Pharmacokinetics Flashcards
What is meant by pharmacokinetics?
Pharmacokinetics describes the journey that a drug takes through the body from the time that it is administered until the time that it is excreted.
What are the factors that affect pharmacokinetics?
Route of administration affects absorption.
Transport by plasma proteins affects distribution.
Changes in cardiovascular function can affect distribution.
Changes in body composition affect distribution.
Changes in liver function affect metabolism/biotransformation.
Changes in kidney function affect excretion.
How are these factors affected by age?
- Absorption of drugs usually doesn’t change very much with advanced age.
- As people get older there are fewer plasma proteins in the blood and that can affect the transport of drugs in the blood.
- As perfusion of the tissues decreases delivery of drugs to the tissues will also decrease. This is a particular problem where you get vascular damage in diseases such as type II diabetes.
- With increasing age fat makes up a larger proportion of the body mass. That means that fat soluble drugs have a larger volume of tissue in which they can be absorbed whereas water soluble drugs have a smaller volume in which they can be distributed. So the effective dose of fat soluble drugs can decrease while the effective dose of water soluble drugs can increase.
- Changes in metabolism can result in an increased half life for some drugs. This increases the risk of toxicity reactions occurring and the interval between doses may need to be extended.
- Changes in renal function can result in decreased excretion of metabolites. Metabolites can have a physiological effect, so the risk of toxicity or other adverse reactions is increased.
Is the following statement true or false? Overprescribing can usually be identified by the specific symptoms it produces.
It’s false. Overprescribing can produce a variety of non-specific symptoms.
Is the following statement true or false? Several drugs have been specifically identified as likely to cause adverse reactions in older people.
It’s true. Although all drugs can potentially cause adverse reactions, there are certain identified drugs that have a much greater risk of causing problems.
Is the following statement true or false? Once daily administration is associated with increased risk of toxicity.
It’s true. That is a disadvantage of once daily dosing stop the advantage is that it simplifies drug use for the older person and helps to overcome the problem of needing to take medications every few hours. Because of that it can help adherence.
What is the relationship between complimentary medicines and overprescribing?
Complimentary medicines are self prescribed drugs, but they must be counted when you are thinking about the total number of drugs a person is taking. They therefore contribute to overprescribing (more accurately polypharmacy) and can therefore be important contributors to adverse drug reactions.
Is the following statement true or false? People in nursing homes are more likely to receive psychotropic drugs, and these drugs are often used to control their behaviour.
It’s true. People in nursing homes are likely to be treated with psychotropic drugs to control their behaviour and the use of these drugs is associated with adverse outcomes such as falls.
Is the following statement true or false? People who have experienced an adverse drug reaction are more likely to experience adverse reactions to any drug in the future.
It’s true. A previous history of adverse drug reactions is a risk factor for an adverse drug reaction in the future. Polypharmacy and the use of drugs from specific groups are also risk factors for adverse drug reactions. However, the absence of risk factors doesn’t mean that a person won’t experience an adverse drug reaction.
