Lecture notes Year 1 MBChB: Introduction to Medical Sciences (IMS)
Lecture notes Year 1 MBChB: Introduction to Medical Sciences (IMS)
Lecture notes Year 1 MBChB: Introduction to Medical Sciences (IMS)
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University of Leeds (UoL)
University of Leeds
Year 1 MBChB: IMS
All documents for this subject (12)
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PHARMOCOGOLY
PHARMACOKINETICS
What is pharmacology? - effect of chemicals on biological entities
Study of drugs: the way drugs react biologically at receptor sites
Study of drug effects: effect the drug has when taken by a person
Considers therapeutic and toxic effects
Drug: a natural product, chemical substance or pharmaceutical preparation intended for administration to a human or
animal to diagnose or treat a disease
What is a medical device?
Any instrument, apparatus, implement, machine, appliance, implant, reagent for in vitro use, software, material or
other similar article, intended for the specific medical purposes of:
o Diagnosis, prevention, monitoring, treatment or alleviation of disease/injury
o Control of conception, disinfection of medical devices
Drug names
Generic name- approved or official name
Trade or brand name- name given to drug by its pharmaceutical company
Chemical name- dependent on the drugs chemical structure
Use name- use for which they are prescribed, anti-inflammatories
Effect name- the physiological or biological response in the body
Route Advantage Disadvantage
ORAL Convenient, safe, economical Cannot be used for that are inactivated by 1st
pass metabolism or that irritate the gut
INTRAMUSCULAR Suitable for suspensions and oily substances May be painful
Rapid absorption from solutions May cause bleeding at site of injection
Slow and sustained absorption from suspensions
SUBCUTANEOUS Suitable for suspensions and pellets Cannot be used to deliver large volumes of fluid
Under the skin Cannot be used for drugs that irritate cutaneous
tissue
INTRAVENOUS Bypasses absorption, causes immediate effect May be painful
100% immediate bioavailability May cause bleeding at site of injection
BUCCAL Rapidly absorbed Effective only for low doses
Avoids 1st pass metabolism Drugs must be water and lipid soluble
TRANSDERMAL Avoids 1st pass metabolism Effective only for low doses of drug that are
Through the skin highly lipid soluble
into bloodstream
INHALATIONAL Produce a localised effect Drug particles must be correct size
Dependent on patient technique
EPIDURAL Provides a targeted effect Risk of failure
Epidural space of Risk of infection
the spinal cord
TOPICAL Non-invasive and easy to administer Poorly lipid soluble not absorbed via skin or
Applying to the mucous membranes
body surfaces Very slow absorption
Types of oral preparations
Tablet Compressed powder
Can be coated - protection against environment or mask unpleasant taste or protect against stomach acid
Capsule Solid dosage forms containing drug and fillers enclosed in a soft or hard gelatine shell
Solution Active constituents (solute) is dissolved in a solvent
Suspension Finely divided drug suspended in a suitable vehicle
Useful method of administering large amounts of drug
, Using modified dose forms
Advantages Disadvantages
Improved patient adherence Cost more per unit dose than conventional forms
Reduction in incidence and severity of GIT effects Possibility of unsafe over dosage if used incorrectly of in
failure of MR tablet
Improved control over therapeutic plasma Rate of transit through GIT limits the maximum period for
concentrations which a therapeutic response can be maintained
Maintenance of therapeutic action overnight Variability in physiological factors
Minimise adverse effects associated with high
plasma concentrations
PHARMACOKINETICS – how drugs are absorbed in body, distributed, metabolised and eliminated
Absorption
Transfer of the drug from the site of administration into the general or systemic circulation
Absorption from the gut or other routes
Oral absorption (approx. 75% of drug absorbed orally in 1-3hrs)
pH and drug absorption
Drugs are either acids or bases
In water, strong acids and bases are 100% ionised
Increasing pH: acids become increasingly ionised and bases become increasingly unionised
The lipophilic nature of the cell membrane only permits the passage of the uncharged fraction
Distribution
The process by which the drug is transferred reversibly
o from the general circulation tissues as concentrations in blood increase
o from the tissues blood as concentrations in blood decrease
Mainly occurs by passive diffusion of un-ionised form across the cell membrane
After IV injection
o High plasma concentration and drug rapidly equilibrates with well-perfused tissue giving relatively high
concentrations
Drug movement
Bulk flow transfer – blood transfer
Diffusion transfer – molecule by molecule – short distances
Drugs can cross cellular barriers by:
o Passive diffusion transfer – only if drug is lipid soluble
o Carrier mediated transfer
Volume of distribution
VoD- size of a compartment that accounts for the total amount of drug in the body based on the amount in the
plasma at time zero
Used to determine the loading dose necessary for a desired blood concentration of a drug
Used for estimating a blood concentration in the treatment of overdose
Large VoD- requires a larger dose for a set conc in the blood
Factors affecting drug distribution
Plasma protein binding, specific drug receptor sites, regional blood flow, lipid solubility, disease
Drug-protein binding
Drug + Protein ↔ Drug – protein complex
Binding of drugs with albumin and glycoproteins
Reversible structure
Albumin bound: Furosemide, ibuprofen, phenytoin, thiazides, warfarin
Glycoprotein bound: chlorpromazine, propranolol, tricyclic antidepressants, lidocaine
Administration of a drug that becomes highly protein bound to a patient who is already taking a drug that is highly
protein bound:
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