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Pharmacology > Basic principles > Flashcards

Basic principles Flashcards

1
Q

What are the four aspects of pharmacokinetics?

A
  • absorption
  • distribution
  • metabolism
  • excretion
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2
Q

What is pharmacodynamics?

A

the concentration of a drug at its site of action and the resulting pharmacological effects and blood stream/tissue concentrations

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3
Q

Describe the concept of ‘volume of distribution’

A
  • extent of distribution of the drug across the body (space that can contain the drug)
  • usually correlates with roughly with the area it is ‘distributed’ too
    (e.g. aminoglycosides disperse largely to the ECF, 20% is the approx Vd)
  • not usually a ‘range’ as cannot be sepcified in the body per se
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4
Q

What are the two main factors that effect Vd

A
  • distribution across the body (e.g. muscle, fat etc)
  • the extent of tissue binding
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5
Q

What is drug clearance?

A

The measure of the body to eliminate the drug
Equation = rate of elimination / concentration

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6
Q

What does the term bioavailability refer to?

A
  • active pharmaceutical component that enters the systemic circulation (i.e. the bloodstream)
    *oral medications - this would be absorption and first pass metabolism
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7
Q

What is the purpose of a loading dose?

A

This enables reaching an intended concentration instantaneously. The loading dose is obtained from the V(d)
*a maintenance dose is required to keep meeting this concentration

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8
Q

What is the PK parameter that determines the maintainence dose rate

A

Clearance

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9
Q

Why is the half life important?

A

Helps determine the dosing interval and the time needed to reach steady state

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10
Q

What is zero order elimination?

A

This is here concentrations of a drug fall at a constant rate (e.g. ethanol)

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11
Q

What is first order elimination?

A

Elimination depends on a concentration-dependent relationship

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12
Q

What is steady state and how is it calculated?

A
  • medication must be supplied at at equal rate towards its elimination at a given concentration
  • maintainence dose rate = clearance x steady state concentration
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13
Q

True or false - volume of distribution only describes the proportion of unbound drug

A

False - includes protein bound or unbound drug

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14
Q

What is the formula for half life

A

T(1/2) =0.693 Vd / CL
If high Vd, high half life
If high CL, low half life

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15
Q

If there is a drop in albumin, would this affect protein binding of drugs?

A

Unlikely to as clearance is dependent on free drug clearance

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16
Q

What types of drugs traverse lipid membranes - ionised or unionised?

A

Unionized

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17
Q

What is P glycoprotein?

A

It is the efflux transporter protein that helps in transporting drugs to various organs
In the gut, PGP pumps drugs back into the lumen, decreasing their absorption

18
Q

Describe the concept of systemic clearance

A
19
Q

Describe how liver metabolism of drugs occurs

A

1) biotransformation of a parent drug to one or more metabolites
2) excretion of unchanged drug in the bile
3) both

*hard to measure directly, so often calculated by systemic clearance - renal clearance

20
Q

What is the formula for half life?

A

T(1/2) =0.7 x V / clearance

21
Q

List 3 factors that alter absorption

A
  • lack of gut absorption
  • too lipophilic (can’t cross water layer adjacent to cell) or hydrophilic (can’t cross lipid membrane)
  • P glycoprotein - this pumps drug put of gut wall cells
22
Q

What is first pass elimination/metabolism

A

This is when the drug is metabolised by the liver before moving to the systemic circulation

Determined by extraction ratio = liver clearance / hepatic blood flow

23
Q

What is the most important parameter in defining a steady state drug dosage regime?

A

Clearance

24
Q

What is the equation for dosing rate?

A

Dosing rate = clearance x target concentration

25
Q

Explain how the ageing process can affect absorption?

A

Consequence of decreased blood flow to the tissues, GIT and alteration in stomach pH
*clinical application of this - some medications may enhance this effect
» use of omeprazole may lower gastric pH subsequently affecting B12 absorption
» inconsistent eating habits (e.g. a high protein meal with phenytoin results in less absorption due to a higher amount of drug becoming protein bound
» reduction of subcut and transdermal meds due to reduced blood flow

26
Q

Explain the difference between first pass and phase I metabolism

A
  • first pass - metabolism of a drug prior to reaching the systemic circulation
  • phase I - early reactions that break down drugs
27
Q

In the ageing process, how is first pass metabolism affected?

A
  • first pass reduced as part of the ageing process (resulting in a HIGHER peak concentration) - good examples of this are amitriptyline, verapamil, opiods
28
Q

In the ageing process, how is phase I metabolism affected?

A
  • reduced
  • clinical application - decreased clearance of metabolised medications (e.g. warfarin)
    *note no affect on peak concentration
29
Q

Is renal clearance affected by the ageing process?

A
  • not confirmed evidence wise - unsure if reduced renal clearance related to pathophysiology vs. ageing
30
Q

Describe the half life and Vd of ampicillin

A
  • short half life (<1.5 hour) and therefore a low volume of distribution
    *this is enabled by glomerular filtration and renal tubular secretion
31
Q

What is the electrolyte disturbance associated with ampicillin?

A

sodium

32
Q

What is the role of anticholinergics?

A
  • block/inhibit the neurotransmitter acetylcholine at central and peripheral nerve synapses
  • downstream effect of blocking the parasympathetic nervous system
  • two main receptors - antimuscarinic and nicotinic
33
Q

Outline the key adverse effects of anticholinergic medications at toxic levels

A

Central (CNS blockage)
- agitation/confusion/delerium
- seizures

Peripheral (various)
- hyperthermia
- flushed/tachycardia
- reduced gut motility, urinary retention
- blurred vision, NARROW angle glaucoma

34
Q

What are some key contraindications for anticholinergics?

A
  • some conditions make elderly people more susceptible to anticholinergic activity (e.g. dementia)
  • elderly Px - increased permeability of BBB
35
Q

Explain why in a patient with AD, anti-cholinergic medications would not be useful

A
  • in mild-mod dementia - cholinergic medication may be used
    *anti-cholinergics could offset this
  • example - donepazil
36
Q

What is the concept of high anticholinergic load?

A

This is where there can be a cumulative, sedative effect of taking multiple medications with anticholinergic properties

37
Q

What is the risk associated with switching a patient from a biologic to a biosimilar medication?

A
  • potential initiation of anti-drug antibodies
    *possibility to make the biologic and biosimilar medication ineffectie
38
Q

List 3 drugs that are common CYP3A4 inducers

A
  • carbemazipine
  • phenytoin
  • rifampin
  • dexamethasone
39
Q

How is hydrocortisone metabolised and what drugs should be avoided to prevent an addisonian crisis?

A
  • via CYP3A4
  • any inducers could reduce the plasma concentration of hydrocortisone (e.g, carbemazipine)
40
Q

What will happen to a patient on ketoconazole and hydrocortisone?

A

increased levels of hydrocortisone as ketoconozole is an inhibitor of CYP3A4

41
Q

List 3 drugs that are inhibitor enzymes

A

Pharmacology (3 decks)

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