0402 Pharmacokinetics Flashcards
Clearance, Volume of Distribution and Half-life First order and Zero order kinetics Absorption, First Pass Effect and Bioavailability Hepatic and Renal clearance Saturation kinetics
What is the definition of pharmacokinetics
Pharmacokinetics describes the handling of a drug by the body.
What are 4 elements of drug handling that pharmacokinetics studies
- Absorption of drug from site of administration
- Distribution of drug within the body
- Metabolism of drug into a different chemical entity
- Excretion of drug from the body
List a few ways a drug can be administered into the body
Oral/rectal, perucutaneous (skin), intravenous (plasma), intramuscular (muscle), inhalation (lungs)
What is meant by ‘plasma protein binding of a drug’ and what is the major binding protein in human plasma
Plasma protein binding refers to the binding of drugs to proteins in plasma before they reach their target proteins. It is reversible and saturable. Albumin is the major plasma protein
What happens to a drug that is administered when plasma protein is totally saturated
When plasma protein is totally saturated ( when all plasma protein receptors are bound) the proportion of free drug to total concentration of the drug increases (i.e. more drug is available to travel to target sites)
What is the clearance of a drug
Clearance is the irreversible elimination of a drug (usually excretion and metabolism). It is measure in the unit ‘ volume clear per unit of time’ e.g. L/h
Clinically, what does clearance help us determine (in terms of drug administration)
Maintenance dose ( the dose required to maintain a target drug concentration in plasma at a steady state (administration rate = elimination rate). It is measure in mg/h )
What is the volume of distribution?
VOD is the [total drug in the body] divided [drug in plasma]. It is the relationship ebtween drug in plasma and total drug in the patient. It has no measurement and is an absolute value. The smaller the volume the greater the amount of drugi n plasma
Clinically, what does volume of distribution help us determine (in terms of drug administration)
The loading Dose ( a higher initial dose of drug to reach therapeutic level)
What is the half life of a drug
The half life of a drug is the time taken for a drug in the body to be reduced by half
What is the difference between the half life of first order kinetics drugs and second order kinetics drug
First order kinetics drugs always have the same half-life. Second order kinetics drugs do not
Why is the half life of first order kinetics drugs not affected by dose
First order kinetics drugs always have the same half-life, regardless of dose (the proportional clearance is the same)
The serum concentration graph of a first order drug is not always linear in the early phases of administration. Why is this and what is this phase called?
Somes, when a drug is first administered it is distributed to other parts of body before the resumes normal elimination patterns. This early phase is known as the distribution phase
What is the first pass effect and what types of drugs does it happen in
First pass effect is the extraction and metabolism of an orally drug in the liver before they reach systemic circulation. It only applies to drugs ingested orally
What is bioavailability
Bioavailbility is the amount of drug reaching the systemic circulation. It is expressed as a fraction of the total dose
