Forced diuresis

Forced diuresis (increased urine formation by diuretics and fluid) may enhance the excretion of certain drugs in urine and is used to treat drug overdose or poisoning of these drugs and hemorrhagic cystitis.

Diuretics

Most of the drugs are either weak acids or weak bases. When urine is made alkaline, elimination of acidic drugs in the urine is increased. The converse applies for alkaline drugs.

This method is only of therapeutic significance where the drug is excreted in active form in urine and where the pH of urine can be adjusted to levels above or below the pK value of the active form of drug. For acidic drugs, urine pH should be above the pK value of that drug, and converse for the basic drugs. It is because the ionization of acidic drug is increased in alkaline urine and ionized drugs cannot easily cross plasma membrane so cannot re-enter blood from kidney tubules. This method is ineffective for drugs which are strongly protein bound (eg tricyclic antidepressants) or which have a large apparent volume of distribution (eg paracetamol, tricyclic antidepressants).

Forced alkaline diuresis has been used to increase the excretion of acidic drugs like salicylates and phenobarbitone, while forced acid diuresis has been used to enhance the...
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