Pharmaceutical Calculations

Q: How many mL of glycerin would be needed to prepare 1 lb of an ointment containing 5% WIW glycerin? (The density of glycerin is 1.25 g/mL.)

(a) :  1.2 mL
(b) :  18.2 mL
(c) :  22.7mL
(d) :  24 mL
(e) :  28.4 mL
Answer:  18.2 mL
Explanation:   A density or SG of 1.25 indicates that 1 mL of the liquid weighs 1.25 g. Because 1 lb of the ointment contains 5% WjW glycerin, 454 gx 5% WjW = 22.7 g of glycerin D.W enslty=y 1.25 = 22.7 g xmL x= 18.2mL

Q: Calcium chloride (CaCl2 • 2H20) has a for-mula weight of 147. What weight of the chemical is needed to obtain 40 mEq of calcium? (Ca =40.1; Cl =35.5; H20 =18)

(a) :  0.80 g
(b) :  2.22 g
(c) :  1.47 g
(d) :  2.94 g
(e) :  5.88 g
Answer:  2.94 g
Explanation:  fh. 1- (mEg) (mol. wt.) mg 0 c emlCa - (valence) _ (40 mEg) (147) xmg- (2) x = 2940 mg, or 2.94 g It must be remembered that 40 mEq of calcium combines with 40 mEq of chloride to form 40 mEq of calcium chloride. The answer 0.80 is obtained if one multiplies the 40 mEq desired by the atomic weight of calcium and then divides by the +2 valence. The use of the atomic weight of calcium is incorrect because the official hydrated calcium chloride is being weighed to obtain the correct amount of calciu

Q: The concentration of mercury in a water sample is reported as 5 ppm. Express this concentration as a percentage.

(a) :  5.0E-7
(b) :  5.0E-6
(c) :  5.0E-5
(d) :  0.0005
(e) :  0.005
Answer:  5.0E-6
Explanation:   Mercury is a solid chemical. Thus, the 5 ppm concentration indicates 5g of mercury per 1,000,000 mL of solution. Therefore, the grams present in 100 mL will be 5g mercury _ ~ 1,000,000 mL - 100 mL 1,000,000 x = 500 (23:109) x = .0005%

Q: The USP contains nomograms for estimating body surface area (BSA) for both children and adults. Which of the following measurements must be known in order to use this nomogram?

(a) :  age and height
(b) :  age and weight
(c) :  height and creatinine clearance
(d) :  height and weight
(e) :  weight and sex
Answer:  height and weight
Explanation:   The nomogram in the USP consists of three parallel vertical lines. The left line is calibrated with height measurements in both centimeters and inches, whereas the right line lists weights in kilograms and pounds. Using data based on the patient's measurements, a line is drawn between the two out-side parallel lines. The intercept on the mid- dle line, which is calibrated in square meters of body surface area, allows the estimation of the patient's BSA.

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