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Kirstys Flashcards > MDM: Biopharmaceutics > Flashcards

MDM: Biopharmaceutics Flashcards

1
Q

What is biopharmaceutics?

A

The study of factors affecting the rate and extent of drug absorption e.g. physiochemical properties, size of dose, dosgae form

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2
Q

What does biopharmaceutics determine?

A

How fast andhow much drug is available in the blood stream aka bioavialability (F)

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3
Q

What does ‘F’ stand for and why is it important?

A

The fraction of the administered dose that reaches the systemic circulation in its unchanged form

It gives an indication of what proportion of the drug will reach the systemic circulation that will be able to have a theraputic effect

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4
Q

What is the value of ‘F’ for IV injections compare to other routes?

Why is this?

A

IV: F = 1

Other: F< 1

Im IV injections it is directly put into blood stream. Other routes have to pass membranes so not all will be absorbed. Metabolism may occur prior to reaching the systemic circulation

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5
Q

What are factors effecting drug absorption from the GI tract?

A
  • Physiological
  • physiochemical drug properties
  • Excipents
  • tyoes of dosage form
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6
Q

What are physiological factors affecting drug absorption?

A
  • Surface area of absorption sites
  • pH of GI fluids
  • Gastric emptying rate
  • Intestinal motility
  • Chemical degradation in GI
  • Liver metabolism
  • Diet
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7
Q

What are physiochemical factors effecting absorption?

A
  • Solubility and dissolution
  • lipid solubility and log P
  • molecular weigh
  • pKa
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8
Q

What are excipent factors affecting absorption rate?

A
  • Dilutent
  • Surfactant
  • viscosity enhancing agent
  • lubricant
  • binder
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9
Q

What are dosage form types effecting absorption?

A
  • Aqueous solutions
  • aqueous suspensions
  • soft gelatine capsule
  • hard gelatine capsule
  • uncoated tablet
  • coated tablet
  • enteric coated/ GR coated
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10
Q

What factors effect F?

A
  • Physiochemical
  • physiological
  • mechanism of absorption
  • formulation
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11
Q

Explain how the surface area effects the rate of absorption.

Think stomach and intestine

A

The greater the surface area the greater the absorption.

The intestine has a greater surface area due to the presence of folds called villi and micro villi. This means more absorption occurs in the intestine as opposed to the stomach

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12
Q

Explain how pH changes down the GI tract and how this effects absorption

A

The pH increases as you move down the GI tract. It is varies depending on food eaten, the individual and certain diseases.

pH effects absorption as it alters the ionisation of drugs (WA/Bs). Unionized drugs can pass through membranes much easier to be absorbed.

Some drugs are also less stable at certain pHs

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13
Q

How does gastric emptying rate effect rate of absorption?

A

As majority of drug absorption occurs in the intestine, the longer in the stomach the slower the absorption.

  1. Solid dosage forms slow GRT and take longer to be passed into the intestine than liquids forms therfore take longer to be absorbed.
  2. The presence of food slows GRT as the food is broken down by gastric enzymes before being transferred to the liver therefore absorption is slower.
  3. Fluids will increase GRT as the volume in the stomach needs to be maintained at a constant volume. This means the stomach contents will be delivered to the intestines faster after drinking water (not alcohol)
    4.
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14
Q

Why is intestinal motility important in absoprtion?

A

The longer the drug stays in the intestine the greater the absorption

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15
Q

How does chemical degradation effect absorption?

A

Drugs can undergo chemical degradation in different parts of the GI tract e.g. hydrolysis by enzyme in GI/ intestine or metabolised by enzymes in the liver and GI walls.

FIrst pass effect can also occur where the liver metabolises the drug.

These lead to fractions of the drug being lossed and not reaching the systemic circulation in order to have an effect

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16
Q

Explain how diet effects absorption of drug

A
  • Food and drugs may compete with each other to be absorbed therefore less drug absorbed
  • Fatty food can slow GRT therefore slower absorption
  • Fatty food stimulates bile sectrion which can increase the dissolution rate of drugs therefore absorption. They produce a solubilising effect which causes increased contact time of drug with epithelial wall.
  • Bile salts and food may produce and insoluble complex
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17
Q

How does diet effect GI contents viscosity and blood flow to liver. How does this effect absorption?

A

Increases viscosity which reduces absorption and disolution. After a meal blood to liver increases therefore more drug goes to liver and saturate the enzymes so more drug escapes first pass effect

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18
Q

How does a particle dissolve and is absorbed by the GI tract?

A

When a drug enters the GI tract a dissolution layer forms around its surface due to interfacial tension between the drug and GI fluid. The drug must dissolve and pass through the diffusion layer and the rest of the GI fluid to the GI wall to be absorbed by passing through the wall

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19
Q

What is Noyes-Whitneys equation and what does everything stand for?

A

dc/dt = DA (Cs-C)/ h

dc/dt = dissolution rate constant

D = dissociation constant

A = surface area of the drug particle in contact with the GI fluid

Cs = drug intrinsic solubility in diffusion layer

C = drug concentration in GI fluid

h = thickness of diffusion layer

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20
Q

What parameters of the Noyes-Whitneys equations when increased will increase dissolution rate?

A
  • A = smaller particles mean quicker dissolution. Though if very hydrophobic and very small particles may aggregate
  • Cs
  • D
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21
Q

What parameters when decreased will increase dissolution rate?

A

h, C

22
Q

How can increased surface area be achieved and why can this be an advantage and disadvantage in drug delivery?

A

By reducing particle size - micronisation

  • increased SA means faster dissolution rate as greater surface area of drug in contact with GI fluid
  • However some drugs when particle size decreased will aggregate and SA will be reduced. A surfacant should be used during micronisation to prevent this
  • Increased SA also means increased degradation in GI tract
23
Q

Describe how WA/WB drugs solubility varies with pH in the GI tract

A

pH varies along the GI tract which effects the solubility of these drugs

  • WA = become more ionised as pH increases above their pKA so their solubility increases as pH does. They are more soluble in the stomach
  • WB= become more ionised as pH decreases below there pKA so become more soluble at lower pHs. They are more soluble in the intestines

more ionised more likely to dissolve/ dissolude but not absorbed

24
Q

Explain how salt form of a drug may overcome pH dependent solubility of a WA/WB

A
25
Q

State the exceptions where a salt may not produce faster dissolution and absorption of drugs

A
  • Some salts become more unstable than free from
  • Some salts have a lower solubility than free form e.g. aluminium salts of weak acids and palmoate salst of weak bases
26
Q

What is the differences bettwen hydrates/solvates and salts

A

Solvates/ hydrates are produced from recyrstylisation in an organic solvent or water

Solvates/ hydrates are less soluble in GI fluid than parent compoun where as salts are generally more soluble

S/H more likely to produce a substained release effect

solvate - make more soluble. Hydrate - make less soluble but more stable

27
Q

Advantages of crystalline and amorphous solids in dissolution/ absorption.

disadvantages?

A
28
Q

How does partion coefficent effect drug absroption/ dissolution?

What is ideal log P?

A

Partion coefficent is how soluble a drug is in oil and water. Log P = conc in oil/ conc in water

Drug needs a degree of hydrophilicity and lipophilicity.

Drug needs to be lipophillic to be absorbed across membrane but hydrophillic to dissolve in GI fluid

log P: 2-4.5

29
Q

What is the biopharmaceutical classification system (BCS)?

How does thise effect absorption?

A

It classifies drugs according to their water solubility and lipid solubility/permeability

  1. Class I : High solubility and High permeability thruogh GI membrane therefore high F
  2. Class II: Low solubility and high permeability therefore F is limited by dissolution
  3. Class III: High solubility and low permeability therefore F is limited by their permability through membranes
  4. Class IV: Low solubility and low permeability therefore low F
30
Q

How does molecular weigh effect absorption?

A

Larger the poorer the absorption

31
Q

Disscuss how the pH- partion hypothesis explains the dissolution and absorption of WA/WBs

A
32
Q

Limitations of the pH partion hypothesis

A
  • Most WA are also absorbed well in intestines due to high SA and long residance time
  • Quaternary ammonium compounds are ionised at all pHs of the GI tract but still readily absorbed from GI tract. QAC have a permanent, pH independ + charge due to quanternary amine.
  • Long residence time in small intestine is an equilibrium process. unionised form and ionised in equilibrium so will still always be some unionised form
  • Charged drug molecules may interact with other organic ions with the opposite charge and produce a neutral species which can be absorbed
  • solvent drag - bulk transport of water in the GUT lumen to the blood can transport watersoluble drugs
  • some drugs absorbed by activae pathways
33
Q

Describe passive diffusion

A

Drugs pass from a high concentration in the GI tract to a low concentration in the circulation

must have high log P

34
Q

What law describes passive diffusion?

A

Fick’s first law of passive diffusion

dC/dt = kCg

dC/dt = rate of absorption

k = proportionality constant

Cg= drug conc in GI fluid

35
Q

From FIcks first law of diffusion why is k1Cg - k2Cb said to be equal to k1Cg?

A
36
Q

What are taken to be constants in the Ficks equation?

A

k= DA/h

37
Q

What does Ficks first law of diffusion not apply too?

A

This only applies to drugs which are not electrolytes. Electrolytes exist in equilibrium between the ionised and unionised form thefore partion coeffient for them will be different - the unionised form will be more lipohillic and diffuse more quickly

38
Q

What order of kinetics does passive diffusion follow?

A

first order - drug conc in GI tract decreases over time

39
Q

Describe the difference between passive and active trasnport

A
  • Passive most common. It is when drugs are carried along their concentraion gradient without the requirement of energy. In active a carrier protein is used to move the drug against its concentration gradient and requires energy.
  • Active transport only moves drugs with specific structures, where as passive is unspecific
  • Active transport is a one way transport, where as passive can occur both ways
40
Q

Describe the difference between Active and facilitated diffusion

A

Active transport occurs against conc gradient and requires energy, where as facilitated occurs along conc gradient and doesn’t require energy. Facilitated diffusion is not involved in absorption

41
Q

Why is pore transport not involved in absorpiton

A

only occurs with very small molcules e.g. water or individual ions

42
Q

Explain the process of transcytosis/pinocytosis

A

This involves pairing drugs with opposite charges to reduce their overall charge and make them more lipophillic to be absorbed

43
Q

Discuss the effect of dilutent on tablet disintigration

A

Dilutents can either be hydrophobic or hydrophillic.

if hydrophobic they slow down tablet distigaration therefore slow drug dissolution and can slow onset of action

44
Q

Discuss the use of surfactants in liquid and solid dosage forms

A
  • increase drug dissolution by solubilising hydrophobic drugs in GI fluid
  • Increase wetting of solid dosage form to promote disintigration and drug release
  • Increase drug absorption by making the GI membrane more perneable
45
Q

State the effect lubricants and glidants may have on distintigration

A

These are usually hydrophobic so so tablet distigration therefore onset of action

46
Q

Describe the effect binders/ tablets have on drug distigration

A
  • binders can be hydrophibic or hydrophillic. If hydrophobic they slow drug distigration and delay onset of action
  • Distigrants promote drug disintigration
47
Q

Discuss how drug viscosity enhancing agents may effect drug dissolution and absorption from the GI tract

A

Viscosity enhancing agents are used to prevet drug particles from sedimenting in suspensions

These may increase viscosity of GI fluid, reduced gastric emptying rate, dissolution and absorption

may also increase intestinal residence time thereby increasing absorption

48
Q

Rank solutions, suspensions, capsules and tablet in terms of decreasing F. Explain why there is differences

A
49
Q

Discuss the differences in drug dissolution in the GI fluid when administered in soft gelatine capsules when the carrier vehilce is water miscilbe or imisscilbe

A

water miscible - vehicle dissolves on contact with GI fluid so drug rapidly dissolved

immiscible - vehicle first disperse with contact of GI fluid. Drug must diffuse out of carrier then dissolve. This means dissolution is delayed and so is onset of action

50
Q

State the 4 process which effect drug dissolutoin when carrier in hard gelatine capsules

A
  • dissolution rate of gelatine shell
  • fluid penetration into the contents of the shell
  • Rate of dispersion of the contents in the shell
  • Dissolution rate of individual drug particles
51
Q

Why do tablets have a lower F than capsules?

A

Kirstys Flashcards (116 decks)

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