Wk 20 Calculations - Half Life (SG) Lecture Notes PDF

WEEK 20 Pharmaceutical Calculations Half Life - Micro Lecture Susan Gault Dale 121 [email protected] 1 PHA113 MPharm WEEK 20 Learning Outcomes • Understand what a half life is • Be able to complete basic half life calculations 2 PHA113 MPharm WEEK 20 What is a half life?...

WEEK 20 Pharmaceutical Calculations Half Life - Micro Lecture Susan Gault Dale 121 [email protected] 1 PHA113 MPharm WEEK 20 Learning Outcomes • Understand what a half life is • Be able to complete basic half life calculations 2 PHA113 MPharm WEEK 20 What is a half life? • The half-life of a drug is an estimate of the time it takes for the concentration or amount in the body of that drug to be reduced by exactly one-half (50%). The symbol for half-life is t½. • For example, if 100mg of a drug with a half-life of 60 minutes is taken, the following is estimated: • • • • • 3 60 minutes after administration, 50mg remains 120 minutes after administration, 25mg remains 180 minutes after administration, 12.5mg remains 240 minutes after administration, 6.25mg remains 300 minutes after administration, 3.125mg remains. PHA113 MPharm WEEK 20 Example Drug X has a half life of 120 minutes. How long will it take for the plasma concentration to drop from 1g/L to 250mg/L? Give your answer in hours. 1000mg 500mg 120 mins 120 mins 120 + 120 = 240 minutes 4 250mg PHA113 Ans: 4hrs MPharm WEEK 20 Example Drug A has a half-life of 2 hours. If the initial plasma level of the drug, given as a single dose, is 1200mg/L, what will its plasma level be after 8 hours? 1200 ÷ 2 = 600 ÷ 2 = 300 ÷ 2 = 150 ÷ 2 = 75 2hrs 4hrs 6hrs 8hrs Ans: 75mg/L 5 PHA113 MPharm WEEK 20 Need Further Support • Identify the types of calculations that you struggle with • Practise those types of questions • There are books and e-books available from the library • If you identify a calculation that you cannot work out an answer to email me with your workings and I will arrange for you to be given some feedback ([email protected]) • Complete the weekly calculations quizzes on Canvas 6 PHA113 MPharm