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ICPP > Pharmocokinetics > Flashcards

Pharmocokinetics Flashcards

Lecture 17

1
Q

Liquid tablet

A

Slower transport so okay for headaches but not for MI

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2
Q

Focal administration

A

Targeted concentration to the required site

High conc to the site of action
Less systemic absorption
Fewer side effects

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3
Q

Focal areas

A

Eyes
Skin
Inhalation

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4
Q

Enteral

A

Deliver to mouth and intestines. Administration via:

Oral
Sublingual
Rectal

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5
Q

Parenteral

A

Delivery through other routes. Administration via:

IV
Inhalation 
Subcutaneous
Intramuscular
Transdermal
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6
Q

Valproate

A

Weak acid
Mainly unprotonated and charged
Cannot pass bilayer

10% protonated can pass bilayer

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7
Q

Physiochemical factors

A

GI surface area and length
Drug lipophilicity
OAT/OCT number

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8
Q

GI physiology

A

Blood flow
GI motility
Food / pH

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9
Q

First pass

A

The concentration of drug not metabolized travels via the portal vein to the liver where some may be metabolised by hepatic enzymes and deactivated or activated.

Cytochrome P 450s - phase 1 enzymes
Conjugating enzymes- Phase 2 enzymes

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10
Q

Bioavailability

A

Concentration of drug that has not been metabolized and reaches the circulatory system unchanged

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11
Q

Drug distribution factors

A

capillary permeability
Lipophilicity
concentration of protein or lipoprotein drug

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12
Q

Therapeutic ratio/ window

A

Maximum tolerated dose / minimum effective dose

LD50 / ED50

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13
Q

Small therapeutic window

A

May overdose

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14
Q

Fast release

A

At same dose can exceed LD50

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15
Q

Slow release

A

Fall below ED50 quicker therefore more doses required - longer time to reach therapeutic window

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16
Q

Plasma concentration

A

Lower the plasma concentration. The more the drug has distributed

Decrease in plasma concentration = increase in volume of distribution

17
Q

Apparent volume of distribution

A

Theoretical if all conc was given at site of action

Obtained by extrapolating elimination phase to time 0

18
Q

Volume of distribution

A

Total amount of drug in body (dose) / plasma drug conc at t0

19
Q

Smaller Vd

A

Higher plasma conc so less drug distributed to tissues

20
Q

Highly charged hydrophilic Vd
Protein bound Vd
Distributed in TBW
Highly lipophilic (hydrophobic)

A

Low Vd - more in plasma
Low Vd - more in plasma as not free
High Vd - less in plasma
High Vd

21
Q

Protein binding interactions important when:

A

High proportion of protein bound drug
Small therapeutic window
Small Vd

22
Q

Class 1 drug

A

Lower dose than number of protein binding sites

Equilibrium between free drug conc and free binding site conc

Low affinity

Warfarin

23
Q

Class 2

A

Dose is higher than the protein binding sites as all bind them left over = free drug

High affinity

Displaces Class 1

Aspirin and phenytoin

24
Q

Transient binding interaction

A

When drug conc increase rate of elimination increases

Steady state is restored

25
Q

Excretion

A

Predominantly renal - glomerulus

26
Q

Metabolisation

A

Predominantly liver

Make small, uncharged, lipophilic, hydrophobic molecules more soluble

Add a group so it can be filtered and not taken back up

27
Q

Phase 1 metabolisation

A

Mainly redox - add charge
Deacylation
Hydrolysis

By cytochrome P450s

28
Q

Phase 2 metabolisation

A

Conjugation enzymes

Add hydrophilic group
Add charge

Therefore can be eliminated by kidney
More rapid than phase 1

29
Q

Cytochrome P450s

A

Affinity for lipophilic drugs

Inducible and inhabitable so can be controlled

30
Q

First order kinetics

A

Rate of elimination proportional to drug concentration

Half life is constant

Safer

Predictable and can estimate therapeutic effect from dose increases

31
Q

Zero order kinetics

A

Rate so elimination constant

More dangerous

Less predictable

At high doses of drug, rate of elimination is already maxed so cannot increases anymore. Therefore bioavailability increase exponentially which means it can exceed the LD50 (max tolerated dose) - side effects

32
Q

Drug elimination kinetics important for:

A

Zero order kinetic drugs
Small therapeutic window
If drug is used at minimum effective dose

33
Q

Clearance rate

A

Elimination rate/ plasma drug concentration

34
Q

Half life

A

Period of time taken to reduce concentration to half

35
Q

Half life factors

A

Drug elimination kinetics
Vd - more distributed - longer half life
CL - faster cleared - shorter half life

36
Q

Steady state

A

5 half lives = steady state

37
Q

Long half life

A

Steady state will take to long to reach - give higher bolus loading dose

38
Q

Weak acids

A

HA

If more acidic urine :

pH less than Pka
More H+
Protonate

Uncharged pass through membrane - increased absorption

39
Q

Weak base

A

BH+

If alkali urine:

pH more than PKa
Less H+ available
Deprotonates (B)

Uncharged - pass through membrane
Increase reabsorption

ICPP (1 decks)

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