Ethacrynic Acid

Optimization of 3-Cyano-7-cyclopropylamino-pyrazolo[1,5-a]pyrimidines toward the Development of an In Vivo Chemical Probe for CSNK2A

3-Cyano-7-cyclopropylamino-pyrazolo[1,5-a]pyrimidines, including the chemical probe SGC-CK2-1, are potent and selective inhibitors of CSNK2A in cells but have limited utility in animal models due to their poor pharmacokinetic properties. While developing analogues with reduced intrinsic clearance and the potential for sustained exposure in mice, we discovered that phase II conjugation by GST enzymes was a major metabolic transformation in hepatocytes. A protocol for codosing with ethacrynic acid, a covalent reversible GST inhibitor, was developed to improve the exposure of analogue 2h in mice. A double codosing protocol, using a combination of ethacrynic acid and irreversible P450 inhibitor 1-aminobenzotriazole, increased the blood level of 2h by 40-fold at a 5 h time point.

Optimization of 3-Cyano-7-cyclopropylamino-pyrazolo[1,5-a]pyrimidines Toward the Development of an In Vivo Chemical Probe for CSNK2A

3-cyano-7-cyclopropylamino-pyrazolo[1,5-a]pyrimidines, including the chemical probe SGC-CK2-1, are potent and selective inhibitors of CSNK2A in cells but have limited utility in animal models due to their poor pharmacokinetic properties. While developing analogs with reduced intrinsic clearance and the potential for sustained exposure in mice, we discovered that Phase II conjugation by GST enzymes was a major metabolic transformation in hepatocytes. A protocol for co-dosing with ethacrynic acid, a covalent reversible GST inhibitor, was developed to improve the exposure of analog 2h in mice. A double co-dosing protocol, using a combination of ethacrynic acid and irreversible P450 inhibitor 1-aminobenzotriazole increased the blood level of 2h by 40-fold at a 5 h time point.

The clinical pharmacology of ethacrynic acid

Ethacrynic acid (Edecrin) is a loop diuretic that produces a prompt and profound diuresis. The primary action of ethacrynic acid is the inhibition of the activity of the Na⁺-K⁺-2Cl⁻ symporter in the thick ascending limb of the loop of Henle. The onset of action is usually within 30 minutes after an oral dose and within 5 minutes after an intravenous injection. After oral administration, peak diuretic effect occurs in about 2 hours and the effect lasts about 6-8 hours. After intravenous administration, peak diuretic effect occurs within 30 minutes and the diuretic effect is virtually completed in 2-4 hours. The bioavailability of ethacrynic acid approximates 100%, with maximal blood level between 40 and 92 minutes. The elimination half-life has been reported to be less than 1 hour, but highly variable (average 30 minutes with a range of 12-160 minutes). Intravenous ethacrynic acid has a prompt venous dilatory effect and immediately relieves symptoms of pulmonary congestion, before a diuresis can occur. Ethacrynic acid is effective in all types of edema whether there is clinical acidosis, alkalosis, or electrolyte imbalance. Most side effects of ethacrynic acid can be attributed to its effectiveness (volume depletion); however, it may cause metabolic alkalosis that is preventable by KCl replacement. Ethacrynic acid has ototoxic effect that occasionally results in temporally or permanent deafness. Despite limitations, ethacrynic acid has been employed in the treatment of congestive heart failure and other edematous states, especially in patients allergic to sulfa-containing drugs because all the other loop diuretics have a sulfa moiety.

Respiratory adjustment to chronic metabolic alkalosis in man

This study examined the ventilatory adjustment to chronic metabolic alkalosis induced under controlled conditions in normal human volunteers. Metabolic alkalosis induced by buffers (sodium bicarbonate, trishydroxymethylamine methane) or ethacrynic acid was associated with alveolar hypoventilation, as evidenced by a rise in arterial Pco(2), a fall in arterial Po(2), a reduced resting tidal volume, and a diminished ventilatory response to CO(2) inhalation. Alveolar hypoventilation did not occur when metabolic alkalosis was induced in the same subjects by thiazide diuretics or aldosterone despite comparable elevations of the arterial blood pH and bicarbonate concentration.The different ventilatory responses of the two groups could not be ascribed to differences among individuals comprising each group, pharmacological effects of the alkalinizing agents, differences in the composition of the lumber spinal fluid, changes in extracellular fluid volume, or sodium and chloride balance.The differences in ventilatory adjustments were associated with differences in the patterns of hydrogen and potassium ion balance during the induction of alkalosis. Alveolar hypoventilation occurred when hydrogen ions were buffered (sodium bicarbonate, trishydroxymethylamine methane) or when renal hydrogen ion excretion was increased (ethacrynic acid). Alveolar hypoventilation did not occur when induction of similar degrees of extracellular alkalosis was accompanied by marked potassium loss and no demonstrable increase in external hydrogen loss (thiazides and aldosterone).These observations suggest that respiratory depression does not necessarily accompany extracellular alkalosis but depends on the effect of the mode of induction of the alkalosis on the tissues involved in the control of ventilation.

Drug-induced gout

A number of pharmacological agents can induce hyperuricaemia, and sometimes gout, usually by interfering with the renal tubular excretion of urate but also in some instances by increasing the formation of uric acid. Alcohol is well known to have this property and in recent years diuretic-induced hyperuricaemia has become a global phenomenon. Other drugs which can cause hyperuricaemia are salicylates, pyrazinamide, ethambutol, nicotinic acid, cyclosporin, 2-ethylamino-1,3,4-thiadiazole, fructose and cytotoxic agents. A special type of 'drug-induced gout' can follow the rapid lowering of serum uric acid by allopurinol or uricosuric drugs.

Toxicological studies on tienilic acid in rats

The subacute oral toxicity of tienilic acid in male and female Sprague--Dawley rats has been studied. Animals were given tienilic acid 0, 30, 120 and 480 mg/kg body weight as a 3% gum arabic suspension for 28 days. At 30 mg tienilic acid blood pressure and serum uric acid decreased. At the two higher dose-levels a slight decrease in hemoglobin and an increase in S-GPT was noticed and there was a significant increase in the liver weight and serum magnesium concentration of male rats, while the liver weight of female rats increased only slightly. On microscopic examination, unicellular necrosis of small groups of liver cells was noted, together with focal round-cell infiltration and some stasis of the two higher dose-levels in some animals. Tienilic acid had no noticeable effects on other organs or parameters.

Antagonism of endogenous mineralocorticoids in normal subjects by prorenoate potassium and spironolactone

The pharmacological activity of single oral doses of a new aldosterone antagonist, prorenoate potassium, has been compared with spironolactone and placebo in a balanced double-blind crossover study in six healthy subject. Endogenous mineralocorticoids were stimulated by administration of frusemide followed by dietary sodium restriction, and the urinary excretion of electrolytes in response to prorenoate potassium, spironolactone and placebo was measured over a 24 hour period. Significant activity of prorenoate potassium and spironolactone was observed between 2 - 24 hours after medication, with peak activity at 6 - 8 hours. The active drugs significantly increased sodium excretion and the sodium : potassium (Na/K) ratio, but changes in potassium excretion were not significant. The total urine Na/K response to prorenoate potassium 45 mg was significantly greater than to spironolactone 100 mg.

Clinical trial of mefruside, a new diuretic

A controlled clinical trial of a new diuretic-mefruside-is reported, in which it was compared with frusemide in 15 normal subjects and 15 patients with fluid retention. It was found to be an effective diuretic which, in the patients, produced a significantly greater excretion of water and electrolytes than an equal dose of frusemide. Its smooth prolonged action, maximal in the first 12 hours, made it of particular value for maintenance therapy. In a short-term trial on a further 15 hypertensive patients mefruside was shown to have a useful hypotensive action. The drug was well tolerated with minimal side effects.

Frusemide in heart failure of infancy

Twelve infants with heart failure and one with perinatal oedema were treated with intramuscular frusemide (1·0-1·25 mg/kg). Frusemide was found to be a safe effective diuretic in infants with heart failure, resulting in clinical improvement, marked excretion of water, sodium, and chloride, with a lesser and more variable effect on potassium excretion. Complications were uncommon with this dose. The drug is most effective in acute pulmonary oedema or acute worsening of heart failure, but day-to-day control of persistent heart failure is more easily obtained by using repeated doses of oral or intramuscular frusemide plus, if needed, aldactone A or triamterene.

Amiloride. A potassium-sparing natriuretic agent

Amiloride, a new, well-tolerated oral natriuretic and mild diuretic agent, has been evaluated alone and in combination with other diuretics. Its remarkable ability to promote retention rather than loss of potassium makes it a useful adjunct in the management of even the most severe edematous states. It also retards the alkalosis produced by certain of the stronger diuretics by blocking hydrogen secretion and promoting bicarbonate loss. In addition to being a valuable adjunctive agent, the compound may be useful alone because of the advantages inherent in steady, sustained natriuretic therapy with a mild diuresis as opposed to incurring precipitous alterations in fluid and electrolyte balance with the intermittent use of more potent agents. In certain patients it was mildly antihypertensive.

Amiloride produced marked increases in aldosterone secretion with lesser rises in plasma renin. The adrenal stimulation therefore appeared to result from both potassium retention and renin activation consequent to natriuresis.

The compound appears to act primarily in the distal nephron, blocking both sodium-hydrogen exchange and sodium-potassium exchange. Like triamterene, but unlike spirolactone, amiloride has the characteristics of a noncompetitive inhibitor of aldosteronedirected sodium and potassium transport. Because of this, it may be expected to produce more predictable effects than spirolactone and at least in certain instances to be more powerful. It may also be preferable to spirolactone for the acute control of derangements in potassium balance because of its more rapid onset and disappearance of action.

No significant toxicity was encountered; however, serum potassium values should be carefully monitored, especially in situations involving impaired renal function.

Redistribution of renal blood flow produced by furosemide and ethacrynic acid

Outer medullary blood flow ( 85 Kr method) is markedly reduced by furose-mide and ethacrynic acid injected into the renal artery of unanesthetized dogs; juxtamedullary cortical flow is also decreased. Anatomic localization of the redistribution was verified by autoradiography and by silastic injection studies. The injected specimens demonstrated a relative increase in the resistance of the peritubular capillaries of the juxtamedullary cortex and outer medulla, the blood supply of the juxtamedullary tubules, Henle's loops and collecting ducts; the vasa recta were dilated. Total renal blood flow (Doppler Flowmeter) decreased 10% 1 min after injection, and then gradually began to increase at 2 to 3 min, reaching levels 25 to 30% above control as cortical blood flow increased. The vasodilatation in the cortex is probably localized in the pars radiata. The onset of the diuresis coincided with the decrease in renal blood flow, and persisted after total renal blood flow returned to control value. Thus, the time course of the dicresis correlated more closely with the sustained decrease in juxtameduiary and outer medullary blood flow.