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BMS317 - Pharmacology > LECTURE 5-8: PHARMACOKINETICS > Flashcards

LECTURE 5-8: PHARMACOKINETICS Flashcards

1
Q

life cycle of a drug

A

Administration -> absorption -> distribution -> action -> metabolism -> elimination

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2
Q

Drug given by oral route is given the abbreviation

A

PO (per oral)

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3
Q

two main routes of administration

A
  1. oral
  2. parenteral
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4
Q

parenteral administration abbreviations

A
  1. IV
  2. IM
  3. SC, SQ
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5
Q

Bolus dosing

A

single dose, all at once

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6
Q

IV constant rate infusions (CRI)

A

medication continuously administered to a patient and is used to maintain consistent plasma levels of that medication

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7
Q

Absorption

A
  • Getting the drug from the site of administration into the blood
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8
Q

does IV have absorption phase

A

No

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9
Q

bioavailability

A

The fraction of drug that gets into the blood

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10
Q

What’s in a tablet or an injection besides the drug?

A

excipient / bulk / carrier

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11
Q

excipient

A

inactive substance used to carry an active substance

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12
Q

examples of excipients

A

– Salts
– Inactive substances such as talcum, lactose
– Solubilising liquids e.g. alcohol, propylene glycol

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13
Q

why add excipient

A

– to make the drug work better
– sometimes to make the drug easier to work with

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14
Q

what is the rate limiting steps of absorption

A

solubilisation of the drug into the aqueous environment of the gut

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15
Q

how are majority of drugs absorbed

A

passive diffusion

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16
Q

factors affecting absorption

A
  1. lipophilicity/hydrophilicity
  2. surface area
  3. first-pass metabolism
  4. vascularity / disease process
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17
Q

what is bioavailability compared against, what gives 100% bioavailability

A

IV

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18
Q

Drug distribution

A
  • Moving the blood from the body to the extravascular space (i.e. the tissues)
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19
Q

pattern of drug distribution

A
  • Where drugs go around the body
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20
Q

volume of distribution

A
  • the propensity that a drug has for leaving the blood and entering the tissues is calculated by the pharmacokinetic term volume of distribution (Vd)
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21
Q

drug distribution depends upon

A
  1. regional blood flow
    - rapid distribution to organs with high CO
  2. ability to cross lipid membranes
    - lipophilicity/ hydrophilicity
    - pH partition effect
    - extent that drug binds to tissue and fluid constituents (protein binding)
22
Q

pH partition effect

A

o Unionised drug readily diffuses across lipid membranes.
o Acidic drugs are more unionised in acidic environments and alkaline drugs are more unionised in alkaline environments “like likes like”
o Plasma is slightly more basic than tissues.
o Therefore weak bases tend to distribute out of plasma and into tissues. In the relatively more acidic environment of the tissues the basic drugs become “trapped”.

23
Q

most drugs are ___ acids or bases

A

weak

24
Q

proteins in blood and tissues have ___ charges

A

weak

25
Q

NSAIDs examples

A

ibuprofen

26
Q

why do NSAIDs accumulate at site of inflammation despite their low Vd’s (and why they have a low Vd)

A
  • they are highly bound to plasma proteins (e.g. albumin) and so there is little unbound (= free) drug available for distribution, so NSAIDs have low Vd’s
  • but during inflammation (when the drug is most needed) it will follow the blood protein into the inflamed area
27
Q

Do NSAIDs have high or low Vd

A

low

28
Q

Vd =

A

drug amount in body / blood concentration

29
Q

Metabolism

A
  • The biotransformation of a lipophilic compound into a more hydrophilic compound in order to facilitate elimination
30
Q

Why needs to be hydrophilic for elimination?

A

Kidney can do it easier

31
Q

phase 1 metabolism

A
  • substance is converted to a more polar metabolite
  • oxidation, reduction and hydrolysis
  • often involves cytochrome p450 enzyme system
32
Q

Phase II metabolism

A
  • following or independent of phase I
  • involves conjugation with an endogenous hydrophilic compound
  • this phase makes it more hydrophilic
  • gluccurondination is most common
33
Q

where does phase II occur

A

liver!!
but sometimes kidney and intestine

34
Q

hepatic enzymes can be induced by

A

some older anticonvulsant drugs

35
Q

hepatic enzymes can be inhibited by

A

omeprazole

36
Q

sequelae to metabolism

A
  • excretion of the water-soluble metabolite
  • conversion of prodrugs -> active molecule
  • enterohepatic cycling
37
Q

enterohepatic cycling

A

Drug absorbed from gut straight into hepatic circulation, metabolised and eliminated in the gut, reabsorbed from the gut into hepatic…

38
Q

Elimination

A

removal of drug form body

39
Q

elimination can be accelerated by

A

diuresis

40
Q

elimination can be slowed by

A

kidney disease or heart disease

41
Q

Metabolism and elimination is quantified by

A

drug clearance

42
Q

Major modes of elimination

A
  • Hepatic excretion – passed in faeces via bile
  • Renal excretion – passed in urine
  • Combination of hepatic AND renal
  • Miscellaneous e.g. exhalation, sweat, milk etc
43
Q

Renal drug removal vie

A
  • Glomerular filtration
  • Tubular secretion
44
Q

renal drug reabsorption by

A
  • Tubular reabsorption
45
Q

what kind of drugs may be reabsorbed from kidney

A

highly lipophilic drugs

46
Q

what is the upper MW limit of filtration through glomerulus

A

20,000

47
Q

what affects renal elimination

A

pH of drug and environment effects drug lipophilicity / hydrophilicty which effect renal elimination

48
Q

If someone had an entire packet of weak acid drug - how could elimination be hastened

A

alkalinise their urine - will make drug more ionised meaning less reabsorbed and faster elimination

49
Q

Drug clearance

A
  • The volume of blood from which a drug is removed per unit time
  • Usually expressed in mL/min/kg (alternatively L/hr/kg)
50
Q

M and E together are quantified by

A

drug clearance

51
Q

ratio between the proportion of unioinsed to ionised is determined by

A

pH of drug relevant to pH of the environment

BMS317 - Pharmacology (22 decks)

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