. For a 5-feet 8-inch 150-lb patient, calculate the (a) BSA using the Mosteller formula, (b) loading dose, and (c) maintenance dose, and indicate whether each dose is within the safe limit.
8.D. The pediatric oral dose of ciprofloxacin is given as 10 to 20 mg/kg every 8 hours, not to exceed a single dose of 400 mg irrespective of body weight. If a child weighing 55 lb is prescribed a one-teaspoonful dose of a 5% ciprofloxacin oral suspension every 8 hours, calculate whether or not the dose prescribed is within the therapeutic range.
8.E. The drug peginterferon alpha-2b is sometimes administered according to a “step- down” protocol from a starting dose of 1.5 mcg/kg/week to 1 mcg/kg/week to 0.5 mcg/kg/week. Calculate the three doses for a 5-feet 5-inch 132-lb patient (a) in micrograms and (b) on a mcg/m2 basis.
67. Cefixime, an anti-infective agent, is available in oral suspensions of the following strengths: 100 mg/5 mL, 200 mg/5 mL, and 500 mg/5 mL. T he pediatric dose is 8 mg/kg/day, administered in divided dosage. Calculate (a) the daily dose of cefix- ime for a 55-lb patient, (b) the most appropriate product strength to dispense, and (c) the quantity of oral suspension, in milliliters, required for a 10-day course of treatment.
68. Pertuzumab, for the treatment of late-stage breast cancer, is administered at an initial dose of 840 mg by intravenous infusion. It is coadministered every 3 weeks with trastuzumab 8 mg/kg and docetaxel 75 mg/m2. Calculate the doses of trastu- zumab and docetaxel, for a patient who is 60 inches in height and weighs 158 lb.
Use the BSA equation as needed.
8 • c al ulation of Doses: Patient Parameters 153
ANSWERS TO “CASE IN POINT” AND PRACTICE PROBl EmS Case in Point 8.1
T he metric weight of a 3-lb 7-oz neonate is calculated:
1 lb = 454 g; 1 oz = 28.35 g 3 lb × 454 g/lb = 1362 g
7 oz × 28.35 g/oz = 198.45 g
1362 g + 198.45 g = 1560.45 g, weight of the neonate
According to the dosing table, the dose for a 3-day-old neonate weighing less than 2000 g is 10 mg/kg/day divided every 12 hours.
T he dose, in mg, may be calculated by dimensional analysis:
1 1000
10
1 1560 45
15 6 kg
g
mg
kg day g
mg clindamycin day
× ×
=
/ .
. /
Since the daily dose is administered in two divided doses, each divided dose is:
15 6 2 . mg
= 7.8 mg clindamycin every 12 hours T he volume of injectable solution is then calculated:
50
600mL 7 8 0 65
mg × . mg = . mL