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CMOD Block 2 > Pharm: Terms & Equations to Know > Flashcards

Pharm: Terms & Equations to Know Flashcards

1
Q

Henderson-Hasselbach Equation

A

pH = pKa + log(A-/HA)

unprotonated divided by protonated

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2
Q

What is the ration of unrotonated to protonated form of a weak acid drug (pKa=3.0) at the duodenum? (pH = 4.0)

A

On pH unit above the pKa indicates a ratio of unprotonated to protonated = 1/10.

2 pH units above pKa = 1/100

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3
Q

Is a lipid soluble drug ionized or non-ionized?

A

Non-ionized.

DRUGS ARE ONLY ABSORBED THROUGH MEMBRANES IN THE NON-IONIZED STATE

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4
Q

Apparent Volume of Distribution of a drug =?

A

Vd =

amount of drug administered / plasma drug [ ]

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5
Q

A uniformly distributing drug is given to you. 1000 mg, to be exact. What is the Vd of this drug?

A

1000mg
_________ = 25 mg/L
40L body fluid

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6
Q

Define Pharmacodynamics

A

The actions of a drug on the body

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7
Q

Define Pharmacokinetics

A

The actions of the body on a drug:

ADME: Absorption, Distribution, Metabolism, and Excretion of a drug.

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8
Q

Elimination of a drug involves which 2 processes?

A

Metabolism and excretion.

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9
Q

Are drugs more lipid soluble when charged or uncharged?

A

Uncharged = lipid soluble

Charged = water soluble

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10
Q

Are drug elimination and drug excretion the same thing?

A

No. Drugs may be eliminated ( no more activity) by metabolism long before it is physically excreted by the body.

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11
Q

Define First-Order elimination

A

First order elimination is proportional to the concentration of the drug in the body.

An equal PROPORTION of the drug is eliminated per unit time. It varies with each passing half-life.

The concentration of a drug in the blood will decrease by 50% with each passing half-life

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12
Q

Define Zero-Order elimination

A

Enzymatic, saturable elimination.

A fixed amount of drug is eliminated per unit time.

Like alcohol and aspirin! One drink per hour.

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13
Q

Therapeutic dose =?

A

MTC/MEC

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14
Q

Most drugs cross biologic membranes via what process?

A

Passive Diffusion:

Remember: Only lipophilic, non-polar, and non-ionized drugs can cross a membrane.

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15
Q

If taken orally, acidic drugs will be in the nonionized form in the ________________.

A

Stomach. The non-ionized form of a weak acid is its protonated form HA. Acidic drugs will ready cross the lipid membranes of the stomach and be absorbed.

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16
Q

If taken orally, weakly basic drugs will be in their non-ionized form in the ___________________.

A

Small intestines. The nonionized form of basic drugs is the UNPROTONATED form. B.

In the stomach, weak bases remain protonated and charged, therefore unable to cross a lipid membrane.

remember: acids are in their uncharged form when they are PROTONATED.

They are opposites.

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17
Q

Acidic drugs bind to ________ in the plasma, while basic drugs bind to _______ in the plasma.

A

Acidic drugs bind to ALBUMIN

Basic drugs bind to GLOBULINS

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18
Q

At low drug concentrations, what determines the fraction of drug bound to plasma proteins?

What about at high drug concentrations?

A

At low concentrations of drug, binding site affinity determines the fraction of drug bound.

At high concentrations of drug, the # of binding sites becomes the limiting variable.

19
Q

The chemical modification of xenobiotics by endogenous enzymes is called ___________.

A

Biotransformation - necessary for the function of many drugs administered in pro-form.

Metabolism does not necessarily mean inactivation.

20
Q

What are some of the outcomes of biotransformation of a drug?

A

Biotransformation is pretty much the same thing as metabolism.

  1. Conversion of active compounds or toxins into less active/toxic compounds.
  2. Convert them to more polar/less lipid soluble substances to promote excretion.
  3. Convert an inactive prodrug to its active form
  4. Generate a toxic metabolite
21
Q

Describe a Phase 1 Reaction.

A

Convert a parent drug to an inactive metabolite by introducing or unmasking a functional group.

( -OH, -NH2, -SH)

Phase 1 metabolites are usually polar, and may be readily excreted in urine

Bad part: Te products of phase 1 reactions are often highly reactive(free radicals) or toxic.

Good part: They can then undergo Phase 2 reactions.

22
Q

Describe a Phase 2 reaction.

A

Covalent addition fo a functional group onto the parent compound, which can be a random drug, or a product of phase 1 reactions.

(glutathione, amino acids, acetate, etc… added)

Covalent modifications of this sort render the parent compound inactive and readily excreted.

23
Q

Main organ of brio transformation.

A

Liver, but all tissues, even brain, have a little metabolic capacity.

24
Q

Most phase 1 reactions take place in the _______________ (sub cellular location)

Phase 2 reactions take place in the ______________.

A

Phase 1 reactions take place in the ER

Phase 2 reactions take place in the cytosol.

25
Q

What happens more often, Phase 1 or Phase 2 reactions? Based on this observation, what is the most common sub cellular location of biotransformation?

A

Phase 1 reactions occur more often, therefore the ER is the most common sub cellular location of biotransformation.

26
Q

What protein family is responsible for Phase 1 reactions?

A

CYP-P450 in LIVER!

27
Q

What protein family is responsible for Phase 2 reactions?

A

UDP-glucuronosyl-transferases. (UGTs)

28
Q

Describe the following reactions as Phase 1 or Phase 2:

  1. Oxidation
  2. Conjugation
  3. Reduction
  4. Hydrolysis
A
  1. Oxidation - Phase 1
  2. Conjugation - Phase 2
  3. Reduction - Phase 1
  4. Hydrolysis - Phase 1
29
Q

What is the main conjugation (Phase 2) reaction in the body?

A

Glucoronidation. - occurs in the liver

Addition of a glucuronide.

Catalyzed by UDP-glucaronosyl-transferases.
(UGTs)

30
Q

Name all the Type 2 Conjugations. (Need to know this, so you can know that all others NOT on this list are Phase 1)

Think covalent bonds!

A
  1. Acetylation
  2. Glucaronidation
  3. Sulfation (-SO4)
  4. Glutathione conjugation (-GSH)
  5. AA conjugation
  6. Methylation

Anything that says conjugation = PHASE 2

31
Q

Name the 3 main groups of Phase 1 reactions.

A

Oxidation
Reduction
Hydrolysis

32
Q

Where (sub cellular location) are the CYP-P450 enzymes located?

A

On the smooth ER of various tissues, with the greatest concentration in the Liver.

33
Q

What CYP is primarily located in the GI tract? What is the main problem with this CYP, relating to drug administration?

A

CYP3A in the GI tract metabolizes many drugs as they are absorbed, DECREASING THE BIOAVAILABILITY.

34
Q

What’s the significance of CYP3A4 and CYP3A5?

A

They are involved in the metabolism of 50% of drugs.

35
Q

What is the ONLY energy source for CYP-P450 enzymes?

A

NADPH - NO ATP is required.

36
Q

CYP-P450 family members are enzyme COMPLEXES. what are the 2 subunits?

A

An Enzyme and a Reductase.

37
Q

Describe the process of enzyme INDUCTION with certain drug doses over time.

A

Induction occurs when a drug induces the up regulation of metabolic enzymes in the liver. This can affect the drug itself (induces its own metabolism, and next dose must be higher to be effective), or other drugs.

The more CYPS you have, the faster you metabolize not only the CYP inducing drug, but other drugs concurrently administered. CYPS are not specific. Have overlapping specificity.

It’s a REVERSIBLE, yet vicious cycle of DOSE ESCALATION.

38
Q

What is an idiosyncratic drug response?

What factor underlies this concept?

A

One you weren’t expecting.

You give a guy a drug that has been successful in every other case like his. Nothing happens. That was unexpected.

Genetic differences underlie idiosyncratic response.

39
Q

The main organ for the excretion of drugs is the…..

What is this organ’s functional unit?

A

Kidney

Functional unit: Nephron

40
Q

What is the GFR and what is it a measure of?

A

GFR= glomerular filtration rate.

The kidney receives 20-25% of cardiac output, and 20% of that blood that enters the glomerulus is filtered:

110-130 ml/min

41
Q

Glomerular Filtration is a (passive/active) and (saturable/nonsaturable) process.

A

Glomerular filtration is a PASSIVE and NONSATURABLE process.

Nonsaturable because it is NOT ENZYME MEDIATED

42
Q

How is the GFR usually monitored?

A

Determining the renal clearance of CREATININE.

43
Q

Acidification of unripe promotes the clearance of ________ drugs and metabolites, while alkalization of the urine promotes clearance of __________ drugs and metabolites.

A

Acidification of urine promotes excretion of BASIC drugs/metabolites

Alkalinization of urine promotes excretion of ACIDIC drugs/metabolites.

44
Q

What is Enterohepatic Cycling?

A

Drugs are sometimes eliminated via biliary secretion, and their identity, therefore absorption and function, changed by the pH of their environment.

EXAMPLE: A drug gets conjugated with glucaronide in the liver (phase 2 rxn), secreted in the bile, and in the intestine, the microflora cleave the glucaronide group back off via hydrolysis.

The drug is able to be reabsorbed into the circulation and used again, prolonging the presence and effects of the drug by reducing its elimination rate.

Conjugates are reabsorbed, though less and less with each cycle. Lose some in the feces.

CMOD Block 2 (14 decks)

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