Biomedical subjects

R Farinotti

Publications and source records attributed to R Farinotti.

At least 37 records · Page 2Linked to original sources

PubMed2000

Chronic nifedipine dosing enhances cephalexin bioavailability and intestinal absorption in conscious rats.

Cephalexin, a beta-lactam antibiotic, is rapidly absorbed via the di-and tripeptide intestinal transporters, as for many peptidomimetic drugs. Acute nifedipine has been shown to increase intestinal absorption of several beta-lactams: amoxicillin and cefixime in humans, and cephalexin in the rat. We showed previously that the nervous system was involved in the increasing effect of nifedipine on cephalexin intestinal absorption in anesthetized rats. The aim of the present study was 2-fold: 1) to investigate whether the effect of nifedipine is maintained in conscious rats, and 2) to determine whether the nifedipine effect will persist during chronic nifedipine administration. Acute and chronic oral administration of nifedipine significantly increased oral cephalexin area under the plasma concentration-time curve (34 and 25%, respectively) and maximum concentration in plasma (57 and 51%, respectively), while the distribution and elimination parameters of intra-arterial cephalexin were not affected by acute or chronic nifedipine administration. In conclusion, acute nifedipine effect on intestinal absorption of cephalexin is independent of anesthesia in rats. Since nifedipine could still enhance cephalexin intestinal absorption after a 7-day b.i.d. treatment, it can be envisaged to apply this effect to increase bioavailability of poorly absorbed peptidomimetic drugs in man.

Animals↗

PubMed1999

Determination of nelfinavir, a potent HIV protease inhibitor, and its active metabolite M8 in human plasma by high-performance liquid chromatography with photodiode-array detection.

We developed and characterized a high-performance liquid chromatographic assay for the determination of nelfinavir (NFV), a potent HIV protease inhibitor, and its active metabolite M8 in human plasma. Extraction of the internal standard, M8 and NFV from the plasma buffered at pH 9.5 was achieved by a liquid-liquid extraction with a mixture of methyl-tert.-butyl ether and hexane. Following two washes of the reconstituted sample with hexane, separation was achieved on an octadecylsilyl analytical column with a mobile phase containing 0.1% trifluoroacetic acid-acetonitrile-methanol (51:46:5, v/v). Detection was performed using an ultraviolet photodiode-array detector. The signal was monitored at a wavelength of 220 nm. The assay was found to be linear and has been validated over the concentration range of 25 to 3000 microg/l for M8 and 25 to 6000 microg/l for NFV, from 500 microl of plasma. Recoveries were 98.9% (SD 8.9%), and 100.2% (SD 11.7%) for M8 and NFV, respectively. Concentrations that gave a signal-to-noise ratio of three (15 microg/l for both M8 and NFV) were selected to determine the limit of detection. The lower limit of quantification (25 microg/l for both M8 and NFV) was defined as the concentration for which the relative standard deviation and the percent deviation from the nominal concentration were lower than 20%.

Anti-HIV Agents↗

PubMed1999

Drug interactions with diosmectite: a study using the artificial stomach-duodenum model.

Drug interactions with diosmectite, a gastric-protective drug, were studied in vitro using an artificial stomach-duodenum model. The behavior of neutral and ionisable drugs with pKa values ranging between 2 and 8 was monitored to determine the physicochemical characteristics of the interactions. The main neutral (digoxin) and acid (valproic acid) drug substances were moderately fixed by clay (<27%), in a pH-independent manner. Basic compounds with a pKa<7 (dapsone, metronidazole, cimetidine) were strongly fixed in acid medium (?62%), and fully released under neutral conditions. Amphoteric (fluoroquinolones) and basic compounds with a pKa>/=7 (ranitidine, pyrimethamine) were adsorbed by more than 81% by diosmectite in gastric and duodenal compartments. In the part of the model representing the distal duodenum, the potential site for drug absorption, only the active substances which remained positively charged (amphoteric and basic compounds) showed a large reduction (>/=80%) in their available free fraction. Ionisation of drug substances administered per os concomitantly with diosmectite plays a crucial role in these interactions.

Adsorption↗

PubMed1999

Cerium-doped diosmectite for topical application studies of the cerium-clay interaction.

Cerium is used for its antiseptic and immunomodulatory properties in burn injury. We have developed a cerium-doped clay to replace existing ointments. Adsorption and release of cerium (Ce3+) by diosmectite were studied at 22+/-2 degrees C, in the presence of various other cationic species. Simple spectrofluorimetric determination of cerium was used (lambdaexc=240 nm/lambdaem=360 nm). Cerium binding reached a plateau within 2 min and was a function of the electrolyte content of the solution in contact with the clay. Langmuir isotherm treatment led to a maximal binding capacity of 66 mg of Ce3+ per gram of clay. Partial release occurred within 2 min (19% in the presence of isotonic NaCl solution). The ionic strength of the solution, and the ionic radius and charge of the electrolytes present in the bathing solution significantly influenced cerium release, in contrast to pH and temperature changes. These results strongly point to a cationic exchange mechanism between diosmectite and cerium solution.

Administration, Topical↗

PubMed1999

Stereoselective binding of zopiclone to human plasma proteins.

The binding of racemic zopiclone (ZOP) and of its two enantiomers to plasma proteins, albumin and alpha 1-acid glycoprotein were compared. Our work shows that the binding of ZOP to human plasma proteins is stereoselective. The total plasma protein binding percentages were 79.3 +/- 5.5%, 83.8 +/- 5.2%, and 75.1 +/- 2.1%, for racemic zopiclone, (-)zopiclone and (+)zopiclone, respectively. These results were confirmed by the analysis of samples obtained from healthy volunteers after the oral administration of ZOP. The anticoagulant used for sampling was also shown to have an influence on the percentage binding and on its stereoselectivity. Considering albumin and alpha 1-acid glycoprotein separately, stereoselectivity was also observed.

Azabicyclo Compounds↗

PubMed1999

Binding of chlorpheniramine enantiomers to human plasma proteins.

The in vitro binding of RS-chlorpheniramine to human proteins was studied by equilibrium dialysis. The binding to total plasma proteins and to individual albumin and alpha-glycoprotein acid is stereoselective. (+)S-chlorpheniramine is more extensively bound than its antipode to total plasma proteins (38% vs. 23%), to albumin (20% vs. 15%) and to alpha-glycoprotein acid (23% vs. 5%).

Blood Proteins↗

PubMed1999

Active intestinal elimination of ciprofloxacin in rats: modulation by different substrates.

1. Two in vivo models, in the rat, were used to investigate, in the presence of different substrates, the overall and net intestinal elimination of ciprofloxacin: an open-intestinal perfusion model and an intestinal loop model respectively. 2. In the presence of quinidine, verapamil and cyclosporin (substrates of the P-glycoprotein (P-gp)), plasma AUCs of ciprofloxacin were 1.5 - 2 fold increased, while biliary clearance (1.5 - 2 fold), intestinal overall and net clearances (2 - 4 fold and 1.5 - 8 fold respectively) decreased. The weak effect obtained with cyclosporin as compared to verapamil and especially quinidine, suggests, for ciprofloxacin, the existence of transport systems distinct from the P-gp, as the OCT1 transporter which could be inhibited by quinidine. 3. With cephalexin and azlocillin, two beta-lactam antibiotics, plasma AUCs of ciprofloxacin increased and biliary and intestinal overall clearances decreased in a similar fashion (1.3 - 2 fold), suggesting the involvement of organic anion and/or cation transporters. 4. In the presence of structural analogues, the effect was dependent on the compound administered: Sparfloxacin had no effect on intestinal clearance of ciprofloxacin. In contrast, with pefloxacin, overall intestinal clearance of ciprofloxacin was decreased and net intestinal clearance increased. 5. The specificity of ciprofloxacin intestinal transport appears to be different from P-gp as outlined by the lack of competition with sparfloxacin, a P-gp substrate. Ciprofloxacin intestinal elimination seems to be mediated by organic anion and/or cation transporters and a mechanism sensitive to quinidine and verapamil.

Animals↗

PubMed1999

In vitro effects of racemates, separate enantiomers and major metabolites of mefloquine and halofantrine on metoprolol biotransformation by rat liver microsomes.

1. The effects of the anti-malarial drugs mefloquine and halofantrine and of their major metabolites on metoprolol metabolism by rat liver microsomes have been investigated. 2. The observed Km and Vmax, and the formation kinetics of alpha-hydroxymetoprolol and O-demethylmetoprolol, two major metoprolol metabolites, were in keeping with published data. 3. In vitro, mefloquine competitively inhibited metoprolol biotransformation, whereas halofantrine did so in a mixed fashion. The mefloquine Ki of metoprolol alpha-hydroxylation and O-demethylation were 3.4 and 5.8 microM respectively, whereas those of halofantrine were 0.15 and 0.32 microM respectively. 4. The main metabolites, N-debutylhalofantrine and carboxymefloquine, were 4-10-fold less inhibitory than the parent drugs. The difference in inhibitory potency of parent drugs and metabolites was higher for halofantrine than for mefloquine. The potency order for metoprolol metabolism inhibition was halofantrine >> mefloquine = N-debutylhalofantrine > carboxymefloquine. 5. A preliminary study with anti-malarial enantiomers showed a weak difference, in metoprolol metabolism inhibition between the enantiomers of halofantrine or mefloquine. 6. It is concluded that halofantrine is a potent inhibitor of metoprolol metabolism and that halofantrine metabolites or its enantiomers may have a different inhibitor potency than the parent drug: (1) the inhibition potency of these compounds should be studied in vitro and (2) their in vivo elimination half-life and plasma concentrations should be taken into be account to extrapolate this experimental results to in vivo.

Animals↗

PubMed1999

Kinetics of antiviral activity and intracellular pharmacokinetics of human immunodeficiency virus type 1 protease inhibitors in tissue culture.

We have examined the kinetics of the inhibition of human immunodeficiency virus type 1 (HIV-1) particle infectivity by protease inhibitors (PIs) in cell culture, using either transfected HeLa cells or infected peripheral blood mononuclear cells (PBMCs) as producers of infectious virions. Both the kinetics of the initiation of antiviral activity after addition of the PIs to these cultures and the kinetics of restoration of virion infectivity after removal of the PIs from the treated cultures were examined. We found that the kinetics of initiation of particle infectivity inhibition produced by a high extracellular concentration (5 microM) of the inhibitors were similar for all five inhibitors tested: loss of particle infectivity was perceptible as early as 1 h after the initiation of PI treatment and increased gradually thereafter. By contrast, the durability of this antiviral effect following removal of the drug from the culture varied dramatically according to the drug studied. In transfected HeLa cells, saquinavir and nelfinavir exerted the most prolonged inhibition, with the half-lives of their antiviral activities being greater than 24 h, while ritonavir exerted an intermediate length of inhibition (18 h) and indinavir and amprenavir exerted a reproducibly shorter length of inhibition (5 h). For all five tested PIs, these kinetics were significantly faster in PBMCs than in HeLa cells. The striking differences in antiviral kinetics observed among the different PIs appear mostly due to differences in their intracellular concentrations and/or rates of cellular clearance. Our observations, although limited to tissue culture conditions, may help delineate the cellular parameters of the antiviral activities of HIV-1 PIs and further optimize the efficiencies of these antiretrovirals in vivo.

Antiviral Agents↗

PubMed1999

Influence of renal failure on intestinal clearance of ciprofloxacin in rats.

Following intravenous doses, ciprofloxacin pharmacokinetics in control and nephrectomized rats were studied. There were no differences between control and nephrectomized rats for area under the concentration-time curve in plasma or biliary clearance. The intestinal clearance of ciprofloxacin was increased in nephrectomized rats. Intestinal elimination seems to compensate partially for the decrease in urinary excretion of ciprofloxacin in nephrectomized rats.

Animals↗

PubMed1999

In vivo efficacies of combinations of beta-lactams, beta-lactamase inhibitors, and rifampin against Acinetobacter baumannii in a mouse pneumonia model.

The effects of various regimens containing combinations of beta-lactams, beta-lactam inhibitor(s), and rifampin were assessed in a recently described mouse model of Acinetobacter baumannii pneumonia (M. L. Joly-Guillou, M. Wolff, J. J. Pocidalo, F. Walker, and C. Carbon, Antimicrob. Agents Chemother. 41:345-351, 1997). Two aspects of the therapeutic response were studied: the kinetics of the bactericidal effect (treatment was initiated 3 h after intratracheal inoculation, and bacterial counts were determined over a 24-h period) and survival (treatment was initiated 8 h after inoculation, and the cumulative mortality rate was assessed on day 5). Two clinical strains were used: a cephalosporinase-producing strain (SAN-94040) and a multiresistant strain (RCH-69). For SAN-94040 and RCH-69, MICs and MBCs (milligrams per liter) were as follows: ticarcillin, 32, 64, 256, and >256, respectively; ticarcillin-clavulanate, 32, 64, and 512, and >512, respectively; imipenem, 0.5, 0.5, 8, and 32, respectively; sulbactam, 0.5, 0.5, 8, and 8, respectively; and rifampin, 8, 8, 4, and 4, respectively. Against SAN-94040, four regimens, i.e., imipenem, sulbactam, imipenem-rifampin, and ticarcillin-clavulanate (at a 25/1 ratio)-sulbactam produced a true bactericidal effect (>/=3-log10 reduction of CFU/g of lung). The best survival rate (i.e., 93%) was obtained with the combination of ticarcillin-clavulanate-sulbactam, and regimens containing rifampin provided a survival rate of >/=65%. Against RCH-69, only regimens containing rifampin and the combination of imipenem-sulbactam had a true bactericidal effect. The best survival rates (>/=80%) were obtained with regimens containing rifampin and sulbactam. These results suggest that nonclassical combinations of beta-lactams, beta-lactamase inhibitors, and rifampin should be considered for the treatment of nosocomial pneumonia due to A. baumannii.

Acinetobacter↗

PubMed1999

Halofantrine metabolism in microsomes in man: major role of CYP 3A4 and CYP 3A5.

We have clarified the contribution of the different enzymes involved in the N-debutylation of halofantrine in liver microsomes in man. The effect of ketoconazole and cytochrome P450 (CYP) 3A substrates on halofantrine metabolism has also been studied. The antimalarial drug halofantrine is metabolized into one major metabolite, N-debutylhalofantrine. In microsomes from nine livers from man, N-debutylation of halofantrine was highly variable with apparent Michaelis-Menten constant V(max) and K(m) values of 215+/-172 pmol min(-1) mg(-1) and 48+/-26 micromol L(-1), respectively, (mean+/-standard deviation). Formation of N-debutylhalofantrine was cytochrome P450 (CYP)-mediated. Studies using selective inhibitors of individual CYPs revealed the role of CYP 3As in the formation of N-debutylhalofantrine. alpha-Naphthoflavone, a CYP 3A activator, increased metabolite formation. In microsomes from 12 livers from man the rate of N-debutylation of halofantrine correlated strongly with CYP 3A4 relative levels (P = 0.002) and less strongly, but significantly, with CYP 2C8 levels (P = 0.025). To characterize CYP-mediated metabolism of halofantrine further, incubations were performed with yeast microsomes expressing specific CYP 3A4, CYP 3A5, CYP 2D6, CYP 2C8 and CYP 2C19 from man. The rate of formation of N-debutylhalofantrine was six- and twelvefold with CYP 3A4 than with CYP 3A5 and CYP 2C8, respectively. CYP 2D6 and CYP 2C19 did not mediate the N-debutylation of halofantrine, but, because in-vivo CYP 2C8 is present at lower concentrations than CYP 3A in the liver in man, the involvement of CYP 3As would be predominant. Diltiazem, erythromycin, nifedipine and cyclosporin (CYP 3A substrates) inhibited halofantrine metabolism. Similarly, ketoconazole inhibited, non-competitively, formation of N-debutylhalofantrine with an inhibition constant, K(i), of 0.05 microM. The theoretical percentage inhibition of halofantrine metabolism in-vivo by ketoconazole was estimated to be 99%. These results indicate that both CYP 3A4 and CYP 3A5 metabolize halofantrine, with major involvement of CYP 3A4. In-vivo, the other CYPs have a minor role only. Moreover, strong inhibition, and consequently increased halofantrine cardiotoxicity, might occur with the association of ketoconazole or other CYP 3A4 substrates.

Aryl Hydrocarbon Hydroxylases↗

PubMed1999

Cerebral uptake of mefloquine enantiomers in fatal cerebral malaria.

PATIENTS AND METHODS: The brain disposition of the enantiomers of the antimalarial mefloquine was studied in two post-mortem human cerebral biopsies after oral administration of the racemic mixture. BACKGROUND: Mefloquine (MQ) is an effective antimalarial drug used both for prophylaxis and treatment of chloroquine resistant Plasmodium falciparum. MQ is generally well tolerated in treatment. Minor side-effects have been described. Potentially serious neuropsychiatric reactions occur. The mechanism underlying the neurotoxicity is unknown, although a dose relationship is evidently involved. RESULTS: Mefloquine enantiomer concentrations were determined using a chiral liquid chromatographic method. Mefloquine concentrations were higher in brain compared to plasma. Studied in one patient, white matter concentrations were higher compared to grey matter concentrations. CONCLUSION: Based on the ratios brain concentration/plasma concentration, the brain penetration of the (+) enantiomer is much higher than that of the (-) enantiomer.

Autopsy↗

PubMed1999

Neural modulation of cephalexin intestinal absorption through the di- and tripeptide brush border transporter of rat jejunum in vivo.

Intestinal absorption of beta-lactamine antibiotics (e.g., cefixime and cephalexin) has been shown to proceed through the dipeptide carrier system. In a previous study, nifedipine (NFP), an L-type calcium channel blocker, enhanced the absorption of cefixime in vivo but not in vitro, and it was suggested that neural mechanisms might be involved in the effect of NFP. The aim of the present study was to assess the involvement of the nervous system on the intestinal absorption of cephalexin (CFX). To investigate this, we used a single-pass jejunal perfusion technique in rats. NFP and diltiazem enhanced approximately 2-fold the plasma levels of CFX in treated rats versus untreated controls. NFP also increased approximately 2-fold the CFX level in portal plasma and increased urinary excretion of CFX, thus indicating that CFX did effectively increase CFX intestinal absorption. Perfusing high concentrations of dipeptides in the jejunal lumen competitively reduced CFX absorption and inhibited the enhancement of CFX absorption produced by NFP. Hexamethonium and lidocaine inhibited the effect of NFP, whereas atropine, capsaicin, clonidine, and isoproterenol enhanced CFX absorption by the same order of magnitude as NFP. Thus, complex neural networks can modulate the function of the intestinal di- and tripeptide transporter. Sympathetic noradrenergic fibers, intestinal sensory neurons, and nicotinic synapses are involved in the increase of CFX absorption produced by NFP.

ATP-Binding Cassette Transporters↗

PubMed1999

Effect of selected antimalarial drugs and inhibitors of cytochrome P-450 3A4 on halofantrine metabolism by human liver microsomes.

Halofantrine (HF) is used in the treatment of uncomplicated multidrug-resistant Plasmodium falciparum malaria. Severe cardiotoxicity has been reported to be correlated with high plasma concentrations of HF but not with that of its metabolite N-debutylhalofantrine. The aim of this study was to investigate the effects of other antimalarial drugs and of ketoconazole, a typical cytochrome P-450 3A4 inhibitor, on HF metabolism by human liver microsomes. Antimalarial drug inhibitory effects were ranked as follows: primaquine > proguanil > mefloquine > quinine > quinidine > artemether > amodiaquine. Artemisine, doxycycline, sulfadoxine, and pyrimethamine showed little or no inhibition of HF metabolism. Mefloquine, quinine, quinidine, and ketoconazole used at maximal plasma concentrations inhibited N-debutylhalofantrine formation noncompetitively with Ki values of 70 microM, 49 microM, 62 microM, and 0.05 microM resulting in 7%, 49%, 26%, and 99% inhibition, respectively, in HF metabolism. In conclusion, we showed that quinine and quinidine coadministered with HF might inhibit its metabolism resulting in the potentiation of HF-induced cardiotoxicity in patients. This requires a close monitoring of ECG. For the same reasons, the concomitant administration of HF and ketoconazole must be avoided. By contrast, none of the other antimalarials studied inhibited HF metabolism and, by extrapolation, cytochrome P-450 3A4 activity.

Adolescent↗

PubMed1998

Determination of 2-n-propylquinoline in mouse plasma and liver by high-performance liquid chromatography.

A high-performance liquid chromatographic method was developed for the specific determination of 2-n-propylquinoline, a new anti-leishmaniasis drug, in plasma and liver homogenates of mice. 2-n-Propylquinoline was extracted with methyl-tert.-butyl ether with quinoline as internal standard. Separation was carried out using a Nucleosil C18 column. The mobile phase consisted of methanol-0.005 M ammonium acetate buffer (60:40) at pH 5.5 and 8 for plasma and liver homogenates, respectively. Detection was monitored at 233 nm. The method was validated and shown to be accurate and precise for plasma and liver homogenates. Extraction yield was 96% in plasma and 81% in liver homogenates. This method was used to determine the pharmacokinetic profile of 2-n-propylquinoline following oral administration to mice.

Animals↗

PubMed1998

Determination of the inhibitory effect on Toxoplasma growth in the serum of AIDS patients during acute therapy for toxoplasmic encephalitis.

In 26 AIDS patients treated for toxoplasmic encephalitis, the inhibitory effect on Toxoxplasma growth of sequential sera taken before and after initiation of therapy was determined using a culture-based immunoassay and compared with pyrimethamine blood levels. A marked inhibition of Toxoplasma growth was observed 1 day after initiation of therapy with pyrimethamine plus sulfadiazine and was maintained between 67% and 93% throughout the 15-day follow-up period. The degree of inhibition was not correlated to pyrimethamine blood levels and seemed highly potentiated when sulfadiazine rather than macrolides was given in combination with pyrimethamine.

Acquired Immunodeficiency Syndrome↗

PubMed1998

Chiral chromatographic method to determine the enantiomers of halofantrine and its main chiral desbutyl metabolite in erythrocytes.

We describe a direct liquid chromatographic method with spectrofluorimetric detection to quantify the two enantiomers of halofantrine and the two enantiomers of its main chiral N-monodesbutylated metabolite in erythrocyte pellets. The method involves a Chiralpak AD column and a rapid one-step extraction procedure with acetonitrile. The method was validated for the four enantiomers within the range 0-1000 ng/ml. The absence of stereoconversion was studied in samples stored frozen for up to eight months. The optical rotation of the halofantrine and metabolite enantiomers was determined after separation on a semi-preparative Chiralcel OD column with polarimetric detection.

Administration, Oral↗