Pharmacology: kinetics/dynamics + some drugs Flashcards
Enzyme kinetics
- 3 types and their axes and their shapes
- Michaelis-Menten: Velocity vs. [Substrate] - hyperbole
- Lineweaver-Burk: 1/V vs. 1/[S] - linear
- Enzyme inhibition: 1/V vs. 1/[S] - linear
Km and affinity
inversely related to affinity of enzyme for substrate
Vmax and enzyme concentration
Vmax directly proportional to enzyme concentration
sigmoid curve indicative of what?
cooperative kinetics, like Hb
Kinds of enzyme inhibitors (3)
reversible competitive
irreversible competitive
noncompetitive
which ones bind to active sites
the competitive ones
how does Vmax change with inhibitors
unchanged with reversible competitive
you need less enzyme for irreversible and noncompetitive inhibition b/c less substrates to act at
how does Km change with inhibitors
increased with reversible competitive b/c that’s how reversible compt acts, by being more affinitive for substrate
unchanged for irreversible and noncompetitive inhibition
how does pharmacodynamics change with inhibitors
reversible: decreased potency
irreversible: decreased efficacy
noncompetitive: decreased efficacy
Pharmacokinetics: what is it
what the body does with drugs
absorb, distribute, metabolize, excrete
Pharmacodynamics: what is it
how the body is affected by drugs
Bioavailability
- IV
- PO
fraction of unchanged drug in systemic circulation
- IV: 100%
- PO: < 100% 2/2 incomplete absorption and first-pass metabolism
Vd (volume of distribution)
amount of drug in body / plasma drug concentration
where is it low Vd
medium Vd
high Vd?
low: blood
medium: ECF
high: all tissues, including fat
half life
t = (0.693 x Vd) / CL
how many half-lives does it take at costant infusion to ready steady state
4-5
Clearance (CL)
- what is it
- equation
- what can affect it
- volume of plasma cleared of drug per unit time
- CL = Vd x Ke (elimination constant)
- CL = (rate of elimination) / (plasma drug concentration)
- renal, hepatic, or cardiac f(x)
Loading dose calculation
(Cp x Vd) / F
Cp = target plasma concentration at steady state F= dosing frequency
Maintenance dose calculation
(Cp x CL x tau) / F
tau = dosage interval
Time to reach steady state dependent on?
only half life
independent of dose and dosing frequency
zero-order elimination
constant amount of drug eliminated per time
examples of zero-order elimination meds
Phenytoin
Ethanol
ASA
PEA is round, like 0
first-order elimination
rate directly proportional to drug present
constant proportion of drug eliminated per time
exponential curve
what is each elimination process “limited/dependent on?
zero-order is capacity limited
first-order s flow-dependent
urine clears ionized or neutral forms
ionized
neutral ones reabsorbed
weak acids
- trapped where?
- examples
- treat overdose with?
- basic environments
- Phenobarbital, MTX, ASA
- bicarbonate to pull off the proton from the toxin and make it ionic so it stays in urine for excretion
weak bases
- trapped where
- examples
- treat overdose with?
- acidic environments
- amphetamines
- ammonium chloride to add proton to base and make it ionic so it stays in urine for excretion
phase I drug metabolism
- steps
- who loses it
- what does it yield
- Reduction
- Oxidation
- ## Hydrolysiswith Cyt P-450
- geriatrics lose phase I
- usu yields slightly polar, water-soluble metabolites (often still active)
phase II drug metabolism
- steps
- what does it yield
- Conjugation:
1. Glucoronidation
2. Acetylation
3. Sulfation - usu yields very polar, inactive metabolites that are renally excreted
- geriatrics still have this phase of drug metabolism
efficacy vs. potency
- efficacy: maximal EFFECT a drug can produce
- potency: AMOUNT needed for given effect
high efficacy drugs classes (4)
- analgesia meds
- abx
- anti-histamine
- decongestant
highly potent drug classes (3)
- chemo
- anti-htn
- lipid-lowering
reversible competitive antagonist for Diazepam
- which receptor
flumazenil on GABA rec