Most of the drugs are excreted in ?
Ans. is 'b' i.e., Urine Most impoant channel of excretion for most drugs is through kidney (in urine). EXCRETION OF DRUGS Drugs and their metabolites are excreted in : 1. Urine Through the kidney It is the most impoant channel of excretion for most drugs. Net renal excretion = (Glomerular filtration + tubular secretion) - Tubular reabsorption. Glomerular filtration Depends on plasma protein binding and renal blood flow. Does not depend on lipid solubility. Tubular reabsorption Depends on lipid solubility More lipid soluble drugs are absorbed more and less excreted. Ionized drugs, being less lipid soluble, are more excreted. Acidic drugs (salicylates, barbiturates) are more ionized at alkaline pH. So urine should be alkalinized in poisoning of these drugs. Similarly, urine should be acidified in poisoning of basic drugs (morphine). Tubular secretion Does not depend on plasma protein binding or lipid solubility. This is active transpo of organic acid and bases by two separate classes of relatively nonspecific transpoers (OAT and OCT). In addition, efflux transpoers P-gp and MRP2 are located in the luminal membrane of proximal tubular cells. Organic acid transpo (through OAT) for Penicillin, Probenecid, uric acid, salicylates and sulfinpyrazone. Organic base transpo (through OCT) for diuretics (thiazide, amiloride, furosamide, triameterene), quinine and procainamide. Both transpo processes are bidirectional, for drugs, secretion into the tubular lumen predominates, whereas an endogenous substrate like uric acid is predominantly reabsorbed. 2. Faeces Drugs present in the faeces are derived from unabsorbed fraction plus actively secreted into bile. Drugs that attain high concentration in bile are - Erythromycin ral contraceptives Rifampin Ampicillin Tetracycline Phenolphthalein 4. Exhaled air Gases and volatile liquids are eliminated by lungs. 4. Saliva and sweat These are of minor impoance. Lithium, Pot. iodide and rifampin are present in these secretions. 5. Milk Most drugs enter breast milk by passive diffusion. Lipid soluble and less protein bound drugs cross better.
Faeces
Urine
Saliva
None