Nitazoxanide: pharmacokinetics and metabolism in man.

OBJECTIVES: Nitazoxanide (N), a new broad-spectrum parasiticidal agent, is rapidly deacetylated to tizoxanide (T). The objective of the study was to determine if metabolites other than T are present in the plasma and excreted after single dose oral administration of radiocarbon-labelled N in healthy subjects. METHODS: Six healthy volunteers received a single 500 mg oral dose of N labelled with 2.92 MBq radiocarbon. The radioactivity in blood, plasma, urine, feces and expired air was monitored at scheduled intervals for up to 10 days. Selected samples were assayed by HPLC for T and submitted to metabolite identification by mass spectrometry. In vitro experiments were also conducted (incubation with animal and human microsomes, deacetylation kinetics). Plasma and bile samples obtained in a patient treated with N for sporozoal infection were also assayed for T. RESULTS: Elimination of radiocarbon occurred both in the urine (31.5% of the dose on average) and in the feces (66.2% on average). T and T-glucuronide contributed 15% of total urine radioactivity. N was found to deacetylate extremely rapidly to T in plasma (half-life of about 6 minutes at 37 degrees C) as well as in presence of liver microsomes. T was the only species obtained by incubation with human microsomes while rat microsomes yielded hydroxylated T in addition. The main species identified in human plasma, urine and bile was T-glucuronide, the identification of which was confirmed by comparison with an authentic sample. No species other than T was detected in feces, indicating intensive intestinal deconjugation, while radioactivity and absorbance detectors showed largely unresolved clusters.

Pharmacokinetic profile of 14C-labeled clopidogrel.

In order to obtain a global assessment of circulating clopidogrel-related products and of the excretion of the drug, the pharmacokinetic behavior and the excretion balance of 14C radioactivity following the administration of a single dose of 75 mg of 14C-labeled clopidogrel were compared in 6 clopidogrel-free healthy male subjects (Period I) and after 7 days of once daily therapy with the unlabeled drug in these subjects (at steady state) (Period II). The two study periods were separated by a 4-week washout period. For each administration of 14C-clopidogrel, blood samples were collected before and at regular intervals over 28 days after administration of the radiolabeled drug. Expired air samples were collected before and over 24 hours after the administrations of 14C-clopidogrel. All urine voided and all stools were collected before and for up to 120 hours after the administration of 14C-clopidogrel, in consecutive periods of 12 to 24 hours. The mean radiocarbon plasma concentration profiles after administration of 14C-clopidogrel given as a single dose (Period I) and during steady state (Period II) were superimposable. There were no statistically significant differences between the two treatments for any parameters. A Cmax of 3.9 mg-Eqv/L was reached after a median time of 1 hour (Tmax). The plasma elimination half-life, t1/2, ranged from 336 hours to 672 hours in Period I and from 275 to 433 hours in Period II. The radiocarbon excretion over 10 to 12 hours post-dose (time to last measurable radioactivity) in expired air represented 0.31 to 0.35% of the administered dose. Mean cumulative urinary excretion over 120 hours represented 41% of the dose after a single-dose administration and 46 % after administration at steady state. The cumulative fecal recovery over 120 hours ranged from 35 to 57% of the dose in Period I and from 39 to 59% of the dose in Period II. Mean total excretion of radioactivity was 92% of the dose during Period I and 93% during Period II. These data indicate that, following multiple-dose administration of clopidogrel, the biodisposition of the drug remains unaltered compared to a single dose.

Nature of the inhibition by amiodarone of isoproterenol-induced tachycardia in the dog.

Inhibition of in vivo isoproterenol-induced tachycardia by i.v. amiodarone was studied in anesthetized dogs. Significant dose-response curves to isoproterenol could not be obtained in single animals because of the time-dependent lowering of the inhibitory effect of the drug. Single isoproterenol injections after amiodarone in 105 dogs allowed dose-response curves to be obtained. The slope of these curves decreased with increasing doses of amiodarone, and the maximal rate stimulation diminished also in a dose-dependent manner. These features are consistent with a non-competitive inhibition pattern. A mechanism of the beta-adrenergic antagonism developed by amiodarone is suggested.

Comparative pharmacodynamics of torasemide and furosemide in patients with oedema.

The pharmacodynamics of torasemide (1-isopropyl-3- ([4-(3-methyl-phenylamino)pyridine]-3-sulfonyl)urea), a new potent loop diuretic, were compared to those of furosemide in a double-blind controlled study in 18 patients with oedema of various origin. Torasemide behaved like furosemide in exerting a potent diuretic effect which culminated during the first 4 h after its administration. Nevertheless, torasemide was about 8 times more potent, exerted a longer lasting diuretic effect and was more potassium sparing than furosemide. Torasemide did not accumulate during repeated administration (5 days). It was well tolerated and efficient in the treatment of oedema due to congestive heart failure and hepatic cirrhosis. The long duration of action and the potassium sparing effect of torasemide compared to furosemide are promising features of this new potent loop diuretic.

Torasemide, a new potent diuretic. Double-blind comparison with furosemide.

The pharmacodynamic effects of torasemide, a new potent loop diuretic, were compared with those of furosemide in a double blind controlled study in 18 hypertensive patients with oedema of various origins. Given orally for 5 days, torasemide was clinically very effective and well tolerated. On a weight basis, the diuretic, natriuretic and chloruretic effects of torasemide were about 8-times greater than those of furosemide. However, the kaliuretic effect of torasemide was only 3-times greater than that of furosemide, suggesting that torasemide is more potassium sparing than furosemide. Torasemide displayed a rapid onset of action, similar to that of furosemide but had a longer diuretic effect without any rebound phenomenon. Torasemide and furosemide did not effect creatinine clearance or uric acid excretion. Both furosemide and torasemide lowered systolic blood pressure but the effect of torasemide was more marked than that of furosemide. In this group of aged and hypertensive patients with oedema, the pharmacokinetics of torasemide was comparable to that reported in young healthy volunteers, and were similar on the first and fifth days of treatment. The long duration of action and the potassium sparing effect of torasemide compared to furosemide are promising features of this new loop diuretic in the treatment of oedema and hypertension.

Effect of oxametacin on endogenous uric acid clearance rate in healthy volunteers.

Oxametacin, a new non steroidal anti-inflammatory compound, with analgesic, antipyretic and anti-inflammatory properties comparable to those of indomethacin, has been claimed to be effective in treatment of acute attacks of gout. The present study comprises an investigation in 8 healthy volunteers of the effect on the endogenous uric acid clearance rate, of oxametacin administered alone or in combination with the conventional hypouricaemic agents benzbromarone or allopurinol. Whether given alone or in combination with these drugs, oxametacin failed to alter the clearance rate of endogenous uric acid. In view of its good tolerance and its possible efficacy in treatment of acute attacks of gout, the present data help to validate use of oxametacin in acute gout.

Pharmacokinetic study of cefuroxime in the elderly.

1 The pharmacokinetics of cefuroxime have been investigated in 18 patients at least 70 years old. The drug was given either by continuous infusion (7 cases) or by multiple injections (11 cases) for 3 to 11 days (mean duration: 7 days). 2 The unchanged drug was assayed in blood plasma and in the urine by high performance liquid chromatography (h.p.l.c). 3 Cefuroxime was cleared, unchanged, almost exclusively by the kidneys, even when kidney function was impaired. Creatinine clearance ranged from 1.02 to 4.08 1/h (17 to 68 ml/min) in this group of patients and plasma clearance of cefuroxime varied from 1.02 to 8.16 1/h (17 to 136 ml/min) (r = 0.7 P less than 0.001 for linear correlation), but the apparent rate constant for nonrenal elimination remained quite small (average: 0.04 h-1) and independent of creatinine clearance (r = 0.06, n = 17). 4 Since creatinine clearance decreases sharply with age, it might be suggested that cefuroxime dosage be related to creatinine clearance in the elderly, even when no renal impairment is suspected.