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Prescribing > Pharmacokinetics > Flashcards

Pharmacokinetics Flashcards

1
Q

What is Pharmacology

A

Effect of chemicals on biological entities

Study of drugs: the way drugs react biologically at receptor sites

Study of drug effects: effect the drug has when taken by a person

Considers therapeutic and toxic effects

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2
Q

What are the two main branches of Pharmacology

A

Pharmacodynamics - The mechanism whereby drugs exert their effect on the body

Pharmacokinetics - The movement of the drug within the body

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3
Q

Mechanism of Action - specific to drug or drug class

A

Pharmacodynamics

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4
Q

Non specific mechanism - general processes

A

Pharmacokinetics

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5
Q

What is a Drug

A

A natural product, chemical substance or pharmaceutical preparation intended for administration to a human or animal to diagnose or treat a disease

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6
Q

What are the benefits of oral administration

A

Convenient, safe and cost effective

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7
Q

What are the Disadvantages of Oral administration

A

1st Pass metabolism - Deactivated in the liver

Irritant to the gut

Potential adherence issue

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8
Q

What are the benefits if intravenous administration

A

Bypasses absorption and as such immediate effect

100% bioavaliability

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9
Q

What are the Disadvantages of IV administration

A

Increased risk of toxicity

Staffing - patient not able to self administer

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10
Q

If a drug is going ot have an effect on the body its going to need to be

A

In the right place
At the right concentration
for the right amount of time

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11
Q

What are the 4 main components of Pharmacokinetics

A

Adsorption
Distribution
Metabolism
Excretion

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12
Q

What effects oral absorption of a drug

A 
Particle size and formulation
GIT Enzymes/Acid
GIT motility
Physicochemical factors
Food
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13
Q

What affect will GI Motility have on the absorption of drugs

A

Rate of gastric emptying determines the rate at which a drug is delivered to the small intestine

Increased motility increases the rate of absorption as the stomach empties more quickly

Decreased motility will decrease the rate of absorption as it takes longer for the drug to reach the small intestine

In hyper motility states absorption may decrease as the drug is not in the small intestine long enough to be absorbed

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14
Q

What form of a drug is needed to be absorbed by the GI tract

A

Lipophillic and hydrophobic - to pass through the endothelium

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15
Q

What physiochemical factors can effect absoprtion

A

Physicochemical reactions can occur between food and medicines or medicines and other medicines resulting in reduced absorption

Calcium and Iron can act as chelating agents - inactivating the drug prior to absorption

Example: calcium can form insoluble complexes with some drugs –> affects absorption
Iron salts and many antacids have a similar effect

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16
Q

What affect can food have on the absorption of drugs

A

May delay gastric emptying
May increase the absoprtion of some drugs

May reduce adverse events eg NSAIDS

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17
Q

What is an acid

A

A substance with the ability to donate a proton - hydrogen ion and become dissociated

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18
Q

What is a base

A

A base is a proton acceptor

An alkali is a soluble base

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19
Q

What is Distribution

A

The process by which the drug is transferred reversibly from the general circulation into the tissues as concentrations in blood increase and from the tissues into blood as blood concentrations decrease

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20
Q

What is Drug protein binding

A

Some drugs are distrubted around the body bound to plasma proteins

Two main types are Albumin and Glycoproteins

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21
Q

What is the issues with giving two drugs that are highly protein bound

A

Results in displacement of drug already bound to protein

Produces increased unbound concentration of drug and biological activity

22
Q

What are some of the Albumin bound drugs

A 
Furosemide
Ibuprofen
Phenytoin
Thiazides
Warfarin
23
Q

What are some of the Glycoprptein bound drugs

A

Chlorpromazine
Propranolol
TCAs
Lidocaine

24
Q

What factors can affect drug distribution

A
  1. Plasma protein binding
    Competition for protein binding sites
  2. Specific drug receptor sites in tissues
    e. g. domperidone does not cause extrapyramidal side effects because it doesn’t reach dopamine receptors in the brain
  3. Regional blood flow
    Reduced blood flow
    Enhanced blood flow
  4. Lipid solubility
    Blood/brain barrier
  5. Disease
    Liver disease can cause low plasma protein levels
25
Q

What are the 4 types of ways that drugs can cross the phospholipid bylayer

A

Passive diffusion
Transporters
Membranous Pores
Vesicle mediated transport - Pinocytosis

26
Q

Define Simple Diffusion

A

The movement of a substance from an area of high concentration to an area of low concentration

Ion channels may enable this down a concentration gradient

27
Q

Define Facilitated Diffusion

A

Molecules combine with the membrane bound carrier protein - still moving down the concentration gradiaent - Faster process

28
Q

Define Active transport

A

Using energy in the form of ATP moves molecules against the concentration gradient

29
Q

What is Pinocytosis

A

Molecules engulfed by cell membrane and vesicle formed

Vesicle moved into the cell

Molecule may then be released within the cell

30
Q

What is the Blood-brain barrier

A

Functional basis of barrier is reduced capillary permeability owing to:
tight junctions between endothelial cells

decrease in size and number of pores in the endothelial cell membranes
presence of surrounding layer of astrocytes

31
Q

What are the 4 aspects of drug metabolism

A

Activation of inactive drug
Production of active drug with increased activity from active drug
Inactivation of active drugs
Change in the nature of the activity

32
Q

What is First Pass metabolism and when does it occur

A

Metabolism occurs prior to and during absorption

Intestinal Lumen
Digestive enzyme secreted by the mucosal cells and pancreas
Certain enzymes break down proteins and stop them from being absorbed
Intestinal Wall
Rich in enzymes that further metabolise drugs
Liver
Major site of drug metabolism
Lung
Cells of the lung have high affinity for many drugs and are the site of metabolism for many local hormones

33
Q

Phases of Metabolism

A

Phase I Reactions
Oxidation, reduction and hydrolysis
Usually form more reactive products, sometimes toxic
Often involve mixed function oxidase system in which Cytochrome P450 plays a key role

Phase II Reactions
Conjugation
Usually form inactive and readily excretable products

34
Q

What are the phases of Metabolism in order for a hydrophobic drug to be excreted in the urine

A

Lipophillic Drug - Phase 1 reaction causes the formation of a more active drug
Phase 2 reaction causes conjugation and it to be transformed into a hydrophillic form - able to be excreted in the urine

35
Q

What is the significance of the Cytochrome P450 system

A

Isoenzymes that can inhibit or induce an affect either inhibiting the action or potentiating the affect

36
Q

What is the affect of an enzyme inducing drug

A

Enhance the production of liver enzymes which break down drugs

Faster rate of drug breakdown

Larger dose of affected drug needed to get the same clinical effect

37
Q

What is the affect of an enzyme inhibiting drug

A

Inhibit the enzymes which break down drugs

Decreased rate of drug breakdown

Smaller dose of affected drug needed to produce the same clinical effect

38
Q

What can affect drug metabolism

A

First pass effect

Hepatic blood flow

Liver disease

Genetic factors e.g. acetylation status

Other drugs- hepatic enzyme inducers, hepatic enzyme inhibitors

Age
Impaired hepatic enzyme activity
Elderly
Children < 6 months (especially premature babies)

39
Q

Define Bioavaliability

A

Bioavailability is the proportion of a dose which actually gets into the systemic circulation

40
Q

What can affect bioavaliability

A
  1. Pharmaceutical Preparation
    Particle size, composition of formulation
  2. Physicochemical Interactions
    Other drugs or food may interact with or inactivate the drug
  3. Patient Factors
    Malabsorption syndromes, gastrointestinal motility
  4. Pharmacokinetic interactions and first-pass metabolism
41
Q

What is the definition of Drug Clearance

A

This is the measure of the removal of drug from the body or the volume of plasma completely emptied of drug per unit time

42
Q

How can the body excrete or eliminate a drug

A

1 cFluids:
Urine, bile, sweat, tears, milk
Important for low-molecular weight polar compounds

  1. Solids:
    Hair, faeces
    Faecal elimination important for high-molecular weight compounds that are excreted in bile
    Distribution of drug along hair shaft can be used to indicate the history of drug intake during the preceding weeks
  2. Gases:
    Important only for volatile compounds
43
Q

What affect can altered renal function have on eliniation

A

Reduced excretion
Increased renal impairment
active metabolytes may be nephrotoxic

44
Q

Who is at risk of renal impairment

A

Elderly - renal blood flow decreases after the age of 30
Neonates

CKD
AKI

45
Q

How can renal blood flow be estimated

A

Creatinine Clearance

It is neither passively reabsorbed or actively secreted

Estimation of Creatinine clearance estimates the clearance of drugs filtered at the glomerulus

46
Q

What is the equation used to calculate the CrCL

A

Cockcroft-Gault equation

(140-age) x weight x constant
Serum Creatinine

Constant - male 1.23 and female 1.04

47
Q

True or False

Un-ionised molecules cross phospholipid membranes more readily than their ionised forms

A

True

48
Q

True or False

The half-life of a drug is longer in babies than in adults

A

True

49
Q

True or False

A decrease in renal function decreases oral bioavailability

A

False

50
Q

True or False

The activity of cytochrome enzymes is consistent among individuals

A

False

51
Q

True or False

First-pass metabolism may limit the bioavailability of oral drugs

A

True

Prescribing (18 decks)

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