EXCRETION OF DRUG

1. ANSUMAN SAHU
DRUG EXCRETION

2. Excretion is the passage out of systemically
absorbed drug. Drugs and their metabolites are
excreted in:
1. Urine
2. Faeces
3. Exhaled Air
4. Swaet & Salive
5. Milk

3. 1. Excretion by Urine :
RENAL EXCRETION
 The kidney is responsible for excreting all water
soluble substances. The amount of drug or its
metabolites ultimately present in urine is the sum total
of glomerular filtration, tubular reabsorption and
tubular secretion (Fig. 3.2).
 Net renal = (Glomerular filtration +
tubular
excretion secretion) – tubular reabsorption
Ex - (a) Organic acid transport - penicillin, probenecid,
uric acid, salicylates, indomethacin, sulfinpyrazone,
nitrofurantoin, methotrexate, drug glucuronides and
sulfates, etc.
(b) Organic base transport - thiazides, amiloride,
triamterene, furosemide, quinine, procainamide,

4. 2. EXCRETION BY FAECES :
Apart from the unabsorbed fraction, most of the drug
present in faeces is derived from bile. Liver actively
transports into bile organic acids ,organic bases, other
lipophilic drugs and steroids by separate nonspecific
active transport mechanisms. Relatively larger
molecules (MW > 300) are preferentially eliminated in
the bile. Most of the drug, including that released by
deconjugation of glucuronides by bacteria in
intestines is reabsorbed (enterohepatic cycling) and
ultimate excretion occurs in urine. Drugs that attain
high concentrations in bile are erythromycin,
ampicillin, rifampin, tetracycline, oral
contraceptives, phenolphthalein.
Certain drugs are excreted directly in colon, e.g.
anthracene purgatives, heavy metals.

5. 3. EXCRETION BY AIR :
Gases and volatile liquids (general
anaesthetics, paraldehyde, alcohol) are
eliminated by lungs, irrespective of their lipid
solubility. Alveolar transfer of the gas/vapour
depends on its partial pressure in the blood.
Lungs also serve to trap and extrude any
particulate matter injected i.v.

6. 4. EXCRETION BY SALIVA &SWAET :
These are of minor importance for drug excretion.
Lithium, pot. iodide, rifampin and heavy
metals are present in these secretions in
significant amounts. Most of the saliva along with
the drug in it, is swallowed and meets the same
fate as orally taken drug.

7. 5. EXCRETION BY MILK :
The excretion of drug in milk is not important for the
mother, but the suckling infant inadvertently
receives the drug. Most drugs enter breast milk
by passive diffusion. As such, more lipid soluble
and less protein bound drugs cross better. Milk
has a lower pH (7.0) than plasma, basic drugs
are somewhat more concentrated in it. However,
the total amount of drug reaching the infant
through breast feeding is generally small and
majority of drugs can be given to lactating
mothers without ill effects on the infant.
Nevertheless, it is advisable to administer any
drug to a lactating woman only when essential.

8. A. Drugs whose amount in milk is too small & found
to be safe in ordinary doses:
Acetazolamide, Albendazole, Antacids
Antifungal drugs Aspirin , Cephalosporins ,
Cisapride, Cloxacillin, Codeine,
Diclofenac, Digoxin, Domperidone,
Folic acid, Gentamicin, Heparin,
Ibuprofen, Insulins, Iron
Paracetamol, Permethrin , Piperacillin,
Salbutamol, Sucralfate, Terbutaline,
Valproate sod., Vitamins , Warfarin

9. B. Drugs to be used with special precaution in
breastfeeding women or drugs contraindicated :
 Amlodipine : S/P; no data on risk to infant
 Alcohol : Intoxication, reduced suckling
 Amphetamines : C/I; significant amount in milk
 Chloroquine : S/P; amount in milk small; haemolysis in
< 1 month old infant and in G-6-PD deficient
 Cimetidine : S/P; significant amount in milk, but no
harmful effect reported
 Ciprofloxacin : C/I; high concentration in milk,
theoretical risk of arthropathy
 Metformin : C/I; secreted in milk; hypoglycaemia, lactic
acidosis
 Metoclopramide : S/P; watch for diarrhoea, dystonia in

10. THANK U