nuts and bolts of therapeutics Flashcards
(18 cards)
what are the 4 main goals of rational prescribing?
- maximise effectiveness
- minimise harms
- avoid wasting healthcare resources
- respect the patients choice
what do you need to know to provide effective therapy?
drugs - pharmacokinetics, pharmacodynamics, interactions, formulations
patient - ideas, concerns and expectations. this will increase adherence
disease - diagnosis and comorbidities
define pharmacodynamics and pharmacokinetics
pharmacodynamics - the study of the biochemical and physiological effects of drugs on the body, the mechanisms of drug action and the relationship between drug concentration and effect
pharmacokinetics - the study of drug absorption, distribution, metabolism, and excretion
what is the difference between specific and non specific drug actions?
non specific - eg. neutralisation of gastric acid by antacids
specific - usually chemically sensitive proteins, aim to restore normal function or disrupt abnormal function in diseased cells, acting on receptors or other target molecules in the diseased tissues.
what do drug-receptor interactions depend on?
chemical composition
stereochemical disposition
ability for the drug to reach the receptor binding zone
The drug-receptor complex is usually reversible and the proportion of receptors occupied (response) is directly related to the dose.
outline agonism vs antagonism
agonist - chemical binds to the receptor and activates it to produce a biological response
antagonist - chemical binds to the receptor and blocks it / dampens the agonist-mediated response rather than provoking a biological response
partial agonism - binds and activates a given receptor but only has a partial response compared to a full agonist
define affinity
the probability of the drug occupying receptors at any given time. This depends on various factors such as other drugs, aging, genetic mutations
define selectivity
degree to which a drug acts on a given site relative to other sites. Some drugs are relatively non selective and others are relatively selective eg. bisoprolol which is a cardioselective beta-blocker and therefore only works on beta receptors in the heart
define efficacy
the relative ability of a drug-receptor complex to produce a maximum functional response which relates to the extent of functional change imparted to the receptor by the drug.
define therapeutic efficacy
effectiveness of a drug to produce an effect. For drugs acting via the same mechanism this relates to efficacy as above however some drugs produce the same responses via different mechanisms and the difference in effectiveness are of great clinical importance.
define potency
a measure of drug activity expressed in terms of the amount required to produce an effect of given intensity. This is proportional to affinity and efficacy. A highly potent drug evokes a larger response at low concentrations compared to less potent drugs.
define tolerance
decrease response with repeated doses which usually occurs over days to weeks through a number of potential mechanisms including decreased receptor numbers (down regulation), decreased receptor binding ability and modulation of downstream response to the initial signal.
define withdrawal reactions
when tolerance is present the body is desensitized to the effect of the drug which involves chemical, hormonal or physiological changes offsetting the action of the drug. Therefore when the drug is withdrawn these changes tend to cause a rebound reaction or withdrawal effect.
how do you balance toxic and therapeutic effects?
toxic effects are usually dose related in a similar way to beneficial effects. The challenge is to titrate doses to establish the dose for patients with maximum benefit but minimum toxicity. This is important in drugs with a narrow therapeutic index.
what is the difference between on target and off target responses?
On target - drug intended to modulate the function of a specific receptor in a particular tissue
Off target - drug and/or metabolites modulate the function of a target for which it was not intended
define dose and dosage
dose - the total quantity of an active agent taken in or absorbed at any one time
dosage - includes characteristic of the organism eg. body weight or surface area
why do we formulate medication?
to make the medicine more effective and more acceptable to the patient
outline the different forms of administration of drugs
topical - has a local effect and the substance is applied directly where it is needed
- transcutaneous
- inhalation
- enema
- eye drops
- ear drops
- intranasal
- vaginal
enteral - the desired effect is systemic and the substance is given through the digestive tract
- orally
- gastric feeding tube
- rectally
parenteral - the desired effect is systemic and the substance is given by other routes other than the digestive tract - IV - intra-arterial - intramuscular - subcutaneous - intracardiac - intratracheal - transdermal - transmucosal - inhalation -
