Exam Flashcards
Bioavailability
Amount of drug present in the body that reaches the systemic circulation unchanged
I.e IV = 100%
First Pass Metabolism
The amount of drug lost though Gastrointestinal Transit due to large surface area for absorption before it reaches systemic circulation
Pharmacokinetics
What the body does to the drug in the process of ADME, This includes the process of drug through , into and out of the body
Pharmacodynamics
What the drug does to the body and the mechanism of action
Free drug
A drug unchanged not bound to a protein
Water soluble
Has difficulty crossing the cell membrane so remains in circulation so not as well distributed, so rapidly cleared by the liver and kidneys
Lipid Soluble
Easier to cross cell membrane distribution is more widespread and elimination/excretion is slower but absorption is higher as is distribution
Distribution
How a drug is dispersed or disseminated around the body to get to its site of action.
The amount of drug in the body - how widely a drug is distributed in body tissue.
Into body fluids, tissues, organs or protein bound
Half Life
The amount of time it takes a drug to reduce by 50% in the body
Steady State
When there is the same amount of drug entering the body as being eliminted
Metabolism
How the body breaks down a drug into its component parts for activation, elimination or excretion.
Reduces drug activity, creates metabolites or activates a drug such as a prodrug as a metabolite
Renal Excretion
The process or removing a drug from the body via the kidneys after being metabolised by the liver into a water soluble state
EGFR
A measure of how well the kidney are working/filtration via the Glomerulus and Bowman’s capsule. Identified via a blood test and calculated taking into account : ethnicity, sex and age
Enterohepatic recirculation
When a drug is excreted in the bile, and then re absorbed into the intestines/gut and transported back to the liver by the hepatic portal
Type A drug reaction
Augmented drug reaction , usually dose dependant, likely predictable and can be anticipated as part of a side effect or normal drug reaction
Type B drug Reaction
Bizzare and non predictable, not dose related and likely related to the individual response
Absorption
The movement of the drug into blood circulation.
The process of the drug moving from site of administration to the systemic circulation - diffusion facilitated by movement from an area of high concentration into an area of low concentration by active and passive transport
Excretion
The process of removal of a drug from the body as a metabolite or unchanged drug
8 Modes of excretion
- Bile
- Tears
- Breast milk
- Saliva
- Renal
- Faecal
- Respiration
- Perspiration
BNF ADR’s in the Elderly
- Constipation
- Confusion
- Hypotension
- Falls
Drug Affinity
How well a drug binds to a receptor
Therapeutic Index /Window
The range of dose at which a drug is effective without unacceptable adverse reaction/events
I.e. the window of a dose between ineffective or toxic
Agonist
Binds to a receptor to create, illicit or active a response
Antagonist
Binds to a receptor to block, prevent or stops a response
Cytochrome P450
A Hemoprotein that plays a key role in the metabolism of drugs in the liver, more than 50 enzymes in this class, with 6 main active to metabolise approx. 90% of known drugs
Albumin
Is a transport protein in drug circulation
Ligand
Is a protein molecule that binds to a receptor , can be a hormone, a neurotransmitter or a chemical from a pharmaceutical drug
What is a prescribing error
Can occur at any stage of teh prescribing process including:
Prescribing
Administering, preparing, dispensing, monitoring and reviewing or upon providing advice about a drug
Topical Administration
For higher absorption at site reducing amount of drug else where in the body
Transdermal administration
Used to prolong the administration of a drug via the skin
Factors affecting absorption
Physiological:
Renal & hepatic impairment
Blood flow
Surface area
Site of administration and contact time
Chemical:
Lipid/water soluble
Ion Channels and degree of ionisation
Chemical stability
Factors affecting distribution
Renal and hepatic impairment
Blood flow/circulation/barriers
Solubility
Amount of drug bound to proteins
Muscle and a tissue mass
Obesity and oedema
Pro Drug
A drug that needs to be metabolised to become active
Targets for drug blinding
Ion channels
Receptors
Enzymes
Receptors
Is a glycoprotein in cell membrane that bind to ligands
Specificity
When a drug binds to a specific receptor
Ion Channels
aids movement between cell membranes though ionisation
Eg channel blockers or channel modulators in order to block or open the flow
Drug interaction
When a drug encounter another natural or unnaturally occurring chemical that alters the intended action of a drug
Enteral routes of administration
- Oral
- Sublingual
- Rectal
- PEG/NG
Parenteral Routes of Administration
- IV
- IM
- SC
- Topical/Transdermal
Blood Brain Barrier
In place to prevent toxic substances from reaching the brain or progressing through the placenta in pregnancy.
Crossing is usually by passive diffusion in small molecules that dissolve into lipid membranes
Three Key distribution Pathways
- Protein Bound - takes longer to excrete
- Into body Fluids - is quicker to excrete as water soluble
- Into tissues and organs - free drug have a higher bioavailability
Factors affecting Plasma Protein levels
Can be affected by Hepatic Impairmet due to less albumin being made reducing amount of protein.
Muscle wasting diseases can affect this
In ITU proteins and albumin can be replaced .
Patients with reduced Plasma proteins will require dose adjustment to prevent toxicity from increased free drug levels
Phase 1 Metabolism
Modification :
Reduction, Oxidisation or hydrolysis reactions converts lipophilic drugs into polar molecules
Phase 2 metabolism
Conjugation:
By coupling a drug and/or its metabolites to another molecule in order to make it water soluble
Enzyme Inhibitors
Reacts with Enzymes to reduce/stop a reaction
Enzymes Inducer
Increases metabolic activity by binding and activating it
Competitive Antagonist
Binds to the same site as a agonist blocking its action
E.g. Naloxone
Irreversible Antagonist
An antagonist that binds permanently to a receptor until the cell produces a new receptor
Carrier ION
Helps move IONS between lipophilic and hydrophilic mediums to permeate membranes
