Phenobarbital adsorption

Figure 4.2 shows the Langmuir isotherms of (a) phenobarbital and (b) mephobar-bital adsorption on activated carbon. The maximum adsorption capacity (K,/K2) of activated carbon for mephobarbital is lower than that for phenobarbital. The affinity constant (1/K2) for mephobarbital is higher than that for phenobarbital. This is expected because higher solubility gives a lower adsorption affinity. Table 4.1 illustrates the Langmuir constants of various drugs on carbon black. 

Figure 4.6 shows the competitive adsorption of mephobarbital by activated carbon in the presence of phenobarbital. It clearly illustrates that the extent of mephobarbital adsorption decreases in the presence of phenobarbital. This result shows that the two solutes are competing for the same adsorption sites on the activated carbon. The extent of mephobarbital adsorption in the presence of phenobarbital can be predicted by the competitive Langmuir adsorption isotherm. 

Changes in the erythrocytes osmotic resistance were not observed. Adsorption of total plasma proteins on modified MC was lower than 12 %, but it was about 60 - 70 % on unmodified particles. Table 6 summarizes the results obtained of MC sorption efficiency to substances of different molecular mass in donor plasma. The sorption mechanism of low and middle molecular weight substances (phenobarbital and cyanocobalamin) on iron-carbon and restored-iron MC is apparently connected with absorption of molecules into the sorbent s pores. Iron-carbon composites have a more porous structure than restored-iron, therefore the... 

Pieper, J.A. Rutledge, D.R. Determination of verapamU and its primaiy metabolites in serum by ion-pair adsorption high-performance liquid chromatography. J.Chromatogr.Sci., 1988,26,473-477 [fluorescence detection normal phase LOD 0.22 ng extracted metabolites, N-acetylprocainamide, procainamide, propranolol, quinidine non-interfering digoxin, diltiazem, hydrochlorothiazide, lidocaine, phenobarbital, phenytoin, theophylline]... 

Barbital, Phenobarbital, Pentothal. Barbital can be determined in a borate buffer of pH 9.3 by means of an anodic wave that corresponds to mercury-salt formation. Since the wave height is governed by adsorption at higher concentrations, it is necessary to keep the concentration of barbital below 1 x 10 Af. 

F. Repeat-dose activated charcoal. Repeated doses of activated charcoal (20-30 g or 0.5-1 g/kg every 2-3 hours) are given orally or via gastric tube. The presence of a slurry of activated charcoal throughout several meters of the intestinal lumen reduces blood concentrations by intermpting enterohep-atic or enteroenteric recirculation of the dmg or toxin, a mode of action quite distinct from simple adsorption of ingested but unabsorbed tablets. This technique is easy and noninvasive and has been shown to shorten the half-life of phenobarbital, theophylline, and several other dmgs (Table 1-41). However, it has not been shown in clinical trials to alter patient outcome. Caution Re-peat-dose charcoal may cause serious fluid and electrolyte disturbance secondary to large-volume diarrhea, especially if premixed charcoal-sorbitol suspensions are used. Also, It should not be used in patients with ileus or obstmction. 

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