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Week 2&3 FCP > Drug Regimes > Flashcards

Drug Regimes Flashcards

1
Q

Name 4 factors which help to determine dosage regimen for drugs

A
  1. Activity/toxicity - therapeutic window, side effects
  2. Pharmacokinetics - dose, onset, loading dose, maintenance dose
  3. Clinical factors - state and compliance of patient
  4. Other factors e.g. route of administration, drug interactions
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2
Q

Define dosage

A

The giving of medicine in prescribed amounts over time

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3
Q

Name 4 considerations when deciding dosage of a drug

A
  1. Potency of the drug
  2. Absorption - route, proteins aiding movement
  3. Bioavailability and first-pass metabolism
  4. Distribution - staying in circulation or need to enter tissues
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4
Q

Define “first pass metabolism” and why is it an important factor

A

Definition - The degree of metabolic breakdown of an orally administered drug that occurs in the intestine or liver before it reaches the systemic circulation
Importance - as it can reduce total exposure of the body to the drug

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5
Q

What 3 factors can affect onset of action of a drug

A
  1. Route of administration - if oral then is affected by poly pharmacy, gut contents, splanchnic blood flow
  2. Chemical structure and formation - is pH effects release rate
  3. Clinical situations - change in pH, states of shock, tissue perfusion
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6
Q

Define “loading dose”

A

A large initial dose of a substance or series of such doses given to rapidly achieve a therapeutic concentration in the body.

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7
Q

How is the loading dose determined

A

By the volume of distribution of the drug

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8
Q

What does increasing the frequency of administration do to the plasma concentration of drug

A

Reduces the peaks and troughs of drug conc in plasma

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9
Q

What is the difference between normal kinetics and saturation kinetics

A

Normal = Plasma concentrations (at Css) increase proportionally with the dose
Saturation = If dose is increased, then disproportionate increase in steady-state concentrations

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10
Q

Which plasma proteins binds mainly to basic drugs

A

B-globulin

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11
Q

Which plasma protein binds mainly to acidic drugs

A

Plasma albumin

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12
Q

What does extensive protein binding do to rate of drug elimination

A

Slows it down

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13
Q

Which form of a drug is active in the body

A

Free/unbound drugs

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14
Q

Name the factors relating to the drug which affect drug absorption

A

Lipid soluble drugs - high absorption
Large molecules - low absorption
Small particle size - high absorption
High degree of ionisation - lower absorption

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15
Q

Name the factors relating to the body which affect drug absorption

A

High surface area of absorptive surface - increases
pH affects the level of ionisation
GI motility - slow motility increases absorption
Integrity of absorptive surface
Diseases

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16
Q

Name the factors relating to the body which affect drug distribution

A

Increases with high body fat content for lipid-soluble drug
Increases with high body water content for water-soluble drugs
Low for drugs highly bound to plasma proteins

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17
Q

Name the factors relating to the drug which affect drug distribution

A

High for lipid-soluble drugs
High for weak base drugs
Low for water-soluble drugs
Low for weak acid drugs

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18
Q

Name the factors relating to the drug which affect drug metabolism clearance

A

Lipid soluble drugs - high
Water soluble drugs - low
Drug-drug interactions - inhibition reduces clearance, induction increases clearance

19
Q

Name the factors relating to the body which affect drug metabolism clearance

A

Quantity of drug-metabolising enzymes
Enzyme polymorphisms
Decreasing blood flow to metabolising organs - decreases clearance
Low binding to plasma proteins - increases clearance
Diseases

20
Q

Name the factors relating to the body which affect drug excretion clearance

A

Quantity of drug transporters
Decreasing blood flow to excreting organ - decreases
Decreased GFR in the kidney - decreases clearance
Low binding to plasma proteins increases clearance
Diseases

21
Q

Name the factors relating to the drug which affect drug excretion clearance

A

High for water-soluble drugs
High for ionisable drugs
Low for lipid-soluble drugs
Inhibitory drug–drug interactions

22
Q

How is the absorption of a drug altered in the neonate and what is the outcome

A

Absorption is variable due to:
- altered gastric emptying
- irregular peristalsis
- increased permeability of the mucosa
- rapid topical absorption due to immature percutaneous barrier
Outcome => variable bioavailability

23
Q

How is the distribution of a drug altered in the neonate and what is the outcome

A

Increased distribution for non-lipid drugs due to:
- Greater water content in the neonate
- Decreased plasma protein binding
Decreased distribution for lipid drugs due to:
- Lower adipose content in the neonate, therefore less fat uptake
Outcome => affects plasma level, dose and doing frequency

24
Q

How is the metabolism of a drug altered in the neonate and what is the outcome

A

Neonates have reduced hepatic function
- Very species specific
- Foals can biotransform drugs within a few days
- Other species can take 3-6 weeks
Outcome => possible lower metabolic clearance

25
Q

How is the excretion of a drug altered in the neonate and what is the outcome

A

GFR is normal
Drug tubular secretion in the nephron takes longer on neonate
- Weak acidic or basic drugs can take 3-4 weeks
Outcome => possible lower excretion clearance

26
Q

Why is there a risk of undesired CNS penetration in the neonate

A

The blood-brain barrier is not full complete

27
Q

How is the absorption of a drug altered in the geriatric and what is the outcome

A

Absorption is reduced
Gastric pH is increased - alters drug ionisation
Fewer microvilli
Less mixing and dissolution
Delayed disintegration of tablets
Outcome => reduced bioavailability, lower Cmax and later Tax

28
Q

How is the distribution of a drug altered in the geriatric and what is the outcome

A

Body mass decreases
Less water content
Increased adipose tissue
Increased volume of distribution for lipid-soluble drugs => increased half-life
Decreased Vd for water-soluble drugs => decreased half-life
Outcome => affects plasma level, dose and dose frequency

29
Q

How is the metabolism of a drug altered in the geriatric and what is the outcome

A

Effects on metabolism are minimal
Decreased plasma albumin - less binding can lead to more free drug for metabolism
Outcome => little change

30
Q

How is the excretion of a drug altered in the geriatric and what is the outcome

A

Decreased renal elimination
Decreased renal mass, GFR and tubular secretion
Outcome => lower excretion clearance

31
Q

For the geriatric, how to alter dose regimen for renal excreted drugs

A

Reduce dose or dosing frequency
Use a drug that is metabolised by the liver instead

32
Q

For the geriatric, how to alter the dose regimen for lipid-soluble drugs

A

Reduce dose or dosing frequency

33
Q

For the geriatric, how to alter dose regimen for water-soluble drugs

A

Rarely need to change the dose

34
Q

How are the pharmacokinetics of a drug altered with chronic cardiovascular disease

A

Decreased mentation - increased effects of sedatives
Decreased blood flow - lower clearance for highly cleared drugs e.g. anaesthetics

35
Q

How are the pharmacokinetics of a drug altered with liver disease

A

Content and activity of phase I and II reactions are decreased
Little effect on metabolism until 80% loss
Most antimicrobials are well tolerated

36
Q

How are the pharmacokinetics of a drug altered with respiratory disease

A

Altered serum pH and protein binding
Mainly an issue for IV anaesthetics

37
Q

How are the pharmacokinetics of a drug altered with renal disease

A

Gradual loss of urine concentrating ability and ability to acidify
Altered drug distribution patterns
Change in acid-base balance
Uraemia: chronic acidosis, reduced albumin binding of a drug, less hepatic metabolism

38
Q

How to change the dosing regimen for a patient with renal disease

A

Avoid renally cleared drugs
Adjust dose down for changes in GFR

39
Q

How to change the dosing regimen for a patient with hepatic disease

A

Rarely an issue
Reduce dose if necessary
Use a drug that is renally cleared instead

40
Q

How to change the dosing regimen for a patient with chronic cardiovascular disease

A

Avoid drugs with high clearance
Reduce dose

41
Q

How to change the dosing regimen for a patient with respiratory disease

A

Adjust dose down for IV anaesthetics

42
Q

What types of drugs have a high therapeutic index

A

NSAIDS - aspirin, tylenol, ibuprofen
Sedatives - benzodiazepines
Most antibiotics
Beta blockers

43
Q

What types of drugs have a low therapeutic index

A

Neuroleptics - phenobarbital
Lithium
Some antibiotics - gentamicin
Digoxin
Immunosuppressives

44
Q

Why do we do therapeutic monitoring

A

Detect changes in pharmacokinetics
Optimize dose/therapeutic response
Monitor compliance
Avert toxicity

Week 2&3 FCP (20 decks)

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