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CPT > L1 Pharmacokinetics And Pharmacodynamics > Flashcards

L1 Pharmacokinetics And Pharmacodynamics Flashcards

1
Q

Pharmacokinetic factors

A 
Bioavailability 
Half - life
Drug elimination 
Inter subject variability 
Drug - drug interactions
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2
Q

Human factors affecting pharmacokinetics

A 
Renal function - clearance
Stress
Pyrex is
Alcohol - CYPs
Smoking - CYPs
Age
Sex
Exercise 
Diet 
Pregnancy and lactation - tetrogenic 
Liver function - Albumin
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3
Q

Bioavailability (F)

A

Measure of drug absorption where it can be used i.e. concentration of drug after it has been metabolised

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4
Q

IV bioavailability

A

100% i.e. 1

Bypasses the liver and transferred directly to the plasma concentration

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5
Q

Other routes bioavailability

A

Fraction of IV bioavailability

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6
Q

Factors affect bioavailability

A 
Age - luminal changes 
Sex 
Food - chelation and gastric emptying 
Vomiting and malabsorption e.g. Crohn’s 
Absorption 
Formulation 
Liver function - first pass metabolism
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7
Q

Modified release preparations

A

Drugs can be modified to be absorbed slower
Therefore take less pills per day
Increases adherence

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8
Q

Factors affecting volume of distribution

A

Blood flow
Capillary structure i.e vasoconstriction
Lipophilicity - higher Vd
Protein binding - difficult to distribute to other compartments therefore decrease Vd

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9
Q

Protein binding

A

Albumin - acidic drugs
Globulins - hormones
Lipoproteins - basic drugs
Glycoproteins - basic drugs

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10
Q

Free drug

A

Only free drug that isn’t bound to proteins can elicit a response and be eliminated

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11
Q

Class II precipitate drugs

A 
Displace class I object drug from protein binding sites as the class II drug has a higher affinity 
Therefore more Class I drug is free to elicit an effect
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12
Q

Factors that cause more free drug

A

Pregnancy - increased blood volume
Renal failure - less clearance
Hypoalbuminaemia - less protein to bind to drug therefore more is free

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13
Q

Volume of distribution

A

= dose (mg)/ plasma drug concentration at t=0 (mg/L)

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14
Q

Vd and plasma concentration

A

Vd is inversely proportional to plasma drug concentration

When there is a high plasma drug concentration the Vd is lower as less has been distributed

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15
Q

Phase 1 metabolism - first pass

A
  • oxidation
  • dealkylation
  • reduction
  • hydrolysis
  • converts drug into lipophilic metabolites
  • by cytochrome P450 - liver enzymes
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16
Q

Phase II metabolisation

A
  • add covalent bonds to change size by conjugating enzymes
  • glucuronide
  • sulphate
  • glutathione
  • N-acetyl
  • can be excreted by the kidney via urine or by the liver in bile
17
Q

CYP3A4 inhibition

A

Grapefruit and citrus juice

  • less metabolism of lovastatin so increased concentration in blood plasma
18
Q

CYP 2D6 epigentics, metabolism and inhibition

A

Absent in 7% of Caucasians
Hyperactive in 30% of East Asians

Metabolises:

  • Beta blockers
  • SSRI
  • opioids

Inhibited by:

  • some SSRIs
  • other anti arrhythmic drugs
  • other antidepressants
19
Q

St Johns Wort and carbamazapine

A

Induces CYPs

  • increased oestrogen and progesterone break down so COCP less effective
  • carbamazepine induces CYPs for increased carbamazepine metabolism
20
Q

Renal clearance factors

A
  • GFR and protein binding
  • competition for transporters
  • lipid solubility
  • pH
  • flow rate
  • other drug interactions e.g. gentamicin is nephrotoxic
21
Q

What is regally cleared

A

Low molecular weight polar molecules

22
Q

What is cleared hepatically

A

High molecular weight metabolites conjugated with glucuronic acid

23
Q

Zero order clearance

A

Rate of elimination is constant regardless of concentration

  • dangerous as overdose can reach max tolerated dose quicker
24
Q

First order clearance

A

Rate of elimination increases proportionally to the concentration given

25
Q

Half life

A

Time taken to reduce the concentration by half

  • Independent of concentration
26
Q

Clearance ml/min

A

Volume of blood cleared per unit time

Elimination rate (UV)/ plasma drug concentration

27
Q

Clearance, half life and Vd

A

High Vd - more distributed means it takes longer for the drug to be cleared

Therefore longer half life

28
Q

Half life calculation

A

(0.693 (constant) x Vd )/ CL

29
Q

Which drugs exhibit zero order kinetics

A

High dose
Alcohol
Salicylic acid
Phenytoin

30
Q

Drug monitoring

A

Zero order kinetics
Long half life
Narrow therapeutic window
Drug - drug interactions

31
Q

Steady state concentration

A

Reached in 5 half life’s

Where the therapeutic benefit is optimal

At steady state the infusion = elimination

32
Q

Rate of administration

A

(Dose x bioavailability)/ dose interval (how often given per day)

33
Q

Stead state concentration equation

A

(Maintenance dose x bioavailability) / (dose interval x clearance)

34
Q

Loading dose

A

CSS x Vd

35
Q

Why is adrenaline often do-administered

A

Acts on alpha 1 receptors for vasoconstriction, reducing the blood flow and rate of absorption

  • keeps the anaesthetic in the desired area
36
Q

How to increase rate of steady state concentration

A

Increase the rate of infusion by:

  • increasing dose
  • increase bioavailability
  • decrease dose interval

CPT (23 decks)

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