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

Question 1

Drug excretion

Answer 1

Removal of drug from body via a number of routes:

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

Question 2

Renal elimination

Answer 2

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

Question 3

Glomerular Filtration

Answer 3

• 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

Question 4

Active tubular secretion

Answer 4

• 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

Question 5

Passive diffusion across tubular epithelium

Answer 5

• 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

Question 6

Renal Clearance (ml/min)

Answer 6

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

Question 7

Half life of drug

Answer 7

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

Question 8

Steady state

Answer 8

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

Question 9

Extraction ratio

Answer 9

• 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

Question 10

Excretion rate

Answer 10

Excretion rate = [clerance] x [plasma]

Question 11

Drugs with salivary excretion

Answer 11

Clindamycin

Rifampicin

Caffeine

Metroidazole

Theophyline

Question 12

Drugs affecting salivary excretion

Answer 12

Atropine + atropine-like antispasmodics

Tricyclic antidepressants ⇢ amitriptyline

Tetracycline antidepressants ⇢ maprotiline

Clonidine

Anti muscarinic drugs ⇢ pirenzepine