Week 1 - Drugs and physiology Flashcards
What is a ‘drug’?
- A substance used in the diagnosis, treatment , or prevention of a disease or as a component of a medication 2. such a substance as recognised or defined by Food and Drug Administration (TGA in Australia) 3. A chemical substance, such as a narcotic or hallucinogen, that effects the central nervous system, causing changes in behaviour and often addiction (american heritage dictionary)
In MIMS (Drugs guide), what is the ‘use’?
Use (main effect): what disorder is it used to treat
In MIMS (Drugs guide), what is the ‘Contraindications’?
Contraindications: Drugs or disorders that this drug should not be prescribed with/for
In MIMS (Drugs guide), what is the ‘Precautions’?
Take care when using with other drugs (e.g., with alcohol)
In MIMS (Drugs guide), what is the ‘
Adverse reactions
‘?
Unwanted effects
In MIMS (Drugs guide), what is the ' side effects'?
Unwanted effects for one treatment yet may be wanted for another (e.g., sedative effect of antihistamines, slow GIT gastro-intestinal-track motility with Opiates)
In MIMS (Drugs guide), what is the ' Pack'?
How the drug is packaged
In MIMS (Drugs guide), what is the ' dose'?
what dose to prescribe depending no what it is used to treat
What is the LD50?
Dose at which 50% of ‘population’ found to be Lethal, keep below this does
What is the ED50?
Dose at which 50% of the ‘population’ found the drug to be Effective - therapeutic (intended) dosing)
Each drug has a ‘therapeutic index’, what does this mean? (what does a low therapeutic index and a high therapeutic index mean?)
A margin of safety, it is the difference between LD50 an ED50 (Stay within here)
Low therapeutic index - little marin for dosing, easier to overdose e.g., heroin (injectable results in lower therapeutic index)
High therapeutic index - Large margin for dosing, difficult to harm patient e.g., alcohol (orally results in higher therapeutic index)
What is drug potency?
Ability for drug to take effect (how much is needed?)
What is drug toxicity?
Potential to do irreversible harm to body functions - poisons or excessive amount of any substance
What dose is it generally considered safe to stay around?
ED50 (but depends on severity of the condition being treated and dosage curve)
What area of the brain is implicated in memory?
Hippocampus
What area of the brain is broadly implicated in vision?
Occipital Lobe
What area of the brain is broadly implicated in pain?
Thalamus and spinal cord
What area of the brain is broadly implicated in judgement?
Prefrontal cortex and Cingulate Gyrus
What area of the brain is broadly implicated in movement?
Motor cortex
What area of the brain is broadly implicated in sensation?
Parietal lobe - Somatosensory
What area of the brain is broadly implicated in Reward?
The basal ganglia circuit, specifically the mesolimbic pathway (ventral tegmental area and nucleus accumbens), is the center off the reward system yet there are more circuits and brain structures such as the anterior cingulate cortex, and midbrain dopamine pathways. The major neurochemical pathway of the reward system in the brain is the mesocorticolimbic pathway, which includes both the mesolimbic and mesocortical pathways. The ventral tegmental area (VTA) is a source of many dopamine pathways in the brain, which are neurons which use theneurotransmitter dopamine to transmit a signal to other structures. Dopamine acts on D1-like receptors or D2-like receptors to either stimulate (D1-like) or inhibit (D2-like) the production ofcAMP.[11]
What two components make up the peripheral nervous system?
Somatic (Sensorimotor) [touch, sensation]
Autonomic (Parasympathetic [digestion, growth, immune responses], Sympathetic [fight or flight, fright, fornicate])
In the autonomic component of the peripheral nervous system, what does the parasympathetic and sympathetic nervous systems do respectively?
Parasympathetic [digestion, growth, immune responses],
Sympathetic [fight or flight, fright, fornicate]
What brain parts for the main brain hormone system?
- Hypothalamus leading to the…
- Pituritary (and adrenals [atop of kidneys] - cortisone, adrenalen)
- Pineal Gland (sleep and circadian rhythms)
Drugs targeting the PNS are generally _____ than those targeting hormones, which have a greater _____ but are _____.
Faster, range of effect, slower
What is homostasis?
The body naturally wants to promote homestasis (balance) - safe ranges of:
- Oxygen
- Rid waste products (Feaces, Urine, Co2)
- Have good Nutrients
- pH range 7.2
- Temperature 37.2 C
What internal systems support oxygen homeostasis?
- Respiratory (air inhale)
- Cardio-vascular system (getting oxygen to cells via blood)
What internal systems held rid waste products?
- Renal (liquids)
- GIT (Faeces) including Liver
- Respiratory (expel CO2)
- Cardiovascular system (blood, drained to lymphatic system and waste is transported out)
What internal systems help keep nutrient homeostasis?
- GIT
- Cardiovascular (transport)
- Renal (kidney, helps with electrolyte balance charged ions)
What internal systems help keep pH range around 7.2 (homeostasis)?
(level of acidity, changes in this can make neutrons fire erratically or stop - a measure of free charged ions, electrolytes)
- Renal
- Respiratory (reduces CO2)
- Cardiovascular system (buffering [push in either direction] capacity other chemicals in the blood that helps to keep pH balanced)
- GIT (brings in the chemicals that help the blood)
What internal systems help keep temperature around 37.2 C (homeostasis)?
- Skin
- Cardiovascular (blood moves closer to the skin), Respiratory (breathing out hot air)
- Gastrointestinal (changing the temperature of the food we eat)
The effect of a drug is modulated by what four things? (pharmacokinetics - what happens to the drug once it has entered the body [fate])
- Absorption (bioavailability - routes of administration)
- Distribution (blood flow, tissue permeability)
- Metabolism (biotransformation) - liver, enxymes in tissue
- Excretion - Kidneys, lungs
What is bioavailability?
Fraction amount of drug which reaches its site of action (or biological fluid).
Once at site of action, drug may work for mins or hours (Depending on how well it binds and how much is given)
What are the 7 main routes of drug aministration (4 x parenteral [i.e., injectable], 3 x other)
INJECTABLES:
-
Oral (p.o) - first pass metabolism (must ass through the liver) going through the liver results in half-loss of drug, so only need half when injected.
- Sublingual
- Rectal (suppository)
- Pulmonary absorption (inhalants)
- Topical applications - transdermal, eye - via mucous membranes
- Subcutaneous (S.c) ( parenteral [past the mouth] injectable) = Injection into the subcutis skin layer [below the dermis and epidermis i.e., below the cutis]
- Intraperitoneal (i.p.) ( parenteral [past the mouth] injectable) - injection of a substance into the peritoneum (body cavity) [Large body fluid replacement, chemotheraphy and vetenarian treatments]
- Intramuscular (i.m.) ( parenteral [past the mouth] injectable) - the injection of a substance directly into a muscle, limited to 2-5ml of fluid [often deltoid muscle in the arm, vastus lateralis muscle of the leg; and the ventrogluteal and dorsogluteal muscle of the buttocks]
- Intravenous (i.v.) ( parenteral [past the mouth] injectable) - the infusion of liquid substances directly into a vein. (Intravenous therapy may be used to correct electrolyte imbalances, to deliver medications, for blood transfusion or as fluid replacement to correct, for example, dehydration. Intravenous therapy can also be used forchemotherapy. Compared with other routes of administration, the intravenous route is the fastest way to deliver fluids and medications throughout the body.)
What affects the pharmacokinetic of drugs?
- Absorption (bioavailability - routes of administration)
- Distribution (blood flow, tissue permeability)
- Metabolism (biotransformation) - liver, enxymes in tissue
- Excretion - Kidneys, lungs
- Half-life = time to remove half of active drug amount, affected by all of the above
- Pharmacokinetics are determine by chemical properties of the drug (e.g., liphophilicity [soluble in lipids-fat i.e., all cell membranes]
What are the disadvantages and advantages of oral administration of drugs?
Advantage
- Most convenient, economical *safe*
Disadvantage
- Variable absoption pattern - depends on food in stomach etc - e.g., 20-30minutes to work
- Needs patient co-operation
- No use for drugs that are poorly soluble, slowly absorbed, unstable or extensively metabolised by the liver
- Emesis due to irritation of gastric mucosa
- Drug metabolised by gut enzymes or high acidity in gut *enteric coating*
- Metabolised by liver - must give higher dosage (half lost to liver)
What is sublingual drug administration? and what is it good for?
An enteral method of drug administration - Under the tongue dissolving -
dissolve quickly through mucosa (e.g., nitroglycerin) to vena cava (no first past) [straight into blood system]
Good for high lipophilic drugs.
What is rectal drug administration? and what are its advantages and disadvantages?
An enteral method of drug administration -
Drugs put in the rectal cavity.
Advantage:
- Very good when patient can not take drugs orally (vommiting, unconscious).
- 50% will bypass the liver
Disadvantage
- 50% still goes through liver
- Irregular absorption and many drugs irritate rectal mucosa. (therefore highly variable)