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Biomedical subjects

M Krishna Kumar

Publications and source records attributed to M Krishna Kumar.

7 recordsLinked to original sources
PubMed2006

Nanostructured Pt functionlized multiwalled carbon nanotube based hydrogen sensor.

Nanostructured Pt functionalized multiwalled carbon nanotubes (MWNTs) produced by catalytic chemical vapor deposition are good room-temperature hydrogen sensors. MWNTs have been synthesized by catalytic chemical vapor deposition of acetylene using a fixed-bed catalytic reactor over hydrides of Mm(0.2)Tb(0.8)CO2 obtained through hydrogen decrepitation technique. Purified and chemically treated MWNTs have been functionalized by Pt resulting in nanostructured dispersion of Pt on CNTs. Structural, morphological, and vibrational characterizations have been carried out using XRD, SEM, TEM, HRTEM, Raman spectroscopy, and FTIR spectroscopy, respectively. Dispersion of Pt on MWNTs was confirmed by elemental analysis using EDX. Systematic investigations of hydrogen sensing properties of Pt-MWNT ensembles have been carried out. The Pt-MWNTs thin films are stable after several cycles of adsorption and desorption. The change in electrical resistance due to hydrogen adsorption is reversible, with increases to saturation on exposure to hydrogen gas. The result demonstrates that the Pt-MWNTs are p-type semiconductor materials, and chemically treated MWNTs functionalized with Pt show the better hydrogen sensing response at room temperature.

Journal Article↗
PubMed2003

Influence of rifampicin pretreatment on the pharmacokinetics of celecoxib in healthy male volunteers.

The effect of rifampicin pretreatment on the pharmacokinetics of celecoxib was investigated in 12 healthy male human volunteers. After an overnight fast, celecoxib 200 mg was administered to the volunteers, either alone or after 5 days pretreatment with once daily dose of 600 mg rifampicin. Serum concentrations of celecoxib were estimated by reverse phase HPLC. Pharmacokinetic parameters were determined based on non-compartmental model analysis using the computer program KINETICA. A significant difference was observed in AUC(0-1) (4531.28 +/- 2147 vs 1629.1 +/- 1006 ng x h x ml(-1), p < 0.0001), AUC(0-infinity) (4632.42 +/- 2221.75 vs 1629.46 +/- 1012.61 ng x h x ml(-1), p = 0.0006), Cmax (544.89 +/- 273.91 vs 238.61 +/- 146.34 ng/ml, p = 0.04), t(1/2) (9.3 +/- 3.58 vs 4.0 +/- 1.43 h, p = 0.0317) and Cl/f (43.14 +/- 36.23 vs 122.85 +/- 95 l x h(-1), p < 0.0001) of celecoxib administered before and after rifampicin pretreatment. However, time to reach peak concentration, tmax (4 +/- 0.88 vs 4 +/- 0.83 h) and volume of distribution Vd/f (583 +/- 251 vs 710 +/- 690 l/kg) were not affected significantly. Rifampicin pretreatment reduced the AUC of celecoxib by 64% and increased the clearance by 185%. This may be due to increased metabolism of celecoxib due to the induction of cytochrome P4502C9 (CYP2C9) in liver. This interaction has a significant clinical relevance and may warrant dosage adjustment when celecoxib is co-administered with rifampicin in chronic treatment conditions, such as tuberculosis, leprosy and other infections of joints, bones, etc.

Adult↗
PubMed2002

An efficient gel-phase synthesis of peptides on a high capacity flexible crosslinked polystyrene support: comparison with Merrifield resin.

A highly solvating copolymer was prepared in high yield by introducing a flexible crosslinker, 1,4-butanedioldimethacrylate, into the polystyrene matrix by a free radical aqueous suspension polymerization. A 2 mol% crosslinked resin showed rigidity and mechanical characteristics comparable to those of divinylbenzene-crosslinked polystyrene (Merrifield resin, DVB-PS) support. Swelling and solvation characteristics of the new resin, BDDMA-PS, were much higher than DVB-PS support in all solvents used for solid phase peptide synthesis. The diacrylate crosslinks in the resin network were found to be highly stable even after 48 h treatment with neat TFA, 6 N HCl and 6 N KOH at 110 degrees C. To demonstrate the usefulness of the new resin in high capacity peptide synthesis, a typical difficult peptide, acyl carrier protein (ACP) fragment (65-74), was synthesized on commercially available 1 mol% crosslinked DVB-PS and 2 mol% crosslinked BDDMA-PS resins under identical conditions. A protocol using NMP/DMSO mediated coupling was employed for chain assembly. The yield and purity of the product from BDDMA-PS resin was higher than when the DVB-PS resin was used. The mechanistic reason behind the synthetic efficiency of the new resin was found to be its ability to induce random coil conformation to the growing peptide chains.

Chromatography, High Pressure Liquid↗
PubMed2002

Effect of cephalexin on the pharmacokinetics of metformin in healthy human volunteers.

The purpose of this study was to assess the effect of a single dose of cephalexin on the pharmacokinetics of metformin in healthy human volunteers. A 2 x 2 double blind randomized crossover study was conducted in 12 healthy human volunteers. Each subject received orally either 500 mg of metformin with a placebo or a combination of 500 mg of metformin and 500 mg of cephalexin. Serum and urine levels of metformin were estimated by a validated HPLC method. The systemic disposition of metformin was altered by the co-administration of cephalexin. Cephalexin increased Cmax and AUC by an average of 34% and 24%, respectively, and reduced renal clearance to 14%. The renal clearance of metformin was reduced in a time-dependent manner in the presence of cephalexin. Hence, it is concluded that cephalexin inhibits the renal tubular secretion of metformin resulting in higher circulating serum concentrations.

Area Under Curve↗
PubMed2002

Validated HPLC method for the determination of celecoxib in human serum and its application in a clinical pharmacokinetic study.

A simple high performance liquid chromatographic method using UV detection for the determination of celecoxib, a specific COX 2 inhibitor, in serum was developed. Serum samples containing the internal standard, tolbutamide, are eluted through a C18, Wakosil column. After extracting with dichloromethane, the eluent is monitored at 250 nm. The mobile phase comprised of 10 mM potassium dihydrogen ortho phosphate (pH 3.2) and acetonitrile (50:50 v/v) with a flow rate of 1 ml/min. Retention times of celecoxib and tolbutamide were 9.6 and 3.5 min, respectively. The mean absolute recovery value was about 70-80%, while the intra day and inter day coefficient of variation and percent error values of the assay method were less than 10%. The calibration curve was linear over a concentration range of 10-1000 ng/ml.

Adult↗