7: Pharmacology Flashcards
Define a drug
any substance or product that can alter function when entering the body.
Define pharmacodynamics
the drugs effect on the body
- mode of drug action
Define pharmacokinetics
the bodies effect on the drug
What are some of the sources drugs are derived from?
- Plants
- Animals
- Minerals
- Synthesised in labs
- Microorganisms
Name one drug developed from a fungus
penicilin
Name 2 drugs derived from plants
Morphine- poppy plant
Caffeine- caffea aravica plant
Name 2 drugs derived from animals
Adrenaline- adrenal glands of pigs, monkey and cows. Now synthesised artificially
- for treatment of anaphalcix
Insulin- from pigs and cows. Now synthesised artificially
- for treating diabetes
Describe the term “chemical name”
describes the chemical composition/molecular structure of the drug.
Describe the term “Generic name”
an abbreviated name given to the drug by the manufacturer that first develops the drug.
- This is a patient. The owner can only see the drug for a limited time by themselves before someone else is allowed to start making it.
- The cant sell it under he original name. (non-proprietary)
Describe the term “trade name”
or brand name is a generic name given by other companies for the same drug to market it. E.g. for paracetamol there is Panadol, Panamax, dymadon and tylenol.
What factors effect the choice of route of admission
- Physical properties e.g. solid, liquid, gas
- Chemical properties e.g. pH at site of action
- Other factors e.g. conscious state
What does the route of administration determine?
It changes how well the drug effects the body and does it job.
How quickly and easily it reaches its target.
how much reaches target
Name for swallowing a drug
oral route
Name for drug still undergoing 1st pass metabolism but not being swallowed e.g. via tube
enteral route
Mediums for oral administration
tablets
capsules
lozenges
liquid preparation
Advantages of oral (enteral) administration
economically benificial
non-invasive
pain free
easily administered if good patient compliance
good absorption along whole GI tract
Plasma concentration of drug does not increase to rapidly
Disadvantages of oral administration
requires patient compliance
patient must be concious and cooperative
may cause GI irritation
medication effectiveness may be altered by food, gastric secretions, emotional stress or physical activity.
Drug may denature in digestive tract (e.g. insulin is a protein and so acid would denature it so it isn’t given orally)
longer for drug to take effect
subject to first pass metabolism
Explain sublingual administration
under the tonged
- The network of capillaries just under the tonged facilitated quick absorption.
through cappillaries of mucosal membrane
avoids first pass metabolism
Explain buccal
placed between cheek and tongue
- capillaries in cheek absorb drug quickly
- But slower then sublingual as capillaries aren’t as close
through cappillaries of mucosal membrane
avoids first-pass metabolism
Describe the parenteral route
any non-oral method of drug administration
- Most commonly injections such as;
intravenous (IV) subcutaneous (SC) intramuscular (IM) - Also include; epidural and intra-arterial
Other placed that can be injected include
- Intra subarachnoid
- Intra plural
These are much less comon
Advantages of the parenteral route
- provides alternative to avoid disadvantages of oral admin
- IV and Intra-arterial= immediate onset
- IM and SC can be used to achieve slower or delayed onset of action.
- problems with compliance and cooperation can be avoided
- avoids first-pass metabolism
Disadvantages of the parenteral route
- requires skill to administer
- higher risk of infection
- onset of drug can be rapid
- painful
- requires accurate does
- more expensive
- may require additional; equipment
Describe the inhalation/pulmonary route
drugs administered by gas or fine mist
- lungs provide large surface area for absorption.
- lungs= rich capillary network
e. g. bronchiole dilators (asthma puffers)
Describe the topical route
applying drug to the skin or mucous membranes
- used to produce local or systemic effects
includes administration via skin, eyes, ears, nose, vagina and rectum.
- medication may take the form of an ointment, transdermal patch, drops, pessaries and suppositories
- must be applied to intact skin
What 4 factors influence how the drug reaches it molecular target.
influenced by how the drug is:
- absorbed into the body
- Distributed around the body
- Metabolised by the body
- Excreted from the body
Define drug absorption
process a drug takes to go from site of administration to the systemic circulation.
Intravascular admin= means drug skips many complication of absorption as it is injected straight into the blood stream.
Describe the absorption process of an oral drug (tablet in this case) that enters outside the bloodstream
- disintegrated (broken down)
- goes into solution (dissolution)
- is absorbed from the small intestine
- into the hepatic portal system (blood supply - liver)
- then into the systemic circulation
Factors affecting drug absorption
Formulation
- liquid > tablet (oral rouet)
Route of admin
- IV > tabet
Tissue surface area and thickness
>surface area= increased absorption and rate
Explain how the solubility of drug affects absorption
Lipid soluble drugs- easily cross membrane via simple diffusion- rapid absorption
Water soluble drugs- cross the membrane via facilitated diffusion or active transport- slower absorption
How can drugs be distributed?
Drugs can be distributed to both fluid and intracellular compartments throughout the body.
fluid compartment- in particular, blood
Intracellular compartments- target tissue plus other tissue e.g. bone and fat
- this can be both where we want and drug but also not where we want the drug.
Define distribution
process of reversible transfer of a drug between on location and another in the body.
Depending on the drug, the drug may;
- remain in the blood
- be distributed to organs that are well perfused (good blood supply)
- Be distributed more slowly to areas that are poorly perfused (e.g. adipose tissue)
What does the movement of drug to body tissue depend on?
- drug solubility (water or liquid soluble)
- cardiovascular functioning (especially cardiac output)
- perfusion of the area
(vascularity and permeability of capillaries) - pH of area
- Binding of drug to plasma protein
Explain binding of drug to plasma proteins
- a portion of drug molecules binds reversibly to plasma proteins
- a proportion of drug molecules remain “free” or unbound
- pharmacological action is exerted by unbound drug, so high degree of plasma protein binding will effect drug efficacy.
- once “free” drug is removed from circulation (e.g. via metabolism, excretion) more protein-bound drug will be released.
Explain tissue binding drug
Drug binds to a certain tissue and is stored then released later which decreases pharmacological effect.
adipose tissue= lipid soluble drugs have a high affinity for adipose tissue. Low blood flow to this tissue means some drugs may be stored here.
bone tissue= some drugs have a special affinity for bone and can accumulate here.
This decreases immediate distribution. Drugs having accumulated here may be released slowly over time.
Barriers to drug distribution- explain the blood brain barrier
tightly joined endothelial cells protect CNS from potentially damaging microorganisms and other substances.
- drugs can be subject to such barriers and not work
Barriers to drug distribution- Placental barrier
membranes and enzymes providing incomplete protection to fetal circulation.
Define metabolism
aka biotransformation is the process where drugs are broken down into substances more easily eliminated.
These chemicals are termed metabolites
Define a metabolite
what is left after metabolism breaks down a drug
What is the most important site of metabolism?
liver- facilitated by many enzymes that are located there.
Factors effecting metabolism
- genetics
- Environmental factors (medications, diet, alcohol, activity)
- Age and gender
(infants have immature liver function, elderly have slowed metabolism, pregnancy can alter drug metabolism) - disease state
(presence of hepatic, renal or CVD will slow metabolism)
these factors affect BIOAVAILABILITY of a drug
Define bioavailability
portion (%) of the administered drug that reaches the systemic circulation. aka amount of drug that is available to exert a pharmacological effect.
Factors effecting bio availability
- route of administration
- first pass metabolism (if orally)
to accommodate for hepatic first pass metabolism, the administered dose is often more than needed.
Explain Hepatic first-pass metabolism
drung travels from oral administration site throgh GI tract where it is absorbed or excreted.
If not excreted- passes through hepatic portal vein into liver where it undergoes metabolism before reaching systemic circulation.
Name points during hepatic first pass metabolism where drug can be lost
when not absorbed by intestines into blood
- when not absorbed by liver from hepatic portal vein
- when not metabolised by the liver
what remains and passes is called bioavailability
Define elimination
irreversible loss of a drug from plasma that occurs via metabolism and excretion.
liver is the main site of elimination due to metabolism.
Define excretion
irreversible loss of drug from body
- kidneys excrete most drugs and their metabolites
- eliminated in bile so removed with faeces
- lungs excrete volatile substances such as inhalation anaesthetics
- other routes include; intestine, salivary, sweat and mammary gland.
both drug and metabolite can be excreted
What is the kidneys role in excretion?
- free unbound drugs can be filtered from the blood into the renal filtrate
- lipid soluble drugs may be reabsorbed from renal filtrate back into systemic circulation
- water soluble drugs can also be secreted from blood into filterate
What does the process of excretion depend on?
urinary pH (4.6-8.2) renal and cardiovascular function
Define therapeutic range
range of concentration of a drug that has potential to produce desired therapeutic effect and low probability of toxic effects. (we get what we want from the drug)
How is therapeutic range reached
Drug dose regime which includes;
- the amount of drug administered
- how often the drug is administered
ranges derived from past studies and uses
Does every individual respond the same to a drug?
Every individual response to a drug differently
- Some may experience no effects
Some may experience toxicity even when a drug is within therapeutic range
What two concentrations does the therapeutic range lie between
- minimum effective concentration
minimum amount of drug required to cause a pharmacological effect
And
- ,minimum toxic concentration
Minimum toxic concentration- minimum amount of drug that causes toxic effects.
What impacts the therapeutic range of a drug?
- route of administration
- pharmaokinetics
- characteristics of the individual that include; age, gender, health/disease status, CVD, liver and kidney function.
Define drug half life
the time taken for the drug concentration to be reduced by 50% from its maximum concentration.
- 100mg- administered
- 50mg- 4hs
- 25mg- 8hrs
Why is drug half life useful to a nurse?
tells us;
- how quickly a drug is absorbed
- how often we need to redose
Define minimum effective concentration
when there is enough drug in the plasma to being exerting a pharmacological or therapeutic effect
Define onset of action
time at which minimum effective concentration is reached
Define termination of action
concentration of drug has dropped below minimum effective concentration longer has a therapeutic effect.
Define duration of action
time between minimum effective concentration and termination of action
Define Cmax
maximum plasma concentration of drug
Define Tmax
time taken to reach max concentration of drug (time taken to reach Cmax)
Define T1/2
time taken for drug concentration to be reduced by half- 50% of max concentration
The mode of drug action depends on the drug’s molecular target. What are the two drug target types?
1- proteins (primary type)
- carrier proteins
- ion channels
- emzyme/chemcial reactions
- receptors
2- DNA
- chemotherapy drugs
Explain pharmacodynamics on carrier proteins
- drug alters the function of the drug involved in facilitated diffusion and/or active transport
- drug cn prevent carrier protein from moving molecule into cell.
- block the reuptake of molecules at synapses.
Explain pharmacodynamics on ion channels
- drug can alter function of protein involved in facilitated diffusion.
- drug can act on ion channel by binding to the channel causing it to;
- open
- close
- blocking the channel
e.g. Local aesthetic work by blocking sodium gates channels which inhibits action potential from travelling along the nerve cell which inhibits the feeling of pain.
Explain pharmacodynamics on enzymes
affected the biocatalyst in either a;
- competitive inhibitors
- non-competetaive inhibitor
Explain competitive inhibitors
- drug binds enzyme active site- substrate can not bind - slows or inhibits activity
e. g. anti- inflammatory drugs
Explain non-competitive inhibitors
- drug binds to enzyme changing its shape- fully preventing substrate from binding
- enzyme is destroyed
e. g. penicillin (acts on peptidoglycan wall in bacterial cells)
Explain pharmacodynamics on receptors
receptors are
- present on cell membrane and within cytoplasm
- involved in signaling between and within cells
- a major drug target
Drugs that bind receptors:
- bind in place of the natural ligand
- agonist- initiates or enhances the normal response
- antagonist- blocks the normal response
Define a ligand
Molecules (eg, drugs, hormones, neurotransmitters) that bind to a receptor
Describe some of the considerations for geriatric considerations
- polypharmacy
- most hospital admissions for ADR
- reduce gastric acid secretion and slowed gastric motility impacting on absorption
- changes in hepatic and renal physiological function which can have significant impacts on metabolism and excretion.
- aka alters pharmacokinetics
- often a decrease in lean body mass and total body water.
increased body fat= increased T1/2 decreased water decreases= toxicity increases (of water soluble drugs) - decreased target organ or receptor sensitivity.
Describe some bariatric considerations
affects 4 aspects of pharmacokinetics
- absorption
(IV access may be difficult, increased gastric emptying can mean increased absorption of oral medications, poor subcutaneous blood supply, needle may be to short)
- distribution
(Cmax reduces, altered protein binding, lipid drugs= increased volume of distribution, accumulation of lipid-soluble drugs in adipose tissue)
- metabolism
- excretion
- underrepresented in clinical trials so less knowledge on ADR’s so patients need to be more closely monitored
Describe peadatratic consideration when administering drugs
- increased body water content (water soluble drugs handled differently)
- lack of child clinical trials
- usually calculated on weight or body surface area.
Describe hypersensitivity
allergic reaction
bodies immune system showing an exagerated response to a drug percieved as a foreign substance
- substances foreign to the body act as antigens and can stimulate the bodies immune system.
present in anaphylaxis or rash
Explain ADR’s
= an unintended and/or undesirable effect of a drug
- includes drug hyposensativity
- requires alteration of the drug dosage regime or withdrawal of the medication.
What are some of the consequences of ADR’s
- decreased effectiveness of treatment
- poor therapeutic outcomes
- prolonged illness
- increased length or hospital stay
- increased costs
- higher mortality rates
Identify some predisposing factors for ADR’s
age- elderly or neonates
gender- more common in female
Dose- many are does related
Polypharmacy- increased risk, especially in elderly
- history- frequent presenter/chronic condition at higher risk
- genetic factors- possible liver enzyme deficiency
Define drug-drug interaction
pharmacological effect of one drug is altered by another drug
- effect could be an enhanced or decreased therapeutic effect
- ADR
can occur with both prescription and non prescription
Define drug contradiction
a factor that makes the administration of a drug undesirable or even dangerous
Factors affecting drug contradiction
- patient status (prem infants when liver and kidney function isn’t great, preganat women- drugs can cross to baby)
- disease state(kidney disease= excretion/clearance will be reduced, liver disease= metabolism will be reduced)
Explain drug transfer
- any drug given to a pregnant women may reach fetus via circulation or breast milk.
factors contributing to potential harm:
- drug properties and dosage
- gestational age of fetus
Define teratogenic drugs
drugs known to cause harm to a foetus
