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Biomedical subjects

V K Prasad

Publications and source records attributed to V K Prasad.

At least 37 records · Page 2Linked to original sources
PubMed1986

Simultaneous determination of prednisolone acetate, prednisolone, prednisone, cortisone and hydrocortisone in swine plasma using solid-phase and liquid-liquid extraction techniques.

A high-performance liquid chromatographic (HPLC) method for the simultaneous determination of prednisolone acetate (PA), prednisolone (PO), prednisone (PN), cortisone and hydrocortisone in swine plasma is described. Extraction of the steroid mixture from swine plasma with dexamethasone as internal standard was accomplished by solid-phase extraction (SPE) or the more traditional liquid-liquid extraction (LLE) techniques. These compounds were analyzed by normal-phase HPLC with ultraviolet detection. Although a detectable sensitivity of 5 ng/ml is achieved by the SPE technique, the practical sensitivity is established as 10 ng/ml. Conversely, the practical sensitivity is 5 ng/ml for all compounds by the LLE technique. Calibration curves were found to be linear between 10 and 500 ng/ml by the SPE technique and between 5 and 100 ng/ml by the LLE technique. The average recovery of the steroids PA, PO and PN at 20 ng/ml is between 70 and 90%. PA is stable for up to 3 h in swine plasma at room temperature (22 degrees C) but is completely converted to PO within 24 h. PA is stable in swine plasma in an ice bath for over 24 h. The usefulness of this analytical technique is demonstrated by the intraperitoneal administration of 125 mg of PA to swine and the quantitative determination of PA, PO and PN in the plasma as a function of time.

Animals↗
PubMed1984

Bioavailability of hydrochlorothiazide from tablets and suspensions.

The bioavailability of hydrochlorothiazide was determined following single oral 25-, 50-, 100-, and 200-mg tablet and suspension doses in 12 healthy male volunteers. Plasma and urine levels of hydrochlorothiazide were determined by HPLC. Plasma levels of hydrochlorothiazide were satisfactorily described by a triexponential function. Mean peak plasma levels, Cmax (127-135, 270-280, and 437-490 ng/mL from the 25-, 50-, and 100-mg doses, respectively) were dose proportional, as were areas under plasma profiles, AUC0----36. Mean percentage recovery of unchanged hydrochlorothiazide in 48-h urine samples accounted for 50-59, 54-55, 60-63, and 54-57% of the 25-, 50-, 100-, and 200-mg doses, respectively. There were no significant differences among these values. Correlation coefficients between 48-h urinary recovery of hydrochlorothiazide and the plasma values (Cmax and AUC0----36) for the 25-, 50-, and 100-mg doses were 0.73 and 0.84. There were no differences in the net increases in electrolyte excretion among the treatments during the 0-12-h postdose period. The systematic availability of hydrochlorothiazide, unlike that of chlorothiazide, is dose proportional in the therapeutic range.

Adult↗
PubMed1984

Bioavailability of hydrocortisone from commercial 20-mg tablets.

The relative bioavailability of hydrocortisone was determined from four different 20-mg tablet formulations and one suspension in 15 healthy male volunteers; results were compared with in vitro dissolution rates. Plasma levels of hydrocortisone were determined by a liquid chromatography method developed in this laboratory. Dissolution of the tablet formulations, using the official USP test, varied from 7.8 to 93.8% in 30 min. Similar plasma profiles were obtained from all tablet products, and there were no differences among tablets in the cumulative percentage of drug absorbed. There were no clear trends in any pharmacokinetic parameter values among the tablet dosages, and the four products were considered bioequivalent. The suspension dosage yielded significantly higher plasma levels compared with some of the tablet formulations during the initial 30-min postdose, significantly higher cumulative absorption at 0.5 and 1.0 h compared with one tablet formulation, and significantly higher ka and Cmax, and shorter tmax values, compared with some of the tablets.

Adult↗
PubMed1983

Evaluation of basket and paddle dissolution methods using different performance standards.

Dissolution studies using both basket and paddle methods were carried out to evaluate two prednisone standards. Results of the experiments showed that the USP prednisone calibrator is sensitive to perturbations by the basket method but not to perturbations by the paddle method. However, the National Center for Drug Analysis (NCDA) prednisone performance standard is sensitive to perturbations by the paddle method but not to perturbations by the basket method. These results suggest that no single standard can predict the suitability of the dissolution equipment by the basket and paddle methods.

Evaluation Studies as Topic↗
PubMed1983

Phenytoin I: in vitro-in vivo correlation for 100-mg phenytoin sodium capsules.

Dissolution profiles for 11 brands of phenytoin sodium capsules were carried out by the basket and paddle methods (USP) and the spin-filter method. The results from the dissolution studies have been correlated with observed differences in in vivo parameters (Cmax and tmax). The dissolution by the basket method at 50 rpm in water gave a correlation greater than 0.9. The results suggest the existence of two types of phenytoin sodium products on the market.

Biological Availability↗
PubMed1983

Phenytoin II: in vitro-in vivo bioequivalence standard for 100-mg phenytoin sodium capsules.

A bioequivalence study was undertaken using an oral solution, a fast-dissolving capsule and a slow-dissolving phenytoin sodium capsule. The AUC, tmax and Cmax correlated with in vitro dissolution data. The results of the present studies substantiate the presence of two types of phenytoin sodium products on the market. On the basis of these studies, in vitro specifications for fast- and slow-dissolving phenytoin sodium capsules as well as the in vivo bioequivalence requirements for these two types of products are recommended.

Capsules↗
PubMed1983

Thiazides. VIII: Dissolution survey of marketed hydrochlorothiazide tablets.

The dissolution profiles of 50-mg hydrochlorothiazide tablets representing all approved manufacturers (at the time of the study) were determined in two vehicles [purified water and dilute (1:100) hydrochloric acid] by three methods (rotating basket at 150 rpm; spin filter at 300 rpm; paddle method at 50 rpm). The paddle method was preferred on the basis of overall ease of operation, reproducibility, and discrimination. The paddle data were validated in both vehicles on the same lots of tablets by a second laboratory. A standard of not less than 80% dissolution in 60 min by the paddle method in water is proposed for hydrochlorothiazide tablets.

Chemistry, Pharmaceutical↗
PubMed1983

Thiazides III. Evidence of dose proportionality of hydrochlorothiazide 25, 50 and 100 mg tablets.

A pilot bioavailability study was carried out where two subjects each were administered a dose of 25, 50 or 100 mg of commercially available hydrochlorothiazide (HCT) tablets. Plasma and urine samples were collected and analyzed by HPLC. A maximum plasma concentration of 50-285 ng/ml was reached in 1-2 hours, and plasma levels declined very rapidly with a half life of about 2-4 hours during first 12 hours period. The AUC was calculated using the trapezodial rule. A linear correlation was seen between the dose administered and amount of drug excreted.

Adult↗
PubMed1982

Improved method for the analysis of furosemide in plasma by high-performance liquid chromatography.

Modifications of existing rapid high-performance liquid chromatographic procedures for the determination of furosemide in plasma were made in order to achieve greater sensitivity. To a small volume of plasma was added in internal standard structurally related to furosemide. Then, following previously described procedures, acetonitrile was added to precipitate the proteins and the clear supernatant was separated. However prior to injection of the supernatant the pH and composition of the sample were adjusted. This modification of the sample enabled an injection volume of up to 300 microliters of the supernatant to be injected onto the chromatographic column. The effluent was monitored spectrofluorimetrically. A standard linear calibration curve with a mean precision of +/- 4.4% was obtained for plasma samples containing 20--900 ng/ml of furosemide. Two structurally related compounds were used as internal standards in the furosemide assay.

Administration, Oral↗
PubMed1982

Oral hydrocortisone pharmacokinetics: a comparison of fluorescence and ultraviolet high-pressure liquid chromatographic assays for hydrocortisone in plasma.

Three fasted, male subjects received single 10-, 30-, and 50-mg oral doses of hydrocortisone tablets on separate occasions. Endogenous hydrocortisone was suppressed by giving 2 mg of dexamethasone 9 hr prior to dosing. Plasma samples obtained serially for 8 hr after hydrocortisone dosing were assayed by reversed-phase high-pressure liquid chromatography (HPLC) with UV detection and by normal-phase HPLC with fluorescence detection of the dansylhydrazine derivative of hydrocortisone. The two assay methods yielded equivalent plasma hydrocortisone concentrations. Metabolite interference was absent in both assay methods. Drug concentrations in plasma from all three doses of hydrocortisone were described by one-compartment open-model kinetics, with first-order absorption and elimination, and an absorption lag time. Mean Cmax values of 199, 393, and 419 ng/ml were obtained at 1.0, 1.0, and 1.7 hr following the 10-, 30-, and 50-mg doses, respectively. Hydrocortisone was cleared from plasma with an elimination half-life of approximately 1.5 hr. Within the dosage range studied, plasma levels of hydrocortisone were related, but not directly proportional, to dose size. This apparent lack of proportionality may be due to reduced drug availability or altered distribution with increasing dose.

Administration, Oral↗
PubMed1982

Thiazides IV: Comparison of dissolution with bioavailability of chlorothiazide tablets.

Based on the initial dissolution rate profiles in water, a slow-dissolving, an intermediate-dissolving, and a fast-dissolving chlorothiazide 250-mg tablet were selected for the bioavailability and bioequivalence study. In addition, two marketed 500-mg chlorothiazide tablets were studied. The three 250-mg tablets were bioequivalent, as were the two 500-mg tablets. Therefore, the dissolution test conditions were modified to associate in vitro dissolution with in vivo performance of the product. Based on these results, it was concluded that a dissolution of 75% in 60 min by paddle method at 75 rpm in pH 7.4 phosphate buffer can be used as a quality assurance test for 250- and 500-mg chlorothiazide tablets.

Biological Availability↗
PubMed1981

Reversed-phase high-performance liquid chromatographic analysis of liothyronine sodium and levothyroxine sodium in tablet formulations: preliminary studies on dissolution and content uniformity.

Levothyroxine sodium was estimated from tablet formulations of levothyroxine sodium and liotrix (liothyronine sodium-levothyroxine sodium combination tablet). The procedures consisted of the addition of 3,3-,5-triiodothyronine as the internal standard to the pulverized sample, followed by an acidic butanol extraction, evaporation, and injection onto a muBondapak reversed-phase high-performance liquid chromatographic column. The eluent was methanol-water-phosphoric acid (50:50:0.1), and the effluent was monitored by UV detection at 254 nm. A standard linear calibration curve was obtained for direct standard solutions equivalent to 18-225 micrograms of levothyroxine sodium/tablet. The procedure is sensitive enough for single-tablet analysis. Using this procedure, content uniformity studies were performed on liothyronine sodium tablets, levothyroxine sodium tablets, and liotrix tablets. The procedure also was adapted for conducting dissolution studies on levothyroxine sodium tablets in deionized water using the rotating-paddle method.

Chromatography, High Pressure Liquid↗
PubMed1981

Simple high-performance liquid chromatographic assay for norethindrone--mestranol in combination tablets.

A simple, sensitive, and specific high-performance liquid chromatographic procedure was developed to assay norethindrone--mestranol combination tablets. The method involves a chloroform extraction of a single pulverized tablet. After centrifugation, and aliquot of the supernate was injected into a modular high-performance liquid chromatograph. The effluent from the silica column was monitored serially with a fixed-wavelength UV detector (254 nm) for norethindrone quantitation and a fluorescence detector (230 nm for excitation and 280 nm cutoff filter for emission) for mestranol quantitation. Progesterone was used as an internal standard. The method was employed successfully in content uniformity studies of several brands of commercially available tablets.

Chromatography, High Pressure Liquid↗
PubMed1981

Dissolution profiles and specifications for dihydroergotoxine sublingual tablets using a new in vitro method.

A dissolution method (paddle method) for determining the dissolution rate profile for 0.5- and 1.0-mg dihydroergotoxine methanesulfonate sublingual tablets was developed. A fluorometric method was used for measuring drug concentration in the dissolution medium, distilled water. It was essential to filter the dissolution sample to avoid interference from undissolved excipients. When different kinds of filters were used with the dissolution samples and standards, different degrees of apparent drug binding to the filter occurred. The dissolution rate profiles for several different products were compared to the innovator's product. The in vitro method and data obtained were used to propose dissolution specifications for these sublingual products.

Dihydroergotoxine↗