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Pharm Block 9 > Drug Movement In The Body: Ionization > Flashcards

Drug Movement In The Body: Ionization Flashcards

1
Q

What are most drugs

A

Weak acids or bases

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2
Q

________ release H+ causing a charged anions (A-) to form HAH+ + A-

A

Acidic drugs (HA)

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3
Q

______ can also release a H+ but the pronated form of basic drugs is charged; loss of the proton produces an uncharged base (B); BH+ B+ + H+

A

Weak bases (BH+)

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4
Q

What kind of drugs are readily absorbed (ionized, unionized)

A

Unionized, uncharged

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5
Q

When will you get an unionized acid? (HA)

A

In an acidic ienvironment

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6
Q

When will you get Na unionized base (B)

A

In a basic environment

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7
Q

Drugs pass mroe readily through membranes if they are __________

A

Uncharged. (HA or B)

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8
Q

What happens to charged or ionized drugs in the system

A

They get trapped, cannot get across the membrane

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9
Q

The concentration of the forms on either side of a membrane is determined by the relative concentration of charged vs uncharged forms, which is, in turn, determined by

A

The pH at the site of absorption and the Pka

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10
Q

This is a measure of the strength of the acid or base

A

Pka

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11
Q

The lower the pka, the ______the acid

A

Stronger

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12
Q

The higher the Pka, the ______ the base

A

Stronger

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13
Q

50% ionized, 50% unionized

A

Pka

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14
Q

What is the relationship between Pka and ph expressed by

A

The Henderson-hasselbalch equation: pH-Pka

If you get a negative, pH is lower than pka=acidic

If you get positive, pH is higher than Pka=basic

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15
Q

Ionized or unionized is lipid soluble?

A

Unionized, this is why it can cross the membrane

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16
Q

When the pH-Pka is negative

A

Weak acid will be mostly nonionized

Weak base will be mostly ionized

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17
Q

When the pH-pKa is positive

A

Weak acid will be mostly ionized

Weak base will be mostly nonionized

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18
Q

Changing the pH by 1 log unit

A

You actually are changing it by 10 fold

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19
Q

Where is a weak acid best absorbed in the body?

A

In the stomach because of the low pH

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20
Q

Where is a weak base best absorbed in the body?

A

Small intestine because of the higher pH

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21
Q

Stomach pH

A

1

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22
Q

Small intestine pH

A

6

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23
Q

Blood pH

A

7.4

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24
Q

Urine pH

A

5-8

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25
Q

What can you manipulate in terms of pH in order to help eliminate drugs

A

You can manipulate the urine pH, can make it more basic to get rid of weak acids (8), and make the pH more acidic to get rid of weak bases (5)

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26
Q

Clearance of drugs

A

As you go towards the bottom of the graph, you can see that charged drugs get eliminated more easily (ionized)

27
Q

When pH is less than pKa what forms of the weak acid and base predominate

A

Protonated forms, HA and BH+

28
Q

When the pH is greater than the pKa, what forms of the weak acid and base predominate

A

Deprontonated forms, A- and B

29
Q

When pH=pKa

A

HA=A- and BH+=B

30
Q

What kind of environment must you put a drug in for it to stay?

A

Like. Put a weak acid in an acidic environment and it will stay, but a weak base in a basic environment and it will stay

31
Q

What kind of environment must you put a drug to eliminate it

A

Opposite. Put a weak acid in a base or put a weak base in an acidic environment

32
Q

How do you fix a weak acid overdose?

A

Bicarbonate, fixed amount will change urine pH without changing blood pH too much.

33
Q

How do you fix a weak base overdose

A

Acidity urine with ammonium chloride (NH4Cl)

34
Q

What is hepatic encephalopathy treated with

A

Lactulose

35
Q

What does lactulsoe do for people with hepatic encephalopathy?

A

It is converted by gut bacteria into lactic acid. The acid environment in the guy converts ammonia (NH3) to ammonium (NH4+) and can now get eliminated

36
Q

Physical factors influencing absoprtion

A

Blood flow to absoprtion site
Total surface area for absoprtion
Contact time at the absoprtion site

37
Q

The fraction (F) of the administered dose that reaches the systemic circulation

A

Bioavailability (F)

38
Q

What is the F of drugs given IV

A

100% F=1.0

39
Q

Can a drug with F=0.8 be an IV drug

A

No. IV will always be F=1.0

40
Q

Factors that influence bioavailability

A
  • first pass hepatic metabolism (decrease)
  • solubility of drug (hydrophilic drugs have decreased)
  • chemical instability (penicillin G, insulin)
41
Q

When looking at a bioavailability curve, what are we always comparing it to

A

IV. We look at AUC (area under the curve), IV will always have the bigger area

42
Q

Plasma level curves: lag time

A

Time from administration to appearance in blood (0-first time appearing in blood)

43
Q

What does not have a lag time on the plasma level curve?

A

IV

44
Q

Onset of activity for plasma level curve

A

Time from administration to reaching MEC (min effective cxn)

45
Q

Duration of action

A

Time plasma cxn remains above MEC

46
Q

Minimum effective concentration (MEC)

A

Where drug first starts working in the body

47
Q

How do tums influence drug absoprtion

A

Will increase the pH of stomach

48
Q

How can elimination of a drug be affected

A

In people with renal issues. Effects the duration of action too so you want to lower the dose

49
Q

How would a plasma level curve look for an IV drug

A

Concentration would start high and fall away. Also there would not be absorption.

50
Q

Distribution of drugs determined by

A
  • size of organ
  • blood flow
  • capillary permeability (easy in liver, not so much in brain)
  • hydrophobic vs hydrophilic nature of the drug
51
Q

Binding of drug to plasma proteins

A
  • plasma albumin is the primary binding protein

- binding to proteins in the blood or tissue compartments will increase the drug concentration in that compartment

52
Q

Why do some drugs bind albumin

A

Because they are lipid soluble and need a carrier. If water soluble, does not need carrier

53
Q

A hypothetical volume of fluid in which the drug is disseminated

A

Volume of distribution (Vd)

54
Q

Total body water

A

42 liters

55
Q

Total intracellular volume

A

28 liters

56
Q

Total extracellular volume

A

14 liters

57
Q

Total interstitial volume

A

10 liters

58
Q

Total plasma volume

A

4 liters

59
Q

Total body water in percent

A

60% of body weight

60
Q

What does Vd relate

A

The amount of the drug in the body to the plasma concentration of the drug according to this equation:

Vd=(amount of drug in body)/(concentration in the blood)

Tells if drug is mostly in the blood or out of the blood

61
Q

Low plasma levels = ____Vd

A

Increased

62
Q

Increased plasma levels= ____Vd

A

Decreased

63
Q

When is Vd very low

A

When most of the drug is staying the blood

64
Q

When is Vd very high

A

When most of the drug is in the tissue

Pharm Block 9 (7 decks)

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