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828 Dosage > Drugs in Solution pH and Solubility > Flashcards

Drugs in Solution pH and Solubility Flashcards

1
Q

weak electrolytes

A

-many drugs (slightly more are bases than acids)
-partially ionized
-degree of ionization is pH dependent

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2
Q

effect of change in pH on weak electrolytes

A

-large change in ratio of ionized to unionized
-affect solubility, dissolution rate, partition coeficient

= change in Absorption, distribution, elimination

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3
Q

pH difference between vein and artery

A

-vein is slightly more acidic than artery by 0.01
-due to carbonic acid in deoxygenated blood

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4
Q

clinically relevant questions

A

-Is absorption of a drug affected by H2 blockers, proton pump inhibitors, antacids, or achlorhydria?
-pH affect on solubility
-precipitation of drug
-effect of alkalization of urine

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5
Q

groups with resonance

A

-more acidic
-lower pKa

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6
Q

pKa of amine

A

-9-11
-actually pKa of ammonium salt is taken instead (R-NH3+ –> R-NH2)

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7
Q

common acidic functional groups

A

-carboxylic acid (-COOH) 5
-sulfonic acid (-SO3H) -7
-thiol (-SH)
-phenols (-OH on ringe)
-imide (NH between 2 ketones) 7

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8
Q

common basic functional groups

A

-amine (-NH)
-imidazoles (pentagon)
-anilines (-NH2 off ring)
-pyridines (-N in ring)

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9
Q

non-ionizable functional groups

A

-alchol
-aldehydes
-ketones
-amides (-NH2 off of C=O)
-esters
-ethers

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10
Q

Proton donor

A

acid
-protonated

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11
Q

proton acceptor

A

base
-deprotonated

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12
Q

Lowry-Bronsted

A

HA + H2O <-> A- + H3O+
acid base base acid

B+ H2O <-> BH+ + OH-
base acid acid base

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13
Q

Ka

A

-dissociation constant
=[H+][A-]/[HA]

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14
Q

henderson-hasselbach

A

pH = pKa + log [A-]/[HA]

[B]/[BH+] for base

base/acid
-plot is S shape for acid
-Z for base

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15
Q

high pKa

A

stronger base

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16
Q

pKa

A

-pH where 50% of compound ionized
- -logKa

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17
Q

Salt

A

-precipitation stops indefinite solubility
-at high pH for acidic drugs
-at low pH for basic drugs

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18
Q

solubility

A

-dependent on pH
-sum of [ionized] + [unionized]

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19
Q

Which form of the drug is MORE soluble

A

IONIZED

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20
Q

Which form of the drug is LESS soluble

A

UNionized

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21
Q

physiological pH range

A

1-8.5

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22
Q

Solubility equation

A

Stot = SHA(1+10^(pH-pKa))

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23
Q

solubility of acidic drug when pH &laquo_space;pKa

A

-nearly independent of pH

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24
Q

Crystals

A

-opposite of salt
-neutral form
-at LOW pH for acidic drug
-at HIGH pH for basic drug

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25
Q

Crystalluria

A

-formation of CRYSTALS in urine
-can be caused by precipitation of drug
-at LOW solubility

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26
Q

Indinavir

A

-weak base
-HIV protease inhbitor
-excreted by kidney
=kidney stones, renal failure etc due to precipitation in the urinary tract (low pH=very soluble)

-crystals formed at HIGH pH

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27
Q

Glomerular filtration

A

-drugs with MW LESS than 20,000 pass irrespective of charge
-some drugs actively secreted into proximal tubule
-passive absorption of LIPID (UNionized) soluble components occurs in DISTAL tubule

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28
Q

Distal tubule of glomerulus

A

-passive absorption of LIPID (UNionized) soluble components
-**does NOT reabsorb ionzed compounds = excretes them **

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29
Q

Affect of urine pH on amphetamine (BASIC drug) clearance

A

-half-life of drug increases with pH

-low pH: faster

-high pH: slower, reabsorbed

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30
Q

Amphetamine

A

-weak base (pKa=9.8)
-low pH = more ionized
-high pH = unionized

31
Q

Amphetamine (basic drug) at low pH

A

excreted into urine

32
Q

Amphetamine (basic drug) at high pH

A

reabsorbed into circulatory system

33
Q

Urine pH

A

-varies ionization state of drug
-can impact rate of clearance
-ionzied drugs excreted
-unionized drugs absorbed

34
Q

Alter Urine pH by

A

-sodium bicarbonate
-ex: aspirin (acidic drug) overdose: alkanize urine = ionization = more clearance

35
Q

Enteric Coating

A

-delays release until higher pH
-protects drug through stomach pH
-dissolves in small intestine to release drug there
-pKa 5 ideal (between stomach pH and small intestine pH) = Carboxylic acid

36
Q

Food affects absorption

A

-affects solubility
-coke increases absorption of proton pump inhibitor

37
Q

Salt formation

A

-formed by acid-base reaction
-allows modification of drug: solubility, crystallinity, particle size, bulk density

38
Q

typical pharma salts

A

-acid + basic counterion
-base + acidic counterion
(pKa difference should be 2-3 units)
-strong + weak
-weak + weak
-50% of drugs
-sodium, calcium, magnesium etc

39
Q

Salt forms

A

-identical drug molecule BUT with new properties
-different ionization
-different crystal lattice with ionic interactions
-way to manipulate solid state properties

40
Q

Salts and melting points

A

-can be changed by counterion
-high temp = crystal = more stable = low solubility

41
Q

Reasons for salt formation

A

-bioavailability (kinetics)
-developability (stability, crystallinity, melting point)
-purification (optical resolution)
-patent

42
Q

Ksp (solubility product)

A

-[counterion][A-]
-determines solubility of salt
-dependent on counterion

43
Q

salt vs Acidic free form

A

-region 1: solubility depends on acid
until pH max
-region 2: AFTER PH MAX solubility depends on salt (max solubility is solubility of the salt)

44
Q

salt vs basic free form

A

-region 1: salt
-region 2: base

45
Q

H2 blockers

A

-raise pH
-bind to cells to inhibit acid production
-treat ulcers in stomach
-reduce acid in stomach

46
Q

Antacid

A

-weak base to buffer
-neutralizes acid
-raise pH

47
Q

Achlorhydria

A

-condition where stomach cannot produce stomach acid

48
Q

Cocaine math at pH 4.5 (pKa = 8.4)

A

4.5 = 8.4 + log[B]/[BH+]
1.259 x 10^-4 = [B]/[BH+]
1/(1+1.259 x 10^-4) * 100 = %BH+ = 99.99%

49
Q

Cocaine math at pH 8 (pKa = 8.4)

A

8=8.4 +log[B]/[BH+]
10(^-0.4) = [B]/[BH+]
(1/(1+0.398)) * 100 = 71.53% = %BH+

50
Q

solubility of acidic drug

A

-increases with pH

51
Q

solubility of basic drug

A

-DEcreases with pH

52
Q

Crystalization of acidic drug

A

-at LOW pH
-at LOW solubility

53
Q

Crystalization of basic drug

A

-at HIGH pH
-at LOW solubility

54
Q

Salt formation of acidic drug

A

-at HIGH pH
-at HIGH solubility

55
Q

Salt formation of basic drug

A

-at LOW pH
-at HIGH solubility

56
Q

Rate of clearance of ACIDIC drug

A

-at HIGH pH
-HIGH solubility

57
Q

Rate of clearance of BASIC drug

A

-at LOW pH
-HIGH solubility

58
Q

reabsorption of ACIDIC DRUG

A

-at LOW pH
-at LOW solubility

59
Q

reabsorption of BASIC DRUG

A

-at HIGH pH
-at LOW solubility

60
Q

Effect of counterion on salt

A

-changes melting point

61
Q

Higher melting point of salt

A

-less soluble
-more crystal
-more stable
-tighter structure

62
Q

Different salt formulations needed

A

for different formultions: injection, capsule, etc

63
Q

Solubility of salt

A

-maximum solubility of drug

64
Q

Solubility equation for weak base

A

Stot = Sb (1+10^(pKa - pH))

65
Q

partition coefficient

A

P=Corg/Cwater

66
Q

aqueaous phase

A

neutral and ionized

67
Q

organic phase

68
Q

Low partition coefficient

A

-drug more ionized
-favors aqueous

69
Q

High patition coefficient

A

-drug more neutral
-favor organic

70
Q

Absorption of acid

A

-neutralized in stomach
-able to pass through GI barrier
-ionized in mucosal cell (pH7)

71
Q

gastric mucosal cell damage caused by

A

ion trapping by aspirin

72
Q

Absorption of Base

A

-neutralized in small intestine

73
Q

meth extraction (ionic equilibria)

A
  1. add to water
    -adjust pH to 1 (with HCl)
    -extract
    =ionized sudafed in AQ phase
  2. adjust pH to 12 (NaOH)
    -extract
    =sudafed as free base in organic phase

828 Dosage (27 decks)

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