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Pharmacology > Pharmokinetics > Flashcards

Pharmokinetics Flashcards

1
Q

Pharmokinetics

A

The study of the rate and extent to which drugs are absorbed into the body and distributed to the body tissues

The rate and pathways by which drugs are eliminated from the body by metabolism and excretion

The relationship between time and plasma drug concentration

‘What the body does to the drug’

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2
Q

Four main stages of pharmokinetics

A

Absorption, distribution, metabolism, excretion

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3
Q

Enteral routes for drug absorption

A

Oral, buccal(mucosal orally), sublingual (under the tongue), rectal

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4
Q

Parenteral routes of drug absorption

A

Intravenous, intramuscular, subcutaneous, inhaled

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5
Q

Topical application

A

Method of drug absorption

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6
Q

For a drug to be successful after oral administration it must

A

Be swallowed -> survive gastric acid -> avoid unacceptable food binding -> be lipid soluble so can be absorbed across the gastro-intestinal mucosa -> survive hepatic (liver enzymes) first-pass metabolism and the enterohepatic circulation

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7
Q

Benefits of oral routes

A

Convenient, simple, can be easily self administered, Better for long term treatments for less acute illnesses

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8
Q

Intravenous route

A

No concerns about absorption, rapidly achieves high drug concentrations, no ‘first pass’ effect -> better for very ill patients where rapid, certain effect is critical to outcome

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9
Q

Intramuscular route

A

Simple to administer, unpredictable rate of absorption, painful, drug only gets into bloodstream if there is good circulation

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10
Q

Subcutaneous route

A

Good for drugs that have to be administered parenterally, are absorbed well from subcutaneous fat (lipid soluble), that ideally can be injected by patients themselves

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11
Q

Inhaled route

A

For a drug to be successful after inhalation in must be inhaled into the target airways in the lung -> i.e. if drugs are too small they will only go to the alveoli not the small airway

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12
Q

Speed and efficiency of distribution into the body by passive diffusion depends on

A

Molecular size, lipid solubility and protein binding

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13
Q

Volume o fdistribution

A

The apparent volume of distribution is the volume that the dose appears to have distributed into shortly after intravenous injection based on the plasma drug concentration

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14
Q

Drugs with high volume distribution

A

Take long time for body to get rid of the drugs after it is stop being administered

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15
Q

Liver is a major site of drug metabolism it

A

Reduces biological activity (so its not a threat) and increases water-solubility (so they can get out of the body)

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16
Q

Phase 1 metabolism

A

Enzymes which cause oxidation in microsomal mixed function oxidase system -> Make molecules more polar so that they can be excreted through the urinary system

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17
Q

Phase 2 metabolism

A

No always needed -> conjugation by either acetylation or glucoronidation

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18
Q

Factors effecting drug metabolism

A

Genetics, age, gender, nutrition, disease, dose, drugs, route

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19
Q

Increased metabolism

A

Faster elimination,shorter half life, reduced activity, potential for increased exposure to toxic metabolites

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20
Q

Decreased metabolism

A

Slower elimination, longer half life, increased activity, potential drug accumulation and toxic effects

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21
Q

Hepatic drug interactions

A

Presence of one drug may influence the metabolism of another

The first drug may induce metabolism of the second by stimulating the liver to produce more metabolising enzymes - takes days/weeks

The first may inhibit metabolism of the second by competing for the metabolising enzyme - immediate

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22
Q

First pass metabolism

A

Occurs in the gut wall and liver -> is a major determinant of the peak plasma drug concentration and thus of drug response after an oral dose

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23
Q

Drug molecules undergoing first pass metabolism

A

QAre vulnerable to metabolism by enzymes in the intestinal wall and liver prior to entry into the systemic circulation

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24
Q

Portal vein and liver sinusoids

A

Drugs absorbed through the stomach or any part of the small intestine must pass through these before entering the systemic circulation

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25
Q

Bio transformation of unchanged drug to inactive metabolite

A

Reduces drug response

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26
Q

Bio transformation of active drug to active metabolite

A

Results in no change in drug response

27
Q

Bio transformation of inactive drug(pro-drug) to active metabolite

A

Results in increased drug response

28
Q

Potential routes of drug excretion

A

Renal excretion, biliary excretion, faeces, breast milk, sweat

29
Q

Excretion

A

Process by which drugs and their metabolites are removed from the body and may involve fluid, solids or gases

30
Q

Urinary excretion

A

Usual route for low-molecular weight drugs that are sufficiently water-soluble to absorb reabsorption from the tubule

31
Q

lipid soluble molecules

A

Can cross the renal tubular membranes so are not lost renally so must be converted into water soluble

32
Q

Drugs bound to plasma proteins

A

Are not filtered renally

33
Q

Sodium bicarbonate

A

USed to make renal tubule more alkaline in the result of an overdose of lipid soluble molecules e.g. aspirin

34
Q

Faecal excretion

A

The preferred route of elimination for large-molecular-weight drugs, including those that are conjugated with glucoronide in the liver

Molecules enter bile after liver metabolism are then carried into intestinal lumen and are excreted in the faeces

35
Q

If molecules are still sufficiently lipid soluble in the faecal excretion route

A

They may be reabsorbed and re-enter the portal vein

36
Q

Entero-hepatic circulation

A

The recycling between the liver, bile, gut and portal vein

37
Q

Enterohepatic circulation

A

Prolongs the residence time of drugs in the body sustaining their effects

38
Q

Bacterial flora

A

Have enzymes capable of hydrolysing conjugates which release the drug or active metabolite for reabsorption - allowing the recycling of glucoronide conjugates

39
Q

Drugs that inactivate or kill micro-organisms e.g. broad spectrum antibiotics

A

Can reduce reabsorption and drug availability

40
Q

Clearance

A

Volume of plasma which is completely cleared of drug per unit time

41
Q

Clearance is caused predominantly by

A

either metabolism of the drug in the liver or excretion at the kidneys

42
Q

Bioavailability (oral)

A

Area under the curve of drug given orally/ area under curve of drug give intravenously - for the plasma concentration-time graph expressed as a percentage

43
Q

Ora bioavailability depends on

A

Gastric acid destruction, formulation, first-pass metabolism, solubility, ionisation, food, diarrhoea

44
Q

Drugs must be … in order to be absorbed into the body

A

Lipid-soluble

45
Q

Drugs must be more … in order to be eliminated in the urine or faeces

A

Water soluble

46
Q

The conversion of lipid soluble to water soluble through

A

Metabolism

47
Q

First order (exponential) kinetics

A

A constant fraction of drug is cleared in unit time

48
Q

Zero-order (saturation) kinetics

A

A constant amount of drug is cleared in unit time

49
Q

In first order kinetics rate of metabolism/elimination of a drug depends on

A

It’s concentration

i.e. as conc increases, rate increases -> as conc decreases rate decreases

50
Q

Increasing drug dose in first order kinetics has a

A

predictable effect

51
Q

In zero order kinetics

A

Elimination rate reaches a maximum0> so if a drug is administered at a rate faster than its clearance then it will progressively accumulate

52
Q

Examples of zero order kinetics

A

Ethanol, phenytoin

53
Q

Half life

A

The time taken for the plasma concentration of the drug to halve

54
Q

Increasing drug dose in zero order kinetics has a

A

very unpredictable effect

55
Q

Progressive accumulation

A

Repeated doses of a drug are given at a time when the previous doses have not been completely eliminates

56
Q

Accumulation continues until

A

Steady rate is reached where the rate of elimination = the rate of administration

57
Q

Steady state actually involves

A

Fluctuations in drug concentrations - with peaks just after administration and troughs just prior to the next administration

58
Q

Long half life

A

Slow to reach steady state, loading dose may be needed, slow to be eliminated, requires less regular dosing

E.g. atenolol 8hrs

59
Q

Short half life

A

Rapid steady state, not suitable orally, more regular dosing required

E.g dobutamine 2mins

60
Q

Loading doses

A

Used for drugs with long half lives which will not reach a steady state concentration for Na long time -> an initial dose is given which is much larger than the maintenance dose in order to achieve a peak plasma concentration close to the plateau concentration which can then be maintained

61
Q

Maintenance dose

A

Regular dose given to ensure a steady state of drug above therapeutic effects is maintained

62
Q

Dose interval

A

A compromise between convenience for/adherence of patient and benefit of reduced fluctuation in plasma concentration

63
Q

Therapeutic drug monitoring

A

Done too look for beneficial effects and avoid adverse effects

Can also be used to check for adherence

Pharmacology (6 decks)

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