Pharmacology Flashcards
who regulates the use of medicines in the uk
the medicines air and human medicines regulations 2012 regulate the use of medicines In the uk
before any meeiidicne can bee supplied it is required to have marketing authorisation granted by thee medicines and healthcare products regulatory authority
what is the legality we need for prescription only medicines
has to be prescribed – in order to use the medicine you need a prescriber to supply the medicine ,
what are prescription only medicines
can only be obtained with a prescription
what is pharmacy medicine
can only be purchased under the supervision of a pharmacist in registered premises
what is general sales list medicines
can be sold in general shops without supervision
why can we allow access to medicines without a prescription
If anyone buys gsl and someone dosnt follow instructions the harm they can cause is limited
what legal category does paracetamol 500mg x 32 fall under
legal category is pharmacy only
what legal category does paracetamol caplets 500mg fall under
this is a pom
prescription only medicine - has to be prescribed
what legal category do small packs of paracetamol fall under
small packs (16) of paracetamol are general sales list
what are p and gsl medicines referred to
often the p and GSL medcines are described as ‘‘over the counter’’ medicines
the term oct has no legal meaning
what is the legislation behind ahps being able to prescribe drugs
The Crown Reviews (1998/99) - recommendations about the use of medication without a prescription (Medicines Act exemptions and Non-Medical (independent) prescribing)
“Legal authority for new professional groups to prescribe or to authorise NHS expenditure ..limited to medicines in specific therapeutic areas related to the particular competence and expertise of the group and may include prescription only medicines within those areas.”
Legislation amended to enable adequately trained HCPs to become Ips- independent prescribers- and some to exemptions to supply and administer POMs (Eg. Paramedics, midwives and most recently, podietrists & orthoptists).
what is pharmacokinetics
the movement of drugs into and out of the body
'’what the body does to the drug’’
what is pharmacodynamics
how drugs work when they reach their site of action
'’what the drug does the body’’
what is first pass metabolism
First pass metabolism is the process in which a drug is partially metabolized or broken down by the liver before it enters the bloodstream and reaches the rest of the body. Essentially, when you take a medication by mouth, it travels to the liver first, where some of it may be changed into different forms before circulating throughout the body. This can affect the effectiveness and concentration of the drug that actually reaches the target tissues or organs.
describe the pharmokinetic process
starts with administration of the drug this can be extravacualrly or intravscualry e.g. swallowing pills or injections (intravascular administration)
it then gets absorbed into the gut wall and then the blood and then it gets distributed to the body tissus and then it gets metabolised by the liver and eliminated by the kidney
what type of metabolism does extravascular administration of drugs elicit
first pass metabolism
First-pass metabolism, also known as the first-pass effect, is a phenomenon that occurs when drugs or other substances are taken orally (by mouth) and pass through the liver before entering the systemic circulation (the bloodstream). This process can significantly affect the bioavailability and effectiveness of the drug.
Not all drugs are subject to significant first-pass metabolism. Some drugs are designed to be resistant to this process, while others are intentionally administered orally because first-pass metabolism can lead to the formation of active metabolites.
how are people are long term drugs managed to ensure there kidney and liver function isn’t affected
Blood tests done once a year to check liver and kidney functions
Blood level against time when durg is put into body
Liver – LFT, KIDNEYS – U and E
(urea and electrolytes)
where are the following routes of administration absorbed in the body:
sublingual
buccal
intraocular
respiratory tract
sublingual
under tongue
buccal
oral mucosa
intraocular
eyes
rectal
lower GIT
respiratory tract
nasal passages or lungs
where are the following routes of administration absorbed in the body;
intravenous
intramuscular
subcutaneous
intracathcal
intravitrial
intravenous
directly into venous blood
intramuscular
muscles
subcutaneous
into blood from skin layers
epidural
epidural space
intracathecal
directly into cerebrospinal-spinal fluid
intravitrial
into vitreous space near retina
what are the advantages of taking medication orally
Advantages
Convenient
Self administration
Simple
Economical
Liquids often available
“first pass metabolism”- formulate drug to undergo first pass metabolism and produce a metabolite
what are the disadvantages of taking medication orally
Not all drugs active orally e.g. insulin
Unpredictable absorption- some loss as the drug crosses lipids in the body
Delayed onset of action
Gastrointestinal side effects
“first pass metabolism”
what are the advantages of taking medication intraveously
Advantages
Immediate
Predictable effect
Large volumes
Infusion allows maintenance of effect
Avoids ‘1st pass’ metabolism
Not extravscuallry going straight into blodtsrem therefore immeadite relase in blood stream ni lipid lyers for durg to be broken down at
what are the disadvantages of taking medication intravenously
Risky
Infection
Phlebitis
Preparation time
Anaphylaxis
Infusion calculations
Expensive
Staff involvement
Incompatibilities
what are topical drug examples
Topical drug therapy ‘Apply to affected area’
Creams
Ointments
Nasal sprays
Eye drops / ointment
Ear drops
Inhalers
[Nasal sprays]
[Eye drops / ointment]
[Transdermal Patches (Buprenorphine, fentanyl, hyoscine, HRT)]
transdemeral patches are not topical drugs
what are the advantages of topical drug therapy
ADVANTAGES
↓ systemic side effects-
Useful if swallowing difficulties
Onset of action may be quicker
Compliance
what are the disadvantages of topical drug therapy
Compliance?
Physical difficulties?
Reactions at site
Staining of clothing
Delayed onset of action-relys on skin intergrity e.g. hydrated
Misconception that topical = safe
what does the pharmokinetic paramete ‘‘half life’’ refer to
Half life is the time required to reduce the (drug) plasma concentration to half of its original value
Also refered to as t ½
Can vary from drug to drug and from person to person
Does not depend on dose / dose frequency
Use to calculate dosage frequency / time to ‘steady state’
what does the pharmokinetic parameter bioavailabliity refer to
Bioavailability is the fraction of the administered dose that reaches the systemic circulation of the patient- fraction of the drug we give that reaches systemic circulation – e.g. by iv injection = 100 percent
Affected by:
Dosage form
Dissolution and absorption of drug
Route of administration
Stability of the drug in the GI tract (if oral route)
Extent of drug metabolism before reaching systemic circulation
Presence of food/drugs in GI tract
what is half life
Half-life is the time taken for the concentration of the drug in the blood to fall by half
how is the frequency of drug dosing affected by half life (e..g. short life drugs)
Generally a drug with a short half-life is given more frequently
E.g. paracetamol t ½ = 2 – 4 hours
Usual dose? -
1g every 4 to 6 hours to maintain effective pharmcodynamic effect from paracetamol;
how is the frequency of drug dosing affected by half life (e.g. long half life drugs)
Generally a drug with a long half-life is given less frequently
E.g. warfarin t ½ = 24 hours
Usual frequency? -
Given once daily
what is the significance of bioavailablity
How do we need tp change doses if we are going from iv route to oral route
Bioavailability when changing from IV to oral route of administration
e..g propanol iv 100%
oral 30 to 40%
\
what are the four processes of the pharmokinetic process
4 process
Absorptiion
Dstribution
Metabolism
Eliminarion
describe the adsorption part of pharmokinetics
Most medicines are given orally and they must pass through the semi-permeable (lipid) membrane of the gut before reaching the systemic circulation (blood stream). – risk of loss of molecules – what yo put in ihg tnot be available for pharmacodynamic reaction
Absorption can be affected by many factors – including the route in which the medicine is given but is generally proportional to the lipid solubility of the medicine. – main barrier to absorption = has pt used meds and have they used it in the right way
Therefore, the absorption of non-ionised molecules is favoured as these are far more lipid soluble.
A medicine given by intravenous injection is put straight in to the blood stream and is therefore rapidly distributed to tissues
what are barriers to absorption
Concordance *******
Food / Drink
Formulation
Blood flow- e.g. diabetes
Route of administration
Lack of specific receptor needed for absorption
Gastric emptying- drug on empty stomach – drug is dormant
GI motility
Inactivation of drug in gut or liver
Pre-existing medical conditions
Drug interactions
describe the distribution part of pharmokinetics
required to distribute the medicine to body tissues
Process where drug moves away from site of absorption to other areas of the body
Each drug is uniquely distributed in the body, some go into the fat (lipid) and others remain in the extracellular fluid
Drugs are found remotely from the desired site of action which can account for some side effects
Major barriers to distribution: Cell membranes
Capillaries
Blood Brain Barrier- thick lipid barrier
what are the barriers to distribution
Plasma protein binding Competition for protein binding sites (distribution may rely heavily on plasma protein binding)
NB Bound drug– inactive / free drug – active- protein acts as a drug carrier – makes the drug inactive because using energy to adhere to protein when it reaches site of action drug is active – if drug becomes dsrbuted wrongly can become active in wrong places
Regional blood flow - Reduced blood flow e.g. Diabetics
Lipid solubility - Blood/brain barrier – generally if increased lipid solubility then increased penetration
Disease - Liver disease can cause low plasma protein levels. Renal disease causes high blood urea levels
describe the metabolism part of pharmokinetics
The liver is the main site of drug metabolism. However, the gastrointestinal system and the lungs have considerable metabolic activity.
The primary aim of drug metabolism is to render a molecule as water soluble as possible so that it can be eliminated from the body by the kidneys.
Metabolites tend to be less active than the parent compound although some, termed ‘active metabolites’ may be more potent if the parent compound was administered as a ‘pro-drug’ (an inactive compound on administration which is activated by metabolism).
what is first pass metabolism
Compounds given orally are primarily absorbed in the small intestine and enter the portal system which takes the drug molecule to the liver before effective distribution to body tissues.
If the result of this first pass metabolism is an ineffective compound, then the medicines is not therapeutically viable by the oral route
what factors affect metabolism
Genetic factors
e.g acetylation status – breakdown meachanism in liver = acetylation (‘fast- break down meds to quick /slow- risk of accumalatig meds metaboliser’)
Age
Impaired or immature hepatic enzyme activity
Elderly- may metabolise less effectively
Children < 6 months (especially premature babies)
Other drugs
hepatic enzyme inducers- quickens metabolism in liver
hepatic enzyme inhibitors- slows down metabolism could result in accumulation of medication
describe the process of elimination/ excretion
Many compounds are primarily excreted by the kidneys.
Water soluble compounds appearing in the glomerular filtrate will be eliminated in urine whereas lipid soluble compounds will be reabsorbed by passive diffusion in to the renal tubules.
Some compounds are concentrated in bile and excreted in to the intestine where they may be re-absorbed (enterohepatic re-circulation-can increase the persistence of the drug in the body) or eliminated in faeces.
Other routes of elimination include sweat, tears, genital secretions and breast milk
how is kidney function and age correlated
Kidney function declines with age – drop In filtration rate in the kidneys
deine pharmacodynamics
How drugs work when they reach their site of action
what are the actions of drugs
Drugs may act on:
One of the components of the cell
One of the critical chemical pathways of the cell
Transport mechanisms allowing chemicals into and outside of cells
Chemical messaging systems between cells
DNA / RNA replication
how to drugs interact with animal cells
drugs can damage cell walls
how to drugs act on cell walls
Some antibiotics damage the bacterial cell wall
Cell becomes leaky and dies and therefore as bavteria usually proliferate to creates infection stops bacteria from proliferating
Example: penicillin
how to cells transport molecules though cell walls
Cells need to transport molecules into and out of the cell
Some molecules can pass through according to:
Size Smaller the better
Electric charge Less highly charged the better
Polarity
how to cells ensure a molecule gets through a cell
By giving the molecule polartity it forces the molecule through the cell membrane even though it is to big
what is osmosis
Osmosis is the passage of solvent such as water through a semi-permeable membrane from a less concentrated solution into a more concentrated one
ie.spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides).
