Pharmacokinetic-pharmacodynamic relationship of piretanide in healthy and uremic subjects. Determinants of the diuretic effect of a loop diuretic

Acute tolerance to furosemide. Pretreatment with captopril or prazosin does not influence diuresis and natriuresis

To investigate whether the development of acute tolerance to furosemide in human subjects could be prevented or delayed by angiotensin converting enzyme inhibition or alpha 1-receptor blockade, a study was conducted on healthy volunteers. The protocol on the experimental days was identical except for pre-treatment with placebo, captopril or prazosin. During continuous furosemide infusion with urinary furosemide excretion at a constant rate, the subjects became progressively dehydrated, with a maximal decrease in plasma volume of 9-11%. The diuretic/natriuretic response to furosemide was similar in the three protocols. Acute tolerance to diuresis developed earlier than that to natriuresis, again with no differences between the protocols. Not until the plasma volume had decreased by 9% did the natriuresis diminish significantly. In the placebo and captopril protocols acute tolerance was caused mainly by a decreased glomerular filtration rate, and in the prazosin protocol mainly by increased tubular reabsorption. It is concluded that neither ACE inhibition nor alpha 1-receptor blockade prevented or delayed the acute tolerance to furosemide. The results suggest that acute tolerance to furosemide can be induced through different but complementary homeostatic mechanisms in the kidney.

Renal excretory responses to single and repeated administration of diuretics in healthy subjects: clinical connotations

Administration of an initial oral dose of hydrochlorothiazide 25 mg to healthy subjects is followed by increased 24-hour urinary outputs of sodium, chloride, and potassium. On the fourth day of once-daily dosing with hydrochlorothiazide 25 mg, 24-hour natriuresis and chloriuresis are no longer augmented, but the elevation in 24-hour kaliuresis that follows the first dose remains unchanged. Twenty-four-hour urinary calcium output is consistently reduced during repeated once-daily administration of hydrochlorothiazide 25 mg. The first oral dose of the loop diuretic torasemide augments the average natriuresis and kaliuresis in the 6 hours immediately after dosing in healthy subjects, in a dose-dependent fashion, within the 2.5 to 10-mg range. These increased urinary outputs are followed by rebounds below postplacebo values between 6 and 24 hours after dosing. As a result of this biphasic response, torasemide 2.5 mg qualifies as a nondiuretic formulation (it does not elevate 24-hour natriuresis), whereas torasemide 5 and 10 mg qualify as diuretic formulations. After the seventh dose of torasemide 5 or 10 mg during a regimen of once-daily therapy, 24-hour urinary sodium and chloride outputs no longer differ from their postplacebo counterparts. Twenty-four-hour kaliuresis tends to increase in a dose-dependent fashion after the first dose of torasemide (torasemide 2.5 and 5 mg do not augment it significantly), but this tendency is no longer present after the seventh once-daily dose, when torasemide (2.5, 5, or 10 mg) does not elevate the mean 24-hour kaliuresis. Twenty-four-hour calciuresis tends to increase in a dose-dependent manner (torasemide 2.5 mg does not elevate it significantly) after the first dose of torasemide; this calciuretic effect does not change in intensity after 7 days of once-daily treatment. The time course of natriuresis over the 24 hours following the administration of any given formulation of a loop or of an early distal tubular diuretic to healthy subjects is alike after the first and after the nth once-daily dose; therefore, it constitutes a definite characteristic of any given oral formulation. In the case of torasemide, lower doses have more protracted effects on natriuresis, to the extent that the time course of natriuresis over the 24 hours after administration of torasemide 2.5 mg to healthy subjects resembles the time course after administration of hydrochlorothiazide 25 mg, rather than the time course after administration of the overtly diuretic formulation torasemide 10 mg.

Response to furosemide during dehydration with and without naproxen pretreatment of kidney donors and renal transplant recipients

The response to 40 mg furosemide p.o. in 6 healthy kidney donors and 6 renal transplant recipients with and without naproxen pretreatment has been studied. No volume replacement was given in order to study the development of tolerance. The subjects showed an average dehydration of 1.5 kg.6 h-1. While mean creatinine clearance was equal in patients and donors (76 vs 80 ml/min), renal furosemide clearance was significantly lower in the patients (47 vs 81 ml min; P less than 0.05). The patients also excreted a smaller fraction of the dose in the urine (5.7 vs 7.8 mg/6 h; P less than 0.05). As the overall renal sensitivity was similar in the two groups, the natriuretic response was correspondingly smaller in transplant recipients as compared to donors. Within the observation period of 6 h after dosing, acute tolerance developed in the donors and in 4 of the 6 patients, as shown by clockwise hysteresis in the dose (urine furosemide excretion rate)-response (natriuresis) curves. Pretreatment with naproxen reduced renal sensitivity to furosemide (right shift of the dose response curve) in all the donors but in only 2 of the patients. In both groups acute tolerance was less pronounced after naproxen, which may indicate involvement of the prostaglandin system in the development of acute tolerance. The results may also indicate regeneration of sympathetic nerves with functional capacity in at least some renal transplants, or that other mechanisms of salt regulation compensate for loss of sympathetic nerve activity.

Effects of diuretics on outputs and flows of urine and urinary solutes in healthy subjects

The effects of single oral doses of common formulations of diuretics (i.e. formulations on the market or designed to be marketed) on 24-hour diuresis and natriuresis in healthy subjects are considered as a measure of the renal excretory potency of diuretics. Common formulations of distal tubular diuretics (e.g. hydrochlorothiazide 25mg, xipamide 10mg and 20mg) are more potent diuretics and natriuretics than common formulations of loop diuretics [e.g. furosemide (frusemide) 40mg, torasemide 2.5, 5 and 10mg]. Indeed, some common formulations of loop diuretics, such as torasemide 2.5, do not increase 24-hour diuresis or natriuresis in healthy subjects. 24-hour kaliuresis and magnesiuresis are elevated by common formulations of distal tubular diuretics, but they are only slightly increased or (more usually) not affected by common formulations of loop diuretics, when single doses are administered to healthy individuals. Common formulations of loop diuretics have lower diuretic and natriuretic potency and lower kaliuretic and magnesiuretic effects than common formulations of distal tubular diuretics, because the pronounced elevations in urinary excretions caused by loop diuretics during the first 6 hours after dosing are followed by rebounds, with respect to post-placebo excretions, between 6 and 24 hours after dosing. These rebounds, which affect the urinary flows of fluid, chloride, sodium, potassium and magnesium, do not occur after administration of common formulations of distal tubular diuretics, at least during the first 24 hours after administration of single doses to healthy subjects. The time courses of urinary excretions after loop diuretics are dose dependent. Higher doses produce more rapid changes in the urinary flows of fluid, chloride, sodium, potassium and magnesium than lower doses, to the extent that single administration of torasemide 2.5 or 5mg to healthy subjects is followed by urinary fluid and solute flows whose time courses resemble those after administration of hydrochlorothiazide 25mg.

Clinical pharmacokinetics of some newer diuretics

Several new diuretics have recently been developed. This review summarises the published knowledge about some of them. Azosemide is a loop diuretic. The bioavailability is about 15% and it has a half-life of 2 to 3 hours. Renal and non-renal clearance are 1.32 and 5.4 L/h, respectively. Etozolin is also a loop diuretic. It is rapidly metabolised to the active metabolite, ozolinone. The gastrointestinal uptake of etozolin is almost complete. The plasma half-life of etozolin and ozolinone are 2 and 10 hours, respectively. The compounds are mainly eliminated as metabolites. Renal and liver impairment do not seem to change the pharmacokinetics. Fenquizone has properties similar to the thiazides. The plasma half-life is approximately 17 hours. Apparent volume of distribution averaged 686 L and renal clearance is 7.2 L/h. Indapamide acts predominantly on the proximal segment of the distal tubule and also has direct vasodilatory effects. Gastrointestinal uptake is at least 80%. The drug binds highly to carbonic anhydrases of red blood cells. Protein binding is about 80%, while terminal plasma half-life is 15 hours and the apparent volume of distribution 25 L. Renal clearance is 0.3 L/h and non-renal clearance 0.9 L/h. Several metabolites have been described, of which one major metabolite is pharmacologically active. Muzolimine is a loop diuretic. Its uptake is almost complete, but decreased substantially by food. The protein binding is about 65%, the apparent volume of distribution is about 1 L/kg and average terminal half-life 10 to 20 hours. Elimination is mainly non-renal, and non-renal clearance ranges between 0.5 and 1.32 L/h. The pharmacokinetics of the drug do not seem to be changed in cardiac failure. Terminal plasma half-life is essentially unchanged in patients with renal failure, except in those with very severe reduction of glomerular filtration rate. Piretanide is a loop diuretic which is about 6 times as potent as frusemide (furosemide). Its bioavailability is most likely complete in healthy subjects and in renal patients. Protein binding in healthy subjects is about 95%. The plasma half-life of the drug is about 1 hour and apparent volume of distribution averages about 17 L. Renal and non-renal clearance are about 6 L/h, although renal clearance is decreased in renal failure: this decrease is correlated with glomerular filtration rate. Non-renal clearance is unchanged in renal failure, as is the apparent volume of distribution.(ABSTRACT TRUNCATED AT 400 WORDS)