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Analytical methods for the determination of diuretics in bovine milk
Diuretics are chemically heterogeneous compounds used as therapeutic agents in certain pathological conditions to eliminate bodily fluids.
They not only promote renal excretion of water and salt but also affect the renal absorption and excretion of other ions, e.g., potassium, calcium, and magnesium. The diuretics, due to their variety of chemical structures, have different pharmacological properties and accordingly are classified into four groups: carbonic anhydrase inhibitors, loop, thiazide and thiazide type, and potassium sparing diuretics. The carbonic anhydrase inhibitors, e.g., acetazolamide, decrease the conversion of bicarbonate ion to carbonic acid resulting in an increase in sodium, potassium, and bicarbonate renal excretion. This also increases the pH of the urine. Furosemide has been reported to be the most potent and short-acting loop diuretic. It is widely used to treat edematous states of hepatic, cardiac, and renal origin. It is also a common drug of abuse in livestock shows since it reduces tissue water resulting in improved muscle tone appearance. The thiazide diuretics, chlorothiazide (CTZ), hydrochlorothiazide (HCTZ), and trichlormethiazide (TCMTZ) increase the excretion of potassium and can cause hypokalemia during long-term maintenance therapy. Therefore, thiazides are often given with potassium sparing diuretics such as amloride, in order to maintain electrolyte balance in the body. Trichlormethiazide is given in combination with dexamethasone. The combined diuretic activity of TCMTZ and the specific anti-inflammatory activity of dexamethasone are complementary in the reduction of physiological parturient edema of the mammary gland and associated structures. Because the two drugs are complementary in their action, effects are achieved with a minimum dosage of TCMTZ. The clinically determined saluretic potency of TCMTZ is estimated to be 10-20 times that of HCTZ and 100-200 times that of CTZ, resulting in a decrease in the incidences of hypokalemic manifestation (ref. 1). Diuretic toxic effects include bone marrow depression, altered carbohydrate metabolism, and elevated levels of urea, uric acid and sugar.
Furosemide and thiazide diuretics, CTZ, HCTZ, and TCMTZ are approved for use in dairy cattle for the treatment of post-parturient edema of the mammary gland and associated structures (ref. 2). Furosemide is also a common drug of abuse in livestock shows since it reduces tissue water resulting in improved muscle tone. The unauthorized use of these diuretics, or the failure to follow label directions for approved use in cattle, could lead to unacceptable residues in meat or milk destined for human consumption.