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FunMed Pharmacology > Drug administration, metabolism and Elimination > Flashcards

Drug administration, metabolism and Elimination Flashcards

1
Q

what are the routes of administration

A
  • oral
  • IV
  • IM (Inter-muscular) - slow release to the system
  • subcutaneously into fat depot - slow released (really slow due to poor blood supply running through it)
  • rectum - goes to the liver, used if person cannot swallow, same bioavailability as oral
  • inhalation - directly to the lungs then blood stream such as asthma
  • transfermal - applied to skin, crosses skin to enter systemic blood supply
  • topical - applied to skin action intended to be local at site of administration
  • sublingual - under the tongue, enters systemic blood directly bypassing the liver, bypasses 1st pass metabolism
  • interanasal - can be local or affect or into the blood stream
  • intrathecal - into CSF, bypasses the blood brain barrier to allow drug to work on the brain and directly into the ventricle system
  • epidural outside of spinal dura
  • intraarticular – into joint space such as the synovial fluid and cavity fluid
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2
Q

what is the bioavailability in oral

A

– 10-50% bioavailability
– cheapest and most common
– depending on physical properties goes into different parts of the body and only a small portion goes onto the target tissue that you need to ingest

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3
Q

what is the bioavailability in IV

A

100% bioavailability – more drug does work and goes to target tissue

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4
Q

how much time does intravenous take

A

30 -60 seconds

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5
Q

how much time does inhalation take

A

2-3 minutes

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6
Q

how much time does sublingual take

A

3-5 minutes

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7
Q

How much time does rectal take

A

– 5 – 30 minutes

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8
Q

How much time does intramuscular/subcutaneous take

A

10-20 minutes

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9
Q

How much time does oral take

A

30 to 90 minutes

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10
Q

Describe 1st pass metabolism

A
  • All drugs absorb by the GI tract enter the liver via the portal blood supply
  • Liver enzymes metabolises many drugs before they enter the systemic blood supply
  • GI = portal vein = liver = IVC (inferior vena cava) = systemic
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11
Q

what does 1st pass metabolism effect

A
  • This affects bioavailability
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12
Q

describe the effect of 1st pass metabolism on oral medication

A
  • 90% of oral medication is metabolised and destroyed by the liver before it gets to the heart, therefore only 10% of the drug comes out of the liver in one piece to have an effect on the body
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13
Q

describe what happens when the drug enters the body

A
  • Sits in the stomach for 30 to 45 minutes and is absorbed across the small intestine, goes into the Venus return blood stream and goes via the hepatic portal vein into the liver into a non-active destroyed drug, which goes out and is eliminated and excreted.
  • Goes into the portal circulation – all blood form intestines is taken to liver for medication
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14
Q

what is a prodrug

A
  • Prodrugs are inactivated and become activated when metabolised by liver enzymes
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15
Q

what makes a prodrug become activated

A
  • A biological inactive parent drug that requires a chemical or enzymatic translation to release the active drug, this can happen in the liver
  • When a pro-drug makes there 1st pass through the liver they are converted into the active as the liver enzymes cleave of the side chains this means that more active drugs enter the blood supply
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16
Q

Describe an example of a prodrug

A
  • Some drugs are not able to pass through physiological barriers, pro-drug can e.g. L-dopa
  • L-dopa protected from bodies enzymes that degrade dopamine, it can get across the blood brain as a protected dopamine molecule so you can give a dose
  • 2009 15% of the 100 best selling drugs were prodrugs
  • they can either be inactive as administered and metabolised to active or they are active as administered and they are metabolised to other active metabolites that still work
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17
Q

list the example of pro drugs

A
  • Levodopa - inactive as administered and metabolised to active
  • L dopa – inactive as administered and metabolised to active
  • Minoxidil – inactive as administered and metabolised to active
  • Benzodiazepines – active as they are administered and they are metabolisted to other active metabolites that still work
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18
Q

Describe pro-drug and cancer

A
  • A toxic drug can be given as a prodrug that is metabolised to the active toxic drugs and activates the suicide cascade in the cell with the correct gene
  • If the drug was given in its active for systemically it would have adverse effects
  • Gene therapy can be used – gene can be used to deliver something that will code for the drug and target the tumour cell making the tumour cell make the destructive enzymes and prodrug which will kill the toxic cells and its neighbours as it is passed on
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19
Q

what are the types of prodrugs targeting cancers

A
  • ADEPT = antibody directed enzyme prodrug therapy
  • GDEPT = gene directed enzyme prodrug therapy
  • VDEPT = viral directed enzyme prodrug therapy
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20
Q

what are the two phases of excreting a lipid soluble non polar drug

A

phase I reactions

phase 2 reactions

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21
Q

what are the phase 1 reactions

A

BOHR

  • Biotransformation
  • Oxidation
  • Hydrolysis
  • Reduction
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22
Q

what is biotransformation (phase 1 reaction)

A
  • A polar group is either attached or unmasked to the remaining drugs
  • This makes it water soluble so the kidney can remove it
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23
Q

what is oxidation (phase 1 reaction)

A
  • Family of enzymes – cytochrome (CYP)

- Cytochrome P450 – oxdise drugs and make them more polar so they can be eliminated by the kidney

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24
Q

What are the phase 2 reactions

A

SC

  • Synthesis
  • conjugation
25
Q

describe synthesis

A

adds something to the drug that makes it more water soluble

26
Q

describe conjugation

A
  • Liver takes a big chemical and adds it to the drug to make it water soluble for example (glucose) this allows excretion to happen
  • conjugation can also occur with sulphate, acetyl, methyl, glucuronic acid
27
Q

why don’t all drugs undergo phase I and phase II reactions

A

Not all drugs require both phase 1 and phase 2 reactions, some can only have just phase 1 for example if they are small and polar then they can just be excreted in the kidney, but if they are not small and polar then they go to phase 2

28
Q

what are the aims of phase 1

A
  • Degradative reaction
  • Introduces a functional group
  • Metabolites formed may be smaller polar, non-polar or inactive
29
Q

what are the 2 ways of elimination

A
  • renal
  • hepatic
    these clear the majority of drugs
30
Q

describe the ways drugs are removed

A
  • Urine
  • Defecate (faeces)- hepatic elimination via bile back into GI tract
  • Most drugs require both
31
Q

what is clearance

A

the rate of elimination in relation to the drug concentration

32
Q

how do you work out clearance

A

rate of elimination (mg/hr)/ concentration remaining (mg/ml)

33
Q

what does high clearance mean

A
  • means more drugs is lost

- 120mg/hr lost in urine= 6ml/hr, 200mg/ml

34
Q

what does low clearance mean

A
  • more drug in body - 40mg/hr (lost in urone) = 2mL/hr, 20mg/ml
35
Q

what is the half life of a drug

A
  • Time take for plasma concentration to reduce to half its original concentration
36
Q

drugs with a low half life ..

A

are quickly eliminated from the body

37
Q

drugs with a high half life …

A

are slowly eliminated from the body

38
Q

what is the correct factor

A

0.7

39
Q

how do you work out VD volume of distribution

A

amount of drug in the body/plasma concentration

40
Q

what is half life equation

A

half life = vd(volume of distribution)/ clearance x 0.7

41
Q

what does a zero order do

A

it eliminates the drug by a fixed amount per unit time

42
Q

describe examples of a 0 order reaction

A
  • examples include alcohol, phenytoin and aspiring
  • Rate occurs when elimination system saturated (phenytoin and aspirin)
  • Ethanol at all concentrations
43
Q

what is first order elimination proportional to

A
  • Elimination is proportional to drug concentration
44
Q

describe elimination

A
  • E.g. 100g – 50g,- 25g, - 12.5g always loosing 50 % not 50g like in zero order
  • Elimination is proportional to drug concentration
  • 95% of drugs use this (most drugs are like this)
45
Q

describe the therapeutic window

A
  • This is the widow has therapeutic effects
  • Safe range – between minimum therapeutic concentration and the minimum toxic concentration/ adverse response and bottom is desired response
  • Above this drug has unwanted pharmacologic effects – side effects, this is in the toxic range
  • Duration is dependent on administration, distribution, delivery and elimination
46
Q

what do you need to know for the therapeutic window

A
  • need to know how long the half life is
47
Q

describe how drug accumulation occurs

A
  • When drug doses are repeated the drug will accumulate until dosing stops
  • If dosing interval is shorter than 4 half lives accumulation will occur (for most drugs 5 half lives will remove a drug from the system)
  • Can give another dose to keep it in therapeutic range, but a smaller dose not the same dose otherwise could end up in toxic range
  • Need to know where you are going to start the toxic range
48
Q

what is the loading dose

A
  • The initial large dose is given to get the drug concentration in the plasma within the therapeutic window
49
Q

why is the loading dose used

A
  • Gets to therapeutic range quicker – emergencies
  • Mainly for drugs with a large volume of distribution
  • Can be given via IV rather than orally
  • If dosing interval, is shorter than 4 half-lives accumulation occurs (for most drugs 5 half-lives will remove a drug from the system)
50
Q

what is the maintenance dose

A
  • Drug dose which is small and given to maintain drug concentration within the therapeutic window
  • small dose
  • maintains drug in therapeutic range
51
Q

describe an example of a loading and maintenance dose

A

An example of a drug that is used with a loading dose and maintenance doses is the anti-platelet drug clopidogrel. Intravenous clopidogrel is given as a loading dose in percutaneous coronary intervention to prevent clotting straightaway before the surgery, and this is followed by oral maintenance doses to prevent coagulation, as the subject recovers from the surgery.

52
Q

what are the factors that affect drug metabolism

A
  • pharmacogenmocis
  • ethnicity
  • age
  • gender
  • diet and environment
  • drug to drug interactions
  • diseases
53
Q

describe pharmacogenmocis as a factor that effects drug metabolism

A
  • Genetic variation in population

- E.g. succinylcholine caucasains have enzymes 1,000 fold reduces affinity so drug has slower elimination

54
Q

describe ethnicity as a factor that effects drug metabolism

A
  • Cytochrome P450 2D6 is functionally inactive in 7-8% of Caucasians but only 1% of Asians therefore make less morphine and hyperactive in 30% of east Africans , therefore make higher amount of morphine
  • Cytochrome P450 2D6 catalyses metabolism of codeine into active morphine, and many beta blockers and many tricyclic antidepressants
  • Have no got enzyme to break codeine down and metabolise it
55
Q

describe age as a factor that affects drug metabolism

A
  • Many reactions of biotransformation’s are slowed in children and elderly
56
Q

Describe gender as a factor that affects drug metabolism

A
  • Decreased oxidation of ethanol, estrogens, benzodiazepines and salicylates reported in women relative to men
57
Q

describe diet and environment as a factor that affects drug metabolism

A
  • Can alter drug metabolism by inducing or inhibiting enzymes
  • Grapefruit juice can cause enzyme to become less active or overactive
  • Grapefruit juice can affect transporters in the body
58
Q

describe drug to drug interactions that affect drug metabolism

A
  • Binding to plasma proteins

- Metabolism

59
Q

describe diseases that affect drug metabolism

A
  • Liver and kidney diseases can alter drug metabolism and elimination

FunMed Pharmacology (5 decks)

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