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Pharmaceutics > Test 2 Content > Flashcards

Test 2 Content Flashcards

1
Q

Buffer systems

A

-minimize the changes in a solution’s pH
-if there is a sudden addition of acid or base, the buffer will maintain the pH

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2
Q

What are buffers composed of?

A

-a weak acid and the salt of the acid (i.e. it’s conjugate base)
-a weak base and the salt of the base (i.e. it’s conjugate acid)

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3
Q

Most pharmaceutical buffers are made of….?

A

a weak acid and the salt of the acid (i.e. conjugate base)

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4
Q

Buffering region works best within how many pH units of pKa?

A

Buffering region works best within 1 pH unit of pKa

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5
Q

Polyprotic acids

A

Acids that are capable of losing more than a single proton per molecule (protons lost in stages - one at a time)

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6
Q

When are buffers used?

A

-When you need to alter the pH or try to keep the pH of a solution or a dosage form in a particular range to prevent drug degradation
-to help minimize irritation of tissues

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7
Q

Types of dosage forms that commonly contain buffers to minimize irritation/stinging

A

-injection/infusion
-ophthalmic solutions
-nasal solutions

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8
Q

acidifying agents

A

added to make dosage form more acidic; can be without the addition of buffers

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9
Q

alkalizing agents

A

added to make dosage form more basic

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10
Q

How to select a buffer:

A

-consider route of administration
-buffers often prepared to be isotonic solutions
-select a buffer pair with a pKa approx. equal to (+/- 1 pH of the pKa) to the pH you need to use
-calculate from the Henderson Hasselbach equation what ratio of the buffer pair you need to add to get the desired pH
-may need to adjust the pH of the buffer with an acidifying or alkalizing agent in order to arrive at the exact pH desired

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11
Q

Henderon-Hasselbalch

A

allows for the calculation of the concentration of constituents necessary to make a buffer a certain pH; the pH of the buffer will be determined by the pKa and the ratio of weak acid to conjugate base

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12
Q

Buffer capacity

A

-a measure of the resistance to a change in pH when an acid or base is added to the solution
-expressed as the amount of strong acid or base, in gram-equivalents, that must be added to 1 liter of the solution to change its pH by one unit

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13
Q

Buffer capacity depends on….?

A

-ratio of salt to the acid or base (optimal ratio = 1:1)
-total buffer concentration (takes more acid or base to deplete 0.5M buffer than 0.05M)

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14
Q

Buffer capacity requirements

A

-must be low enough to allow for rapid adjustment upon administration to physiological pH (ophthalmic and parenteral products)
-must be large enough to maintain the product pH during shelf-life

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15
Q

Disintegration time

A

-the time required for the tablet to break down into particles
-particles can be measured how the particles pass through a sieve while agitated in a specified fluid (defined by the USP)

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16
Q

Factors that affect disintegration

A

-dosage form formulation (delayed release, extended release)
-tablet hardness
-use of disintegrants within formulation

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17
Q

Disintegrants

A

-swell upon contact with water
-break solid dosage form into smaller granules
-many are starch and cellulose derivatives
-promotes disintegration

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18
Q

Dissolution

A

-the transfer of molecules from solid state into solutions

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19
Q

Dissolution rate

A

-how quickly the solubility limit is reached
-measured in a dissolution apparatus defined by the USP

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20
Q

solution

A

a homogeneous mixture of the molecules of one substance with another (homogenous down to the molecular level)

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21
Q

Noyes-Whitney equation

A

-molecules of the dissolving particle move into solution forming a high concentration at the surface of the particle (Cs)
-molecules diffuse from the saturating film (high concentration) to the bulk fluid (low concentration)

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22
Q

D in Noyes-Whitney equation and how it affects dissolution rate

A

-Diffusion coefficient (how quickly the solute/drug molecule will diffuse through the solvent)
-viscosity of dissolution medium (this can be decreased by drinking water)
(the viscosity of the solvent is inversely proportional to the diffusion coefficient)

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23
Q

A in Noyes-Whitney equation and how it affects dissolution rate

A

-Surface area of the particle (how large the particle is “macro or micro”)
-particle size (the smaller the particle size, the larger the surface area and the higher the dissolution rate)

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24
Q

Cs in Noyes-Whitney equation and how it affects dissolution rate

A

-The concentration of drug in the saturating film equal to the solubility of the drug
-Increasing solubility increases dissolution rate
-molecular structure of solute
-pH of dissolution medium
-temperature

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25
Q

h in Noyes-Whitney equation and how it affects dissolution rate

A

-The thickness of the diffusion layer
-agitation of dissolution medium will change the thickness of this layer by making it smaller, thus increasing the dissolution rate (highly controlled in in vitro strudies)
-h is inversely proportional to the dissolution rate

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26
Q

C in Noyes-Whitney equation and how it affects dissolution rate

A

-the concentration of drug in bulk solvent
-sink conditions and the volume of the bulk fluid
-increasing the volume of the bulk fluid increases the dissolution rate (can be done by drinking water)

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27
Q

Solubility

A

The extent to which a drug (solute) dissolve in a given solvent at a given temperature
-aka equilibrium solubility

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28
Q

Apparent solubility

A

The observed solubility of a solute in a solvent system; might be higher or lower than the equilibrium solubility

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29
Q

Factors that influence apparent solubility

A

-physiochemical properties: surface area, particle size, crystal form
-properties of the solubility media: pH, polarity, added surfactants/co-solvents, temperature

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30
Q

Supersaturated solutions

A

Solutions with a concentration of solute greater than that attained under normal circumstances
-these are unstable because they will move back to true solubility resulting in precipitation

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31
Q

Miscibility

A

When both the solute and the solvent are liquids

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32
Q

Immiscible

A

liquids that will not produce a homogenous solution in any proportion (e.g. oil and water)

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33
Q

Miscible

A

liquids that form a homogenous system when mixed in any proportion (e.g. water and ethanol)

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34
Q

Miscible in certain proportions

A

e.g. water and chloroform
Its miscibility depends on the ratio of solvents

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35
Q

How is solubility expressed?

A

-as a weight in a specified volume of solvent (aqueous or other solvent) at a specific temperature. e.g. mg/L, g/L, mg/mL
-sometimes expressed as how much solvent it takes to dissolve 1 gram of solute (ratio strength such as 1g in 50mL)

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36
Q

Difference between solubility and concentration?

A

-solubility: weight in specified volumes of solvent
-concentration: weight in specified volume of solution

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37
Q

What type of drugs don’t need to have as good of solubility?

A

Drugs with high potency because a small amount can have its intended effect

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38
Q

FDA definition of solubility

A

-high potency drugs don’t need to have good solubility
-looks at solubility in a glass of water (approx 250mL)
-takes into account pH-dependent solubility (oral drugs must have sufficient solubility over the entire pH range of 1 to 7.5)

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39
Q

High solubility (FDA definition)

A

highest dose strength is soluble in less than or equal to 250mL of water over the entire pH range of 1 to 7.5

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40
Q

Low solubility (FDA definition)

A

Highest dose strength is not soluble in less than or equal to 250mL of water over a pH range of 1 to 7.5

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41
Q

Factors that contribute to water solubility

A

-polar covalent bonds
-hydrogen bond donors and acceptors
-ionizable functional groups

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42
Q

Factors that detract from water solubility

A

Nonpolar functional groups

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43
Q

How to alter the apparent solubility of a drug

A

-change the temperature
-alter the solid state properties (crystalline form vs. amorphous form); polymorphisms
-modify the pH of dissolution medium
-make a salt form
-use a solvent with a different polarity
-formulate with solubilizing agents (sufactants, cyclodextrins)
-make a drug derivative (prodrug)
-use of water-immiscible solvents (oils)

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44
Q

Amorphous form vs. crystalline form

A

Amorphous form of a drug will have better solubility than crystalline form

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45
Q

Polymorphs and what type will have better solubility

A

-polymorphs of the same drug will have different dissolution rates
-metastable polymorphs will have a better solubility than the ground state polymorph

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46
Q

Hydrates vs. anhydrous drug solubility

A

-anhydrous form of a drug will often have better solubility and a faster dissolution rate than the hydrate form
-depends on the drug and if the water incorporated into the crystalline structure strengthens or weakens the crystalline lattice

47
Q

pH-dependent solubility

A

-a basic drug will be more soluble at an acidic pH
-an acidic drug will be more soluble at a basic pH
a drug will be more soluble in water when it is ionized

48
Q

Is dissolution usually an endothermic or exothermic process?

A

Endothermic (heat is absorbed when dissolution occurs); raising temperature will increase solubility

49
Q

Cosolvents

A

a second solvent that is added to a solution (usually water) that is water miscible that is used to increase the solubility of poorly water soluble drugs

50
Q

Examples of cosolvents

A

-water
-dimethyl sulphoxide (DMSO)
-glycerine
-propylene glycol
-ethanol
-isopropanol
-polyethylene glycol 400 (PEG 400)

51
Q

When are cosolvents often used?

A

Often used for neutral drugs where solubility cannot be altered by adjusting pH

52
Q

Like dissolves like

A

Increased structural similarity or polarity between solute and solvent leads to increased solubility

53
Q

High dielectric constants correspond to….?

A

High polarity

54
Q

If wanting to dissolve a nonpolar hydrophobic drug, use a solvent with….

A

low dielectric constant

55
Q

If wanting to dissolve a polar hydrophilic drug, use a solvent with….

A

high dielectric constant

56
Q

Disadvantages of cosolvents

A

-oral mixtures are not palatable
-not comfortable when injected or applied to mucous membrane
-often very viscous
-may precipitate when mixed with aqueous injectables
-may cause precipitation of drug after administration
-toxicity of cosolvents via certain routes

57
Q

Dosage forms that always contain cosolvents

A

-Elixirs
-Tinctures

58
Q

Elixirs

A

clear, sweetened/flavored solutions that contain both water and alcohol
-used for oral admin

59
Q

Tinctures

A

solutions prepared from vegetable or chemical substances
-made entirely of alcohol or of a water and alcohol mix
-contain high percentages of alcohol (15-80%)

60
Q

Surfactants

A

amphipathic molecules that align themselves at surfaces to remove the hydrophobic portion from water. aka surface-active agents

61
Q

4 types of surfactants

A
  1. nonionic
  2. anionic
  3. cationic
  4. zwitterionic
62
Q

Nonionic surfactant

A

Have a water-soluble group that is not charged

63
Q

Anionic surfactant

A

carries a negative charge

64
Q

Cationic surfactants

A

carries a positive charge

65
Q

Zwitterionic surfactant

A

carries both a positive and negative charge

66
Q

Surfactants can act as the following:

A

-solubilizing agents
-wetting agents
-flocculating agents
-emulsifying agents
-dispersing agents
-skin penetration enhancers

67
Q

What happens when concentration of the surfactant is above the critical micelle concentration (CMC)?

A

Surfactants will form micelles

68
Q

Disadvantages of surfactants

A

-can disrupt normal cell membranes causing toxicity/irritation
-some can only be used for certain routes of administration
-may cause precipitation of drug due to dilution below CMC

69
Q

Cyclodextrins

A

another type of solubilizing agent used to improve drug solubility
-consists of cyclic oligosaccharides that contain a hydrophobic interior/cavity and a hydrophilic outer surface
-contain 6 or more (a-1,4) line a-D-glucopyranose units
-enhances solubility of poorly soluble compounds

70
Q

Passive Diffusion

A

Molecules diffuse from a region of high concentration to an area of low concentration until an equilibrium is reached (no energy is needed)

71
Q

What are the two types of passive diffusion?

A

Transcellular and paracellular

72
Q

Transcellular

A

Passive diffusion into and out of the the cell

73
Q

Paracellular diffusion

A

Passive diffusion between cells

74
Q

How is permeability defined?

A

The distance traveled by a drug through the membrane per unit time (measured as a velocity - distance/time)

75
Q

How are blood capillaries affected by permeability?

A

-very permeable
-permeability is independent of lipophilicity, charge and size

76
Q

How is nasal mucosa affected by permeability?

A

affected by lipophilicity, charge, and size but more porous than GI tract

77
Q

How are buccal mucosa, GI tract and lungs affected by permeability?

A

affected by lipophilicity, charge, and size

78
Q

How is blood brain barrier affected by permeability?

A

highly affected by lipophilicity, charge and size

79
Q

Arrange the permeability of cell types in order from excellent permeability to poor permeability

A

simple squamous –> simple columnar —> stratified squamous (non-keratinized) –> stratified squamous (keratinized)

80
Q

Three types of Cytosis

A

pinocytosis, phagocytosis, recepter-mediated cytosis

81
Q

Cytosis

A

Used by cells to engulf larger macromolecules and particles

82
Q

Pinocytosis

A

cells endocytose water/fluids

83
Q

Phagocytosis

A

endocytose large particles or macromolecules

84
Q

Receptor-mediated cytosis

A

endocytosis that is inititated by binding of a ligand to a cell-surface receptor

85
Q

Apical side

A

faces inward towards the lumen

86
Q

Basolateral side

A

faces underlying connective tissue

87
Q

Facilitated diffusion

A

-does not require energy
-drugs move along a concentration gradient
-allows charged and/or polar molecules to cross plasma membrance

88
Q

Two types of facilitated diffusion

A
  1. channel-mediated diffusion (pores)
  2. carrier-mediated diffusion (transporters)
89
Q

Channel-mediated diffusion (pores)

A

-channel is either open or closed
-allow the diffusion of ions, water, small molecules

90
Q

Carrier-mediated diffusion (transporters)

A

-bind specific substrates, undergo conformational change to transport across the membrane
-can be passive or active (if active, no longer considered facilitated diffusion)

91
Q

Active transport

A

-require input of energy
-actively move substances across membranes against the concentration gradient

92
Q

Two types of active transport

A
  1. Primary
  2. Secondary
93
Q

Primary active transport

A

active transport is driven by ATP hydrolysis

94
Q

Secondary active transport

A

-active transport is driven by ion gradients
-uphill transfer of one solute is coupled to the downhill transfer of a second solute (called co-transporters)

95
Q

Two types of co-transporters in secondary active transport

A
  1. Symporter
  2. Antiporter
96
Q

Carrier-mediated diffusion follows which form of kinetics?

A

-Michaelis-Menten kinetics making it a saturable process

97
Q

Transporters are most concerned about transporters in….

A

-intestinal epithelia
-hepatocytes
-kidney proximal tubules
-brain capillary endothelial cells

98
Q

Transporter types

A

uptake and efflux

99
Q

Transporters

A

essential for the absorption, distribution and elimination of many drugs

100
Q

Superfamilies of transporters

A
  1. Solute carrier (SLC)
  2. ATP binding cassette (ABC)
101
Q

Solute Carrier Family

A

-facilitated transporters, symporters, or antiporters;
-primarily uptake transporters
-OATP (anion transporting polypeptide), OAT (anion transporter), OCT (cation transporter)

102
Q

ATP Binding Cassette (ABC)

A

-primary active transport
-efflux transporter
-p-glycoprotein (MDR1), MRP2-6, BCRP

103
Q

Three physiological properties that affect permeability

A

size, lipophilicity, charge (degree of ionization)

104
Q

Lapinski’s Rule of Five

A

Compounds likely to have good absorption and permeation if they have:
1. </= 5 hydrogen-bond donors
2. </=10 hydrogen-bond acceptors
3. Molecular weight </= 500 g/mol
4. Log P</= 5

105
Q

rate-limiting step

A

slowest step in a series of kinetic processes

106
Q

Dissolution rate limited

A

drugs with poor water solubility and poor dissolution

107
Q

permeability rate limited

A

permeation across cell membrane is rate-limiting

108
Q

How to improve solubility/absorption in dissolution rate limited drugs

A

alter pH or add a cosolvent

109
Q

How to improve absorption in permeability rate limited drugs

A

form a prodrug

110
Q

Biopharmaceutics Classification System (BCS)

A

classifies drugs based on their solubility and membrane permeability
-four different classes
-used to predict drug absorption and potential drug candidates

111
Q

Biopharmaceutics Drug Disposition Classification System (BDDCS)

A

classifies drugs based on their solubility and metabolism
-can also be used to predict drug-drug interactions and food effects in vivo

112
Q

Bioprecursor prodrug

A

type of drug that does not contain a promoiety
-still considered a prodrug because the structure is modified by enzymatic action to form the active drug

113
Q

Reasons to make prodrugs

A

-improve solubility or permeability
-decrease first pass loss
-improve oral absorption
-protect against chemical stability problems
-mask taste/odor of drug
-minimize toxicity or local irritation
-enable site-specific delivery
-provide extended release of drug

114
Q
A

Pharmaceutics (7 decks)

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