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Dosage Forms II > Exam 1 Solutions > Flashcards

Exam 1 Solutions Flashcards

1
Q

What are the three different types of liquid dosage forms?

A
  1. solutions
  2. emulsions
  3. suspensions
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2
Q

What is a solution?

A

a homogenous molecular dispersion → like water but has the drug dissolved in it

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3
Q

What is an emulsion?

A

not homogenous → is heterogenous in which liquid is suspended → can be oil in water or water in oil

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4
Q

What is a suspension?

A

solid particles are suspended in liquid → examples are calamine lotion and pepto bismol

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5
Q

What are some examples of solution dosage forms?

A

injectables, nasal solutions, ophthalmic solutions, otic solutions, irrigation solutions, enemas, douches, gargles, mouthwashes, juices

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6
Q

What are some advantages of solution dosage forms?

A
  1. homogenous → there are no problems of content uniformity (since it is essentially one phase because the drug has dissolved and is in solution)
  2. easy to manufacture
  3. good bioavailability → the drug is ready to be absorbed since the drug is already dissolved in the molecular level
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7
Q

What are some disadvantages to solution dosage forms?

A
  1. greater chance for the drug to be exposed to adverse reactions
  2. not all drugs are suitable for solutions (like water soluble drugs)
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8
Q

When can oil be used as a dosage form?

A

can be used for solutions but not for straight IV injections → IM injections are good but oil straight into the bloodstream is bad

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9
Q

What are the components of solution dosage forms?

A
  1. active ingredient (aka the drug)
  2. solvent
  3. buffering agent
  4. preservative
  5. antioxidant, chelating agent
  6. flavor and sweetener
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10
Q

What are some examples of solvents to be used in a solution dosage form?

A

water and vegetable oils (for long acting parenterals)

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11
Q

What is a co-solvent?

A

helps the drug dissolve in addition to the solvent → examples include ethanol, glycerin, propylene glycol

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12
Q

What is the role of a preservative in a solution dosage form?

A

is used for stability issues → usually antimicrobial agents

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13
Q

What is the role of an antioxidant/chelating agent in a solution dosage form?

A

reduces chemical agents

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14
Q

What is the role of a flavor/sweetener in a solution dosage form?

A

used for oral solution products → examples include sorbitol and sucrose

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15
Q

What is the principle behind a buffer?

A
  1. keeps the pH constant
  2. is a solution of a weak acid and a salt of its conjugate base
  3. weak acid can remove added base (OH-)
  4. salt (aka conjugate base) can remove added acid (H+)
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16
Q

What is the Henderson-Hasselbach equation used for?

A

to calculate how much acid and salt we have (pH = pKa + log ([A-]/[HA]))

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17
Q

What is the buffering capacity?

A

the ability of a buffer to resist a change in pH due to added OH- or H+ → the Van Slyke equation which is β = 2.3C*(Ka[H3O+]/(Ka+[H3O+])^2) where C is the total buffer concentration = [Ha] + [A-] → the max is when pH = pKa

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18
Q

When is buffering capacity (β) the greatest (aka at maximum)?

A

when pH = pKa of the buffer

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19
Q

What are some common pharmaceutical buffers?

A

acetic acid, citric acid (has 3 ionization constants), glycine (has 2 ionization constants), phosphoric acid (has 3 ionization constants)

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20
Q

How do you choose a buffer (aka acid and the conjugate base) when given the pH?

A

choose the pair (acid and conjugate base) with a pKa closest to the pH value for the highest buffering capacity

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21
Q

What is the difference between monobasic, dibasic, and tribasic?

A 
monobasic = one negative charge
dibasic = two negative charges
tribasic = three negative charges
22
Q

When given a graph of log k vs pH, how do you know what pH is where the drug is most stable?

A

the dip in the graph (aka the lowest point) is where the drug will be kept and not be degraded the fastest so it’s the pH where the drug would be most stable (since higher k value = higher degradation)

23
Q

What are things to keep in mind with the selection of the pH?

A
  1. use pH that provides the maximum stability for the drug
  2. want to minimize irritation with parenteral, ophthalmic, or nasal dosage forms by adjusting pH to be the same as the pH of the body fluid (like blood, interstitial fluid, or tears at pH of 7.4) → want to match pH of body fluid is possible, but if not, can minimize buffering capacity, minimize volume, and administer slowly
24
Q

Why is it important to match the pH with the pH of body fluid when possible?

A

it is painful for the patient is the pH is quite different than physiological pH → want more on the lower side than higher side since higher pH can cause more pain

25
Q

Why is it important to match the pH with the pH of body fluid when possible?

A

it is painful for the patient is the pH is quite different than physiological pH → want more on the lower side than higher side since higher pH can cause more pain

26
Q

What is the purpose of antimicrobial preservatives?

A
  1. protect the patient from pathogens

2. maintain the potency and stability of the dosage form

27
Q

What is the mechanism of action behind antimicrobial preservatives?

A
  1. they can absorb the bacterial membrane and disrupt it → the membrane is lipophilic and has a net negative surface charge
  2. absorption is due to lipid solubility → alcohols, acids, esters
  3. absorption is due to electrostatic attraction → quaternary ammonium compounds which are cationic and can interact with the negative surface charge of the membrane
28
Q

What is the bacterial content allowed in ampules?

A

has to be sterile, single dose, and no preservative is needed

29
Q

What is the bacterial content allowed in multiple dose vials?

A

has to be sterile, may contain up to 10 doses, need a preservative to kill microorganisms introduced during use

30
Q

What is the bacterial content allowed in ophthalmic solutions?

A

has to be sterile, must contain a preservative if it’s packaged in a multiple dose container

31
Q

What is the bacterial content allowed in oral liquids?

A

doesn’t need to be sterile but shouldn’t contain pathogens (the immune system can manage organisms) → FDA has limited the number of organisms (such as E. coli) to be less than 100 per mL → preservative is needed if packaged in multiple dose packages

32
Q

What is the bacterial content allowed in oral solids?

A

is less likely to carry bacteria than liquid forms so it does not need to be sterile (pathogens don’t like solids since there is no water) → pathogen contamination is still a concern (like Salmonella) so raw materials are tested and the manufacturing facility should be clean

33
Q

What are the characteristics of an ideal preservative?

A
  1. effective in low concentrations against a wide variety of organisms
  2. soluble in formulation → to be available
  3. non-toxic → should only be toxic to bacteria
  4. stable → to keep the drug active
34
Q

What is the main mechanism behind a pharmaceutical preservative?

A

to affect the bacterial membrane of the pathogen but to leave the patient’s cell membranes intact and unharmed

35
Q

What are the classes of pharmaceutical preservatives?

A
  1. alcohols
  2. acids
  3. esters of p-hydroxybenzoic acid (parabens)
  4. quaternary ammonium compounds
36
Q

What are some examples of alcohol preservatives?

A
  1. ethanol → required to be greater than 15%, limited to oral products, can be lost due to volatility (since concentration can drop as it evaporates once it’s opened and closed over time)
  2. benzyl alcohol → has local anesthetic action, burning taste so not used orally, is water soluble and is stable over a wide pH range so it is widely used in parenterals
  3. chlorobutanol → campor like odor and taste so not used orally, used in parenterals and ophthalmics, is volatile (like ethanol) in which its concentration can drop as it is lost through rubber stoppers and plastic containers
37
Q

What is important about acid pharmaceutical preservatives?

A
  1. is only active in unionized (lipid soluble) form since if it is ionized/charged, it won’t work
  2. needs to be fully protonated → the pH needs to be below the pKa value
38
Q

What are some examples of acid pharmaceutical preservatives?

A
  1. benzoic acid (pKa is 4.2) → used in oral products (active in pH below 4.2)
  2. sorbic acid (pKa is 4.8) → used in oral products, is excellent for molds and yeasts (effective at pH below 4.8)
39
Q

What’s important to know about esters of p-hydroxybenzoic acid (parabens) as pharmaceutical preservatives?

A
  1. widely used orally → not ionized but hydrolyzed rapidly at pH values above 7 (aka loses its activity at pH above 7), anesthetizes the tongue
  2. low solubility is a problem
  3. can cause skin sensitization when used in dermatological products
40
Q

What are some examples of parabens as pharmaceutical preservatives?

A

the most lipophilic ones (propyl paraben and butyl paraben) are best against mold and yeast while the least lipophilic ones (methyl paraben and ethyl paraben) are best against bacteria

41
Q

What is important to know about quaternary ammonium compounds?

A
  1. widely used in ophthalmics and is very water soluble and fast killing
  2. there may be some incompatibility issues due to positive charge → is okay to use in small amounts like eyedrops but no systemic use (aka no injectables) because of the charge that can damage proteins and membranes
42
Q

What are some examples of quaternary ammonium compounds as pharmaceutical preservatives?

A
  1. benzalkonium chloride (Zephirin)

2. cetyltrimethylammonium chloride (Cepryn)

43
Q

What are the factors that affect preservative action?

A
  1. pH → only the unionized (aka fully protonated when pH is below pKa) species of weak acids are effective → have to add more total weak acid when pH is above pKa in order to have effective concentration of unionized species
  2. complex formation → only the uncomplexed (free) preservative is active
  3. absorption by solids → only the unabsorbed preservative is active
  4. chemical stability → consider the shelf life
44
Q

What are antioxidants?

A

they are used as protectants of liquid products

45
Q

Why are antioxidants used?

A

drug substances are less stable in aqueous media than solid dosage forms → acid base reactions, acid/base catalysis, oxidation, or reduction may occur from ingredient-ingredient interactions or container-product interactions

46
Q

What is the main degradation pathway of pharmaceuticals?

A

oxidation! (examples include vitamins, essential oils, fats, and oils)

47
Q

What are the two types of oxidation?

A
  1. auto-oxidation → an automatic reaction with oxygen without drastic external interference in which the molecule is turned to something else
  2. can be initiated/accelerated by heat, light, peroxides, metals (copper, iron) to make free radicals that react with oxygen to create more free radicals
48
Q

What are the three types of antioxidants?

A
  1. free radical scavengers
  2. reducing agents
  3. chelating agents
49
Q

What are free radical scavengers?

A

they retard/delay oxidation by rapidly reacting with free radicals (aka removes them) → examples include

  1. propyl, octyl, dodecyl esters of gallic acid
  2. butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT)
  3. tocopherols, Vitamin E
50
Q

What are reducing agents?

A

react with oxygen before the active compound can (consumes oxygen) → has lower redox potentials than the drug so it’s more readily oxidized → examples:

  1. sodium bisulfite
  2. ascorbic acid
  3. thiols
51
Q

What are chelating agents?

A

they don’t do anything regarding free radicals or oxygen, but they get rid of metals → considered antioxidant synergists and have little antioxidant effect themselves but removes trace metals → examples:

  1. citric acid
  2. EDTA (ethylenediaminetetraacetic acid)

Dosage Forms II (20 decks)

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