Lecture 6 review Flashcards
The four processes of pharmacokinetics
ADME Absorption Distribution Metabolism Excretion
Minimum effective concentration (MEC)
Below this level, there will be no therapeutic effects
The wider the band is between the MEC and toxic concentration _______
The easier and safer the drug is to administer
What is the drug’s half life used for?
The half-life is used to determine the dosing interval so the duration of action of the drug is maintained
General rule for half-lives
It takes 4 half-lives for a drug to reach steady state in the plasma and similarly it takes 4 half-lives for a drug to be eliminated from the body
Drugs can only produce therapeutic effects….
That are already physiologic activities normally regulated by the endogenous receptors
How do drugs produce their effects?
By primarily binding with receptors in the body. When a drug binds to its target receptor, the physiologic activity controlled by that receptor can either be increased or decreased
What are the four families of receptors that drugs act on?
1) cell membrane-embedded enzymes
2) ligand-gated ion channels
3) G protein-coupled receptor systems
4) transcription factors
Cell membrane-embedded enzymes
When a drug binds to these receptors, the enzymes is activated and increased catalytic activity within seconds
Ligand-gated ion channels
When a drug binds to these receptors on the cell membrane, the flow of ions in and out of cells is regulated. This occurs rapidly, in milliseconds
Transcription factors
These receptors are located on the DNA of the cell nucleus. When activated by a drug, messenger RNA is transcribed and specific proteins are synthesized. There is a delay in this response
How can drugs affect receptors?
- agonists
- antagonists
- Partial agonists
Agonists
By activating or mimicking the receptor’s activity
Antagonists
By preventing the receptor from being activated by an endogenous regulatory molecules or drugs.
Requirement for an antagonist drug to have any effect
For an antagonist drug to have any effect at the receptor site, there must be some agonist molecules present or nothing will happen
Partial agonists
By partially activating the receptor for modest effect. They are used to produce modest effects and to minimize adverse effects that can result from full activation of the receptor
Maximal efficacy
The biggest effect a drug can produce. The goal of drug therapy is to match the drug’s maximal efficacy with the intensity of the patient’s needs.
Potency
The amount (dose) of a drug needed to produce an effect. A potent drug is one that produces the desired effect at a lower dose.
The average effective dose (ED50)
Defined as the dose required to produce a defined therapeutic response in 50% of the population. This means that this dose will be too low or too high for the other 50% of the population
The LD50, or average lethal dose
The dose that is lethal to 50% of the animals treated in a lab
The therapeutic index
A measure of a drug’s safety. TI = LD50/ ED50. The closer this number is to zero, the more unsafe the drug.
Drug-drug interactions
When two or more drugs interact, the result can be 1) intensified affects, 2) diminished effects or 3) a new effect which could be detrimental or beneficial
Drug-food interactions
Food may affect the rate or extent of absorption of drugs taken orally. Some foods can inhibit the metabolism of certain drugs and others may increase the toxicity of the drug
Direct chemical or physical interactions
Occur when two incompatible drugs are mixed together or combined in a solution such as in an IV solution. Often (but not always) produces a visible precipitate, clumping, or clouding of the solution
Pharmacokinetic interactions
When one drug causes alterations in absorption, distribution, metabolism or renal excretion, it can impact the effect of other drugs
Anti-histamines could result in……
anti-cholinergic side effects
Anti-cholinergic side effects
“Blind as a bat (mydriasis), mad as a hatter (delirium), red as a beet (flushing), hot as a hare (hyperthermia), dry as a bone (decreased secretions and dry skin), the bowel and bladder lose their tone (urinary retention and paralytic ileus), and the heart runs alone (tachycardia)”
Drugs to avoid/ use with caution in older adults
- Non-selective NSAIDs
- tri-cyclic anti-depressants
- first generation anti-histamines
- Benzodiazepines
- proton-pump inhibitors
- alpha blockers/ agonists
