general pharmacology, part 2 pharmaco- dynamics & medication administration f ‘08 p. andrews
Post on 20-Dec-2015
218 views
TRANSCRIPT
Pharmacodynamics
• Most drugs bind to a receptor– Protein molecules– Can be stimulated/inhibited by chemicals– Each receptor’s name generally corresponds to
the drug that stimulates it• Affinity– Force of attraction between a drug and a receptor– Different drugs may bond to same receptor site,
but strength of bond may vary – binding site’s shape determines receptivity to chemicals
• Drug’s pharmacodynamics involves its efficacy• Generally, drugs either stimulate or inhibit the
cell’s normal actions.• Efficacy and affinity not directly related– Drug A causes a stronger response than drug B– Drug B binds to the receptor site more strongly
than drug A
• When drug binds to receptor, chemical change occurs
• Drugs– Interact with receptor and result
in desired effect– Interact with receptor and cause
release/production of a second compound
Giving medications safely
• Know:– Indications– Contraindications– Precautions
• Practice proper technique• Observe & document• Take careful drug histories
Remember the 6 rights of medication administration!
• Right– Person– Drug– Dose– Time– Route– Documentation– And - refusal
Cells talk to each other
• Three distinct languages– Nervous system• neurotransmitters
– Endocrine system• hormones
– Immune system• cytokines
In disease, all systems are affected
• The three systems can’t exist without each other
• The actions of one impact the actions of the others– I.e., stress (nervous system) disrupts
endocrine system which may respond with glucocorticoid production = suppressed immune response
Drug Class Examples
• Nitroglycerin– Body system: “Cardiac drug”– Action of the agent: “Anti-anginal”– Mechanism of action: “Vasodilator”
• Indications for nitroglycerin– Cardiac chest pain– Pulmonary edema– Hypertensive crisis
• Which drug class best describes this drug?
Another way to classify drugs • Mechanism of Action– Drugs in each category work on similar sites in the
body and will have similar specific effects/side effects• Beta blockers: metoprolol• ACE inhibitors: lisinopril• Alpha blockers: prazosin• Calcium-channel blockers: verapamil
• Example: beta blocker actions and impacts– Suppress the actions of the sympathetic nervous
system– Prehospital administration of epinephrine may not
produce as dramatic effects with a patient taking a drug in this class
Prehospital example: Hyperglycemics
• Dextrose 50% and glucagon– Both will raise blood glucose
• Mechanism of action– Glucagon: hormone that works in the liver to convert
stored chains of carbohydrate to glucose– Dextrose 50%: ready-made simple sugar that is ready
to enter into the cell• Which drug is considered first-line for
hypoglycemia? Why?• What are some limitations for glucagon in the
presence of severe hypoglycemia?
Distribution
• Some drugs bind to proteins in blood and remain for prolonged period
• Therapeutic effects due to unbound portion of drug in blood
• Drug bound to plasma proteins can’t cross membranes
• Changing blood pH can affect protein-binding action of drug.
• TCA’s are strongly bound to plasma proteins.
Drugs bind to proteins
• Albumen is one of the chief proteins in the blood available for binding with drugs.
• When a pt. Is malnourished, albumen is low.
• What significance does this have re; drug therapy?
The blood – brain barrier
• Tight junctions of capillary endothelieal cells in CNS form a barrier
• Only non-protein-bound, highly lipid-soluble drugs can enter CNS
• Placental barrier similar
Other deposits
• Fatty tissue serves as drug reservoir• Bones and teeth can accumulate drugs that
bind to calcium– Ie., tetracycline
Biotransformation
• Drugs are metabolized – broken down into metabolites
• Transforms drug into more or less active metabolite
• Make drug more water soluble to facilitate elimination
• Protein-bound drugs are not available for biotransformation
Biotransformation, cont.
• Occurs in liver primarily• Also occurs in kidney, lung, GI
tract• First-pass effect– Some drugs can’t be given orally
What alters drug response?
• Age• Body mass• Sex• Environmental• Time of administration• Pathologic state• Genetic factors• Psychological factors
• Drugs that change physical properties– Osmotrol
• Drugs that chemically bind with other substances– Isopropyl alcohol – denatures proteins on surface
of bacterial cells• Drugs alter a normal metabolic pathway– Anticancer, antiviral drugs
Response to drug administration
• We must carefully weight risk vs benefit!• Allergic reaction– Hypersensitivity
• Idiosyncrasy– Effect unique to person; not expected
• Tolerence – Decreased response to drug after repeated administration
1) Brain sends out the response via nerve paths2) Nerve moves the response: depolarization3) Depolarization stimulates norepinephrine sacks
• Sacks move to the end of the nerve and dump out their contents
23
4) Norepinephrine travels across the synapse• Attaches to a receptor on the organ, organ responds
to the signal5) Norepineprhine detaches and is deactivated
• 2 options: destroy it or move it back into its sack
2
3
4
5
Elimination
• Most drugs excreted in urine– Some in feces or air
• Glomerular filtration– A function of glomerular filtration pressure (BP
and kidney blood flow)– Active transport system; requires ATP
• Tubular secretion– Urine pH affects reabsorption in renal tubules
Elimination, cont.
• Some drugs and metabolites are eliminated in expired air– Breathalyzer
• Feces, sweat, saliva, breast milk
Drug Routes
• Enteral– Oral (PO)– Orogastric/Nasogastric
(OG/NG)– Sublingual (SL)– Buccal – Rectal (PR)
Drug routes, cont. Parenteral
– Intravenous (IV)– Endotracheal
(ET)– Intraosseous
(IO)– Umbilical– Intramuscular
(IM)
– Subcutaneous (SC, SQ, SubQ)
– Inhalation/Nebulized– Topical– Transdermal – Nasal– Instillation – Intradermal
Drug forms
– Liquid: (solute - solvent) - Solution– Tinctures: drug extracted
chemically with alcohol.– Suspensions - liquid preparations
don’t remain mixed– Spirits: Volatile chemicals dissolved
in alcohol– Gaseous – Oxygen, Nitrous Oxide
– Emulsions: oily substance mixed with a solvent that won’t dissolve it. (oil and vinegar).
– Elixirs: Drug in an alcohol solvent. (Nyquil)– Syrups: Drug dissolved in sugar and water
(cough syrup).– Solids: capsule, tablet, lozenge, powder– Topical use: ointment, paste, cream, aerosol
Drug response relationship
• Plasma level profiles– Length of onset, duration, termination of action, minimum
effective concentration and toxic levels
• Onset of action– A medication reaches it’s minimum effective
concentration
• Minimum effective concentration– Level of drug needed to cause a given effect
• Duration of action– How long the drug remains above it’s minimum effective
concentration• Termination of action– Time from when a drug drops below minimum effective
concentration until it’s eliminated• Therapeutic index– Ratio of a drug’s lethal dose for 50% of population to its
effective dose for 50% of population• Half-life– Time the body takes to clear one half of the drug
• Cross tolerence– Tolerence for a drug that develops after administration of
a different drug
• Tachyphylaxis– Rapidly occuring tolerance to a drug
• Decongestants, bronchodilators
• Cumulative effect– Increased effectiveness when a drug is given in several
doses
• Drug dependence– Pt becomes accustomed to drug; will suffer withdrawal
symptoms• Drug interaction– Effects of one drug alters response to another drug
• Drug antagonism– Effects of one drug blocks response to another drug
• Summation – Additive effect; two drugs that both have same effect are
given together
Second messenger
• Calcium or cyclic adenosine monophosphate (cAMP)– Most common second messenger– Activates other enzymes; cascading
• Number of receptor sites on target cell constantly changes– Receptor proteins destroyed during function– Reactivated or remanufactured
• Down regulation– Binding of a drug or hormone that causes number of
receptors to decrease
• Synergism – Two drugs that have the same effect are given together
and produce a response greater than the sum of their individual responses
• Potentiation – One drug enhances the effect of another
• Interference– One drug affects the pharmacology of another drug