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Biomedical subjects

A M Taburet

Publications and source records attributed to A M Taburet.

At least 55 records · Page 3Linked to original sources
PubMed1990

Pharmacokinetics of zidovudine in patients with liver cirrhosis.

The pharmacokinetics of zidovudine (azidothymidine, AZT) was investigated after oral administration (200 mg) in 14 human immunodeficiency virus seronegative patients with liver cirrhosis. They were divided in three groups according to the severity of the liver disease quantitated by the Child-Pugh score. Plasma and urine concentrations of zidovudine and its glucuronidated metabolite (GAZT) were measured simultaneously by HPLC assay. Findings were compared with those previously measured in six healthy volunteers. As a consequence of a marked drop in oral clearance (10 +/- 4 versus 38 +/- 15 ml/min/kg), zidovudine concentrations, half-life, and mean residence time were increased in patients with cirrhosis. No difference could be established between the three groups. The reason for such a decrease in oral clearance of zidovudine was the reduction in the GAZT formation clearance (236 +/- 73 versus 1540 +/- 540 ml/min); this led to a decrease in the AUC ratio of GAZT and zidovudine (1.3 +/- 0.6 versus 4.6 +/- 0.7), which was directly related to the severity of the cirrhosis. In patients, as in volunteers, formation of GAZT rate limits its elimination. To avoid important cumulation of zidovudine after repeated dosing in patients with acquired immunodeficiency syndrome who have hepatic impairment, a dosage adjustment could be proposed.

Adult↗
PubMed1990

Pharmacokinetics of sodium fusidate after single and repeated infusions and oral administration of a new formulation.

The pharmacokinetics of sodium fusidate were studied in eight healthy volunteers (five males and three females) aged 21 to 33 years (29.1 +/- 1.5), weight 46 to 79 kg (61.6 +/- 4.0 kg). First, the subjects were given 500 mg of sodium fusidate by infusion over two hours; secondly, one month later, the volunteers were given 500 mg of fusidate by infusion every eight hours for three days; thirdly, two 250 mg tablets of a new film coated formulation were administered as a single dose. Plasma concentrations of fusidate were measured by HPLC. Peak plasma concentrations reached at the end of the first and the last infusions were 52 +/- 5 mg/l and 123 +/- 12 mg/l respectively. The following mean pharmacokinetic parameters were obtained after single intravenous administration: elimination half-life 10 +/- 1 h, total clearance 22 +/- 2 ml/min and volume of distribution 0.30 +/- 0.04 l/kg. After repeated administration the half-life and the volume of distribution remained unchanged whereas total clearance was halved (11 +/- 1 ml/min). This leads to an experimental accumulation ratio (3.6 +/- 0.2) higher than the theoretical one (1.8 +/- 0.1; P less than 0.01). Consequently, mean trough and peak steady state plasma concentrations (81 +/- 9 and 123 +/- 12 mg/l respectively) are higher than those expected from the single dose kinetics (33 +/- 4 and 76 +/- 7 mg/l respectively). This dose regimen leads to concentrations well above the MIC for most sensitive strains.(ABSTRACT TRUNCATED AT 250 WORDS)

Administration, Oral↗
PubMed1990

Disposition of fleroxacin, a new trifluoroquinolone, and its metabolites. Pharmacokinetics in renal failure and influence of haemodialysis.

The pharmacokinetics of fleroxacin and its metabolites following a single oral dose of fleroxacin 400mg were examined in 6 healthy subjects and 24 patients with various degrees of renal insufficiency. Plasma and urine samples, collected at various times after administration, were assayed by high performance liquid chromatography (HPLC). In healthy subjects, Cmax was 6.8 +/- 0.7 mg/L; tmax = about 1h, t1/2 = 14 +/- 2h, total clearance = 4.86 +/- 0.72 L/h and the percentage of unchanged fleroxacin excreted in urine in 48 hours was 48 +/- 4% (HPLC). Plasma concentrations of metabolites were very low and accounted for no more than 5% of the levels of unchanged fleroxacin. In uraemic patients Cmax did not change, whatever the degree of renal failure; tmax was increased in patients with a glomerular filtration rate below 0.6 L/h, and Vd/f was independent of the severity of renal failure. These data suggest that bioavailability of the drug is unchanged. In uraemic patients t1/2 was prolonged and AUC multiplied by a factor of 2 to 3. A linear relationship was found between total and renal clearances of fleroxacin and creatinine clearance. Accumulation of N-demethyl-fleroxacin and N-oxide-fleroxacin was very high in uraemic patients, due to slow formation of these metabolites and decreased urinary elimination. Dialysance of fleroxacin and of its metabolites was approximately 3.6 to 4.8 L/h. These findings suggest that fleroxacin dosage may need to be reduced in patients with severe renal disease; in haemodialysed patients, treated every 2 days, a single dose of fleroxacin 400mg is recommended at the end of each dialysis session.

Adult↗
PubMed1990

Disposition of fleroxacin, a new trifluoroquinolone, and its metabolites. Pharmacokinetics in elderly patients.

The pharmacokinetics of fleroxacin and its main metabolites, N-demethyl-fleroxacin and N-oxide-fleroxacin, were studied in 12 elderly patients aged 63 to 88 years. Plasma and urine samples collected at different times after drug administration were analysed by a specific reverse phase high performance liquid chromatography (HPLC) method. The peak plasma concentration (Cmax) of fleroxacin was 15.6 +/- 1.6 mg/L, time to Cmax (tmax) was about 3h, elimination half-life (t1/2) was 16 +/- 1h and the percentage of unchanged fleroxacin excreted in urine was 39 +/- 3% of the dose. The plasma concentrations of metabolites were very low and accounted for no more than 4% of the concentration of unchanged fleroxacin. Plasma parameters were mainly correlated with age and weight; urinary parameters were correlated with creatinine clearance. Compared with results in younger normal patients, no significant change in the t1/2 of fleroxacin or metabolites was observed. Assuming that the bioavailability (f) is complete, the apparent volume of distribution (Vd/f) was lower in elderly (0.9 +/- 0.1 L/kg) than in younger patients (1.3 +/- 0.1 L/kg) and a 2-fold decrease in apparent total clearance (CL/f) was noted (2.58 +/- 0.42 vs 4.86 +/- 0.72 L/h); plasma concentrations were consequently higher in elderly patients. Compared with patients with renal failure, the pharmacokinetics of fleroxacin and metabolites in the elderly were similar to those of patients with mild to moderate renal insufficiency. On the basis of the findings of this single dose study, no major dosage adjustments are needed for patients of this age range except for those with creatinine clearance less than 30 ml/min.

Aged↗
PubMed1990

The effect of respiratory disorders on clinical pharmacokinetic variables.

Respiratory disorders induce several pathophysiological changes involving gas exchange and acid-base balance, regional haemodynamics, and alterations of the alveolocapillary membrane. The consequences for the absorption, distribution and elimination of drugs are evaluated. Drug absorption after inhalation is not significantly impaired in patients. With drugs administered by this route, an average of 10% of the dose reaches the lungs. It is not completely clear whether changes in pulmonary endothelium in respiratory failure enhance lung absorption. The effects of changes in blood pH on plasma protein binding and volume of distribution are discussed, but relevant data are not available to explain the distribution changes observed in acutely ill patients. Lung diffusion of some antimicrobial agents is enhanced in patients with pulmonary infections. Decreased cardiac output and hepatic blood flow in patients under mechanical ventilation cause an increase in the plasma concentration of drugs with a high hepatic extraction ratio, such as lidocaine (lignocaine). On a theoretical basis, hypoxia should lead to decreased biotransformation of drugs with a low hepatic extraction ratio, but in vivo data with phenazone (antipyrine) or theophylline are conflicting. The effects of disease on the lung clearance of drugs are discussed but clinically relevant data are lacking. The pharmacokinetics of drugs in patients with asthma or chronic obstructive pulmonary disease are reviewed. Stable asthma and chronic obstructive pulmonary disease do not appear to affect the disposition of theophylline or beta 2-agonists such as salbutamol (albuterol) or terbutaline. Important variations in theophylline pharmacokinetics have been reported in critically ill patients, the causes of which are more likely to be linked to the poor condition of the patients than to a direct effect of hypoxia or hypercapnia. Little is known regarding the pharmacokinetics of cromoglycate, ipratropium, corticoids or antimicrobial agents in pulmonary disease. In patients under mechanical ventilation, the half-life of midazolam, a new benzodiazepine used as a sedative, has been found to be lengthened but the underlying mechanism is not well understood. Pulmonary absorption of pentamidine was found to be increased in patients under mechanical ventilation. Pharmacokinetic impairment does occur in patients with severe pulmonary disease but more work is needed to understand the exact mechanisms and to propose proper dosage regimens.

Humans↗
PubMed1990

[Severe poisoning with intravenous phenytoin in the newborn. Value of peritoneal dialysis].

A severe poisoning with intravenous phenytoin in a newborn was treated with peritoneal dialysis in spite of its reported poor effectiveness, the drug being 90% protein-bound. During 10 hours, 1.41 mg/hr were eliminated by biotransformation and 1.80 mg/hr were removed with peritoneal dialysis allowing to suppress quickly life threatening cardiac side effects. This efficacy may be explained by an increase in the unbound protein fraction and a diffusion speed through the peritoneum higher than in older patients.

Biotransformation↗
PubMed1989

[Effect of hepatic failure upon the pharmacokinetics of cefixime].

Modifications of cefixime kinetics due to severe impairment of liver function were determined in 9 cirrhotic patients. Cefixime was administered as a single dose of 200 mg and levels were measured by HPLC. Maximum serum concentrations and area-under-the-curves of serum concentrations were not modified. The time for maximum serum concentration was delayed and the cefixime half-life in serum was prolonged, as a reflect of increased volume of distribution resulting from ascites and hypoalbuminemia. Renal clearance increased in these patients, possibly because of reduced extra-renal clearance. No metabolite was detected in serum or urine. Modifications of cefixime kinetics resulting from impaired hepatic function were modest and did not require specific dosage adjustment.

Adult↗
PubMed1989

Zidovudine disposition in patients with severe renal impairment: influence of hemodialysis.

Pharmacokinetics of zidovudine (azidothymidine, AZT) was investigated after oral administration (200 mg) in 25 HIV seronegative subjects: 14 patients with severe renal impairment (creatinine clearance 6 to 31 ml/min), five hemodialyzed anuric patients, and six healthy subjects. Plasma and urine concentrations of zidovudine and its glucuronidated metabolite (GAZT) were measured simultaneously by HPLC assay. In healthy subjects, GAZT concentrations were higher than those of AZT; AUC values were 23.7 +/- 1.9 and 5.2 +/- 0.6 mumol.hr/L, respectively. Formation of GAZT rate-limits its elimination: GAZT half-life (t 1/2) parallels that of AZT, which is around 1 hour. In uremic patients, AZT concentrations were moderately increased (AUC = 11.7 +/- 1.1 mumol.hr/L), whereas t 1/2 and mean residence time (MRT) remain unchanged despite the decreased renal clearance (16 +/- 2 versus 220 +/- 58 ml/min) and decreased urinary excretion (1.6 +/- 0.3 versus 8.1 +/- 1.0% of the dose). In contrast, GAZT concentrations are markedly increased (AUC = 402.9 +/- 88.6 mumol.hr/L). As a consequence of the decreased renal clearance (27 +/- 3 versus 331 +/- 42 ml/min), elimination is the rate-limiting step and t 1/2 is increased (8 +/- 2 versus 0.9 +/- 0.1 hr). Contribution of a 4-hour hemodialysis session to AZT elimination appears to be negligible, whereas elimination of GAZT is enhanced. On the sole basis of AZT pharmacokinetic data, no particular dose adjustment appears to be necessary in patients who have severe renal impairment (creatinine clearance between 10 and 30 ml/min). However, high levels of GAZT should be anticipated with the usual dosage regimen.

Adult↗
PubMed1989

Pharmacokinetics of ornidazole in patients with acute viral hepatitis, alcoholic cirrhosis, and extrahepatic cholestasis.

Pharmacokinetics of ornidazole, a nitroimidazole derivative, was investigated after intravenous injection in 3 groups of 10 patients with different hepatic diseases: hepatitis, noncholestatic cirrhosis and extrahepatic cholestasis. Plasma concentrations of ornidazole and its two major hydroxylated metabolites, M1 [alpha-(chloromethyl)-2-hydroxymethyl-5-nitroimidazole-1-ethanol] and M4 [3-(2-methyl-5-nitroimidazole 1-yl)-1,2-propane diol] were measured by HPLC assay. As a consequence of a decreased clearance (26% to 48%), the half-life and MRT are increased in all patients by 19% to 38% when compared with healthy volunteers. No clear difference could be established between the different groups. The volume of distribution remains the same in all patients and controls except those suffering from cancer. As previously shown in patients with severe liver cirrhosis, both metabolites accumulate in plasma as a result of decreased elimination; formation is no longer the rate-limiting step of their kinetics. This metabolite accumulation is in part due to decreased biliary excretion and to hepatocellular failure.

Adult↗
PubMed1987

Pharmacokinetics of ciprofloxacin tablets in renal failure; influence of haemodialysis.

The pharmacokinetics of ciprofloxacin has been studied after a single oral dose of 500 mg given to 5 normal subjects (N) and to 15 patients grouped according to their residual renal creatinine clearance: Group I, 8-30 ml X min-1, Group II, less than 8 ml X min-1, and Group III, haemodialysed patients studied twice--during an interdialysis period (IIIa) and in a 4 h haemodialysis session (IIIb). Ciprofloxacin was assayed by reverse phase HPLC using a spectrofluorimetric detection. The peak plasma concentration (2-5 mg X l-1) was reached within 2 h after drug administration. Apparent volume of distribution, 6.6 (N), 5.0 (I), 2.7 (II) and 4.2 (IIIa) l X kg-1 and total plasma clearance, 770 (N), 440 (I), 378 (II) and 314 (IIIa) ml X min-1 were decreased in relation to the degree of renal impairment. Mean plasma half-lives for patients in the 4 groups were 7.3 (N), 10.4 (I), 7.2 (II) and 9.3 (IIIa) h. In groups N, I and II, 40, 16 and 8% of the administered dose was eliminated through the kidney, with mean renal clearances of 305 +/- 63, 61 +/- 21 and 21 +/- 3 ml X min-1. A linear relationship was found between the renal clearance of ciprofloxacin and the glomerular filtration rate (r = 0.75, n = 15). Ciprofloxacin was partly removed by haemodialysis (IIIb): the dialyser extraction ratio was 23% and the dialysis clearance was 40 ml X min-1.

Administration, Oral↗
PubMed1986

Pharmacokinetics of ornidazole in patients with severe liver cirrhosis.

Pharmacokinetics of ornidazole, a nitroimidazole derivative, was studied after intravenous injection in 10 patients with severe alcoholic cirrhosis and 10 healthy volunteers. Plasma concentrations of ornidazole and its two major hydroxylated metabolites, M1 (alpha-(chloromethyl)-2-hydroxymethyl-5-nitroimidazole-1-ethanol) and M4 (3-(2-methyl-5-nitroimidazole 1-yl) 1,2 propane diol), were measured by HPLC. The t1/2 of ornidazole was 14.1 +/- 0.5 hours for normal subjects and 21.9 +/- 2.9 hours for patients with cirrhosis. Mean plasma clearance was 50.6 +/- 2.1 ml/min in control subjects and 34.9 +/- 4.9 ml/min in patients, whereas apparent V SS was not modified in hepatic insufficiency. In healthy volunteers, M1 and M4 levels are well below levels of the parent drug; in cirrhosis both metabolites accumulate in plasma as a result of decreased elimination. Hepatic cirrhosis prolongs ornidazole elimination, and to avoid cumulation the interval between repeated doses could be doubled.

Adult↗
PubMed1985

Haemodialysis does not affect the pharmacokinetics of nifedipine.

To establish dosage recommendations in patients with end-stage renal disease undergoing chronic haemodialysis, nifedipine kinetics were studied between and during haemodialysis sessions. In eight patients, during the interdialytic period, peak plasma concentrations of nifedipine (29-332 ng/ml) were reached 0.5-1.0 h after administration of a single 10 mg oral dose. Elimination half-life and oral plasma clearance were respectively 2.6 +/- 0.5 h and 1 176 +/- 412 ml/min. Nifedipine plasma protein binding was decreased in uraemic patients (88.8 +/- 0.3% vs 94.4 +/- 0.1%) but not affected by haemodialysis. Removal by haemodialysis was low: the dialyser extraction ratio and the dialysis clearance were respectively 2.3 +/- 0.8% and 2.8 +/- 0.9 ml/min.

Adult↗
PubMed1985

[Clinical pharmacology of calcium inhibitors].

The pharmacokinetics of the commercially available calcium antagonists, diltiazem (Tildiem), nifedipine (Adalate), perhexiline (Pexid), and verapamil (Isoptine) are well known; the pharmacokinetics of bepridil (Cordium) need further study. The properties of nicarpidine, a molecule currently being tested, will also be described. These products are well absorbed from the gastrointestinal tract but undergo variable degrees of transformation during the first passage through the liver. The bioavailabilities of bepridil, diltiazem and nifedipine are of the order of 40 to 60%; those of verapamil and nicarpidine are lower, 10-20% and 15-30%, respectively. The rates of absorption vary according to the derivatives and galenic preparations; in general, they are rapid; peak plasma concentrations are usually obtained one to four hours after administration. Protein binding is high but does not interfere in the distribution; the volumes of distribution of bepridil, diltiazem and verapamil are large (4-5 l/kg); those of nifedipine and nicardipine are smaller (l l/kg). The halflives of diltiazem, nifedipine, nicardipine and verapamil are short (1 to 5 hours); those of bepridil and perhexiline are longer (2 to 3 days). The main method of elimination is by hepatic transformation with high plasma clearance rates: diltiazem and verapamil have pharmacologically active derivatives whose contributions to the overall activities of the drugs are not fully understood. Physiopathological changes of the pharmacokinetic properties of diltiazem and verapamil (elderly patients, hepatic failure) have been described.

Age Factors↗