Forced diuresis

Forced diuresis refers to the intentional enhancement of urine production and excretion, typically with the use of diuretics and fluids. This therapeutic technique has applications in increasing the elimination of certain drugs from the system, especially during instances of drug overdose or poisoning. It's also utilized in the management of conditions like hemorrhagic cystitis.

Principles

The vast majority of drugs can be categorized as weak acids or weak bases. The efficiency of forced diuresis can be influenced by the pH of the urine, which may either promote or inhibit the excretion of certain drugs.

• For acidic drugs, an alkaline urine environment is preferred, as it increases the ionization of these drugs. Ionized drugs have a diminished ability to cross the plasma membrane, preventing them from re-entering the bloodstream from the kidney tubules.
• Conversely, alkaline drugs are best excreted in an acidic urine environment.

Applicability and Limitations

Forced diuresis is especially beneficial when:

• The drug in question is actively excreted in the urine.
• The urine's pH can be adjusted above or below the pK value of the active form of the drug.

However, this method becomes ineffective for:

Drugs with a strong protein bond (e.g., tricyclic antidepressants). Drugs possessing a high apparent volume of distribution, such as paracetamol or tricyclic antidepressants.

Methods of Forced Diuresis

Forced Alkaline Diuresis

Utilized to enhance the excretion of acidic drugs, such as salicylates and phenobarbitone. This method involves:

• Administering a diuretic, like furosemide, intravenously.
• Adding sodium bicarbonate to the infusion fluid to render the blood and subsequent urine, alkaline.
• Monitoring and replacing potassium, given its propensity to be lost during this process. A deficiency can lead to hypokalemia, which hampers the alkalinization of urine.

Forced Acid Diuresis

Employed to expedite the elimination of alkaline drugs, such as cocaine, amphetamine, quinine, quinidine, and strychnine. The steps include:

• Administering ascorbic acid (vitamin C) to produce acid diuresis. Ammonium chloride has also been used but is less favored due to its toxic nature.
• Noting that this technique typically results in only a marginal increase in renal clearance of the drug. Thus, it's seldom practiced in medical settings.

Other Types of Diuresis

• Immersion diuresis: This phenomenon is triggered when the body is submerged in water or a similar liquid, primarily due to the liquid's temperature and pressure.

Applications

Forced alkaline diuresis is also recommended for treating rhabdomyolysis, a condition characterized by the breakdown of damaged skeletal muscle.

See also

• Ion trapping
• Haemodialysis
• Peritoneal dialysis
• Haemoperfusion
• Haemofiltration
• Charcoal
• Poison

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