Basic Pharmacology Flashcards

1
Q

Drug Definition

A
  • Chemical substance of a known structure, which when administered, produces a measurable biological effect
  • Can be therapeutic, toxic, cosmetic or illegal
  • BNF - British national formulary (lists all the current liscenced drugs available in the UK)
  • MOA - mechanism of action
  • ADRs - adverse drug reactions
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2
Q

Drug Interaction

A
  • Drugs have an effect by interacting on a specific target (usually a protein) - either increasing/decreasing function or activity:

Receptors

  • drugs can bind to membrane receptors & either activate/block intracellular processes
  • agonist - activate cell receptors
  • antagonist - block activation

Ion Channels

  • traffic of ions in/out of a cell effect membrane potential & electrical activity
  • e.g local anaesthetic drugs block action potentials in nerve axons

Enzymes

  • drugs can bind to the enzyme’s active site & prevent substrate conversion
  • or can allosterically change the enzyme’s structure (conformational change to block or enhance catalytic activity)

Genes/DNA

  • genes active within a cell determine function/activity
  • drugs containing genes/DNA/rNA are useful in preventing aberrant activity e.g uncontrolled replication in cancers

Other drugs

  • drugs may directly/indirectly target other drugs a patient is taking
  • drug-drug interactions
  • may effect prescribing regime - one drug may cancel out the function of another drug being used
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3
Q

Pharmacodynamics

A
  • The measurement of how effectively a drug works
  • What the drug is doing to the body at a particular dose
  • Being able to quantifiably measure the effect of a drug (e.g blood pressure) allows you to plot the trajectory of how the patient is responding to a course of treatment
  • Can only have a meaningful measurement if there is a baseline to compare against
  • Can never make assumptions - must have a physical measurement
  • Critical component - estabilishing the right dose for the desired affect & patient saftey
  • Typically drugs have a spectrum of doses that are effective - ends of the spectrum are uneffective/toxic
  • Drug trials can determine the ‘goldilocks zone’ - a range of doses that have the right effect but are not toxic
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4
Q

Clinical Trials

A
  • Produce a series of robust & reproducable evidence to prove that a drug is safe and of benefit to a patient
  • Placebo - a person’s hopes & beliefs about a treatment combined with their suggestibility can have a significant biochemical effect

Blinded trial - recipient does not know if he is recieving the actual drug or a placebo - removes bias

Double-blind trial - both the recipient & administrator do not know if it is the actual drug or a placebo - more complete understanding of drugs effectiveness & bias removal

Randomised control trial - a number of similar people are divided into two groups - experimental or control/comparison. One recieves the actual treatment & other recieves a placebo - reduces bias, see how effective the intervention was & allows outcomes to be measured at specific times

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5
Q

Journey of a Drug

A
  • Can be described by considering each of the seperate components of pharmokinetics
  • To track the drug once it has been administered, we need a superficial undertanding of stages, once it has been consumed

Components of Pharmokinetics:

  • absorption
  • distribution
  • metabolism
  • excretion
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6
Q

Drug Absorption

A

Absorption

  • oral drugs need to be absorbed across the physical barriers between stomach & circulation
  • must pass physical barriers e.g enzymes & chemical barriers that may degrade it
  • absorbtion can be via diffusion (lipid-soluable), active transport or aqueous pores (polar drugs)
  • bioavailability: the percentage of pharacologically active drug that makes it into the circulation (is available) following oral administration
  • intravenous adminsteration may give the drug a higher bioavailability but is harder to achieve logistically
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7
Q

Drug Distribution

A

Distribution:

  • the drug distributes itself into various tissues/organs
  • distribution effect is due to body function e.g cardiac output & reigional blood flow to tissue, determines how much of a drug is delivered to a specific tissue
  • chemical structure of the drug & physiological structure of the tissue (similarity of both) determines distribution
  • lipid soluable drug will diffuse into a adipose tissue easily
  • lipid solubility is influenced by local pH, will determine how much of the drug will actually get to it’s target
  • a weakly alkaline drug in alkaline solution will not dissociate (& become highly ionised) so will remain relatively hydrophobic and therefore diffuse - vis versa
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8
Q

Drug Metabolism

A

Metabolism:

  • drug metabolism refers to the enzyme-mediate processes that occur largely in the liver that deactivate a drug & make it water soluable (ready for excretion)
  • body percieves the presence of a drug as a potential biohazard so will actively break it down using liver enzymes
  • drug-metabolising enzymes are inducable - only act in the presence of a drug, efficiency
  • phase I enzymes chemically modify drugs into an intermediate metabolite in preparation for phase II
  • phase II fully deactivates the drug, renders it inert & makes it water-soulable ready for excretion
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9
Q

Drug Excretion

A

Excretion:

  • physically removing the drug metabolite from the body
  • most significant route is via renal extrection - water-soluable drug is filtered out of the blood, into urine by the kidneys then lost as urine
  • ‘hepatobillary excretion’ - the drug metabolite is trafficked direct from the liver through the common bile duct, into the aqueous environment of the lumen of the gut & lost as faeces
  • any disease affecting the kidneys/liver can have a huge impact on drugs excreted via these routes
  • often routine to check kidney function in elderly patients before administering certain drugs as routine doses may build up to toxic levels
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10
Q

Adverse Drug Reactions

A
  • Any unwanted/unexpected effects of drugs
  • If a patient’s pharmokinetic processes are derranged then there may be an unexpected fluctuation in what the drug dose achieves
  • Therapeutic index of a drug - ratio of the highest dose before a side effect occurs: the lowest dose of drug that gives a therapeutic effect
  • As the drug is administered, repeated dosing is needed to keep a therapeutic concentration maintained in the plasma
  • If the kidneys aren’t functioning correctly, each ‘top-up dose’ may push the concentration too high & it will enter the toxic range
  • Drugs with a wide therapeutic index are preferred as there is more of a buffer for pharmokinetic disturbances
  • Pharmokinetics have an effect of pharmodynamics
  • Role of prescriber - knowlegde of both components for saftey & to minimise the risk of patients experiencing ADRs
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11
Q

Contraindications

A
  • Certain patient demographics (e.g pregnancy) should not recieve certain drugs even if on paper, the choice of the drug might seem appropriate
  • BNF lists contraindications for all UK liscenced drugs
  • Pregnancy is an instance where certain drugs may need to be avoided - due to previous evidence or the uncertainty of effects
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12
Q

Trial Components - Controlled

A
  • Control arm - some patients are given a placebo
  • Subjects are not told if they are controls (typically)
  • Provide a vital ‘baseline reference’ to compare other volunteers against
  • Allows researchers to see if the drug/active treatment is actually causing an effect
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13
Q

Trial Components - Blinding

A
  • Occurs to avoid biassing the experimental results
  • Single-blinding - subject of the drug doesn’t know what type of drug they are getting/if they are a control
  • Double-blinding - doctor giving the drug also doesn’t know what type of drug or if placebo is given, only trial co-ordinator knows
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14
Q

Trial Components - Randomisation

A
  • Making sure as diverse a group of subjects recieves the treatment as possible
  • Not to bias any data by concluding results from a single demographic
  • Less bias, more robust conclusions are
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15
Q

Trial Components - ‘Crossed Over’

A
  • Somepoint in the trial, every patient recieves every treatment available (including placebo)
  • Avoids bias & makes conclusions more robust - every patient may respond differently
  • Not always possible - subject may withdraw early, trial treatment may cure their condition & exclude them from trial)
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16
Q

Voluntary Informed Consent

A

Proposed trial must:

  • be legal & ethical
  • be explained to volunteers
  • have a clear purpose
  • have all risks described
  • have clear exclusion/inclusion criteria
  • explain how data will be used

Subjects must have mental capacity, must not have been co-erced & have their consent witnessed and recorded.