Pharmacokinetics And Drug Formulations Flashcards
What’s Pharmacodynamics (PD)?
Refers to effects of drugs on patients body (MOA)
Also used to explain effect of drug on organism eg bacterioSTATIC or bactericidal
What’s pharmacokinetics?PK
Study of time course of drug absorption, distribution, metabolism and excretion
Types of drug admin sites?
Intravascular admin
Extravascular admin
What’s Intravascular admin?
Where drug is placed directly into the blood either intravenously or intra-arterially
What’s extravascular admin?
Oral, sublingual, buccal, IM, SC, dermal, pulmonary, topical ocular, intraocular and rectal
Is there drug absorption when drug is admin intravascular admin?
No! (Drug is placed directly into systemic circulation)
What’s dissolution?
Oral dosage form dissolving in GI tract and drug is released from the dosage form
Why’s protective coating used in some drugs?
To limit drug degradation, which occurs primarily by hydrolysis
By preventing drug dissolution in acidic gut medium, but permits dissolution in basic medium of intestine
How is dissolution rate increased in drug with poor absorption?
To reduce particle diameter, which increases the surface area
What describes rate of dissolution?
Noyes-Whitney eqn
What determines rate and extent to which drug dissolves in GI fluid?
Solubility of drug
T/F? Only dissolved drug is absorbed into the body?
T
How does systemic absorption occur?
Passive diffusion - across gut wall
Active transport - via transport proteins
When does passive diffusion occur?
When there’s a high conc of drug in gut lumen and it moves to equalize drug conc (reach equilibrium) across the gut wall
Whats bioavailability?
Extent to which a drug is absorbed into systemic circulation
% of drug absorbed from extravascular admin RELATIVE TO intravascular admin
Howz bioavailability calculated?
Using Area under the plasma conc time curve (AUC)
How do u calculate absolute bioavailability (F)?
F (%) = 100 x (AUCextravascular/AUCiv) x (DOSEiv/DOSEextravascu)
What properties determine how drugs distribute evenly throughout the body?
Lipophilicity
Molecular weight
Solubility
Ionization status
Extent of protein binding
What’s the primary protein in the body?
Albumin
What’s the vol of distribution (V or Vd)?
How large an area in the pts body the drug has distributed into & is based on properties of that drug
Amt of drug in the body to conc of drug measured in plasma or serum
Formula of Vd?
Vd = amt of drug in body/ conc of drug in plasma
Conc of drug in body = amt of drug remaining in body x vol parameter
Vd formula in bolus IV injection?
Vd = dose/Co
Vd formula following oral dose?
Vd = (F x Dose)/(Kel x AUC)
F = bioavailability Kel = terminal elimination rate constant AUC = area under plasma conc-time curve
What’s clearance?
PK parameter that converts a conc of drug in the body to an amount eliminated per unit time
Rate of elimination = Cl x Conc
What’s half-life?
Time req for drug conc (and drug amt) to decrease by 50%
Half-life formula?
t1/2 = 0.693/Kel
Kel = Cl/Vd
What’s steady state?
When drug accumulates until it reaches steady state where the rate of drug up intake equals the rate of drug elimination
Apparent clearance formula?
CL/F = dose/AUC
What’s first-order kinetics?
Amt of drug given is proportional to the increase seen in plasma conc
What’s Michaelis-Menten kinetics?
Begins as first-order, but when metabolism becomes saturated, the conc increases rapidly.
Drugs with this type of kinetics begin as first-order kinetics, but can change to zero order once a certain dose is reached and metabolizing enzymes are saturated
What’s zero order elimination?
The elimination rate is independent of the drugs conc
Toxicity can occur here e.g. PHT, theophylline and Voriconazole
In saturable kinetics, whats the effect of a small dose on drug conc?
A small increase in dose may result in a large increase in drug conc
Should long-acting formulations be ground up, if pt has difficulty swallowing?
No!
Whats a way to mitigate nausea from meds?
It may be easier to tolerate if it comes as dissolving form
Many drugs that cause stomach come in long-acting formulations
Do patches bypass oral route?
Yes
Sublingual (SL) formulations bypass the oral route?
T
Works faster
Advantages of long-action formulations?
SE occur less readily as less drug is available to interact with wrong receptor
What name or -ending indicated controlled release (other than abbreviations XR, ER, LA, SR, CR, CRT, SA, TR, TD)?
-cont
E.g. For controlled release opioids - ms CONTin or oxyCONTin
Do u usually cut patches? Exceptions?
No!
Lidoderm is only patch that can be cut
Should patch be exposed to heat (from fever or electric blanket or heating pad)?
No!
This causes more drugs to be released and could result in toxicity
What can be done about patch irritating skin?
Is pt alternating application site
No shaving immediately b4 application
Topical steroid eg Hydrocortisone (OTC) can be applied to skin AFTERWARDS
Which patches need to be removed b4 MRI?
Testosterone (Androderm)
Clonidine (Catapress-TTS)
Fentanyl (Duragesic, generics)
Rotigotine (Neurpro)
Scopolamine (Transderm Scop)
Salon Pas Power (OTC)
Nicotine (NicoDerm CQ)
