Adsorption of local anesthetics on activated carbon: Freundlich adsorption isotherms

We have shown that adsorbability of local anesthetics onto activated carbon, expressed by the partition coefficients at infinite dilution, correlated well with the pharmacological activity. However, there is no parameter that can singly express the tendency to be adsorbed. Adsorbability is a loosely defined term and its meaning varies with the adsorption model. This study showed that the logarithm of the adsorbed amount of drugs was linearly related to the logarithm of the free drug concentration, in conformity to the Freundlich adsorption isotherms. The slope of the double logarithmic plot is expressed by 1/N in the Freundlich equation and is considered to be inversely related to the drug affinity to the adsorbent. The slope was used to evaluate the tendency to be adsorbed, or "adsorbability" of seven aromatic amine local anesthetics. Phenobarbital was included to compare anionic drugs in contrast to the cationic local anesthetics. The slopes were nearly equal between the cationic and neutral local anesthetics. Apparently, the lower hydrophobicity of the cationic forms is compensated by the electrostatic attraction from the negative charges present on the activated carbon surface. With phenobarbital, the slope value of the anionic form was larger than the neutral form. The lower affinity of the anionic form may be caused by the electrostatic repulsion. The molecular size parameters (i.e., molecular weight, molar refraction, and parachor) showed a linear relationship to the slope values. It may be possible to estimate the affinity-related slope values from these parameters.     

Heparin adsorption on activated charcoal

By vitro studies have shown that sodium heparin adsorbs significantly at pH 7.4 conditions onto a typical activated charcoal. These results imply that enhanced heparin removal from blood should be anticipated in hemoperfusion systems that utilize uncoated charcoals.     

Parameters for the adsorption of thallium ions by activated charcoal and Prussian blue

Activated charcoal and Prussian blue are effective antidotes in acute thallium (T1+) intoxication in rats. They act by trapping any metal present in or secreted into the gut by the gastro-intestinal epithelium. It was therefore of interest to determine the parameters of the Langmuir adsorption isotherms of T1+ ions for these two adsorbents. The data from equilibration experiments were analyzed by direct least-squares fitting to a hyperbola and with Langmuir's equation to give the following results: Activated charcoal: K1(-1) = 192 micrograms ml-1, K2 = 124 mg g-1 Prussian Blue: K1(-1) = 130 micrograms ml-1, K2 = 72 mg g-1. These high values provide in vitro confirmation of their in vivo antidotal efficacy and show that activated charcoal can replace Prussian blue when this latter drug is unobtainable.     

Fluorocarbon aerosol propellants IX: adsorption on activated charcoal.

The adsorption of three commonly used fluorocarbons, trichloromonofluoromethane, dichlorodifluoromethane, and dichlorotetrafluoroethane, on activated charcoal was studied at 25 degrees. The adsorption versus pressure plots are consistent with the Brunauer, Emmett, and Teller (BET) type II and type IV isotherms, which can be explained as the condensation of the gaseous molecules in a wide range of pores in the activated charcoal. The monolayer capacity derived from the BET equation is discussed and used to estimate the volume of micropores present in the activated charcoal. Below the relative pressure of 0.01, the adsorption deviated from the BET plot. The deviation revealed that the adsorption capacity and adsorption potential at these lower pressures are greater than the extrapolated values. It is concluded that activated charcoal can be used effectively to remove propellants from the air in pollution control.     

The adsorption of isopropanol and acetone by activated charcoal.

This study was performed to determine the adsorption of isopropanol and acetone by activated charcoal over a range of charcoal:solvent ratios. The charcoal binding of isopropanol was studied in both hydrochloric acid and water solutions, while acetone was analyzed in water. Gram ratios of charcoal to solvent ranged from 1:1 to 20:1. After the addition of charcoal the solution was agitated and centrifuged. The supernatant was then analyzed by gas chromatography. Each increment in charcoal dose increased the percent adsorption of both isopropanol and acetone. At the 20:1 ratio 87-92% of the solvent was bound by activated charcoal. In vivo study is needed to determine if activated charcoal therapy can shorten the half-life of isopropanol and acetone and decrease the duration of supportive care needed following ingestions of these solvents.     

In vitro adsorption of tilidine HCl by activated charcoal

In vitro studies were carried out in order to determine the adsorption of tilidine HCl, a narcotic analgesic, by activated charcoal (max. adsorption capacity 185.5 mg/g of charcoal). The path of the adsorption isotherms at pH 1.2 and 7.5 suggests that the in vivo adsorption of tilidine HCl may be increased when the drug passes from the stomach to the intestine, unless the intestinal content exerts a displacing effect. Nevertheless, the adsorption was dependent on the quantity of activated charcoal used, becoming more complete when the quantity of activated charcoal was increased. The effects of additives on the adsorption capacity of activated charcoal were also investigated in vitro. Ethanol, sorbitol and sucrose significantly reduced drug adsorption, while cacao powder, milk and starch had no effect on tilidine adsorption. At an acid pH, Federa Activated Charcoal significantly adsorbed more drug than either Norit A or Activated Charcoal Merck.     

Sucrose as a sweetener for activated charcoal.

The efficacy of sucrose as a flavor for activated charcoal was studied. In vitro adsorption of sucrose (in Simulated Gastric Fluid, USP, without pepsin) to activated charcoal, and of a 1-g/liter sodium salicylate solution to a 1:1 mixture of sucrose and activated charcoal and to plain activated charcoal, was measured spectrophotometrically. In vitro adsorption of sucroses to activated charcoal was minimal. Sucrose reduced in vitro adsorption of sodium salicylate to activated charcoal by only small amounts. For example, at a ratio of 4 g activated charcoal to 1 g sodium salicylate, sucrose reduced salicylate adsorption to activated charcoal from 99% to 95%. A 1:1 sucrose-activated charcoal preparation provides sufficient flavor without substantial loss of adsorbance.     

In vitro study of lithium carbonate adsorption by activated charcoal

The purpose of this study was to determine whether lithium carbonate (Li2CO3) is effectively adsorbed by activated charcoal (AC). Either 0 (control), 1.5, 3.0 or 9.0 grams of AC were added to Li2CO3 (300 mg) in distilled deionized water or simulated gastric fluid USP, filtered and and the filtrate analyzed for lithium by flame photometry. Adsorption of lithium was dependent on AC concentration and pH. In water, lithium was 14.7%, 26.5% and 40.4% adsorbed at AC:Li2CO3 ratios of 5:1, 10:1 and 30:1, respectively (p less than 0.05). In simulated gastric fluid, there was no significant adsorption at any of the AC concentrations studied. Since simulated gastric fluid more closely resembles in vivo conditions, the efficacy of AC in lithium carbonate overdoses is questionable but in vivo studies are needed to confirm these findings.     

Determination of the adsorption of tramadol hydrochloride by activated charcoal in vitro and in vivo

Although tramadol is one of the most widely used centrally acting analgesics worldwide, no literature is available regarding adsorption of tramadol HCl powder or tablets (Ultram; 50 mg tramadol HCl per tablet) by activated charcoal (AC) for use as potential adjunct treatment of overdose. The present study incorporated a novel combination of in vitro and in vivo methods to investigate this question. Based on a binding curve of tramadol UV absorbance (UV(a); 225 nm) plotted against the amount of AC, the ratio of amount of tramadol completely adsorbed by AC was 0.05 mg/mg. Also based on UV(a), no tramadol was detected in filtrate of slurries in which up to 62 tablets of Ultram were mixed with 50 g AC; 4.6% of unbound tramadol was detected when 100 tablets of Ultram were mixed with AC. The ratio of amount of tramadol completely adsorbed by AC in this test was 0.10. In vivo, co-administration of 0.1 g/ml of AC produced a 13- to 14-fold rightward shift in tramadol's antinociceptive dose-response curve and a 1.6-fold rightward shift in tramadol's lethality dose-response curve.     

The adsorption of quinine and quinidine to activated charcoal with and without magnesium sulfate

The effect of magnesium sulfate on the in vitro adsorption of quinine and quinidine to activated charcoal (AC) was studied. Solutions of quinine and quinidine were prepared at concentrations of 5 and 10 micrograms/ml and at simulated toxic concentrations of 62.5, 125 and 250 micrograms/ml in distilled water. Drug-charcoal slurries were vortex mixed, centrifuged and analysed for free drug in the supernatant. Quinine had adsorption capacities of 78.2 to 100% with 12.5 or 50 mg AC; 12.5 or 50 mg AC adsorbed 29.5-87.2% of the quinidine. Quinine (250 micrograms/ml) had adsorption capacities of 0.0, 21.1, 52.4, 78.3 or 93.8% to 12.5, 50, 125, 250 or 500 mg AC, respectively. There was a corresponding increase quinine and quinidine adsorption at increasing concentrations of AC. The adsorption of quinine and quinidine seemed dose dependent. Magnesium sulfate (7.5 mg/ml) enhanced the adsorption of quinine to AC, but increased the amount of AC required for quinidine-charcoal adsorption.     

The effect of ethanol and pH on the adsorption of drugs from simulated gastric fluid onto activated charcoal

The effect of ethanol and pH on the adsorption of acetaminophen (ACET), phenobarbital (PHB), phenytoin (PHY), salicylic acid (SA), and theophylline (THEO) from simulated gastric fluid onto activated charcoal was studied. For the ethanol study, each drug was prepared at a concentration of 10 g/L in ethanol; in hydrochloric acid (HCl), 1.2 mol/L; and in HCl, 1.2 mol/L, containing 75% ethanol, 50% ethanol, and 25% ethanol (v/v), respectively. For the pH study, each drug was prepared at a concentration of 10 g/L in HCl, 1.2 mol/L, pH 1.0, and in buffers of pH 1.7, 3.0, 4.0, 4.8, 5.8, 6.5, 7.4, and 9.4. After the addition of 1 g of activated charcoal to 10 mL of each solution, it was incubated for one hour at 37 degrees C. For comparison, in each experiment a blank consisting of the solution without charcoal was also incubated. With increasing concentrations of ethanol, there were substantial decreases in the adsorption of ACET, PHB, and PHY to charcoal. Ethanol-induced decreases in the adsorption of SA and THEO were less pronounced. Changes in pH did not affect the adsorption of ACET, PHB, PHY, or THEO. However, the adsorption of SA was decreased slightly at pH 1.0 and 3.0.     

Thermodynamic evaluation of activated charcoal as a poison antidote by high-performance liquid chromatography. II: In vitro method for the evaluation of activated charcoal as a poison antidote

A previous report detailed the derivation and validation of an equation for calculating the Gibbs free energy of liquid-solid adsorption via high-performance liquid chromatography (HPLC). This study utilizes an improved form of that equation in conjunction with an in vitro model of solute adsorption to give an ordered listing of the antidotal activity of activated charcoal towards different drugs and other chemicals. The in vitro model consists of an activated charcoal column with a nominal particle diameter of 15 micron and a surface area of 447 x 10(4) cm2/g, together with a series of acetonitrile:water mobile phases at pH 3. A simple and efficient procedure was developed for ranking the solutes. First, each compound was run in an acetonitrile(ACN):water mobile phase chosen to give a convenient retention time and ideal chromatographic response. The capacity factor for this mobile phase was extrapolated to give a predicted capacity factor for a 35:65 (v/v) ACN:water mobile phase using an empirical equation developed from the exhaustive chromatography of four standard compounds (phenobarbital, strychnine, cyclohexanone, methyl ethyl ketone) in a variety of ACN:water mobile phases. In addition to the standards, 12 other compounds (glutethimide, chlordiazepoxide, quinine, brucine, d-propoxyphene, pentobarbital, methyprylon, methadone, meperidine, codeine, antipyrine, morphine) were evaluated. Based on these data, the Gibbs free energies of liquid-solid adsorption for these compounds were calculated and used to evaluate activated charcoal as a poison antidote for them. The results indicate that a rapid and accurate estimation of the utility of activated charcoal as an antidote for drugs and toxic substances can be obtained from a single chromatographic run of the test compound.     

Comparative efficacy of thallium adsorption by activated charcoal, prussian blue, and sodium polystyrene sulfonate

BACKGROUND: Although Prussian blue is considered the antidote of choice for thallium poisoning, the lack of a Food and Drug Administration-approved pharmaceutical formulation has led to the search for other adsorbents. Activated charcoal has been demonstrated to adsorb thallium in vitro, and the similarity between thallium and potassium has led some authors to consider the use of sodium polystyrene sulfonate as a potential adsorbent. This experiment was designed to compare the relative thallium binding efficacy of these agents in a standard isotherm model. METHODS: A standard aqueous solution of thallium acetate buffered to pH 7.0 was agitated at 25 degrees C with activated charcoal, Prussian blue, or sodium polystyrene sulfonate at adsorbent:thallium ratios ranging from 1.5:1 to 100:1. In order to further simulate physiologic conditions, all trials were repeated in a solution containing 4 mmol/L potassium phosphate. After thorough agitation, the mixtures were allowed to settle and were centrifuged and filtered through a 0.22-micron filter. Supernatant thallium concentrations were measured by atomic absorption spectrophotometry. Langmuir isotherms were used to calculate the maximal adsorptive capacity of each adsorbent, using linear regression with Pearson's correlation coefficients (r). Maximal adsorptive capacities were compared statistically with a p < 0.05 considered significant. RESULTS: The maximal adsorptive capacities defined as milligrams of thallium per gram of adsorbent (shown with linear regression p and r values) were as follows: activated charcoal, 59.7 mg/g (p = 0.005, r = 0.995); Prussian blue, 72.7 mg/g (p = 0.004, r = 0.996); and sodium polystyrene sulfonate, 713 mg/g (p = 0.049, r = 0.951). All three values were statistically different from each other. At a physiologic potassium concentration, the maximal adsorptive capacities for activated charcoal and Prussian blue were essentially unchanged (58.3 mg/g and 69.8 mg/g, respectively, p > 0.05 for each vs trials without potassium), while the maximal adsorptive capacity for sodium polystyrene sulfonate fell to 39.1 mg/g (p = 0.003, r = 0.997, p = 0.005 vs sodium polystyrene sulfonate without potassium). CONCLUSIONS: This in vitro study confirms the utility of Prussian blue and activated charcoal as thallium adsorbents. Although sodium polystyrene sulfonate demonstrates exceptional in vitro adsorption of thallium, its greater affinity for potassium probably renders it clinically ineffective.     

Effect of activated charcoal on the absorption of amiodarone.

1 The ability of activated charcoal to prevent the absorption of amiodarone was studied in 18 healthy volunteers, divided into three groups of six subjects. 2 All subjects were administered a single dose of 400 mg amiodarone; one group ingested the drug with water only (control) and the second with 25 g of activated charcoal as a water suspension. The subjects in the third group were given 25 g of charcoal immediately after the 1.5 h blood sample. 3 The extent of amiodarone absorption was reduced by about 98% by simultaneously administered charcoal (P less than 0.001); taking charcoal 1.5 h after amiodarone still resulted in a 50% reduction in amiodarone bioavailability (P less than 0.05). 4 These results indicate that activated charcoal should be effective in preventing amiodarone absorption in acute poisoning.