wer

PERCENTAGE ERROR

 It is calculated using this equation:

% 𝑒𝑟𝑟𝑜𝑟 = ( 𝐴𝑐𝑡𝑢𝑎𝑙 𝑣𝑎𝑙𝑢𝑒 − 𝑇𝑎𝑟𝑔𝑒𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒

𝑇𝑎𝑟𝑔𝑒𝑡𝑒𝑑 𝑣𝑎𝑙𝑢𝑒 ) × 100

Example: You need 23.45 g of your active ingredient to compound a prescription. You have weighed the powder using the pharmacy

balance, which showed 23.45 g. To double-check, you weigh the

powder again using the more accurate and reliable balance in

research lab facility, which shows 23.4461. What is the percentage

error of the first measurement?

EXPERIMENT

 You are trying to measure 50 mL in a cylinder that is

sitting on the bench, while standing up. It seems like you have it. The you crouch to double-check, and

now it looks like you have 49 mL.

 What is the error?

 What percentage error is that?

MWQ

 What is the MWQ of your balance?

 What happens if you weigh something lighter?

𝐴𝑐𝑐𝑒𝑝𝑡𝑎𝑏𝑙𝑒 𝐸𝑟𝑟𝑜𝑟 = 𝑆𝑒𝑛𝑠𝑖𝑡𝑖𝑣𝑖𝑡𝑦 × 100

𝑀𝑀𝑄

ALIQUOT CALCULATIONS

 We need to weigh 5 mg Nadamycin with a balance

with sensitivity of 0.01 g. Perform aliquot calculations.

𝑇𝑜𝑡𝑎𝑙 𝑎𝑚𝑜𝑢𝑛𝑡 𝑜𝑓 𝑑𝑖𝑙𝑢𝑡𝑖𝑜𝑛 =𝑀𝑖𝑛𝑖𝑚𝑢𝑚 𝑤𝑒𝑖𝑔ℎ𝑎𝑏𝑙𝑒 𝑞𝑢𝑎𝑛𝑡𝑖𝑡𝑦 × 𝑀𝐹𝑀𝐹 = 𝑀𝑊𝑄

𝑇𝑎𝑟𝑔𝑒𝑡 𝑊𝑒𝑖𝑔ℎ𝑡

ALIQUOT CALCULATION

 How do you weigh 5 mg of a narcotic on a balance with

sensitivity of 4 mg to ensure a percentage error of less than 1%?

BODY MASS INDEX (BMI)

 What is the BMI for a 54-years-old female who weighs 172 pounds

and is 5’8” tall? Is she underweight, normal, or overweight?

𝑩𝑴𝑰 = 𝑾𝒆𝒊𝒈𝒉𝒕 (𝒌𝒈)

[𝒉𝒆𝒊𝒈𝒉𝒕 𝒎 ]𝟐

IDEAL BODY WEIGHT (IBW)

 A 50-years old woman weighs 167 pounds and is 5’5” tall. What is her ideal

body weight? Is the ideal body weight more than actual body weight?

IBW (kg) = 45.5 or 50 + (2.3 x height in inches over 5 feet)

DOSING BASED ON BODY WEIGHT

 Acyclovir is prescribed with dose of 10 mg/kg for a female patient who weighs

211.2 pounds and is 5’2” tall. Use the actual body weight to calculate dose, if

the patient is normal weight (actual body weight < 1.3 x ideal body weight),

and ideal body weight if she is overweight (actual body weight > 1.3 x ideal body weight.

IBW (kg) = 45.5 or 50 + (2.3 x height in inches over 5 feet)

BODY SURFACE AREA (BSA)

 The recommended dose of 5-fluorouracil is 750 mg/day for an

average adult (BSA = 1.73 m2). What is the daily dose for a 12-

year-old boy who is 4’10’’ tall and weighs 88 pounds?

𝑩𝑺𝑨 = 𝑯𝒆𝒊𝒈𝒉𝒕 𝒄𝒎 × 𝒘𝒆𝒊𝒈𝒉𝒕 (𝒌𝒈)

𝟑𝟔𝟎𝟎

CREATININE CLEARANCE (CrCL)

 Cockcroft-Gault equation

For men: 𝐶𝑟𝐶𝐿( 𝑚𝐿

𝑚𝑖𝑛 ) =

140 − 𝑎𝑔𝑒 𝑦𝑒𝑎𝑟𝑠 × 𝑊𝑒𝑖𝑔ℎ𝑡(𝑘𝑔)

72 ×𝑠𝑒𝑟𝑢𝑚 𝑐𝑟𝑒𝑎𝑡𝑖𝑛𝑖𝑛𝑒 ( 𝑚𝑔

𝑑𝐿 )

For Women: 𝐶𝑟𝐶𝐿 𝑚𝐿

𝑚𝑖𝑛 = 𝐶𝑟𝐶𝐿 𝑓𝑜𝑟 𝑚𝑒𝑛 × 0.85

CREATININE CLEARANCE (CrCL)

 A 58-years-old woman who weighs 152 pounds and has

a serum creatinine level of 33 mg/L, is prescribed

piperacillin/tazobactam. The recommended dose is

based on the table attached. What is the daily dose for

the patient?

For men: 𝑪𝒓𝑪𝑳( 𝒎𝑳

𝒎𝒊𝒏 ) =

𝟏𝟒𝟎 − 𝒂𝒈𝒆 𝒚𝒆𝒂𝒓𝒔 × 𝑾𝒆𝒊𝒈𝒉𝒕(𝒌𝒈)

𝟕𝟐 ×𝒔𝒆𝒓𝒖𝒎 𝒄𝒓𝒆𝒂𝒕𝒊𝒏𝒊𝒏𝒆 ( 𝒎𝒈

𝒅𝑳 )

For Women: 𝑪𝒓𝑪𝑳 𝒎𝑳

𝒎𝒊𝒏 = 𝑪𝒓𝑪𝑳 𝒇𝒐𝒓 𝒎𝒆𝒏 × 𝟎.𝟖𝟓

CrCL (mL/min) Dose (g)

> 40 3.375/4.5 g

20 – 40 75% regular dose

< 20 50% regular dose