# PTCB Pharmacy Calculations #3

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#### Which of the following values is the "mode" or "median"? 120, 135, 140, 118, 175, 105, 115, 190

Correct! Wrong!

Explanation:
When the number of values in an experiment is even, the average of the middle values should be taken into account. To find the median or mode of experiment data, organize it in ascending or descending order first.
In the case at hand,
105, 115, 118, 120, 135, 140, 175, 190
= (120 + 135)/2 = 127.50

#### To make a 250cc 1 percent boric acid solution isotonic with eye tears, how many grams of sodium chloride are needed?

Correct! Wrong!

Explanation:
The freezing point of blood serum is 0.520 C, and all solutions with this freezing point are isotonic with blood serum. The freezing point of 0.9 percent sodium chloride is the same as that of blood serum.
1 percent Boric acid = -0.29o C is provided by FP.
Blood FP = - 0.52o C
NaCl FP (required) = (0.52-0.29)
= 0.23 degrees Celsius
Now that we know that FP gives 1 percent NaCl, the temperature would be -0.58o C, we may state,
1 percent NaCl is required for FP 0.58o.
For FP 0.23o requirements?
0.396 percent NaCl = (0.23 x 1)/0.58
0.396 gram NaCl per 100cc
The amount of sodium chloride (NaCl) required for 250cc,
= 0.991 gm NaCl = 991 mg = (250 x 0.396)/100 = 0.991 gm

#### What factor will influence the rate of a reaction if the concentration of reactant M is half in a reaction that is third order in M?

Correct! Wrong!

Explanation:
In a reaction of third order kinetics, the concentration of reactant M is half:
dx/dt = k (a-x) (b-x) (c-x)
= k (a-x)3 where a=b=c
= k (M)3
now M = M/2
= k (M/2)3
= 1 /8 k (M)3

#### If the initial drug concentration is 500 mg/cc and the final concentration is 50 mg/cc, what is the rate of constant after 90 minutes? (Kinetics of First Order)

Correct! Wrong!

Explanation:
0.025 min-1
For the first order kinetic,
K = 2.303/t x log Co/C
= 2.303/90 x log 500/50
= 2.303/90 x log 10
= 0.025 min-1

#### What is the status of renal function in a patient with a total body clearance of 2100cc/hr and a hepatic clearance of 300cc/hr?

Correct! Wrong!

Explanation:
Creatinine clearance can be used to determine the severity of renal function impairment.
ClH + ClR = ClT
where,
ClT = Clearance of the entire body
Hepatic clearance = ClH
Renal clearance = ClR
300 + ClR = 2100
1800 ml/hr ClR
30 milliliters per minute
The typical creatinine clearance ranges from 80 to 120 milliliters per minute. The patient's creatinine clearance is 30 ml/min, which is considered significantly compromised.

Correct! Wrong!

6.25 mg

Correct! Wrong!

15 ml

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1/2 grain

Correct! Wrong!

0.18 mg

Correct! Wrong!