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510 - Pharmacology > Lecture 2 > Flashcards

Lecture 2 Flashcards

1
Q

What is a pharmacokinetics?

A

The study of the disposition of a drug and/or its metabolites in the body based on time

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2
Q

What is pharmacodynamics?

A

The relationship between drug concentration at the site of action and the pharmacologic responses – what the drug does to the body

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3
Q

What is the main purpose of pharmacokinetics?

A

Predictive nature – to predict plasma concentration at any future time thereby achieving optimal dosing – how diseases impact serum levels, dosing level and intervals necessary to maintain response, whether or not drug is appropriate

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4
Q

What is the therapeutic index or TI? and what is it used for?

A

The TD50/ED50 – medication comparison – higher TI is safer

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5
Q

What is the minimum effective concentration, maximum effective concentration and the therapeutic window

A

The minimum = concentration below which a drug lacks effectiveness
The maximum = anything higher will result in toxicity
Therapeutic window is in between

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6
Q

What are the 4 aspects of pharmacokinetics?

A

ADME – absorption, distribution, metabolism and elimination – dealing with dose of drug

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7
Q

How is pharmacokinetics determined?

A

Venous and urine sampling at various time points to determine drug concentration

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8
Q

What is bioavailability?

A

How much of the drug ends up in the blood stream = F – does not consider rate of absorption only the extent

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9
Q

What are the various routes of administration of drugs?

A

oral, intravenous, intramuscular, subcutaneous, transdermal, rectal, inhalation

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10
Q

What is first order elimination?

A

When the amount of drug eliminated from the body in a specific time is dependent on the amount of drug in the body at a time - fraction eliminated over time remains constant – travels from gut wall to portal blood delivery to liver to systemic circulation

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11
Q

What is the volume of distribution (Vd)?

A

Amount of drug in the body/initial drug concentration – an apparent volume that is a mathematical concept
Vd = Ab/Co (initial plasma concentration at time 0)
= F * dose/Co (where F = bioavailability - can be ignored if IV)

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12
Q

What is the major site of drug absorption?

A

Small intestine

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13
Q

What does absorption rate depend on?

A

Dosage form, drug dissolution gastric emptying time, site of absorption, ratio of ionized to non-ionized drug, metabolism of drug prior to entering circulation and bioavailability

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14
Q

What is the bioavailabllity of an IV drug?

A

100% – no absorption

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15
Q

What is chelating?

A

When drug bind to other molecules that prevents their absorption

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16
Q

What is the absorption rate constant?

A

Ka – the fraction of the administered dose that leaves the site of administration per unit time – larger means drug is absorbed faster

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17
Q

What is the equation for the amount of drug absorbed?

A

F* dose

F = 1 for IV

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18
Q

What factors can affect oral absorption?

A

formation of drug complexes or chelation (activation charcoal, antacids, cholestyramine), alteration in gastric pH (H receptor antagonists or proton-pump inhibitor), changes in GI motility

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19
Q

What is kinetic modeling?

A

Looking a changes in drug concentration from initial timepoint to whatever timepoint is chosen

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20
Q

What is the one compartment model?

A

Depicts body as a single homogenous compartment that assumes instantaneous distribution of the drug from the vascular space (dose –> drug in body –> elimination) –0 not reality

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21
Q

What is the two compartment model?

A

Body is broken into central compartment (containing vital organs) and a peripheral compartment (dose –> central compartment equilibrium with peripheral compartment –> elimination)

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22
Q

What can affect distribution of drugs?

A

Affinity of an agent for a variety of transport pumps, lipid solubility, resdistribution of medication even after administration stops, influence of protein binding (more drug protein bound - less available to go to target site)

23
Q

What proteins do acidic drugs and basic drugs bind?

A

Acidic drugs bind albumin, basic drugs bind to apha1-acid glycoprotein

24
Q

What are the physiological alterations in obese patients?

A

Half-life is increased for lipophilic drugs that go to sites of adipose tissue, the Vd is increased for lipophilic drugs and decreased for hydrophilic drugs, clearance increased, less CO going to adipose tissue

25
Q

What happens to Vd when drugs are bound to protein?

A

It is decreased as it will stay in the plasma – protein bound drugs in the plasma are less likely to cross tissue and BBB, amount of drug not bound exerts the pharmacologic effect and undergoes metabolism

26
Q

Where do protein-bound drugs stay? and where do free drugs go?

A

In the intravascular space whereas free drugs cross capillary wall to target tissues or cells

27
Q

What types of drugs can cross placenta and BBB?

A

Unbound and unionized or uncharged drugs

28
Q

How are drugs preferentially absorbed in relation to ionization?

A

Unionized form are preferentially absorbed – fraction of drug avaailable depends on pKa of drug and pH of environment and lipid solubility [Vd] – absorbed by passive diffusion – most drugs are salts of weak acids or bases

29
Q

What is pKa?

A

The pH at which 50% ionized and 50% nonionized form of drugs exist

30
Q

What is ion trapping? what is an example of elimination?

A

When drug is trapped on side of membrane with higher ionization fraction – giving vitamin C tablets to acidifiy patients on methamphetamines

31
Q

Which drugs are weak acids and which are weak bases?

A

Weak acids are barbiturates and weak bases are opioids and local anesthetics

32
Q

What can area under the curve be used for?

A

Determining whether two formulations of the same dose release the same amount in the body
AUC = F*dose/clearance
elimination = clearance * AUC

33
Q

What is involved in drug metabolism?

A

Hepatic system and intestine using CYP450 enzymes, renal tubules and plasma esterases in bloodstream

34
Q

How are CYP enzymes named?

A

Superfamily = CYP450

Family, subfamily, isoenzyme, and allele variant follows

35
Q

Can the body elimination lipophilic or hydrophlic drugs more easily?

A

Hydrophilic

36
Q

What is zero order elimination rate?

A

The amount of drug (A) eliminated at a constant rate

A = A0 - (rate of elimination) * time

37
Q

What is first order elimination rate?

A

The amount of drug (A) eliminated at a rate proportional to the amount of drug remaining where k is a constant that relations rate of elimination/amount of drug in body
C = C0 * e^(-kt)

38
Q

What does clearance describe?

A

Volume of blood from which a given amount of drug is removed per unit of time
rate of elimination = CL * concentration

39
Q

What are the three components of elimination?

A

Metabolism, excretion and clearance

40
Q

What is metabolism?

A

Biotransformation of the parent drug within the body to one or more products of compounds by various enzymatic reactions

41
Q

What are phase I and phase II reactions of metabolism?

A

Interconversion of lipophilic to hydrophilic drug with phase I focusing on redox (oxidation by cyp450) reactions and hydrolysis and phase II reactions focusing on methylation, acetylation, sulfation ,etc.

42
Q

Why do we need phase I and phase II reactions in metabolism?

A

Certain intermediates of reactions can become harmful and toxic with a buildup

43
Q

What happens in enzyme inductino and inhibition of cyp450 metabolism?

A

In induction certain drugs can increase activity of CYP450 enzymes whereas in enzyme inhibition certain drugs can decrease or stop activity of CYP450 enzymes – there may also be genetic influences

44
Q

What is the main source of CYP isoenzymes?

A

Liver but also kidney and GI tract

45
Q

What is the onset of enzyme induction and inhibition?

A

Induction is slow in onset which is typically days to a week as more enzyme has to be made, inhibition is fast in onset usually within hours to a day

46
Q

What is the major class of CYP enzymes?

A

3A4/5

47
Q

What is excretion?

A

Elimination of the parent drug or metabolite from the body - process in elimination

48
Q

What is clearance?

A

Removal of drug from a given volume within a specified time frame - process in elimination

49
Q

What factors can affect clearance?

A

Efficiency of organs and blood flow by impaired renal/hepatic function, protein binding/ionization, blood flow to kidney/liver, smoking and concurrent medication

50
Q

What is the elimination rate constant (ke)?

A

ke represents the fraction of drug removed per unit of time - a constant that is a function of Vd and CL
ke = CL/Vd

51
Q

What is a first order reaction?

A

A reaction with a rate that is proportional to the amount of reactions, with rate of absorption proptional to dose and elimination rate proportional to serum concentration but total clearance is unchanged - linear relationship

52
Q

What is a zero order reaction?

A

Esentially = constant amount of drug is elimination per unit of time - A reaction with a rate independent to the amount of reactants, rate of absorption independent of dose, and rate of elimination independent of serum concentration, clearance decreases as plasma concentration increases

53
Q

What is elimination half-life?

A

The time it takes 50% of drug to be elimination from the body for first order system, which is dependent on Vd and Cl
T1/2 = 0.693 * Vd/CL
T1/2 = 0.693/Ke where Ke = CL/Vd
Can be calculated mathmatically or graphically

510 - Pharmacology (7 decks)

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