6)Drug excretion. Drugs with salivary excretion. Drugs affecting the salivary secretion Flashcards

1
Q

Drug excretion

A

Removal of drug from body via a number of routes:

  • Most important route ⇢ via kidney into urine
  • Other routes ⇢ tears, perspiration, intestine, lung, saliva
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2
Q

Renal elimination

A

Rate of R.E can vary based on drug, eg penicillin is almost completely cleared from drug in a single transit to kidney

3 aspects to R.E

  1. Glomerular filtration
  2. Active tubular secretion
  3. Passive diffusion across tubular epithelium
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3
Q

Glomerular Filtration

A
  • Drug enters kidneys via renal arteries (divide forming glomerular capillary plexus)
  • The free/unbound to albumin drug flows into bowman’s capsule as part of glomerular filtrate
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4
Q

Active tubular secretion

A
  • There are 2 non-selective carrier systems ⇢ one for acids + one for bases
  • This is the main mechanism for drug elimination in kidneys
  • It works well for drugs bound to proteins ⇢ can be properly excreted
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5
Q

Passive diffusion across tubular epithelium

A
  • 1% of fluid is filtered from glomerular filtration ⇢ excreted as urine
  • If all drugs passed via passive diffusion ⇢ rate of excretion would be very slow
  • Lipid-soluble drugs are poorly excreted as they pass through w/ease
  • Water-soluble polar drugs remain in lumen + more likely to be excreted
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6
Q

Renal Clearance (ml/min)

A

Renal clearance (ml/min) = Urinary conc x rate of urine flow ÷ plasma conc

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7
Q

Half life of drug

A

½ life = time required for [drug] in blood plasma to be reduced by ½

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8
Q

Steady state

A

when a drug has built up therapeutically effective levels in blood stream

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9
Q

Extraction ratio

A
  • The decline of [drug] in plasma from arterial to venous side of kidney
  • Drugs enter kidneys at [C1] and leave at [C2]
  • extraction ratio = C2/C1
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10
Q

Excretion rate

A

Excretion rate = [clerance] x [plasma]

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11
Q

Drugs with salivary excretion

A

Clindamycin

Rifampicin

Caffeine

Metroidazole

Theophyline

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12
Q

Drugs affecting salivary excretion

A

Atropine + atropine-like antispasmodics

Tricyclic antidepressants ⇢ amitriptyline

Tetracycline antidepressants ⇢ maprotiline

Clonidine

Anti muscarinic drugs ⇢ pirenzepine

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