Evaluation of adsorption capacity of acetaminophen on activated charcoal dosage forms available in Nigeria by in vitro adsorption studies and scanning electron microscopy

Purpose: To investigate varying dosage forms of activated charcoal obtained from community pharmacy outlets in Nigeria for their adsorption capacity when challenged with acetaminophen.
Methods: Equilibruim kinetics of acetaminophen adsorption onto activated charcoal surface was determined via batch studies at different adsorbent:adsorbate ratios. The isotherm adsorption experiment was carried out at 37 ^oC and langmuir isotherm models were utilized to describe the equilibrium kinetics data with characterization of adsorption site and porosity elucidated via scanning electron microscopy.
Results: A preponderance of microporosity was observed on the surface of the powder activated charcoal. Maximum adsorption capacity (MAC) of 299.78 mg/g was obtained using activated charcoal powder (276.11; 321.09) at 95 % confidence interval (CI), allowing for maximum adsorption of acetaminophen at pH 1.2. Mixed pore structures, which were not clearly established, were observed with both the tablets and capsules with MAC of 280.54 mg/g (273.22; 290.08) and 140.01 mg/g (135.32; 153.99), respectively at pH 1.2. MAC data at pH 6.5 showed little variation from those obtained at pH 1.2 (p < 0.05 95 % CI).
Conclusion: The presence of excipients in the tablets and capsules caused a retardation in adsorption via intraparticle diffusion especially at basal micropore sites on the activated charcoal surface. Activated charcoal powder is superior to other dosage forms for use in countering acetaminophen poisoning.

Keywords
Acetaminophen; Adsorption; Isotherms; Activated charcoal; Scanning electron microcopy