Forced dieresis with acidification or alkalinization of urine is a common method for elimination of ceain poisons/drugs from the body. The elimination of which of the following drugs is commonly enhanced by alkaline dieresis -
Most drugs taken in overdose are extensively detoxified by the liver to produce inactive metabolites which are voided in the urine. Sometimes hepatic degradation produces active metabolites, but the secondary compounds are then conveed to non-toxic derivatives. Under these circumstances, forced diuresis is inappropriate. The procedure should be undeaken only if the following conditions are satisfied: # A substantial propoion of the drug is excreted unchanged. # The drug is distributed mainly in the extracellular fluid. # The drug is minimally protein-bound. # Principle-- Most drugs are weak electrolytes and exist paly as undissociated molecules at physiological pH. The extent of ionisation is a function of the ionisation constant of the drug (Ka for both acids and bases), and the pH of the medium in which it is dissolved. Ionisation constants are usually expressed in the form of their negative logarithm, pKa. Hence the pKa scale is analogous to the pH notation : the stronger an acid the lower its pKa, and the stronger a base the higher its pKa. Thus when pKa = pH, the concentrations of ionised and non-ionised drugs are equal. Cell membranes are most permeable to substances that are lipid soluble and in the non-ionised, rather than the ionised form. Thus the rate of diffusion from the renal tubular lumen back into the circulation is decreased when a drug is maximally ionised. Because ionisation of acidic drugs is increased in an alkaline environment, and that of basic drugs is increased in an acid solution, manipulation of the urinary pH enhances renal excretion. # Forced alkaline diuresis : This is most useful in the case of phenobarbitone, lithium, and salicylates. Administer 1500 ml of fluid IV, in the first hour as follows : - 500 ml of 5% dextrose - 500 ml of 1.2 or 1.4% sodium bicarbonate - 500 ml of 5% dextrose. # Forced acid diuresis : Forced acid diuresis is no longer recommended for any drug or poison, including amphetamines, strychnine, quinine or phencyclidine. REF:THE SYNOPSIS OF FORENSIC MEDICINE AND TOXICOLOGY:K S NARAYANA REDDY;PAGE NO 289
Amphetamines
Phenobarbitone
Phencyclidine
Theophylline
Poisoning