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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
Crystalluria
-formation of CRYSTALS in urine -can be caused by precipitation of drug -at LOW solubility
26
Indinavir
-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
27
Glomerular filtration
-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
28
Distal tubule of glomerulus
-passive absorption of LIPID (UNionized) soluble components -**does NOT reabsorb ionzed compounds = excretes them **
29
Affect of urine pH on amphetamine (BASIC drug) clearance
-half-life of drug increases with pH -low pH: faster -high pH: slower, reabsorbed
30
Amphetamine
-weak base (pKa=9.8) -low pH = more ionized -high pH = unionized
31
Amphetamine (basic drug) at low pH
excreted into urine
32
Amphetamine (basic drug) at high pH
reabsorbed into circulatory system
33
Urine pH
-varies ionization state of drug -can impact rate of clearance -ionzied drugs excreted -unionized drugs absorbed
34
Alter Urine pH by
-sodium bicarbonate -ex: aspirin (acidic drug) overdose: alkanize urine = ionization = more clearance
35
Enteric Coating
-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
Food affects absorption
-affects solubility -coke increases absorption of proton pump inhibitor
37
Salt formation
-formed by acid-base reaction -allows modification of drug: solubility, crystallinity, particle size, bulk density
38
typical pharma salts
-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
Salt forms
-identical drug molecule BUT with new properties -different ionization -different crystal lattice with ionic interactions -way to manipulate solid state properties
40
Salts and melting points
-can be changed by counterion -high temp = crystal = more stable = low solubility
41
Reasons for salt formation
-bioavailability (kinetics) -developability (stability, crystallinity, melting point) -purification (optical resolution) -patent
42
Ksp (solubility product)
-[counterion][A-] -determines solubility of salt -dependent on counterion
43
salt vs Acidic free form
-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
salt vs basic free form
-region 1: salt -region 2: base
45
H2 blockers
-raise pH -bind to cells to inhibit acid production -treat ulcers in stomach -reduce acid in stomach
46
Antacid
-weak base to buffer -neutralizes acid -raise pH
47
Achlorhydria
-condition where stomach cannot produce stomach acid
48
Cocaine math at pH 4.5 (pKa = 8.4)
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
Cocaine math at pH 8 (pKa = 8.4)
8=8.4 +log[B]/[BH+] 10(^-0.4) = [B]/[BH+] (1/(1+0.398)) * 100 = 71.53% = %BH+
50
solubility of acidic drug
-increases with pH
51
solubility of basic drug
-DEcreases with pH
52
Crystalization of acidic drug
-at LOW pH -at LOW solubility
53
Crystalization of basic drug
-at HIGH pH -at LOW solubility
54
Salt formation of acidic drug
-at HIGH pH -at HIGH solubility
55
Salt formation of basic drug
-at LOW pH -at HIGH solubility
56
Rate of clearance of ACIDIC drug
-at HIGH pH -HIGH solubility
57
Rate of clearance of BASIC drug
-at LOW pH -HIGH solubility
58
reabsorption of ACIDIC DRUG
-at LOW pH -at LOW solubility
59
reabsorption of BASIC DRUG
-at HIGH pH -at LOW solubility
60
Effect of counterion on salt
-changes melting point
61
Higher melting point of salt
-less soluble -more crystal -more stable -tighter structure
62
Different salt formulations needed
for different formultions: injection, capsule, etc
63
Solubility of salt
-maximum solubility of drug
64
Solubility equation for weak base
Stot = Sb (1+10^(pKa - pH))
65
partition coefficient
P=Corg/Cwater
66
aqueaous phase
neutral and ionized
67
organic phase
neutral
68
Low partition coefficient
-drug more ionized -favors aqueous
69
High patition coefficient
-drug more neutral -favor organic
70
Absorption of acid
-neutralized in stomach -able to pass through GI barrier -ionized in mucosal cell (pH7)
71
gastric mucosal cell damage caused by
ion trapping by aspirin
72
Absorption of Base
-neutralized in small intestine
73
meth extraction (ionic equilibria)
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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