ALHT106 Lecture Notes - Lecture 10: Adverse Drug Reaction, Drug Nomenclature, Polypharmacy
Principles of pharmacology;
Pharmacology: study of drugs (actions, uses, mechanisms, adverse effects)
Drug: any chemical that can modify or explore biochemical and physiological processes in a living
organism or tissue. Drugs can be used to prevent, diagnose and cure diseases
Medicine: type of drug; a substance given for therapeutic purposes with potential to reduce
pathology, prevent or cure disease; mixed in a formulation for administration
Dose: recommended drug amount given at a particular time
Characteristics of drugs:
Efficacy: degree to which a drug is able to produce the desired response
Potency: amount of chemical needed to produce 50% of maximal effect that drug is capable of
(more potent, the lower the dose needed for an effect); used to compare compounds within classes
of drugs
Selectivity: narrowness of drug’s range of actions on receptors, cells or tissue (e.g. antibiotic-
broad and narrow spectrum)
Indication: a condition or illness for which a drug is used or prescribed e.g. antibiotic for a bacterial
infection such as an UTI
Contraindication: absolute warning that a drug should not be used in certain conditions or illness
e.g. pregnancy as the patient or foetus may be harmed; known hypersensitivity to nitrates, severe
anaemia
Side effect: an effect other than the primary one for which a drug is devised. May be desirable or
undesirable
Adverse drug reaction ADR: side effect of a drug which is annoying, irritating or harmful;
(unintended/undesirable); more likely in elderly, females, those with multiple diseases e.g. GI
bleeding with high dose or long-term use of aspirin
Considerations by health care professionals when prescribing/administrating medicines:
-Is there an alternative treatment/management?
-the individual, understanding and expectations of medicines
-Patient's clinical condition
-indication, what drug is used for
-how the drug works (pharmacodynamics)
-how the body uses the drug (pharmacokinetics)
-Risks and benefits
-Dosage, frequency, length of treatment, route of administration
-any co-existing conditions e.g. pregnancy, impaired liver, kidney or heart function
-other therapies especially polypharmacy
-monitoring considerations/review
-Cost to individual, community and health system
Main sources of drugs:
-Micro-organisms e.g. fungi produce natural antibiotics; bacteria/yeasts genetically engineered to
produce drugs such as insulin
-Humans and other animals e.g. adrenaline, bovine insulin, hug
-Minerals or mineral products
-Substances synthesised in laboratories e.g. research chemicals, mimic natural compounds
(legal and illegal)
-Plants- leaves, roots, extracts e.g. coffee, quinine, herbs
Drug nomenclature:
Most drugs have 3 names:
-Chemical: based on chemicals structure
-Approved/generic name: non-proprietary name, simplified
chemical name
-Trade name: simple name for commercial distribution, protected
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by patent laws
!
Drug classification- many criteria:
-therapeutic (clinical) use
-mode of action
-molecular structure
-source (microorganisms, plant, animal, synthetic)
-system affected
-Effect on target
-effect on receptor
-drug schedule (TGA)
-Prescription (S4) or over-the-counter (S2)
-pregnancy safety
-Cost
2 important areas of pharmacology:
Pharmacokinetics: study of the absorption, distribution, metabolism and exertion of drugs in the
body i.e. what the body does with a drug (influenced by the route of administration)
Pharmacodynamics: mechanism by which drugs work on body (includes biochemical mode of
action, receptor, target, therapeutic effects)
Drug absorption, rate of onset and magnitude of clinical
effect:
Influenced by:
-route of administration e.g. to local site, for systematic
effect
-type of formulation e.g. cream, capsule, injectable
-type of surface e.g. epithelial, mucosal
-chemical structure e.g. hydrophobic/hydrophilic,
solubility
Oral drug administration:
How- swallowed and absorbed via GIT (including liver); produces systematic effect
Examples:
-tablets- compressed granulated powder (1 or more drugs); may contain excipient (inert binding
material)
-Enteric coating/capsule- protect drug from deactivation/breakdown by stomach acid, dissolves in
alkaline pH of SI
-Sustained-release preparations- combined with resin, slow release in GIT
-Syrups- fast absorption as already soluble
Oral drug administration:!
Advantages:
-easy
-DIY (convenient, 80% go via oral)
-safe
-cheap
-drug action removable (e.g. by an emetic)
Disadvantages:
-irregular absorption- enteric coating
-slow effect/partial loss/inactivation- 1st past effect
-bitter taste- helped by sugar-coated or film coated
-irritation to mucosa- enteric coating helps
1st pass effect in liver- metabolic processing:
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Remember the hepatic portal system?- digested and absorbed monomers from GIT first
transported to the liver for metabolism via hepatic portal vein
Metabolism- 1st pass effect in liver:
Liver- site of metabolism and detoxification (drugs seen as toxic); inactivates a % of drug with each
pass through; a small number of drugs are activated
1st pass = directly after absorption
Sublingual administration:
Drug applied to mucosa under the tongue
Absorption across sublingual mucosa
Advantages:
-little chance of drug mixing with food or gastric juices
-avoids the hepatic 1st pass effect
-E.g. Glyceryl trinitrate, for angina un-ionised, with high lipid solubility, so readily diffuses through
the lipid mucosal membranes, into systematic circulation
-Absorption is rapid with effects within 2 mins
Topical administration:
Administered for either local or systematic effect/s:
-to skin e.g. transdermal patches
-to mucosa e.g. intranasal sprays (rapid absorption-large surface area), vaginal pessaries
(support and delivery of medicine)
Advantages:
-avoids the hepatic 1st pass effect
-good for lipid soluble drugs
-rapid particularly for mucosal surface e.g. asthma medications
Disadvantages:
-can cause pathology in injured surfaces- abrasion, burns
-dosing is difficult
Rectal administration:
Rectal mucosa is highly vascularised = good absorption
Solid drug preparation- suppository- absorbed through rectal mucosa
Lipid drug preparation- Enema- for topical or systematic effect or to cause bowel motion
Advantages:
-Convenient if patient cannot swallow/nausea/vomiting/unconscious/fasting (nil by mouth)
Disadvantages:
-problems with self-administration
-irritation to rectal mucosa
-may avoid first pass or be affected depending on site of application
Parenteral administration:
Parenteral= by injection
Solution must be sterile, filtered (particle free), isotonic and buffered to body pH
Advantages:
-quick administration, high bioavailability (few/no membranes to cross, no effect by stomach acid
and digestive enzymes)
-no hepatic 1st pass
-a rapid drug action/effect
-alternative to oral medication e.g. unconscious
Disadvantages:
-Invasive (tissue/nerve damage)
-Unrecoverable
Types:
-Subcutaneous injections (s.c.)
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Document Summary
Pharmacology: study of drugs (actions, uses, mechanisms, adverse effects) Drug: any chemical that can modify or explore biochemical and physiological processes in a living organism or tissue. Drugs can be used to prevent, diagnose and cure diseases. Medicine: type of drug; a substance given for therapeutic purposes with potential to reduce pathology, prevent or cure disease; mixed in a formulation for administration. Dose: recommended drug amount given at a particular time. Ef cacy: degree to which a drug is able to produce the desired response. Potency: amount of chemical needed to produce 50% of maximal effect that drug is capable of (more potent, the lower the dose needed for an effect); used to compare compounds within classes of drugs. Selectivity: narrowness of drug"s range of actions on receptors, cells or tissue (e. g. antibiotic- broad and narrow spectrum) Indication: a condition or illness for which a drug is used or prescribed e. g. antibiotic for a bacterial infection such as an uti.
