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Biomedical subjects

N Pandit

Publications and source records attributed to N Pandit.

At least 19 recordsLinked to original sources
PubMed2000

Experimental investigation and mathematical modeling of Pluronic F127 gel dissolution: drug release in stirred systems.

We have examined the dissolution of Pluronic F127 gels in a USP dissolution apparatus under stirred conditions, and simultaneously monitored the release of model drugs from these gels. The drugs selected were propranolol HCl, metronidazole and cephalexin. Our results show that drug release is zero-order and is controlled by the dissolution of the gel for all the drugs, under various conditions of temperature, F127 concentration, drug concentration, and for stirring speeds between 20 and 80 rpm. The addition of inorganic salts has no significant effect on dissolution rate or drug release. Increasing F127 concentration in the gel decreases gel dissolution and drug release rates. We have developed a predictive mathematical model based on the assumption that uptake of water into the gel and subsequent disentanglement of F127 micelles control gel dissolution. There is good agreement between experimental results and model predictions for stirring speeds above 20 rpm. As stirring speed is decreased to 20 rpm and below, there are discrepancies between actual and predicted values, presumably due to a significant diffusion component that contributes to drug release.

Algorithms↗
PubMed2000

Effect of Salts on the Micellization, Clouding, and Solubilization Behavior of Pluronic F127 Solutions.

We have examined the effect of NaCl, Na(2)SO(4), Na(3)PO(4), and NaSCN on F127 solutions; properties examined were critical micellization temperature (cmt), cloud point, and solubilization of a model hydrophobic drug, propyl paraben. Static light scattering showed that the first three salts lower the cmt of F127 in the order Na(3)PO(4)>Na(2)SO(4)>NaCl. The extent of lowering depends on the salt concentration and can be ascribed to the water structure-making properties of these salts. NaSCN, a water structure breaker, was found to increase cmt. Pyrene fluorescence was used to study the changes in micellar interior in the presence of salts. We found that the micellar micropolarity is not significantly changed by salts, evidenced by a constant I(1)/I(3) ratio of pyrene. However, the I(e)/I(3) ratio changes significantly with salts, being lower for NaCl, Na(2)SO(4), and Na(3)PO(4) and higher for NaSCN. This is consistent with an increase in the total hydrophobic micellar domain, in micellar microviscosity, or both. Solubilization of propylparaben increases in the presence of Na(3)PO(4), consistent with a larger hydrophobic domain for solubilization. The thermodynamics of micellization continue to be entropically driven in the presence of salts, evidenced by a positive entropy overcoming an unfavorable enthalpy. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

Eosinophilic cholecystitis as a possible late manifestation of the eosinophilia-myalgia syndrome.

We describe a case of acute acalculous cholecystitis occurring in a 43-year-old woman with a history of the eosinophilia-myalgia syndrome, associated with the ingestion of 1-tryptophan. The patient underwent a laparoscopic cholecystectomy and subsequent histological examination of the gallbladder revealed an infiltrate predominantly of eosinophils, suggesting a possible relationship to the underlying condition. This may represent a late complication of the eosinophilia-myalgia syndrome--such an association has not previously been reported in the literature. The gastrointestinal and hepatic complications of this syndrome are discussed.

Adult↗
PubMed1999

A Study of the Temperature-Dependent Micellization of Pluronic F127.

We have examined the temperature-dependent micellization of the pharmaceutically important PEO-PPO-PEO copolymer, Pluronic F127, using static light scattering and various aspects of the pyrene fluorescence spectrum (monomer intensity, excimer formation and the I1/I3 ratio). All techniques gave essentially the same value for the critical micellization temperatures (cmt) of various F127 solutions, and our results agreed with those reported in the literature. Cmt values decrease with increasing F127 concentration. We observed significant solubilization of pyrene in F127 solutions below the cmt, which was also reflected in the measured I1/I3 ratios. The thermodynamics of the micellization process were studied and gave different results at low and high F127 concentrations. In the low F127 concentration range (up to approximately 50 mg/mL), we obtain DeltaH = 312 kJ mol-1 and DeltaS = 1.14 kJ mol-1 K-1. Above 50 mg/mL we obtain DeltaH = 136 kJ mol-1 and a DeltaS = 0.54 kJ mol-1 K-1. This discontinuity in thermodynamic behavior can be due to a change in aggregation number with temperature and/or a change in the micellization process at higher concentrations. Copyright 1999 Academic Press.

Journal Article↗
PubMed1997

The 'mouse face' appearance of the vertebrae in Paget's disease.

Paget's disease is occasionally found as an incidental finding on bone scans performed for the evaluation of metastatic disease, which causes a diagnostic and a subsequent therapeutic dilemma. We have previously described the "Mouse Face" appearance of vertebrae on bone scans (increased uptake in the vertebral body, posterior elements, and the spinous process), which was fairly specific for Paget's disease in a small series. This retrospective study was undertaken to determine if this observation holds true in a larger series. Bone scans performed in 2,881 patients were randomly selected, and were reviewed by 2 physicians. Thirty-nine cases with a "Mouse Face" appearance were identified. Diagnosis was established in 30 of the 39 patients by correlative radiographic studies and/or clinical follow-up. Twenty patients were referred for the evaluation of possible metastases, and 7 were found to have metastases at the sites of "Mouse Face". The other 13 had Paget's disease. However, 6 of the 7 patients with metastases had extravertebral findings compatible with multiple metastases, and the remaining patient had a "Mouse Face" lesion only, with a question of metastases. Ten patients were evaluated for Paget's disease or others, and none of them had metastases at the site of the "Mouse Face". The "Mouse Face" appearance is more suggestive of Paget's disease than metastases even in patients with cancer. These patients should be assumed unlikely to have vertebral metastases, unless proven by another correlative radiologic study.

Adult↗
PubMed1996

Brain perfusion imaging during preoperative temporary balloon occlusion of the internal carotid artery.

UNLABELLED: The main objective of this study was to assess whether 99mTc-HMPAO brain SPECT imaging can identify patients at high risk of developing an infarct following permanent carotid occlusion in the course of brain surgery. METHODS: Test balloon occlusion of the internal carotid artery was performed in 44 patients with a variety of head and neck tumors or aneurysms. Technetium-99m-HMPAO was injected intravenously while the balloon was initiated and a SPECT study was obtained 30 min later. Follow-up CT scans were obtained routinely for all patients at 2 wk and 1 mo following surgery, or earlier when necessary. Thirty patients and five normal volunteers had semiquantitative analysis of cerebral perfusion. RESULTS: Twenty-six patients demonstrated ipsilateral perfusion abnormalities during trial occlusion. Eight patients in this group underwent bypass grafting prior to sacrifice of the artery: two resulting in infarcts. Eighteen patients had symmetric cerebral perfusion during occlusion and four of these patients underwent permanent therapeutic carotid occlusion; three patients had subsequent infarcts and the fourth patient had an impending stroke. CONCLUSION: Patients with symmetric cerebral perfusion measured by 99mTc-HMPAO SPECT may still have a high long-term complication rate following carotid sacrifice. The scan findings in these patients were not predictive of the outcome. Patients with asymmetric cerebral perfusion had alternative therapeutic approach to carotid sacrifice and most of them had good surgical outcomes.

Brain↗
PubMed1996

Reversible cerebral perfusion abnormalities associated with cyclosporine therapy in orthotopic liver transplantation.

A 60-yr-old woman experienced several episodes of generalized seizures following 2 wk of immunosuppressive therapy with cyclosporine for orthotopic liver transplantation. CT showed low density in the white matter of the parieto-occipital lobes. A 99mTc-HMPAO brain SPECT showed diminished perfusion in the parieto-occipital cortex bilaterally. Although the cyclosporine was discontinued, the patient's neurologic status initially worsened and then improved over the next several days. Repeat perfusion brain SPECT showed resolution of most of the perfusion abnormalities, while repeat CT showed persistent white matter changes in the parieto-occipital lobes. We report the presence of reversible cortical perfusion abnormalities in conjunction with cyclosporine therapy. The findings suggest that perfusion brain SPECT may be a sensitive monitor of cyclosporine-induced neurotoxicity.

Brain↗
PubMed1994

Variable expression of the Opc outer membrane protein in Neisseria meningitidis is caused by size variation of a promoter containing poly-cytidine.

Opa proteins of Neisseria meningitidis exhibit translational phase variation via addition or deletion of repetitive coding repeat units within the DNA encoding the protein leader sequence. In contrast, Opc phase variation is the result of transcriptional regulation. Transcription starts 13 nucleotides after the -10 region of an unusual promoter sequence containing a variable number of contiguous cytidine residues and lacking a -35 region. Efficient expression of Opc occurred in strains with 12 to 13 cytidine residues, intermediate expression in strains with 11 or 14 residues and no expression with < or = 10 or > or = 15 residues. This unusual regulation may have evolved because the Opc protein enables meningococcal invasion and is immunogenic.

Bacterial Outer Membrane Proteins↗