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PHRM 513 > Drug Absorption and Oral Route I and II > Flashcards

Drug Absorption and Oral Route I and II Flashcards

1
Q

Process of absorption for Intramuscular and Subcutaneous injection

A

Tissues -> Circulatory system -> Metabolic sites -> Excretion

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2
Q

Biopharmaceutics

A

is the study of the physicochemical properties of the drug and the drug product on the absorption of the drug to produce a desired therapeutic effect

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3
Q

Physicochemical properties

A
  • Molecular weight
  • hydrogen bond donors and receptors
  • salt form and polymorphs
  • pKa
  • partitioning coefficient
  • solubility
  • permeability
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4
Q

Biopharmaceutics links

A

the in-vivo performance of the drug and the drug product to their in-vitro performance

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5
Q

In-vivo performance

A
  • PK studies

- Bioavailability

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6
Q

In-vitro performance

A
  • Dissolution rate

- Drug release rate

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7
Q

Passage of orally administered drugs through the digestive system

A

Oral cavity -> Esophagus -> Stomach -> Small intestines -> Large intestine -> Rectum

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8
Q

Dosage forms for oral administrationg

A

Oral solution : Absorption
Oral suspension or powder: Dissolution -> Absorption
Capsules and Tablets: Disintegration -> dissolution -> Absorption

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9
Q

How can we evaluate the in-vivo performance of an orally administered drug>

A
  • PK profile
  • Onset (lag time and Tmax)
  • Cmax
  • AUC ( area under plasma conc. vs. time curve or exposure
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10
Q

Bioavailability

A

a measure of the amount of drug that can reach systemic circulation

  • can be portrayed by a plasma conc. vs time curve
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11
Q

Looking at the curve the duration of action is when

A

the concentration is greater than the MEC ( minimum effective conc.)

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12
Q

Bioavailability depends on

A

Hepatic extraction ratio (E)
F = 1-E or F=(1-E)Fabs

When F= bioavailable

properties of the drug and its route of administration

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13
Q

The hepatic extraction ratio (E) is

A

a fraction of absorbed drugs (Fabs) which accounts for

  • Not available for absorption
  • Degraded function
  • Metabolized and effluxed fractions

the fraction of the drug entering the liver in the blood

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14
Q

Absolute bioavailability

A

in reference to the same drug administered by a single IV dosing

F= ( [AUC] po )/ Dpo
[AUC] iv / D iv

Oral tablet/ IV solution

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15
Q

Relative bioavailability

A

in reference to the same drug administered by an oral solution

F= ( [AUC] solid / Dsolid )
[AUC] solution / D solution

Oral tablet / Oral solution

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16
Q

Factors affecting oral drug absorption

A

Physicochemical factors
- Drug properties

Physiological factors of the GI tract

  • Anatomic features
  • Food factors
  • Disease states and drugs

Dosage form factors

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17
Q

Physiochemical Factors (solubility)

A

Solubility in the GI tract
- Drug ionization

pH changes along the GI tarct
Stomach pH 1-4
Duodenum pH 5-7
Ileum pH 7-8

Henderson-Hasselbach equation

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18
Q

Ionized forms (less lipophilic) is

A

more soluble that the non-ionized form (more lipophilic)

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19
Q

Physiochemical Factors (pH0

A

Acids
% ionization= 1
1+10^ (pKa -pH) *100

Bases
% ionization= 1
1+10^ (pH -pKa) *100

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20
Q

Physiochemical Factors ( Acids and Bases chart

A

Acidic Drug. Basic Drug
Acidic Environment Unionized Ionized
Basic Environment Ionized Unionized

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21
Q

Physiochemical Factors ( Dissolution)

A

Dissolution Rate : Noyes-Whitney equation

  • Dependent on drug solubility

Smaller particle size -? Increased total surface area (S)

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22
Q

Drug Transport

A

Drug must cross the mucous membrane of the epithelial cells of the GI tract

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23
Q

Mechanisms of drug transport

A
  • Paracellular transport
  • Passive diffusion
  • Carrier-mediated transport
  • Efflux
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24
Q

Paracellular Transport

A

passage of molecules between adjacent epithelial cells

  • passes through the intercellular spaces between the cells
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25
Q

Passive diffusion

A

Also called simple diffusion

  • passage or transport of molecules across a cell membrane from higher conc. to a lower conc. without using energy
  • most common method for drugs to cross cell membrane
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26
Q

Carrier-mediated transport

A
  • energy dependent pathway used by small hydrophilic molecules
  • Uniport, Symport and Antiport
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27
Q

Efflux

A

flowing out of a particular substance or particle

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28
Q

Biological membranes

A

Biomolecule lipoid (fat containing) layer attached on both sides to a protein layer

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29
Q

Fick’s first law of diffusion

A

describes the diffusion process under the condition of “steady state”

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30
Q

Steady state

A

when the concentration gradient does not change with time ( not time dependent)

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31
Q

Flux (J)

A

is the amount of material (M) flowing through a unit cross section (S) of a barrier in unit time (t). J is flux, g/ (cm^2 *s)

J = 1 dM
S dt

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32
Q

Ficks first law states that

A

flux (J) is proportional to the concentration gradient (dC/dx)

J = -D dC
dx

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33
Q

dM/dt is

A

the rate of diffusion (g/s)

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34
Q

P is the

A

permeability coefficient (cm/s)

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35
Q

S is the

A

cross section of the barrier (cm^2)

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36
Q

Cd is the

A

the concentration of the donor compartment

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37
Q

D is the

A

Diffusion coefficient ( cm^2 /s)

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38
Q

K is the

A

Partitio coefficient

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39
Q

h is the

A

thickness of the membrane

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40
Q

Cr is the

A

concentration of the receptor compartment

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41
Q

C1 is the

A

concentration within the membrane on the donor compartment side (g/mL)

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42
Q

C2 is the

A

concentration within the membrane on the receptor compartment side (g/mL)

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43
Q

Permeability coefficient (P)

A

P = DK/ h

related to lipophilicity and pH

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44
Q

Low permeability means

A

High solubility

45
Q

High permeability means

A

Low solubility

46
Q

When Diffusion coefficient (D) increases

A

permeability increases

47
Q

When partition coefficient increases

A

permeability increases

48
Q

When the thickness of the membrane (h) decreases

A

permeability increases

49
Q

When permeability increases

A

diffusion rate increases

50
Q

When cross section of the barrier S increases

A

diffusion rate increases

51
Q

When Cd increases

A

diffusion rate increases

52
Q

Facilitated diffusion

A

movement of a solute across the membrane from a region of higher to lower concentration assisted by transmembrane carriers, does not use energy

53
Q

Active transport

A

a movement of solute across the membrane against a concentration gradient assisted by transmembrane carriers (enzymes/other agents)
- requires energy

54
Q

Anatomic and Physiologic considerations

A

Features of the GI tract

  • Stomach
  • Small intestines
  • Large intestines

Gastric pH
Gastric emptying time
Intestinal transit time

55
Q

Gastric pH

A

Fasted -> 1.4 -2.1

Fed -> 4.3 -5.4

56
Q

Low gastric pH means

A
  • Slower dissolution for acids

- Degradation of some drugs (penicillin)

57
Q

Increases(High) in gastric pH

A
  • Achlorhydria (pH is larger than 5.1 in mean and larger than 6.8 in women
  • ## Intake of antacids, H2 receptor inhibitors or Proton Pump Inhibitor
58
Q

Stomach gastric emptying time

A

Half life: 8-15 mins (liquid-fasted)
Half life: 30 min (liquid-small meal)
Half life: 70-130 min (solid meal)
Liquids empties faster than solids

59
Q

Lying on left side will

A

decrease gastric emptying rate

60
Q

Anxiety will

A

increase gastric emptying rate

61
Q

Eating meals with fatty acids, fats, carbs and amino acids will

A

decrease gastric emptying time

Fats and high energy meals dramatically inhibit emptying

62
Q

GI physiology - Small intestines

A

Duodenum, jejunum and ileum
Length: 6.25 m
Diameter: 4-5 cm
pH: 6.8

63
Q

Bile acids are secreted into the_____ and re-absorbed into the _____

A
  1. Duodenum

2. Ileum

64
Q

Food Effect on Absorption

A
  • presence in the GI tract can affect absorption of drugs
  • is not always predictable
  • is more pronounced when the the drug is taken:
    20 mins before a meal, with a meal and within 2 hours after a meal
  • high in calories and fat content are more likely to affect GI physiology
65
Q

Examples of medications that increase absorption

A

Nitrofurantoin, Vitamin A derivatives, Riboflavin, Diazepam

66
Q

Examples of medications that decrease absorption

A 
Warfarin
Ethanol
Penicillins
Atenolol
Erythromycin
67
Q

Examples of medications that have a delayed absorption

A

Aspirin

Acetaminophen

68
Q

The effect of delayed gastric emptying is less for

A
  • solution formulations

- suspension, powders and multiparticulate formulations

69
Q

The effect of delayed gastric emptying is more for

A
  • Tablets that has long disintegration time
  • enteric coated tablets
  • non-disintegrating tablets
70
Q

Effect of disease states on drug absorption

A
  • Intestinal blood flow
    • congestive heart failure (CHF)- reduced
  • Changes in stomach emptying time
    • Long-standing diabetes - decrease
    • HIV-Aids: increase
    • Celiac disease: increase
- Changes in intestinal motility
• Parkinsons disease: slow
• Depression: slow
• HIV-Aids: fast (diarrhea)
• Celiac disease : fast
  • Changes in gastric pH
  • Changes in permeability of the gut wall and normal GI flora
    • Inflammatory bowel disease (Crohn’s)
71
Q

Effects of drugs on absorption

A
  • Decrease acid secretion in stomach
    • Anticholinergic drugs (atropine, scopolamine)
    •Proton pump inhibitors (Omeprazole, Lansoprazole)
  • Reduce GI mobility
    • Tricyclic antidepressant and antipsychotics (Phenothiazines)
    • Anticholinergic (Propantheline bromide)
  • Increase GI motility
    • Metochlopramide
    • Cisapride
72
Q

Dosage forms can have effects on

A

disintegration, dissolution and absorbtion

73
Q

Disintegration

A
  • Immediate release (IR) tablets need to disintegrate in a short period ( <30 min) in stomach
  • Delayed disintegration can result in a delay in onset of drug action (longer lag time)
  • Non-disintegrating tablets
    • Sustained release formulation
74
Q

Special formulations with fast disintegration

A 
Effervescent tablets (Alka Seltzer)
• Fast disintegration
• Release of CO2

Fast disintegrating tablets
• Suitable for pediatric and geriatric patients

75
Q

Effect of dosage forms

A

Difference among oral solutions, suspensions and solid dosage forms in PK parameters

76
Q

Noyes-Whitney equation

A
  • describes rate of dissolution as a function of time
77
Q

Diffusion layer

A

As a drug particle undergoes dissolution, the drug molecules on the surface are the first to enter into the solution, creating a saturated layer of drug solution that envelops the surface of the solid drug particle -> diffusion layer.

78
Q

dc/dt

A

rate of dissolution

79
Q

k

A

dissolution rate constant

80
Q

S

A

Surface area of the dissolving solid

81
Q

Cs

A

Saturation concentration of the drug in the diffusion layer

  • Max solubility of the drug in the solvent
  • Independent of time
82
Q

Ct

A

Concentration of the drug in bulk solution at time t

  • Bulk solution is a homogenous solution
  • Dependent of time
83
Q

The Noyes-Whitney equation cannot

A

describe the condition when the drug particle first encounters the solvent or when the particle is completely dissolved into the solve

84
Q

Strategies to increase dissolution

A
  1. increase the total surface area (S)
  2. increase the solubility of the drug in the diffusion layer (cs)
  3. increase the dissolution rate constant (k)
85
Q

Surface area must be

A

solvent-accessible

86
Q

Increasing surface area may be bad such as:

A
  • Powders may entrap and absorb air; for tablet into which very minute holes are drilled, surface tension may prevent solvent penetration.
  • Fine particles can float on solvent due to surface tension
87
Q

Crystalline

A

definite identifiable shape, ordered and low energy state

88
Q

Amorphous

A

no definite structure, not order, metastable state

89
Q

How does physical forms of the drug affect solubility?

A

Some drugs are essentially inactive when administered in crystalline form, but when they are administered in the amorphous form, absorption from the G.I. tract proceeds rapidly, producing therapeutic response.

90
Q

Polymorphism

A

substance that exist in more than one crystalline form

91
Q

Salt form is

A

generally more soluble

92
Q

State of hydration

A

the anhydrous form of an organic molecule is usually more soluble than the hydrated form

93
Q

You can increase dissolution rate constant k by

A

Increasing the intensity of agitation of the solvent
•Increasing diffusion coefficient: For a given drug, the diffusion coefficient and usually Cs will increase with increasing temperature
•Reducing the viscosity of the solvent (by drinking water)

94
Q

If the dissolution of a given drug particle is rapid or if the drug is administered as a solution,

A

the absorption rate depends mainly on its ability to traverse the membrane barrier

95
Q

If the rate of dissolution for a drug particle is slow,

A

dissolution itself is the rate-limiting step

96
Q

Absorption and BCS classes

A 
class I - no special formulation strategy needed
class II - formulation strategy is very important
class III - formulation effect is limited
97
Q

Class I

A

High solubility

High permeability

98
Q

Class II

A

Low solubility

High permeability

99
Q

Class III

A

High solubility

Low permeability

100
Q

Class IV

A

Low solubility

Low permeability

101
Q

Formulation Strategies that can improve absorption

A
  1. for BCS class II - improve solubility
  2. lipid-based systems - lipid solutions
  3. solid lipid nanoparticles
  4. self emulsifying or self micro emulsifying drug delivery systems (SEDDS or SMEDDS), 5. two cyclosporin formulations: Sandimmune and Neoral
102
Q

Pharmaceutical equivalents

A

drug products that contain identical amounts of the identical active ingredient that is the same salt or ester of the same therapeutic moiety, in same dosage form

103
Q

Pharmaceutical alternatives

A

drug products that contain the identical therapeutic moiety or its precursors but not necessarily in the same amount or dosage form

104
Q

Bioequivalent drug products

A

pharmaceutical equivalents or pharmaceutical alternatives whose rate and extent of absorption do not show a significant difference when administered at the same molar dose of the therapeutic moiety, can be single or multiple dosage forms

105
Q

Therapeutic equivalents

A

pharmaceutical equivalents that provide essentially the same therapeutic effect when administered to the same individuals in the same dosage regimen

106
Q

Counterfeit drug

A

drugs as those sold under a product name without authorization

  • can apply to both brand and generic products where the identity of the source is mislabeled
107
Q

Counterfeit products

A

may include products without the active ingredient, with an insufficient or excessive quantity of the active ingredient, with the wrong active ingredient or fake packaging

108
Q

Health Risks of counterfeit drugs

A
  • if no active ingredients: no treatment benefit
  • if improper or incorrect ingredients:
  • unexpected side effects
  • allergic reactions
  • worsening of medical condition
109
Q

Gray market

A

aka parallel market

- supply channel that is unofficial, unauthorized or unintended by the original manufacturer

PHRM 513 (13 decks)

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