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Clinical Pharmacology > Pharmacokinetics and Pharmacodynamics > Flashcards

Pharmacokinetics and Pharmacodynamics Flashcards

1
Q

Define Pharmacokinetics

A

What the body does to the drug

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2
Q

Define Pharmacodynamics

A

What the drug does to the body

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3
Q

Which is the only type of drug that can elicit an effect on the body?

A

Only free drug can elicit a pharmaceutical response

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4
Q

What is bioavailability?

A

The fraction of an orally administered drug that reaches the systemic circulation as intact drug (F)

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5
Q

What is the bioavailability of an IV drug?

A

100%

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6
Q

How do you calculate bioavailability?

A

Bioavailability = AUC oral x100%

AUC IV

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7
Q

What factors affect bioavailability?

A
  • Absoprtion
    • Formulation
    • Age
    • Food (chelation, gastric emptying)
    • Vomiting/ Malabsorption (Crohn’s)
  • First pass metabolism
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8
Q

Identify on the curve, absorption, distribution and elimination

A
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9
Q

What are modified release preparations?

A

Standard preparations have to be administered several times a day

Modified release are taken less often and are absorbed over a longer period

  • Plasma concentration determination shifts more towards the rate of absorption
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10
Q

What factors affect the distribution of therapeutic agents?

A
  • Blood flow (to target organ) , capillary structure
  • Lipophilicity and hydrophilicity
  • Protein binding
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11
Q

What are the different types of proteins that drugs can bind to

A
  • Albumin- acidic drugs
  • Globulins - hormones
  • Lipoproteins - basic drugs
  • Glycoproteins - basic drugs
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12
Q

Explain the one compartment model of distribution

A

Drug only distributed in one compartment, no equilibrium established

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13
Q

Explain the 2 compartment model of distribution

A

Slower distribution across the different compartments of the body

Equilibrium established between the different body compartments

Elimination can start to happen before an equilibrium in body tissues is established

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14
Q

How can drug-protein binding affect distribution if a second drug is administered?

When is this clinically important?

A

Bound drug can be displaced from a binding site → now free drug that can elicit a response

Clinically important if:

  • highly protein bound
  • narrow therapeutic index
  • low Vd
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15
Q

What is volume of distribution? (Vd)

A

The apparant volume of drug in the body releative to its concentration in plasma

Low Vd= mainly in plasma

High Vd= well distributed throughout body compartments

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16
Q

How do you calculate Vd?

A

Vd= Dose/ [Drug] plasma

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17
Q

How do you calculate a dose based on Vd?

A

Vd x [Drug] plasma = dose

18
Q

What are the 2 phases of metabolism?

A

Phase 1: CYP450s → oxidation reaction → forms lipophilic metabolites

Phase 2: Conjugation reaction → excretion by kidney to urine or gall bladder in bile

19
Q

What are the main isoenzymes of CYPs? How are these induced/inhibited

A

CYP1A - induced by smoking

CYP2C - many inhibitors

CYP2D - metabolises many drugs

CYP2E - Alcohol metabolism

CYP3A - ~50% therapeutics

20
Q

What are pro-drugs?

A

Drugs that are adminstered inactively, and are activated by CYP450 enzyme metabolism

e. g. perindopril → dopamine
e. g. codeine → morphine

21
Q

What factors can affect the activity of CYP450s?

A
  • age
  • hepatic disease
  • blood flow
  • alcohol
  • cigarette smoking
22
Q

Which CYP does grapefruit inhibit?

A

CYP3A4

Effects statin metabolism - CYP3A4 inhibited so statin levels remain high

23
Q

What are the routes of drug elimination from the body?

A
  • Primarily via the kidneys
  • Other routes:
    • Fluids- sweat, tears, genital secretions, saliva, breast milk
    • Solids- faeces, hair
    • Gases- volatile compounds
24
Q

By which routes are low molecular weight and high molecular weight metabolites respectively excreted?

A

Low molecular weight polar metabolites- by the kidneys

High molecular weight metabolites- by hepatic route

25
Q

What factors affect Renal clearance?

A
  1. Glomerular filtration affected by GFR & Protein binding
  2. Tubular secretion affected by Competition for transporters
  3. Tubular reabsorption affected by lipid solubility, pH, flow rate
26
Q

Briefly explain the principles of hepatic clearance

A
  1. Drug conjugated with glucoronic acid in the liver
  2. Congugated drug enters gut with bile
  3. Eliminated in faeces or reabsorbed into enterohepatic circulation
27
Q

What is first order metabolism?

A

Elimination of drug is concentration dependent

e.g. more drug= faster elimination

28
Q

What is zero order metabolism?

A

Elimination of drug is at a fixed rate, regardless of concentration (e.g. alcohol)

29
Q

What is half life?

A

Time taken for the concentration of drug to half

(independent of concentration)

30
Q

Give the equation to calculate T1/2

A

t1/2 = 0.693 / k

31
Q

How do you calculate clearance?

A

Clearance = Rate of elimination from body/ drug concenration in plasma

32
Q

What is clearance?

A

The volume of bood cleared, per unit time (mL/min)

33
Q

What is the equation for haf life, with clearance?

A

t1/2 = 0.693 x Vd

CL

34
Q

How does t 1/2 vary in first order vs zero order drugs?

A

Most drugs are first order- t1/2 is constant

Zero order- dose can change giving unpredictable [plasma] → t1/2 is not calculable (important for dosing and toxicity)

35
Q

Approximately how many t1/2 does it take to reach steady state concentration?

A

Steady state (Css) reached in ~5 t1/2

(and will take ~5 t1/2 for drug to be elimated from system after termination)

36
Q

How do you calculate steady state concentration?

A

Css= Rate of infusion/ CL

37
Q

For orally administered drugs at steady state administration = elimination.

Give the equation for steady state plasma concenration for an oral drug?

A

Css = Dose (D) x Oral Bioavailability (F)

Frequency of administration (t) x Clearance (Cl)

38
Q

What is a loading dose?

A

A dose given when rapid onset is required or drug has a long half life meaning it would take too long to reach Css

39
Q

How do you calculate a loading dose?

A

Loading dose = Css x Vd

40
Q

How can different drugs exert their action at receptors?

A

Agonists - activate receptors

Partial agonist - partial response even if all receptors occupied

Inverse agonist - binds to receptors preventing basal response happening

Competitive antagonists

Non- competitive antagonist

Clinical Pharmacology (25 decks)

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