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Biomedical subjects

S Niazi

Publications and source records attributed to S Niazi.

At least 37 records · Page 2Linked to original sources
PubMed1977

Fluorocarbon aerosol propellants XI: Pharmacokinetics of dichlorodifluoromethane in dogs following single and multiple dosing.

A three-compartment open model was proposed for the disposition of dichlorodifluoromethane in dogs with average half-lives of 1.47, 7.95, and 58.5 min for the three disposition phases. This proposal is contrary to several studies that monitored blood levels for a shorter period. An analysis of the tissue compartment distribution following a single dose showed that about 1.5 hr was required to achieve pseudodistribution equilibration, following which more than 90% of the dose remaining in the body was retained in the tissue compartments. The pulmonary clearance and volumes of distribution were calculated considering the first-pass effect through the lungs. The volume of distribution after reaching pseudodistribution equilibrium was approximately 10 times the body weight in terms of the blood concentration, and about 68% of the propellant was cleared from the blood passing through the lungs in each cycle. Disposition of the propellant followed dose-independent kinetics after multiple dosing. No volatile metabolites were detected in the blood using GC.

Aerosol Propellants↗
PubMed1977

Application of a programmable calculator in data fitting according to one and two compartment open models in clinical pharmacokinetics.

The plasma or blood concentration profiles are fitted by single or two compartment open models using log-linear regression analyses. For two compartment models, "feathering" is performed at 95% equilibration time obtained from raw pharmacokinetic data. The equations have been programmed onto a Texas Instrument SR 52 pocket calculator and recorded on 8.5 X 1.7 cm magnetic strips, facilitating drug dosage regimen calculations through individual patient titrations in a clinical setting.

Biopharmaceutics↗
PubMed1976

Fluorocarbon aerosol propellants X: pharmacokinetics of dichlorotetrafluoroethane in dogs.

An intravenous dosage form of dichlorotetrafluoroethane, a common fluorocarbon aerosol propellant, was formulated in polyethylene glycol 400 for single dosing to unanesthetized dogs. A three-compartment open model was proposed for the disposition of this compound in dogs, with average half-lives of 1.3, 9.6, and 50.8 min for the three disposition phases. An analysis of tissue compartment distribution following a single dose showed that it took about 2 hr to achieve pseudo-distribution equilibration, following which more than 90% of the propellant remaining in the body was retained in the tissue compartments. Pulmonary clearance and volumes of distribution were calculated considering the first-pass effect through the lungs. The volume of distribution was approximately 10 times the body weight in terms of blood concentration, and about 84% of the propellant was cleared from the blood passing through the lungs in each cycle.

Aerosol Propellants↗
PubMed1976

Effect of polyethylene glycol 4000 on dissolution properties of sulfathiazole polymorphs.

The dissolution rates of the two polymorphic forms of sulfathiazole containing polyethylene glycol 4000 were significantly different in water. The effect of agitation on the dissolution rates also was studied. At higher stirring speeds, the dissolution rates of the stable form were affected more than the metastable form. A high concentration of polyethylene glycol 4000 seemed to affect the dissolution properties of the metastable polymorph more than the stable polymorph.

Isomerism↗
PubMed1976

Volume of distribution as a function of time.

A single definition for all volume terms in pharmacokinetic modeling is proposed; this parameter is considered as a function of time. This definition will represent the kinetic nature of pharmacokinetic models and will provide a highly sensitive parameter for correlation with pharmacological responses.

Binding Sites↗
PubMed1976

Errors involved in instantaneous intravascular input assumptions.

A comparative evaluation of a zero-order input and the generally accepted instantaneous intravascular input assumption is made for two- and three-compartment open model systems. Equations are derived and a nomogram is prepared to calculate the magnitude of error involved in instantaneous input assumptions. It is suggested that all intravascular administrations be considered as zero-order inputs.

Injections, Intra-Arterial↗
PubMed1976

Comparison of observed and predicted first-pass metabolism of imipramine in humans.

The first-pass metabolism of imipramine was calculated based on the dose, hepatic blood flow, and total area under the plasma-time curve after oral administration of 0.71 +/- 0.03 mg/kg of imipramine to four individuals suffering from mild depression. The predicted values of first-pass metabolism ranged from 37 to 68%, consistent with experimentally derived estimates.

Adult↗
PubMed1976

Pharmaceutical applications of solid dispersion systems: dissolution of griseofulvin-succinic acid eutectic mixture.

The dissolution profile of the griseofulvin-succinic acid eutectic mixture system was evaluated using the powder and constant-surface are tablet methods. Factors contributing to the enhancement of griseofulvin dissolution from the dispersion in succinic acid are discussed. Contrary to the original proposal of Sekiguchi and coworkers, dissolution rates of driseofulvin from solid dispersions were found to be markedly affected by the particle size of solid dispersions.

Anhydrides↗
PubMed1976

Comparison of observed and predicted first-pass metabolism of nortriptyline in humans.

The extent of first-pass metabolism of nortriptyline, calculated by comparing the areas under the plasma concentration-time curves following intravenous and oral dosing in six individuals, varied from 41 to 54%. Theoretically predicted values ranged from 41 to 61% based on a plasma flow model, indicating that the clearance takes place mainly from the plasma, which does not represent the whole blood concentration.

Humans↗
PubMed1976

Volume of distribution and tissue level errors in instantaneous intravenous input assumptions.

A comparison was made between instantaneous input assumption and short-term zero-order infusion for 1 and 2 min for several drugs showing fast distribution to the tissue compartments. The errors ranged from 9 to 40% for the volume of the central compartment, from 0.7 to 11% for the volume of distribution following pseudo-distribution equilibrium, and from 11 to 34% for the volume of distribution change at the end of the 2-min infusion period. Significant errors in the tissue levels also were observed. It was suggested that all intravenous administrations be considered as short-term zero-order inputs.

Half-Life↗
PubMed1975

Fluorocarbon aerosol propellants IV: pharmacokinetics of trichloromonofluoromethane following single and multiple dosing in dogs.

An intravenous dosage form of trichloromonofluoromethane, a common aerosol propellant, was formulated in polyethylene glycol 400 for single and multiple dosing to unanesthetized dogs. A three-compartment open model was proposed for disposition of this compound in dogs with average half-lives of 3.2, 16, and 93 min for three disposition phases. This finding is contrary to several reports where blood levels were monitored for shorter periods. A computer analysis of tissue compartment distribution following a single dose showed that about 2 hr was required to achieve pseudodistribution equilibration, following which more than 90% of the dose remaining in the body was retained in tissue compartments. Pulmonary clearance and volumes of distribution were calculated considering first-pass effect through the lung. The volume of distribution was approximately six times the body weight in terms of blood concentrations, and about 30% of the propellant was cleared from blood passing through the lung in each cycle. Disposition of propellant followed dose-independent kinetics after multiple dosing, and accumulation in tissues continued for a much longer period, resulting in high tissue compartment levels.

Aerosol Propellants↗
PubMed1975

Fluorocarbon aerosol propellants. VI: Interspecies differences in solubilities in blood and plasma and their possible implications in toxicity studies.

Solubilities of the three most commonly used fluorocarbon aerosol propellants were determined in the blood and plasma of humans, monkeys, dogs, rats, and mice. Differences as large as approximately fourfold in blood and more than 33-fold in plasma were found in different species. The partitioning of fluorocarbons between blood cells and plasma showed even greater differences between species. An indirect method was suggested for the calculation of plasma concentrations from total blood concentrations. A comparative evaluation was reported for the nonprotein bound fractions of fluorocarbons in the blood samples of various species. A correlation was drawn for the pharmacokinetic properties of the fluorocarbons within and between species, and a rationale was provided for the extrapolation of toxicity data from animals to humans.

Adult↗