Lecture 8. FACTORS INFLUENCING DRUG ACTION Flashcards
Which factors influence drug action?
Species
subspecies,
bloodline,
receptorial,
absorption,
distribution,
metabolsim,
gut flora,
health status,
dosage,
route of application,
gender,
feeding,
tolerance,
dependence/abuse, i
diosyncrasy,
allergies
What is the mydriatic effect?
It is the effect of an antagonist; muscarinic colinergic neuromuscular junction (atropine) or nicotinic cholinergic neurouscular junction (d-tubocurarine)’
how can the health status influence drug action?
- Fever – reduced emptying of stomach, negative effect on absorption
- Diarrhoea » increased gut motility, decreased bioavailability
- Exsiccation → altered distribution, decreased urinary excretion
how can the feed influence drug action?
Feeding (type and composition of feed) can be a factor.
- Decreased bioavailability (Ca2+ → antibiotics) – Increased activity of metabolising enzymes (plant-steroids)
how can the gender influence drug action?
In males the metabolism could be faster (testosterone is a CYP3A inductor), LD50 values may be higher – this is not always true -.
how can Tolerance influence drug action?
The organism builds up a resistance to the effects (receptor regulation, altered metabolism)
how can Dependence, abuse influence drug action?
Habituation – force of habit, mental, not a real psychological Addiction – strong psychological and frequently physiological
Idiosyncrasy
Individual hypersensitiveness, serious symptoms, hereditary, (e.g. doberman against Phenylbutazone)
Allergic reaction
- Allergic reaction is an uncommon and unwanted side effect of medication, less than 10% of adverse drug (human) reactions are allergic.
- Like most allergies, a drug allergy is caused by an over-sensitive immune system.
- It is important to recognize the symptoms of a drug allergy, because they can be life-threatening. Death from an allergic reaction to a medication is extremely rare, however.
When does a allergic reaction most likely occur?
- An allergic reaction does not often happen the first time patient takes a medication. A reaction is much more likely to occur the next time taking that medication.
Factors maintaining drug allergy are:
- contamination of skin,
- inhalation – contamination of airways,
- depot preparations,
- chronic diseases, atopy
Allergic reactions can be subdivided into four types:
- Immediate or anaphylactic reaction
- Cytolytic
- Immune complex associated
- Delayed or cellular
What is the mechanism of the different drug allergies?
- Immediate or anaphylactic reaction :
IgE on the receptors of mass cells or basophile leucocytes + allergens
- Cytolytic :
IgG and IgM maintained, Complement activation dependent
- Immune complex associated:
Immune-Complex formation, mainly IgG + antigens
- Delayed or cellular:
T-lymphocytes and macrophages maintained hypersensitivity
Examples of Adverse reactions for cytolytic drug allergy:
Haemolytic Anaemia, Thrombocytopenia, Cytolysis, Interstitial Nephritis, Systemic lupus erythematosus
-Signs last over months (sulphonamides, kinidin, procaine)
Examples of Adverse reactions for immunecomplex associated drug allergy:
Serum Sickness, Urticaria, Drug fever, some cutaneous eruptions, vasculitis/arthritis
Examples of Adverse reactions for Delayed or cellular drug allergy:
Contact dermatitis, morbilliform eruptions
Examples of Adverse reactions for immediate or anaphylactic reaction drug allergy:
Vasodilatation, oedema, inflammation,
Diarrhoea
Urticaria (hives), atopic dermatitis
Rhinitis, asthmatic seizure
– In sever cases anaphylactic shock
What is the difference between an anaphylaxis and anaphylactoid reaction?
A distinction should be drawn between anaphylaxis and anaphylactoid (or pseudo-allergic) reactions.
- Anaphylaxis refers to a systemic, immediate hypersensitivity reaction due to the IgE-mediated release of mediators from mast cells and basophils.
- An anaphylactoid event refers to a clinically similar event not mediated by IgE. They cause, via an unknown mechanism.
Factors affecting Drug Disposition and Responses in the Elderly: Absorption
Factors affecting Drug Disposition and Responses in the Elderly: body composition and protein binding
Factors affecting Drug Disposition and Responses in the Elderly: metabolism and excretion
