Pharmacology Flashcards
pharmacokinetics
what the body does to the drug
pharmodynamics
what the drug does to the body
non cellular mechanisms by which drugs produce an effect
- physical effects: lacrilube applied to eyes
- chemical: ranitidine on gastric HCl
- physiochemical
- modification of body fluid composition
cellular mechanisms by which drugs produce an effect
- physicochemical/biophysical mechanisms
- cell membrane structure and function mods (insulin)
- enzyme inhibition
- receptor mediated effects (opioids)
molecular targets for drugs
receptors- transduce signal from drug
enzymes- activated or inhibited
transporters- carry molecules across membranes
ion channels- open or close
nucleic acid- affect gene transcription
ligand definition
forms a complex with a bio molecule
receptor
proteins interact with extracellular physiological signals and convert to intracellular effects
characteristics of 4 types of receptor
ligand gated ion channels- miliseconds, ACh
G-protein-coupled receptors- seconds, ACh
kinase-linked receptors- hours, cytokines
nuclear receptors- hours, oestrogen
full agonist definition and example
able to generate a maximal response after binding to a receptor, high affinity and high intrinsic activity
example: methadone
partial agonist definition and example
drug that has an intrinsic activity of less than 1, receptor occupancy produces a sub maximal effect
example: buprenorphine
inverse agonist definition and example
drug binds and inverses the effect to the endogenous agonist.
example: histamine
antagonist definition and example
no effect but blocks endogenous mediators.
example: naloxone
theraputic index
maximum non-toxic dose/minimum effective dose
LD50/ED50
- measure of drug safety
- effective dose can be variable
how do drugs cross membranes
- aqueous diffusion
- passive lipid diffusion
- facilitated diffusion
- pinocytosis (cell drinking)
- active transport
bioavailability definition
the fraction of a dose reaching the systemic circulation after administration compared to the same dose administered intravenously
principles of drug absorption
- drug molecules are usually small weak acids or bases
- ionisation determined by pKa of drug and pH of surrounding tissue
- ionised drug molecules cross by facilitated diffusion or pinocytosis
- tissue pH can change (infection)
- absorption influenced by route of administration and drug formulation
routes of administration and absorbance
- IV- fastest route
- IM- absorption variable
- SC- slower than IM, unpredictable
- oral- absorption in small intestine, low lipid solulbilty
- inhalational
- epidural/spinal
- transmucosal (oral and rectal)
- transepithelial (skin, cornea)
principles of drug distribution
- apparent volume of distribution= amount of drug administered/plasma conc
5 factors determining drug distribution
- protein binding
- tissue binding
- organ blood flow
- membrane permeability
- drug solubility
principles of drug metabolism
- termination of drug effects: primarily biotransformation then excretion
- most drugs are lipophilic and highly plasma protein bound
- kidney excrete polar water soluble compounds most easily
- liver is primary organ of metabolism
clearance definition
the volume of plasma from which drug is completely removed per unit time
half-life definition
the time taken for the plasma concentration to fall 50% of its initial value
rate constant K=clearance/vol of distribution
hepatic metabolism
- convert drug to more polar metabolite
- oxidative, hydrolytic or reductive reactions
- conjugation with substrates
- requires energy
- resultant more polar compound more readily excreted
- glucuronidation (not cats)
- acetylation (not dogs)
- methylation
principles of drug excretion
biliary excretion, lung excretion, GI tract, renal
- renal excretion most common
- active via tubular secretion or passive by glomerular filtration
- may need to alter dose in animals with renal comprimise
bacteriostatic vs bacteriocidal
bacteriostatic- arrest bacterial multiplication
bacteriocidal- act primarily by killing bacteria
mechanisms of action of bacteriocidals
cell wall- interferes with maintenance of bacterial cell wall leading to rupture due to osmotic pressures
cytoplasmic membrane- drugs that interfere with the structure of the plasma membrane
nucleic acid metabolism- drugs may interfere directly with microbial DNA or its replication or repair
principles of antimicrobial therapy
- make diagnosis
- remove barriers to cure
- decide whether chemotherapy is necessary
- select the best drug
- administer the drug in optimum dose and frequency and by optimum route
- test for cure
aims of premedication
- decrease stress and risk of injury to animal and staff
- produce balanced anaesthesia
- reduced dose of induction and maintenance agents
- provide analgesia
- reduce side effects of anaesthetics (lower dose)
5 classes of drugs used for premedication
- phenothiazines
- alpha 2 agonists (analgesic)
- benzodiazepines
- butyrophenones
- opioids (analgesic)
mode of action of phenothiazines
dopamine receptor antagonist in CNS
mode of action of alpha 2 agonists
alpha 2 adrenergic receptor agonist in CNS
mode of action of benzodiazepines
enhance effect of GABA at GABA A receptor
mode of action of butyrophenones
dopamine receptor antagonist in CNS
mode of action of opioids
inhibits neurotransmitter release
phenothiazine licensing and example
- acepromazine (ACP)
- dogs and cats
alpha 2 agonist licensing and example
- dexmedotomidine
- dogs and cats
benzodiazepine licensing and examples
- diazepam (dogs and cats) and midazolam (horses)
butyrophenone licensing and example
- fluanisone (hypnorm)
- rabbit