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LF260 Neuropharmacology > Lecture 1: Pharmacology > Flashcards

Lecture 1: Pharmacology Flashcards

1
Q

Clinical aim of a drug

A

To achieve an effective drug concentration at the site of action long enough to produce a therapeutic action

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2
Q

Therapeutic window/index

A

The bigger the window, the safer the drug

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3
Q

What was the old method to measure therapeutic window/index?

A

LD50
- Put dosage in rats
- See what conc would kill 50% of the population
- Not used anymore [ethics]

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4
Q

Bioavailability

A

Proportion of dose of unchanged drug that reaches the site of action

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5
Q

Intravenous injection advantages

A

100% bioavailability
Rapid action

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6
Q

Oral route advantages

A

Safest, most convenient and economical route

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7
Q

Fick’s Law of Passive Diffusion

A

Rate = permeability x surface area x conc difference / thickness of membrane

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8
Q

How does a drug get into the blood stream from the gut lumen?

A

○ Passive diffusion
○ Factors
§ Membrane permeability
§ Surface area of membrane
§ Conc difference (more conc difference, more it will diffuse across)

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9
Q

Factors determining rate of passive diffusion

A
  • Determined by biological variation
    • Permeability depends on the drug itself
      ○ Lipophilic faster than hydrophilic
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10
Q

What are the four routes of administration?

A

Absorption
Distribution
Metabolism
Elimination

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11
Q

Site of action

A

Systemic circulation

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12
Q

Intravenous injection disadvantages

A

Sterile equipment needed
Trained personnel needed
Expensive
Potentially painful

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13
Q

Oral route disadvantages

A

Nearly always less than 100% bioavailability
Destruction by enzymes, pH and/or bacteria
Drug can complex with food
Absorption depends on rates of passage

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14
Q

How does the drug get into the blood stream from gut lumen?

A
  • Passive diffusion
  • Factors
    • Permeability of membrane
    • Surface area of membrane
    • Conc difference (more conc difference, more it will diffuse across)
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15
Q

What are some other methods of absorption?

A
  • Active transport
    • L-DOPA
  • Ion-pair absorption
  • Pinocytosis
  • Solvent drag
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16
Q

Pinocytosis

A
  • Membrane that engulfs material and removes itself through cytosis
  • Not much evidence for this
17
Q

Solvent drag

A
  • Purely experimental technique
  • Drug dissolves in a[n organic] solvent
  • Works theoretically
18
Q

Small intestine as a main site of absorption

A
  • Large surface area
  • Alkaline pH
  • Blood flow (1l/min) capillaries
19
Q

Stomach

A
  • Little drug absorption
  • Small surface area
  • Blood flow 150ml/min
  • Quick to empty
  • Acid pH (1-2)
  • Ion trapping
20
Q

Colon

A
  • Little drug absorption
  • Lumen filled w bacteria
21
Q

Pen V

A
  • Binds to food → reduces bioavailability
  • Therefore, take on an empty stomach
22
Q

Tetracyclines

A

Chelate muscles so absorption reduced by milk, antacids n iron preparations

23
Q

Aspirins (NSAIDS)

A
  • Irritates the stomach: dyspepsia, nausea, vomit, diarrhea
  • 1/5 chronic users will hv gastric damage
24
Q

First-pass metabolism

A
  • Tend to be absorbed in the small intestine
  • Drug pass through the liver before it gets to the systemic circulation
  • Drug can be completely metabolized
  • Drug broken down by acid
  • Peptide drugs will be broken down completely before there are any effects
25
Q

Inhalation

A
  • Aerosols: absorption depends on particle size
  • Lipid soluble anesthetics: rapid reabsorption
  • Avoids first pass metabolism
26
Q

Transdermal

A
  • Outer layer (stratum corneum) rate limiting step
  • Low input rates
  • Patches (e.g. to give up smoking)
  • HRT (menopause)
  • Opioid analgesic for pain
  • Ibuprofen gel: anti-inflammatory drug
27
Q

Buccal n sublingual

A
  • Passive absorption, pH 6/7, saliva may wash away
  • Examples
    • GTN (angina)
    • Temgesic (buprenorphine, opioid painkiller)
28
Q

Intranasal

A
  • Epithelial metabolism
  • Absorption: passive diffusion
  • Examples
    • GTN (angina)
    • Desmopressin: diabetes insipidus, nocturnal enuresis)
29
Q

Rectal

A
  • Upper rectum: upper rectal vein, first pass metabolism
  • Middle/lower rectum: avid first pass metabolism
  • Absorption: passive diffusion (erratic)
  • Examples
    • Diazepam rectal tubes (status epilepticus)
    • Diclofenac suppositories (pain n inflammation)
30
Q

Plasma Protein Binding

A

The process by which drugs bind to proteins in the blood, affecting their distribution and elimination within the body

31
Q

Tissue Distribution

A

The dispersion of a drug throughout various tissues in the body, influenced by factors such as tissue perfusion and drug lipophilicity

32
Q

Blood Brain Barrier (BBB)

A
  • Prevents drugs entering the brain
  • Layer of tightly joined endothelial cells
  • Lipid soluble drugs pass by passive diffusion
  • Water soluble drugs only pass via carrier mechanisms
  • Endothelial cells contain P-glycoprotein (Pgp) which is an active drug efflux pump
33
Q

What happens to drugs during metabolism?

A
  • Converted to inactive metabolites
  • Converted to active metabolites (i.e. benzodiazepines)
  • Excreted unchanged
34
Q

Phase 1 Metabolism

A
  • Transforms drug’s molecular structure
    • E.g. oxidation, hydrolysis, reduction
  • EFFECT
    • Can introduce polar groups/ increase water solubility
    • Abolish activity
    • Produce toxic/non-toxic metabolites
  • Often mediated by cytochrome P450 enzymes
35
Q

Phase 2 Metabolism

A
  • Attaches endogenous substance (e.g. sulphate/glucoronide) to parent drug/phase 1 metabolite
  • Carried out by transferases (enzymes)
  • Increases polarity/water solubility so can be eliminated in urine or bile
  • Parent drug/metabolites can inhibit/induce the metabolism of other drugs: possible interaction
36
Q

Renal excretion

A
  • Unbound drug excreted
  • Lipid soluble drugs can be reabsorbed in renal tubules; prolongs action
  • Can change urinary pH to aid excretion (i.e. bicarbonate and aspirin)
  • Some drugs (e.g. penicillin) are actively excreted

LF260 Neuropharmacology (14 decks)

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