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0. Foundations of Medicine > Drug Absorption > Flashcards

Drug Absorption Flashcards

1
Q

Define Pharmaceutical process

A

Get the drug into the patient

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2
Q

Define Pharmacokinetic process

A

Get the drug to the site of action

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3
Q

Define Pharmacodynamic process

A

Produce the correct pharmacological effect

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4
Q

Define Therapeutic process

A

Produce the correct therapeutic effect

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5
Q

What determines drug pharmacokinetics

A

Absorption

Distribution

Metabolism

Elimination

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6
Q

What are the methods of administration?

A

Oral

Intravenous

Subcutaneous

Intramuscular

Other GI - Sublingual

rectal

Inhalation

Nasal

Transdermal

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7
Q

What is absorption?

A

the process of movement of unchanged drug from the site of administration to the systemic circulation.

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8
Q

What does ADME allow?

A

understanding of :

Dosage

Drug administration

Drug handling

Patient variability

Potential for harm.

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9
Q

What is sublingual?

A

Under the tongue

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10
Q

What is Tmax? Oral absorption

A

The time to peak concentration, important in relieving pain

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11
Q

What is Cmax? Oral absorption

A

The peak concentration, important in determining a toxic dose

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12
Q

What is the (AUC)? Oral absorption

A

The area under the drug concentration-time curve

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13
Q

Does the dose effect the tmax?

A

No, alters cmax

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14
Q

What does the The area under the drug concentration-time curve represent?

A

The amount of drug which reaches the systemic circulation

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15
Q

What is the Theraputic range?

A

The range of concentrations at which a drug is active.

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16
Q

What happens above or below the theraputic range

A

Toxicity

Insufficient pharmalogical action

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17
Q

What does The AUC allows us to estimate?

A

The amount of drug which reaches the circulation and which is available for action

BIOAVAILABILITY - Used to compare routes of administration

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18
Q

What is the bioavailability of an intravenous drug?

A

100%

19
Q

What are the factors affecting Bioavailability? (oral absorption)

A

Formulation - Slow release preparations

Ability of drug to pass physiological barriers

  • Particle size
  • Lipid solubility
  • pH and ionisation

Gastrointestinal effects

  • Gut motility
  • Food-Illness
  • First pass metabolism (whereby the concentration of a drug is greatly reduced before it reaches the systemic circulation.)
20
Q

What is dissolution?

A

The rate a drug breaks up

21
Q

What is an example of a physiological barrier?

A

Transport across membranes

22
Q

What are the methods of transport across membranes?

A

Passive diffusion

Filtration

Bulk flow

Active transport

Facilitated diffusion

Ion-pair transport

Endocytosis

23
Q

What does the degree of the ionisation of the drug depend on?

A

As most drugs are weak acids or bases the degree of ionisation depends on the pH of the environment

24
Q

What form of the drug crosses the membrane?

A

The unionised form

25
Q

What is the distribution of the un-ionised form of a drug?

A

Should distribute across the membrane until equilibrium is reached - equal concentration on each side.

26
Q

Where will an acidic drug be most concentrated?

A

In the compartment with high pH

27
Q

What does the Henderson-Hasselbalch equation describe?

A

The relationship between the local pH and the degree of ionisation

28
Q

What is The ability of a drug to diffuse across a lipid barrier is expressed as?

A

lipid-water partition coefficient

29
Q

What is the lipid-water partition coefficient?

A

The ratio of the amount of drug which dissolves in the lipid and water phase when they are in contact.

30
Q

Describe passive diffusion

A

Very common.Occurs along concentration gradient.

Non selective Not saturable Requires no energy No carrier is needed Depends on lipid solubility and degree of ionsation

31
Q

Describe Active Absorption

A

Relatively unusual.Occurs against concentration gradient.

Requires carrier and energy. Specific Saturable. Iron ,K , Na , Ca Uptake of levodopa by brainEnergy dependant

32
Q

What is the structure of drugs that undergo active transport?

A

They must resemble naturally occurring compounds

33
Q

Describe facilitated diffusion

A

Occurs along the concentration gradient

Require carriers

Saturable Structure specific

No energy required

Mixed order kinetics

monosaccharides, amino acids, vitamins

34
Q

Where does filtration occur?

A

Through channels in the cell membrane.

35
Q

What is the milecular size of the drug in Filtration / Bulk Flow/ Pore Transport?

A

Low molecular size

36
Q

What is the driving force in Filtration / Bulk Flow/ Pore Transport?

A

Hydrostatic or the osmotic pressure difference across the membrane.

37
Q

What does the speed of gastric absorption affect?

A

speed at which drug reaches site of absorption

38
Q

What is the effect of food on absorption?

A

Can enhance or impair rate of absorption

39
Q

How does illness affect absorption?

A

Malabsorption (eg Coeliac disease) can increase or decrease rate of absorption

Migraine reduces rate of stomach emptying and therefore rate of absorption of analgesic drugs.

40
Q

Decribe the Subcutaneous / Intra-muscular route of administration?

A

Needs small volume

Avoids first pass metabolism

41
Q

Describe Sublingual, Buccal administration

A

Sublingual absorption from the buccal mucosa bypasses first pass metabolism which will inactivate the drug.

Drugs given this way enter the circulation directly i.e. GTN for angina

42
Q

Describe rectal administraion

A

Bypass first pass metabolism.

Absorption tends to be slow.The rectum is often used for drugs which cause irritation of the stomach.

43
Q

Describe the benefits of inhalation/nasal administration

A

Relatively rapid action

Avoids problems with oral absorption

Although only 5-10% absorbed

44
Q

Describe Transdermal absorption

A

Avoids first pass metabolism.

Can provide controlled release.

Few substances well absorbed.

Need to be non-irritant.

0. Foundations of Medicine (167 decks)

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