How drugs work Flashcards
Definition of pharmacology
Pharmacology is the science of interactions between living systems and chemicals introduced from outside the system
Definition of a drug
A drug is a natural/synthetic substance that alters the physiological state of an organism by functioning at a molecular level
Why do drugs not work 100% effectively in reality
Only 1-5% of people comply exactly when taking drugs, non compliance is more likely when:
- More than two administrations a day
- Dehydration
- More than three drugs
- Living alone
- Greater than 85
- Busy lifestyle
- Tiredness
What is the formation of drugs
Drugs contain active ingredients and packing chemicals to stabilise/ slow down/ modify release.
What does accumulation of drugs lead to
Accumulation of drugs can lead to toxicity
What is the therapeutic range
The therapeutic range is the desired range for concentration in the plasma. There may be toxic effects if it goes above or it may not work if it goes below. The size of the therapeutic range varies between drugs.
What does GSL mean
GSL means general sales list, drugs that are widely available
What does P mean
P means pharmacy only, over the counter
What does POM mean
POM means prescription only medication
What is midwives exemption
Midwives exemption is a list of medications in section 17 which allows them to supply certain drugs without a prescription
What does PO mean
PO means put orally such as a tablet, granule, powder, spray, gel or elixir. This can be swallowing, buccal (inside of cheek), sublingual (under tongue) or lozenges (sucked). It is convenient, cheap and non invasive. However patient may be nil by mouth, vomiting or find it difficult to swallow. Is slow to absorb into the GI tract.
What is inhalation
Inhalation is drugs that are inhaled such an entonox or oxygen.
What does PV mean
PV means per vaginam such as a propress or prostin. It has a large surface area and a good blood supply for slow, local absorption. However it can be embarrassing and unpredictable or irritate the vaginal wall.
What does PR mean
PR means per rectum eg laxatives or analgesics. It is very effective absorption for short term use. However it can be embarrassing and faeces can change absorption rate.
What does topical mean
Topical means applied where needed
What does intranasal mean
Intranasal means up the nose
What does IM, SC and IV mean
IM- intramuscular
SC- Subcutaneous
IV- intravenous
What are the five rights of drug administration
1 Right person 2 Right time 3 Right drug 4 Right dose 5 Right route
What do the following abbreviations mean ? OD BD TDS QDS PRN
OD- once daily BD- twice daily TDS- three times daily QDS- four times daily PRN- as required, when necessary
What are the six factors that affect drug distribution
Plasma protein binding, lipid solubility, binding properties, blood flow to organs, stage of life cycle, disease state
How does plasma protein binding effect drug distribution
Some drugs bind to plasma proteins. The amount that is bound and unbound is in equilibrium. Only the unbound drug is biologically active. The bound drug is stored to be released later.
What are the problems with protein binding drugs
Plasma proteins can be reduced in pregnancy, malnutrition or in people with excessive burns.
Using two protein binding drugs at the same time effects the equilibrium as they compete for space
Highly protein bound drugs are unlikely to cross the placenta
How does lipid solubility effect drug distribution
To what extent the drug dissolves in the bodies fatty tissues depends on how much fatty tissue there is and the lipid solubility of the drug.
What are the problems with lipid soluble drugs
Lipid soluble drugs will cross the placenta. People with a raised BMI will need a larger dose but it will also take longer to clear.
How does binding characteristics effect drug distribution
Some drugs have unusual binding characteristics which need to be taken into account before administration
How does blood flow to tissues effect drug distribution
Local and general circulation state determines drug distribution. Some tissues receive a better blood supply than others, meaning they will receive a higher concentration.
How does stage of life cycle effect drug distribution
Age and pregnancy alter drug distribution
How does disease state effect drug distribution
Renal/hepatic failure impairs the bodies ability to eliminate most drugs.
Dehydration allows drugs to accumulate
What is hypersensitivity
The drug acts as an antigen triggering the release of antibodies causing an unpredictable response to the medication
Where does metabolism of drugs take place
metabolism of drugs takes place in the liver
What is anabolism
Anabolism is the buildup of substances
What is catabolism
Catabolism is the breakdown of substances
How does the liver metabolise drugs
Drugs PO are absorbed through the GI tract and pass through the portal vein to the liver then to the general circulation. Drugs given by other routes reach the liver after the general circulation. There are then metabolised by liver enzymes.
What problems can occur in the liver during drug metabolisation
Liver enzymes are effected by malnutrition, alcoholism, age and liver disease. They can also become accustomed to the environment and adapt. Many drugs such as alcohol and caffeine induce (speed up) liver enzymes, and high doses can inhibit them.
How does the kidneys metabolise drugs
Kidneys metabolise drugs through glomerular filtration then tubular secretion and reabsorption.
What is a GFR
A GFR is a glomerular filtration rate. It is a blood test to check how well the kidneys are working. The creatinine levels are tested and combined with other factors.
What factors cause a low GFR
Dehydration, age, ACE inhibitors, NSAIDs, heart failure, shock and renal disorder
What is a half life
A half life is the time taken for the concentration of a drug in the plasma to fall to half of its maximum volume.
What is a steady state
the steady state is the rate of drug elimination which is equal to the rate of administration.
What is a loading dose
A dose of drug given in emergencies so as to not wait 3-5 half lives for the therapeutic range.
How do drugs work on cell receptors
Drugs with the same or similar structure to natural ligands can bind to receptors and either active the cells usual actions or block them.
What us down regulation
Down regulation is a reduced number and action of cell receptors due to continued presence of a drug
How do drugs work on ion channels
Ion channels facilitate the diffusion of ions across membranes. Some drugs bind to ion channels and modulate/block them.
How do drugs work on enzymes
Some drugs bind to enzymes and catalyse/ inhibit thier action.
What are non specific drugs
Some drugs work due to their physiochemical properties rather than the shape of their molecules to produce non-specific actions.
What are some of the possible effects of drugs
1) the main action (can be an extreme of the desired effect)
2) the subsidary action (act on another cell)
3) cell damage
4) hypersensitivity
