Intro Flashcards
10% opthalmic solution. What concentration of drug will result in the anterior chamber if one drop(50ul) is administered and 50% gets absorbed in 200ul of aqueous humor without significantly affecting the volume of the anterior chamber.
1.25%
10 : 100
X : 0.05 (50ul=0.05ml)
X=0.005
50% of 0.005 is 0.0025
(200ul=0.2ml)
0.0025/0.2 = 0.0125g/ml x 100
= 1.25%
How many mg of ephedrine is there in 50ul of a 1:10 000 preparation
0.005mg
1ml=1g
50ul=50mg
1 : 10 000
X : 50
X= 0.005mg
Name the 5 DEA drug categories/shedules
1 No currently accepted medical use and very high abuse potential (heroin)
2 High potential for abuse with use potentially leading to psychological/physical dependence (oxycodone)
3 Moderate to low potential for psychological/physical dependence (testosterone)
4 Low potential for abuse and low potential for dependence (valium)
5 Lower potential for abusethan class 4 drugs (penicillin)
What is the definition of the expiry date according to the FDA?
The date to which full potency of a sealed preparation id guaranteed
True/False
Generic eye drops need to have exactly the same composition to the original
False
Excipients may vary
Topical preparations as well-same active ingredient, vehicle may vary(need not show bioavailability)
Generics- same active ingredient
Same purity/strength/stability
Same bioequivalence/bioavailability
Same labeling regarding indications/
warnings
Same manufacturing
What is an orphan disease?
Rare disease affecting less than 200 000 people
Orphan drug act states clinical trials can have less participants, patients are protected, tax incentives and research subsidies are available to companies
What is off-label prescribing?
Use of drugs/medical devices in a manner not formally approved by governing bodies such as FDA
Deviation from official clinical indication/mode of delivery/ dosing
Malpractice insurance may not cover off label prescribing, but failure to use drugs/devices off label may be considered malpractice
Describe the lock and key model
A drug that has affinity for only one type or receptor
Most drugs are not perfectly selective
Lack of sensitivity results in more side effects
Different types of drug permeation
Aqueous diffusion -within aqueous compartments( interstitial,cytosol), across epithelial membrane tight junctions,through pores in vascular endothelium (except BBB or BloodRetinaBarrier)
Lipid diffusion-critically important for drugs to move from 1 compartment to another
Special carriers-for drugs too big or hydrophilic to pass through membranes eg peptides, amino acids, glucose
Carriers move by active transport or facilitated diffusion, are saturable,selective,inhibitable
What is the Henderson-Hasselbach equation?
It defines the ratio of a weakly basic or acidic drug’s lipid-soluble form to its water-soluble form
Ionisation constant pKa defines pH at which ionized+unionized forms are equal in concentration
Uncharged drugs=lipid soluble
Charged drugs = water soluble
⬆️ acidic environment = more protons in field
(Protonated)
Log ————————— = pKa - pH
(Unprotonated)
Ficks law of diffusion
Describes passive movement of molecules down a concentration gradient
Flux(molecules per unit time) =
Area x permeability coefficient
(C1-C2) x ____________________________
Thickness
C1 -higher concentration
C2 -lower concentration
Area- cross-sectional area of the diffusion path
Perm coeff-measure of drug mobility in medium
Thickness-lenght of diffusion path
How can you double the rate of passage of a drug though a semipermeable membrane?
Ficks law
The rate of diffusion will double if:
surface area or concentration difference is doubled or
thickness of the exchange membrane is halved.
Greater level of flux would result if c1 > c2
Bases _______ protons, amino groups on weak bases become _______ charged at acidic ph
Acids _______ protons, dissociated acids become ________ charged at basic ph
Attract Positively
Donate negatively
Inflamation causes acidic environment
Charged drugs accumulate in aqueous environments
Uncharged drugs readily leave aqueous environments to cross lipid barriers
Describe what happens when a weak base in its uncharged state moves accross a renal nephron membrane into acidic urine environment aka ion trapping
It gets protonated and can thus not reenter the nephron despite the higher concentration that develops in the urine
(Only uncharged drugs can travel through lipid layer)
ion trapping is the build-up of a higher concentration of a chemical across a cell membrane due to the pKa value of the chemical and difference of pH across the cell membrane. This results in basic chemicals accumulating in acidic bodily fluids such as the cytosol, and acidic chemicals accumulating in basic fluids.
Name the 5 types of physiologic receptor motif super families
1 ligand-gated ion channels eg GABA, Acetylcholine w affinity for Nicotinic receptors(AChN), glutamate
2 G-protein coupled eg Acetylcholine w affinity for M receptor(AChM), rhodopsin. Most common receptor type targeted by opthalmic drugs
3 Enzymatic eg insulin, epidermal growth factor
4 Calcium release eg calcineurin, nitric oxide synthase
5 Intracellular or Nuclear eg steroids,hormones
