Fetoplacental passage of 2',3'-dideoxyinosine.
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Adult↗
Biomedical subjects
E Singlas
Publications and source records attributed to E Singlas.
Pharmacokinetics of metoclopramide in patients with liver cirrhosis.
The pharmacokinetics of metoclopramide were investigated after intravenous and oral administration in eight patients with severe alcoholic cirrhosis and in eight healthy volunteers. As a consequence of a 50% lower clearance (0.16 +/- 0.07 vs 0.34 +/- 0.09 l h-1 kg-1, plasma drug concentrations and the half-life of metoclopramide were greater in patients following both routes of drug administration. Volume of distribution (3.1 +/- 0.8 vs 3.4 +/- 1.2 l kg-1) and absolute bioavailability (79 +/- 19 vs 84 +/- 15%) were similar in the two groups. The adverse effects of metoclopramide observed in patients with marked hepatic impairment are likely to result from increased accumulation of the drug as a result of impaired clearance. Consequently a reduction in dose of 50% is recommended in patients with severe liver cirrhosis.
Administration, Oral↗
Pharmacokinetics of newer drugs in patients with renal impairment (Part I).
Many drugs are eliminated via the renal route and the usual dose must be modified in patients with severe renal impairment. This review is an attempt to supply physicians with the more recent data on pharmacokinetic studies of new drugs administered in uraemic patients. The review is in 2 parts: the first indicates the results of studies on the pharmacokinetics of antibiotic agents, antifungal, antiviral and antiulcer drugs, and nonsteroidal anti-inflammatory drugs. Special mention is made of epoetin (recombinant human erythropoietin). It was not possible to give all the information collected from the recent literature: since mild renal failure has little effect on the fate of a drug, pharmacokinetic data obtained in patients with a creatinine clearance (CLCR) of more than 50 ml/min has been omitted. Both the text and tables give recommendations for treating patients with moderate renal insufficiency (CLCR of about 50 ml/min), more severe renal impairment (CLCR between 10 and 50 ml/min) and end-stage renal failure with a very low creatinine clearance (below 10 ml/min). It was not possible to give uniform recommendations (i.e. reducing the dose while maintaining the same interval, or giving the same dose and prolonging the interval). This article follows the recommendations of the authors, which may vary for drugs in similar classes.
Humans↗
Pharmacokinetics of newer drugs in patients with renal impairment (Part II).
Cardiovascular diseases occur frequently in patients with renal failure. Any pharmacokinetic impairment in these diseases should be considered when individualizing drug therapy. The pharmacokinetics of new cardiovascular drugs in uraemic patients are reviewed: alpha- and beta-blocking agents, ACE inhibitors, centrally acting antihypertensive agents, calcium antagonists, antiarrhythmic agents and inotropic agents. Guidelines are proposed for adjustment of dosage regimens as a function of renal impairment. Renal or extrarenal elimination of drugs and their metabolites, and the activity of the latter, are taken into account. The disposition of new drugs such as flestolol, alacepril, delapril, propafenone, milrinone or enoximone, is not well documented in patients with renal failure. Further characterizations of the elimination of these compounds are needed and the potential therapeutic or toxic effects of the metabolites require evaluation to determine whether the dosage needs to be adjusted. Until such investigations are performed, those drugs should not be used in uraemic patients; if no therapeutic alternative is available, clinical controls are necessary at regular intervals. Relationships between pharmacological or therapeutic effects and drug plasma concentrations should be evaluated for such long term use drugs. The knowledge of a plasma concentration therapeutic window is important to provide information which will be useful in determining appropriate drug dosage in renal failure.
Acute Kidney Injury↗
[Clinical pharmacokinetics of an imipenem-cilastatin combination].
In the combination of imipenem (antibiotic of the thienamycin class, in the beta-lactam family) with cilastatin (renal dehydropeptidase I inhibitor) the ratio is 1:1. The urinary excretion of imipenem shows considerable interindividual variations due to the activity of renal dehydropeptidase I which degrades the compound. This makes it difficult to determine a mean dosage for therapeutic uses. However, when the dehydropeptidase I inhibitor cilastatin is given concomitantly with imipenem the urinary excretion and clearance of imipenem reach similar values in all subjects; in addition, the antibiotic is better tolerated by the kidney. Moreover, cilastatin has been shown to increase by 15 to 20 per cent the area under the imipenem plasma concentration curve. Following an intravenous infusion of imipenem 500 mg, the main pharmacokinetic values for the antibiotic are: area under the plasma concentration curve 43.2 +/- 4.7 h.mg/l; plasma clearance 195 +/- 25 ml/min; half-life 1.0 +/- 0.1 h; apparent volume of distribution 10.4 +/- 1.7 l. With repeated infusions of 500 ml every 6 to 8 hours, imipenem and cilastatin do not accumulate. In patients with renal impairment (creatinine clearance below 30 ml/min), cilastatin is excreted more slowly than imipenem and dosage must be adjusted accordingly.
Cilastatin↗
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↗
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↗
Do we need highly sensitive analytical techniques in phase I?
Pharmacokinetic studies constitute part of phase I clinical trials. Initiation of dosage regimen in phase II and III clinical trials depends on drug pharmacokinetics and the choice of dosing interval relies on the elimination rate constant. Consequently, inaccurate determination of these parameters can lead to unexpected drug levels and side-effects in patients and can delay the clinical development of the drug.
Chemistry Techniques, Analytical↗
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↗
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↗
[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↗
Comparative pharmacokinetics of zidovudine (AZT) and its metabolite (G.AZT) in healthy subjects and HIV seropositive patients.
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Adult↗
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↗
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↗
Diffusion of ofloxacin into cerebrospinal fluid of patients with purulent meningitis or ventriculitis.
The penetration of ofloxacin was studied in 22 patients with purulent meningitis or ventriculitis treated with conventional antibiotics. Three successive doses of 200 mg were infused at 12-h intervals during the acute stage of the disease. Ten patients received three additional doses when the meninges were considered to be healed. Cerebrospinal fluid (CSF) was drawn 0.5, 3, 6, or 12 h after the last infusion. Serial plasma and CSF samples were also obtained from patients with ventricular drainage. Concentrations in CSF ranged from 0.96 +/- 0.15 to 1.80 +/- 0.29 microgram/ml, depending on sampling time. The percentage of penetration in ventricular fluid, expressed as the ratio of the CSF area under the curve from 0 to 12 h to the plasma area under the curve from 0 to 12 h, was 73 +/- 6. Ofloxacin readily diffuses into CSF of patients with meningitis or ventriculitis and may be useful for treatment of CSF infections caused by susceptible pathogens.
Adolescent↗
Pharmacokinetics of rilmenidine.
Rilmenidine, an alpha 2-adrenoceptor agonist, was studied (1 mg single dose) in order to determine the effects of pathology on its basic pharmacokinetic parameters. Because of the mainly renal elimination of rilmenidine, studies involved hypertensive, elderly hypertensive, renal insufficient and hepatic insufficient patients. Hypertension was found to influence neither the absorption, the distribution nor the elimination processes; the linearity in the range of 1 to 2 mg and the absence of accumulation in long-term treatment were confirmed. In contrast, in the elderly, the absorption phase was delayed. The slight decrease in the apparent volume of distribution (-12%), with a notable decrease in the apparent total clearance (-50%) led to a prolonged elimination half-life (+50%). In renal failure, linear relations between the degree of renal impairment and the elimination parameters were shown. These relations allow the evaluation of the predicted steady-state level of rilmenidine for a given degree of renal failure. In hepatic insufficiency, the modification of rilmenidine disposition concerned exclusively the elimination phase in which apparent clearance was decreased approximately 20%. In conclusion, these results lead to a decreased dosage regimen in patients with severe renal failure.
Absorption↗
Lack of interaction between nizatidine and warfarin during chronic administration.
Nizatidine is a new antagonist of H2 receptors. The nizatidine warfarin interaction was investigated in healthy volunteers during chronic warfarin (mean warfarin dose: 5 +/- 0.9 mg/d) and nizatidine (300 mg/d) administration. Nizatidine coadministration did not increase the prothrombin time, kaolin-cephalin clotting time, and did not modify the activity of clotting factors II, VII, IX, X. Nizatidine did not influence the steady-state plasma warfarin concentration.
Adult↗
Pharmacokinetics of pefloxacin and amikacin administered simultaneously to intensive care patients.
Ten adult patients with severe infections in an intensive care unit were treated simultaneously with 6 mg/kg pefloxacin and 7.5 mg/kg amikacin, infused i.v. over 1 h every 12 h for 5 days. Twelve h after the last infusion, pefloxacin alone was administered orally (400 mg tablet) every 12 h for 10 days. The pharmacokinetics of pefloxacin and its main metabolites, norfloxacin and pefloxacin N-oxide, were determined after the first (Day 1) and last (Day 5) infusions and after the last oral dose (Day 15). The kinetics of amikacin was determined after the first and the last infusion. The maximal and minimal steady-state plasma concentrations of amikacin were 27.3 and 3.3 mg/l. The total plasma clearance was 83.1 and 67.0 ml/min after the first and the last infusions, respectively, and the half-life was 3.9 and 5.0 h. The maximal and minimal steady-state plasma concentrations of pefloxacin were 13.1 and 7.9 mg/l after i.v. infusion and 13.4 and 9.0 mg/l after oral administration. Pefloxacin elimination (t1/2) increased from 11.3 h after the first infusion to 19.4 h after the last infusion and 21.1 h after the last oral dose. Total body clearance decreased from 90.8 (Day 1) to 51.9 (Day 5) and 56.4 ml/min (Day 15). The volume of distribution did not change significantly over the course of pefloxacin. Mean steady-state plasma concentrations of norfloxacin and pefloxacin N-oxide were respectively 0.5-0.6 mg/l and 0.9-1.3 mg/l after intravenous and oral administration of pefloxacin. There were no pharmacokinetic interaction between the drugs. The dosage regimen led to plasma concentrations of pefloxacin and amikacin within their therapeutic range.
Aged↗