Model Selection for the Adsorption of Phenobarbital by Activated Charcoal

Activated charcoal is known to adsorb a wide variety of substances from solution, and several equations have been used to fit the resulting adsorption data. The determination of the correct model to fit phenobarbital adsorption onto activated charcoal was made using a calorimetric method. The differential heats of displacement of water by phenobarbital for four activated charcoals were determined and found to be linearly related to the amount of phenobarbital adsorbed. The activated charcoals studied had statistically similar heats of displacement. The linear relationship between heat evolved and the amount of phenobarbital adsorbed is consistent with the assumptions implicit in the Langmuir model.     

Phenobarbital Removal Characteristics of Three Brands of Activated Charcoals: A System Analysis Approach

The in vivo phenobarbital removal characteristics of three brands of activated charcoal (Actidose, Charcoaid, Superchar) were studied in normal volunteers using a system analysis approach. The subjects received a 200-mg dose of oral or intravenous phenobarbital followed by a single oral dose of 30 g of one of the three charcoals in a randomized crossover design. The relative merits of the three charcoals in enhancing the removal of oral and intravenous phenobarbital were assessed using a system analysis approach. The removal clearance, time to peak (t _p), peak removal clearance (R _max), percentage of dose removed (PCT), and phenobarbital removal clearance (CL_r) were calculated for the oral and intravenous treatments. Superchar had a pulse-like effect, with the shortest t _p and the largest R _max. Actidose and Charcoaid had similar effects, with Actidose inducing slightly greater phenobarbital removal. Superchar has the highest surface area and relative percentage of surface hydroxyl groups, whereas Actidose has the lowest surface area and relative percentage of surface hydroxyl groups of the three charcoals studied. Although correlations between the in vitro and the in vivo phenobarbital adsorption characteristics of the three charcoals may be difficult due to the presence of preservatives and palatibility enhancers in the commercial preparations, it appears that the in vivo effectiveness decreases as the surface area and the concentration of surface hydroxyl groups decrease. The proposed system analysis approach requires fewer assumptions than methods based on compartmental or physiologic approaches and has the advantage of describing the phenobarbital removal in a dynamic manner.     

Surface Characterization of Activated Charcoal by X-Ray Photoelectron Spectroscopy (XPS): Correlation with Phenobarbital Adsorption Data

X-ray photoelectron spectroscopy (XPS) was used to identify the functional states of carbon existing on the surfaces of various activated charcoals. The relative percentages of carbon, oxygen, and detectable trace elements comprising the activated charcoal surfaces were determined. Analysis of the carbon core-electron binding energy region revealed the existence of one hydrocarbon state (C–H, C–C are indistinguishable) and three oxygen-containing functional states. These states were hydroxyls or ethers (C–O), carbon-yls (C = O), and carboxylic acids or esters (O–C = O). The C–O functional state contributed approximately 60–70% to the total percentage of oxygen-containing states. A very good correlation existed between the apparent areas occupied on the adsorbent surface per phenobarbital molecule and the relative percentages of the C–O functional state. Previously reported heat of displacement results for phenobarbital adsorption are now explained since the C–O state appears to be the primary site involved in the binding of phenobarbital by the activated charcoals.     

Kinetics of Drug Action in Disease States. XXXIX. Effect of Orally Administered Activated Charcoal on the Hypnotic Activity of Phenobarbital and the Neurotoxicity of Theophylline Administered Intravenously to Rats with Renal Failure

The central nervous system (CNS) sensitivity to the hypnotic (general anesthetic) action of pheno-barbital and to the neurotoxic (convulsive) action of theophylline is greater in rats with acute renal failure than in normal animals, consistent with clinical observations. In the case of phenobarbital, this increased sensitivity can be produced in normal rats by infusion of a solution of the lyophilized dialysate of serum from rats with renal failure. It was hypothesized that the relevant constituent(s) of this dialysate may circulate between the blood and the intestinal lumen and that it (they) can be adsorbed by orally administered activated charcoal and thereby removed from the body. If so, treatment of renal failure rats with activated charcoal should partly reverse the increased CNS sensitivity to phenobarbital and to other drugs similarly affected. Accordingly, rats with renal failure produced by bilateral ligation of ureters were given an aqueous suspension of activated charcoal, about 1 g per kg body weight, orally every 8 hr for six doses. Uremic controls received equal volumes of water. About 2 hr after the last dose, the animals were infused i.v. with phenobarbital to onset of loss of righting reflex or with theophylline to onset of maximal seizures. In the phenobarbital study, charcoal treatment partly reversed the hypothermia associated with renal failure and caused a reduction of creatinine and total bilirubin concentrations in serum. The cerebrospinal fluid (CSF) concentration of phenobarbital at onset of loss of the righting reflex was significantly higher in charcoal treated rats than in their controls. In the theophylline experiment, charcoal treatment had no significant effect on the measured biochemical variables but caused a large increase in the dose and concentrations of theophylline required to produce maximal seizures. In both experiments, administration of activated charcoal caused a reversal of the hyperalgesia associated with renal failure, as determined before drug administration by tail flick latency. These results are consistent with the hypothesis that oral administration of activated charcoal can cause a reduction in the concentration of the circulating endogenous substance(s) that alters the pharmacodynamics of certain drugs in renal failure.     

Linear systems approach to the analysis of an induced drug removal process. Phenobarbital removal by oral activated charcoal

The theory of linear systems analysis is applied to the evaluation of induced drug removal processes. The rate and extent of removal are determined by deconvolution for the case of phenobarbital removal from the systemic circulation by orally administered activated charcoal. The proposed method is model independent in the sense that no specific models of intrinsic or induced pharmacokinetic processes are required, and it is readily adapted to the analysis of most types of induced removal processes (hemodialysis, peritoneal dialysis, etc.). Application of the approach indicates that phenobarbital was removed from the systemic circulation to an extent of 25–53% following multiple oral doses of activated charcoal in healthy human subjects.     

Adsorption,kinetics and thermodynamics of phenol removal by ultrasound-assisted sulfuric acid-treated pea (Pisum sativum) shells

In the present study, waste pea shells were used to synthesize an efficient adsorbent (ultrasound-assisted sulphuric acid-treated pea shells, USAPS) and was applied for phenol removal. The USAPS characterization was done by SEM-EDS, FT-IR, XRD, optical profilometry, BET, and PZC techniques. The use of ultrasound during the chemical activation significantly enhanced the adsorption properties. The adsorption of phenol was probed by varying pH (2–9), temperature (25–45°C), the USAPS dose (0.1–0.6 g/100ml), phenol concentration (50–500 mg/L), and inorganic salt addition (0.1 M KCl and 0.1 M CaCl₂). The maximum phenol uptake was found to be 125.77 mg/g for 500 mg/L of phenol concentration at pH 7 and 25°C with 0.1 g/100ml of the USAPS dose. Adsorption was negatively affected by an increase in temperature and the USAPS dose while 0.1 M KCl and 0.1 M CaCl₂ addition decreased the maximum phenol uptake from 125.77 mg/g to 103.45 mg/g and 84.11 mg/g, respectively. The time-dependent phenol removal was best explained by the pseudo-second-order kinetic model while equilibrium data were best explained by the Langmuir model. The thermodynamic study revealed the physical nature of adsorption with no structural alteration at the adsorbent-adsorbate interface.     

Thermodynamic Estimate of the Number of Solvent Molecules Displaced by a Solute Molecule for Enthalpy-Driven Adsorption: Phenobarbital and Activated Carbons as the Model System

A Modified Crisp Equation, describing the differential Gibbs free energy of the adsorption process, is being proposed, which considers multiple sites available on the surface for adsorption and their relative fractions. The differential Gibbs free energy can be calculated by the van't Hoff Equation, which depends on the affinity constant in the Langmuir-like equation. To consider the number of solvent molecules displaced by a solute molecule in the adsorption process, a new derivative of the Langmuir-like equation is being proposed as well. By comparing the differential Gibbs free energies obtained from the 2 thermodynamic relationships, it can be determined that a phenobarbital molecule displaces 5 water molecules on the activated carbon surface for site-specific adsorption from solution. For the series of experimental conditions studied, including 4 activated carbons, pH effects, temperature effects, and solvent effects, the corrected differential Gibbs free energies using n₁ = 5 for site-specific adsorption are quite consistent between the 2 thermodynamic relationships. The difference between the estimates of the differential Gibbs free energies by the Modified Crisp Equation and the van't Hoff Equation provides a new experimental method to calculate the number of solvent molecules displaced by an adsorbing solute molecule.     

Effect of dose of charcoal on the absorption of disopyramide,indomethacin and trimethoprim by man

Summary The efficacy of various charcoal-to-drug ratios for the absorption of drugs was studied in 6 healthy volunteers and in vitro at two pHs. Disopyramide 200 mg, indomethacin 50 mg and trimethoprim 200 mg were ingested on an empty stomach with 100 ml water. After 5 min the subjects ingested a charcoal suspension in 300 ml — 2.5 g, 10 g, 25 g or 50 g of Norit A, or 10 g of PX-21, or water 300 ml only. Increasing the dose of activated charcoal from 2.5 g to 50 g reduced the gastrointestinal absorption of disopyramide and indomethacin from 30–40% to 3–5%, and that of trimethoprim from 10% to 1% of the respective controls. Disopyramide and trimethoprim were best adsorbed by charcoal in vitro at neutral and indomethacin at acid pH, but saturation of the adsorption capacity was apparent at charcoal-to-drug ratios less than 7.5. Combining the in vitro and in vivo results it can be concluded that the dose of activated charcoal to be given in acute intoxication should be as large as possible, because the drug history is often unknown.     

Understanding Differences in Marijuana Use Among Urban Black and Suburban White High School Students from Two U.S. Community Samples

Abstract

To examine community/racial differences in adolescent marijuana use and the variations in factors underlying the observed differences, a questionnaire survey study was conducted with 9th to 12th graders (n = 1,936) from two communities in New Jersey. Marijuana use was significantly higher among suburban (mostly White) students than among their urban (mostly Black) counterparts. Significant differences in marijuana use between the two community sub-samples were explained by differences in type of risk factors, mean number of risk factors, and the strength of the association (slopes) between risk factors and marijuana use. Social-environmental factors (including positive after-school activities and negative peer influences) and, to a lesser degree, family factors (including family income, parental and sibling drug use), accounted for most community/racial differences in marijuana use