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Pharm I > test 1 part 2 > Flashcards

test 1 part 2 Flashcards

1
Q

Absorption

A

• The transfer of a drug from the site of administration to the bloodstream

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2
Q

Rate of absorption depends on

A
  • Environment
  • Chemical characteristics of drug
  • Route of administration
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3
Q

Absorption from the GI tract - oral cavity

A
  • Slightly acidic
  • Thin epithelium, high vascularity
  • Bypasses hepatic metabolism (skips liver)
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4
Q

Absorption from the GI tract - stomach

A

• Folds increase surface area
• Very acidic
-some drugs can be absorbed from the stomach but not the main site

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5
Q

Absorption from the GI tract - small intestine

A

• Deep folds with villi and microvilli

-main site for absorption because of large surface area

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6
Q

Absorption from the GI tract - large intestine

A

• Little absorption throughout
• Rectum- useful site because bypasses hepatic metabolism - lower part of rectum bypasses liver
-secretes mucous

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7
Q

Passive Diffusion

A

-most common means for drugs to gain access to the body
• Concentration gradient is driving force
• Does not involve a carrier
• Not saturable
• Low structural specificity
• Major method of drug absorption
• 2 types (Aqueous and Lipid)

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8
Q

Aqueous Diffusion

A

• Water soluble drugs penetrate the cell membrane through aqueous channels or pores

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9
Q

Fick’s Law

A

Net diffusion ≈ Area for diffusion x Concentration gradient / Thickness of membrane

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10
Q

Lipid Diffusion

A
  • Lipid soluble drugs readily move across most biologic membranes
  • Soluble in the lipid bilayer of membranes
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11
Q

Facilitated Diffusion

A
  • Passage into a cell through transmembrane carrier proteins
  • Conformational changes allow passage
  • High concentration to low concentration
  • Does NOT require energy
  • Saturable
  • Inhibited by competitors for carrier protein
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12
Q

Active Transport

A
  • Drugs that closely resemble naturally occurring metabolites are transported via carrier proteins in the membrane
  • Energy dependent
  • Can move against gradient
  • Saturable
  • Selective
  • Competitively inhibited by other cotransported substances
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13
Q

Endocytosis & Exocytosis

A
  • Transport of exceptionally large drugs across membranes

* Engulfment by membrane and transport into or out of cell by pinching off vesicle

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14
Q

Factors Influencing Absorption

A
  1. pH
  2. Blood flow
  3. Surface area
  4. Contact time
  5. P-glycoprotein
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15
Q

If a drug is ionized, why won’t it cross the lipid bilayer?

A

-an ionized drug forms a hydrophilic polar non-lipophilic molecule with water meaning it will not want to cross the lipid bilayer

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16
Q

the neutral form of a weak acid is

A

protonated

-weak base is not

17
Q

acidic drugs are more soluble at what pH

A
  • more acidic pH

- pushes equation to the left (HA)= non-ionized form

18
Q

a weak base in an acidic environment

A

-cannot be absorbed

19
Q

lower the pKa

A
  • more acidic the drug is
  • BH+
  • HA favored
20
Q

pH > pKa

A

B and A- favored

-deprotonated forms predominate

21
Q

Manipulation of drug excretion by the kidney

A
  • ”Trap” drugs in the urine by ionizing them
  • Acidic drugs excreted faster in alkaline urine
  • Basic drugs excreted faster in acidic urine
22
Q

acidic drugs excreted faster in what urine pH

A

alkaline urine

23
Q

fluids that can trap drugs

A 
• Stomach
• Small intestine
• Breast milk
• Aqueous humor
• Vaginal and prostatic secretions
-urine
24
Q

Blood Flow affecting absorption rate

A
  • Blood flow to absorption site increases absorption

* Intestines receive more flow than stomach so absorption from intestine is favored

25
Q

Surface Area influencing absorption

A
  • Increase in total surface area for absorption increases efficiency
  • Intestines have brush border which increases surface area 1000 fold to that of the stomach
26
Q

Contact time influencing absorption

A
  • Stomach => Slow emptying = decreased absorption

* Intestine => Slow transit time = enhanced absorption

27
Q

P-glycoprotein influencing absorption

A
  • Pumps drugs out of the cells => Reduces drug absorption

* Transmembrane transporter protein

28
Q

Bioavailability

A

how much drug can be absorbed into your bloodstream after any route of administration

  • 100 mg tablet
  • 70 mg unchanged
  • 70% bioavailability
29
Q

Determination of Bioavailability

A

• % Bioavailability= (AUC oral administration / AUC IV administration) X 100

30
Q

Bioavailability: First-pass Hepatic Metabolism

A
  • Drugs absorbed from GI tract enter portal circulation before entering systemic circulation
  • Liver or gut metabolize drug to varying degrees
  • Drugs with high first-pass metabolism must be given in doses large enough to ensure enough active drug remains
31
Q

Bioavailability: Solubility of the Drug

A

• Hydrophilic drugs poorly absorbed
• Extremely lipophilic drugs poorly absorbed
• IDEAL: largely lipophilic, yet have some solubility in aqueous solutions
-THIS IS WHY MOST DRUGS ARE WEAK ACIDS OR WEAK BASES

32
Q

Bioavailability: Chemical Instability

A
  • pH of stomach can cause instability

* Degradative enzymes in GI tract

33
Q

Bioavailability: Nature of Drug Formulation

A
  • Particle size
  • Salt form
  • Crystal polymorphism
  • Enteric coatings
  • Binders and dispersing agents
34
Q

Bioequivalence

A

• A way to compare two drug formulations
• Comparable
- Bioavailability
- Time to peak blood concentration

35
Q

Pharmaceutical Equivalence

A
  • Bioequivalent
  • Same amount of active drug
  • Same dosage
  • Same route of administration
36
Q

Therapeutic Equivalence

A 
• Bioequivalent
• Pharmaceutically equivalent
• Comparable
- Clinical effect
- Safety profile
GENERIC DRUGS

Pharm I (15 decks)

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