Pharmacology 3 Flashcards
What is meant by the term pharmacokinetics?
- The process by which a drug is absorbed, distributed, metabolised and eliminated by the body
- What the body does to drugs
What is meant by the term pharmacodynamics?
- The branch of pharmacology concerned with the action of drugs in the physiology or pathology of the body
- What drugs do to the body
What are the different phases of what happens to drugs in the body? (4 points)
- Absorption
- Clinical effect
- Metabolism
- Excretion
What is meant by the excretion of a drug from the body?
- how the body gets rid of a drug
What are the different routes or administration for drugs into the body? (6 points)
- Oral
- Intravenous
- Intramuscular
- Subcutaneous (under the skin)
- Inhalation
- Sublingually
What does subcutaneous mean?
- Under the skin
What is the advantage of giving drugs orally?
- Socially acceptable
What are the disadvantages of giving drugs orally? (4 points)
- Slow onset
- Variable absorption
- Gastric acid may destroy drug
- ‘first pass’ metabolism
What is first pass metabolism?
- The intestinal and hepatic degradation or alterations of a drug or substance taken by the mouth, after absorption, removing some of the active substance from the blood before it enters the general circulation
Where can first pass metabolism occur?
- In the gut and in the liver
What are 5 factors that can affect oral absorption of drugs?
- Lipid solubility and ionisation
- Drug formulation
- Gastrointestinal motility
- Interactions with other substances in the gut
- GI tract disease
What considerations need to be given about lipid solubility and ionisation I relation to affecting oral drug absorption?
- Can only absorb a drug if it is lipid soluble
- Can’t hold it in the gut unless it is in ionic suspension (polar form)
What considerations need to be given about drug formulation in relation to affecting oral drug absorption?
- Can give a drug that is delayed absorption
- If the drug has a coating on it then different bits of the drug can be absorbed at different times
- Coated bits will take longer to be absorbed as coating will take time to dissolve
What considerations need to be given about gastrointestinal motility in relation to affecting oral drug absorption?
- If stomach is not stimulated the drug will not move through the body
What considerations need to be given about GI tract disease in relation to affecting oral drug absorption?
- If some of the bowel is removed due to disease then you might not have enough bowel for the drug to be absorbed
In first pass metabolism, where does all of the blood from the GIT drain to?
- The hepatic portal vein (except sublingual and rectal veins)
In first pass metabolism, where does the hepatic portal vein drain to?
- The liver
In first pass metabolism, where does the drug need to pass through once before it reaches the systemic circulation?
- Liver
In first pass metabolism, what can the liver do to drugs?
- Inactivate drug = more needed by oral route to get desired clinical effect
- Activates drug = makes an active form of an inactive drug so less in needed by oral route
In terms of considering drug dosage for drugs involved in first pass metabolism what is very important?
- Need to consider if patient has normal or abnormal liver function
- Especially need to consider this when treating someone with abnormal liver function as do not want to give them a dose that is too high
- This can lead to extremes of life, liver disease or drug interactions changing drug metabolism
What are the advantages of giving a drug through non-oral administration? (2 points)
- Predictable plasma levels
- No first pass metabolism
What are the disadvantages of giving a drug through non-oral administration? (3 points)
- Allergic reactions are more severe
- Access difficulties/self-medication
- Drug cost is higher
What is meant by the term ‘bioavailability’?
- The proportion of a drug which enters the circulation when introduced into the body and so is able to have an active/clinical effect
What can bioavailability to modified by? (4 points)
- Dosage form
- Destruction in the gut
- Poor absorption
- First pass metabolism
What is meant by dosage form?
A term for the physical characteristics of a drug product - e.g. tablet, capsule or solution - which contains the drug substance and almost invariably other ingredients
What is meant by the term ‘volume of distribution of a drug?
How much of the body is the drug diluted in?
- Compartments (vascular, tissues, CNS)
- Some drugs will go to an area of the body more easily than other areas of the body
How are drugs distributed by lipid binding?
- Slow release from accumulation
How are drugs distributed by drugs that are binding to plasma proteins?
- Bound drug is inactive (acting as a reservoir)
- Drug actions are possible by competitive binding
What is meant by drug metabolism?
- Preparing the drug for elimination from the body
What are the 2 different phases of drug metabolism (preparing the drug for elimination from the body)?
Phase 1 reactions:
- Oxidation, reduction, hydrolysis
- Can be enough to change the conformation of the molecule and therefore the drug is inactive as it can no longer bind to the receptor
- It might take more than one reaction for this to occur
Phase 2 reactions
- Conjugation (the combination, especially in the liver, of certain toxic substances formed in the intestine, drugs; a mens by which the biologic activity of certain chemical substances is terminated and the substances made ready for excretion
- Glucuronidation, sulphation, methylation, acetylation, glutathione
What are the different ways drugs can be excreted from the body? (5 points)
- Renal - urin
- Liver - bile
- Lungs - exhale gas
- Sweat
- Saliva
What is the most common way in which drugs are excreted from the body?
- Renal excretion - majority of the drug will be excreted through urine
- Renal disease will impact on the ability for the body to get rid of the drug - so the drug will build up in the body circulation
What are the 2 main disorders that can affect drug excretion from the body and what must we do in relation to the drug dose given to the patient?
- Renal disease (chronic renal failure)
- Liver disease (liver failure)
- Drug doses must be reduced
Do drugs distribute themselves evenly throughout the body?
- No
Planning drug use is based in the idea of ‘body compartments’ . What is the single compartment model?
- Drug behaves as if it is evenly distributed throughout the body
Planning drug use is based on the idea of ‘body compartments’. What is meant by two compartment model?
- Drug behaves as if it is in equilibrium with the different tissues in the body
Generally, what is the connection between blood in the tissues and the amount of drug in tissues?
- More blood you’ve got in the tissue the more drug you’ve got in the tissue
What is the plasma half-life of a drug?
- How long it takes for half of the drug to be removed from the body
What 2 things do you need to know to create a dosgae schedule for a drug?
- The clearance of a drug
- The half life of a drug
What are the 2 processes in which drug clearance can work?
- First order kinetics
- Zero order kinetics
Which order of kinetics are most drugs cleared from the body by?
- First order kinetics
What are the properties of drug clearance by first order kinetics? (3 points)
- Drug elimination or absorption is by PASSIVE DIFFUSION only
- Drug removal is proportional to the drug concentration
- Logarithmic graph of elimination is a straight line
What is the drug half life like in first order kinetics?
- Half life is constant, from this you can predict how long it will take for the drug to be removed from the body
What are the properties of drug clearance by zero order kinetics? (3 points)
- Drug elimination is an ACTIVE process and can be saturated by high drug concentrations
- The drug is removed from the body at a stead rate irrespective of how much drug has been consumed
- Linear graph of drug elimination
What is meant by drug accumulation?
- How the plasma concentration builds up if repeated doses of a drug are given
What happens if drugs are given more frequently than the drug schedule suggests?
- TOO FREQUENT will result in plasma levels that may be toxic
- Depends on the drug’s therapeutic index
What happens if drugs are given less frequently than the dosing schedule suggests?
- TOO INFREQUENT will result in sub-therapeutic plasma levels and no clinical effect
What is meant by the therapeutic index of a drug?
The comparison of the amount of a therapeutic agent that causes the therapeutic effect to the amount that causes death or toxicity
