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MEP2 Pharmacology Midterm > Lecture 3 - Sept 23 > Flashcards

Lecture 3 - Sept 23 Flashcards

1
Q

ABCD skip

A

generally alpha constricts and beta dilates

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2
Q

Absorption

A

-once a drug gets in body, how does it get into bloodstream/circulation (across skin, mucous membranes, across GI wall)
-absorption is affected by:
-drug solubility, characteristic of the membrane to be crossed, size of drug molecule, affinity of the drug for other molecules

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3
Q

slide 5 absoprtion chart

A
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4
Q

absorption and passive dissuion

A

-most drugs cross membranes by passive diffusion (down concentration gradient) - the rate of absorption is proportional to the drug concentration

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5
Q

passive diffusion in absorption

A
  1. aqueous diffusion
    -drug passes through aqueous pores in biomembranes
  2. lipid diffusion
    -if a drug is hydrophobic (lipophilic) and uncharged it dissolves in lipid membrane
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6
Q

factors affecting absorption

A
  1. drug solubility
    -water soluble = charged/ionized, lipid soluble = uncharged/unionized
    -drug ionization depends on if drug is acid or base and pH of solution
  2. characteristics of membrane to be crossed
  3. size of drug
  4. affinity if drug
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7
Q

acids and bases

A

-acid = produces hydrogen (H+) when dissolved in water
-most acids in biological systems are weak acids

-base = produces a hydroxyl (OH) when dissovled in water
-bases are H+ acceptors
usually weak bases

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8
Q

pH scale

A

-pH measures H+ concentration
-pH is negative scale (low pH = lots of H+)
-pH is a log scale so difference of pH 5 and pH 6 is 10 times

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9
Q

drug solubility

A

-virtually all drugs are weak acids or bases
-only non-ionized (no charge) form of drugs is soluble in lipid membrane and can get across
-weak acids (HA) donate a proton (H+) to form an anion (A-), whereas weak bases (B) acccept a proton to from cations (HB+)

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10
Q

slide 11 weak acid and bases chart

A
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11
Q

slide 12

A
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12
Q

Ka formula and defintion

A

-Ka = tendency of the acid to dissocidate

Ka = [A-] [H+] / [HA]
Ka = [anion] [protons] / [undisociated acid]

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13
Q

Ka continued

A

-strong acid has a high Ka because it is almost all dissociated

-weak acid has a small Ka because it is almost all undisoccaited

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14
Q

Ka and pKa

A

-pKa = negative log of Ka
-the listed pKa for a substance represents the pH at which 50% of it is disscosciated and 50% is undiscciated (Ka =1)

-drug with a high Ka (strong acid) has a low pKa

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15
Q

-henderson hasselbalch equation
(pH = pKa + log [A-/HA]

A

-henderson hasselbalch equation (pH = pKa + log [A-/HA]
-this equation tells you how much of A- and HA you have at certain pH as long as you know pKa of a drug
-since pKa is a constant for each drug, the equation says the amount of ionised drug (A-) and lipophilic drug (HA) vaties with pH

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16
Q

will an acidic drug be absorbed in the stomach

A

-pH is low in stomach, ratio between A- and HA will be low = there will be lots of HA and little A-
-HA is non-ionized and lipophilic so it coild be easily absorbed into bloodstream from stomach

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17
Q

Drug solubility rules (acidic drugs)

A
  1. acidic drugs become more non-ionized at acidic pH
    -an acid in an acidic solution will not ionize
  2. acidic drugs become ionized at basic pH
    -an acid in a basic solution will ionize
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18
Q

Drug solubulty rules: basic drugs

A
  1. basic drugs become more non-ionized at basic pH
    -a base in a basic solution will not ionize
  2. basic drugs become more ionized at acidic pH
    -a base in an acid solution will ionize
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19
Q

hydrophilic = ionized

A

-hydrophilic = ionized molecule (charged)
-hydrophilc molecules dissolve in water

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20
Q

lipophilc = non-ionized

A

-lipophilic - nonionized molecules (not charged)
-lipophilic molecules pentreate membranes

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21
Q

slide 21-22 (vid explain in textbook?)

A
22
Q

drug solubility summary

A

3 things to know if drug majority is lipophilic or hydrophilic:

  1. whether drug is an acid or bas
  2. the pKa of drug (pH at which # non-ionized molecules = # non-ionized molecules)
  3. the pH into which the drug is being placed
23
Q

pKa = pH at which 50% ionized and 50% unionized

A

slide 24

24
Q

slide 27-30 practice problems

A
25
Q

ion trapping

A

-miconazole/monistat is a drug as antifungal in vaginal yeast infection
-the drug is a base that has a pka of 6.7
-in premenopausal women vaginal ph = 4.5
-drug will be ionized at 3.5-4.5 pH
-if it is ionized it cannot pentrate vainal wall and leave vaginal lumen
-ion trpaping = non-ionized drug enters are of different pH and becomes ionized and cannot leavve

26
Q

slide 32

A
27
Q

slide 33

A
28
Q

charcateristics of membranes

A

Drug has to move across cell membranes:
-phospholipid bilayers → lipid like drugs dissolve in the lipid membrane
-aqueous pores exist in plasma membrane → they are usually too small for drugs
-some drugs use carrier proteins to circumvent the cell membrane (these carrier prtoeins carrry out active transport agaisnt conc gradient or facialtate passibe transport where no energy is required)

29
Q

types of membranes

A

-mucous membranes (vaginal, oral, lung ex)
-cutaneous membrane (drugs given transdermally must travel across skin)
-drugs given IV must pass through capillary memrbane to leave the blood

30
Q

size of drugs

A

-small mleucles pass through membranes easier than large ones

-vancomycin (antimicrobial) is too large to be absrobed in the gut
-given PO for GI issues, IV for systemic

31
Q

stearic hindrance

A

-when some molecules are so complex in shaoe that they cannot be oriented in a way to pentrate the membrane

32
Q

affinity for other molecules

A

-gastric destruction before absorption
-methicillin cannot be given PO because it is poorly absorbed and destroyed by stomach acid

-oral penicillins tend to bind to food so should be given 30 min before or 2 hours after meals

-if drug is not well absorbed then its bioavailability is low (amount of drug that arrives at target organ)

33
Q

distribution

A

movement of drug from site of administration to site of action
(mostly dependent on blood)

34
Q

water solubility and distribution

A

-water solubility = key to drugs solubilty in blood
-polar/charged molecules dissolve in blood –> rapid distribution
-acid drugs will be inozed in blood but dont pentrate tissue well

-nonpolar drugs like peniccilin, sex stroids, lipids need carrier protein or they cannot be distibuteed in bloodstream (these drugs are not active if not bound to carrier protein)

-albumin is the most important carrier protein that acidic drugs bind to

-drug interactins occur when 2 drugs compete for same carrier prtein
-ex warfarin.coumadin an anticouaglant competes with phenytoin an atiepileptic and ASA fight for albumin (giving any of these tgetehr increases plasma concetration)

35
Q

concetration gradeint (factors influencing distribution)

A

-drug will move from high to low concentration
-initially drug flows from blood into organ but as blood levels fall the drug diffuses back into circulation

-tissues are exposeld to blood born drugs ar the rate of perfusion
-kidney and liver are well perfused to get most of the drug
-poorly perfused tissues like adipose get little drug

36
Q

slide 40-41 on different capillary types

A
37
Q

Blood brain barrier

A

-continuous capillaries, tight junctions, thick basal lamina
-only higjhly lipid soluble drugs can pas bbb (but not true in newborns as bbb is not established and have intracellular celfts)

-bilirubin can affect babys bbb more than adults
-loperamid/imodium is an opiod to treat diarrhea that causes opiate like symptos in baby but not adult

38
Q

placental barrier

A

-maternal capillaries are fenestrated (so have membrane but there are few solutes that can pass the membrane and enter placenta)
-pinocytosis (cell drinking) carries maternal serum to the foetal compartment (aids in transfer of maternal antibody and all soluble materials across the placental barrier)

-placenta membrne is highly pemrable to lipids (ex diazepam levels can be higher in baby)

-placenta is realivtyly imperameable to charged, large bound to plasma protein drugs

generally if a drug can be absorbed orally then it can cross placenta

39
Q

breast milk and drugs

A

-foetus is exposed to serum concentrations in utero
-during breastfeeding the newborn is only exposed to a drug in the milk and the drug is then diluted over the newborns volume (therefore dose to foetus during pregnancy is way larger than in pregnancy)

40
Q

drug movement in breast milk

A

-drug enters milk from maternal plasma primarily bu diffusion
-drug passes from maternal plasma coparmtent through contrnous cappilaries then basilar membrane and out throufh apical membrane of alveolar cells in ducts

in first 2 weeks of breastfeeding there are large gaps between alveolar cells which allow IgA, maternal WBC and large proeins to pass easilt

41
Q

impossible to predict drug delivery to newborn through milk

A

depends on lipid solubilty of drug, size, blood level in maternal ciruclation, protein binding, oral biolavailbity in infant, hallf life

42
Q

RID relavent infant dose

A

=the amount of maternal dose received by infant (if RID is less than 10% then safe for breastfeeding)

43
Q

Feeding Person’s Plasma Level:

A

-the feeding persons plasma level is the most important determinant of drug level in milk
-as the level of the medication in the feeding parents plasma begins its rise, the concentration in milk will increase (diffusion)
-any drug delivery system that delivers small amounts of drugs to maternal circulation (ex topical or inhalation) drugs are preferred

44
Q

Protein Building and Lipophilicity:

A

The 2 most important determinants of rate of drug transfer to human milk are:
1. Degree of protein building
-most drugs bound to albumin in circulation; the free drug available for transfer to milk
-drugs that have high protein binding are found in lesser levels in milk

  1. lipid solubility
    -extremely lipid soluble drugs pentetrat e milk in higher concentrations
    -ex. loratadine/claritin is very lipid soluble and found in milk
    -caffeine is very water soluble and doesnt penetrate milk well
45
Q

M/P ratio

A

-M/P ratio = (Concentration of drug in milk) / (Concentration of drug in plasma)

-High M/P Ratio: If the M/P ratio is greater than 1, it indicates that the drug is more concentrated in breast milk than in plasma. This could mean that the baby is exposed to a higher level of the drug through breastfeeding.

-Low M/P Ratio: If the M/P ratio is less than 1, the drug is less concentrated in breast milk compared to plasma. This generally suggests a lower risk for the infant.

46
Q

oral bioavailability

A

-once a drug is ingested by infant through milk it must be absorbed by infants GI tract
-oral bioavailanity is amount of drug that reaches circulation

47
Q

molecular weight of drugs

A

-smaller the molecular weight of drug, the easier it pentrates into milk
-diffusion is fast for smaller molecules
-ethanol has small molecular weight so it rapidly enters milk, same with recreational drugs

48
Q

pKa and human milk

A

-pKa of a drug is the pH at which the drug exists in equal amounts of charged and uncharged forms
-charged form of drug is hydrophilic and moves easily into blood
-uncharged form is lipophilic and moves easily through lipid membranes

-blood ph is 7.4 and milk is 7.2 so a chatged drug is less capable of transferring from milk back to parental plasma - drugs can become trapped in milk if they become uncharged (ion trapping so drug is held in milk and leaves slowly)

49
Q

pka of blood and ph

A

-if oh is higher than pka the drug is moslty deprotonated
-if the ph is lower than pka the drug is mostly protonated

-blood ph 7.4, milk is 7.2
-baseic drugs with pka greater than 7 will be sequestered in more than basic drugs with lower pKa
-acidic drugs will ot be sequestered in milk becasue chnage from 7.4 to 7.2 will make more HA (lipid soluble)
-acidic drugs have lower M/P ratio

50
Q

strategies to avoid drugs in human milk

A

-choose a drug safe for breastfeeding
-choose drug that deosnt readily pass into milk
-lowest dose for shortest time possible
-topical rather than oral when possible
-agents without active metabolites
-sometimes need to pump and dump
-discontinue nursing if drug is needed but not safe for baby
-avoid extended release drugs

51
Q

slide 66 questions

A
52
Q

drugs with extremely large Vd

A

diazepam/valium and digoxin have huge Vd
-either bind to tissues lightly or are highly lipophilic
-drugs with high Vd cross placenta and accumulate in placenta
-if drug crosses placenta this increases Vd

MEP2 Pharmacology Midterm (12 decks)

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