Pharmacokinetics/dynamics

Question 1

Tear film consists of which layers

Answer 1

Question 2

Henderson-hasselbach equation

Answer 2

Question 3

Define half-life

Answer 3

Time it takes for 50% of a drug to be processed.

Generally it is considered that it takes 5.5 half-lifes for a drug to be removed from the body, in that it is considered to no longer have a clinical effect

Question 4

Dosing schedules for drugs being metabolised via

1. Zero-order kinetics
2. First-order kinetics

Answer 4

Zero order:

• Greater demand for dose modification: loading vs maintenance
• Doubling a dose calls for twice the time to be metabolized

First order:

• Steady state is achieved when rate of intake equals rate of
  elimination

Question 5

How to best avoid undesired fluctuation of plasma drug levels

Answer 5

• Dosing intervals are recommended at less or equal to a drug’s half-life; in this way drug concentration never drops below 50%
• Dosing according to a drug’s half-life is readily accomplished with sustained release drugs
• Dosing intervals less than 1/3 of a drug’s half-life result in plasma drug levels that are similar to those seen with continuous infusion
• Because most antibiotics have a high therapeutic index (very safe), dosing for severe infection is often done in a loading dose fashion since large peaks in plasma levels are not toxic

Question 6

How can the desired therapeutic drug level be achieved

Answer 6

• By dose concentration modulation
• By dose frequency
• Or both concentration and frequency

Question 7

Define anaphylaxis

Answer 7

• Anaphylaxis is a systemic type I hypersensitivity reaction with a substance to which the body has been previously sensitized
• Serious anaphylactic reactions require immediate emergency treatment with epinephrine
• O2, IV steroids, and airway management, including intubation, should also be considered as indicated