Abstract
In certain situations of peptic ulcers ampicillin has been co-administered with bismuth carbonate with an implication for adsorption of the ampicillin. To quantify this effect the kinetics and extent of adsorption of ampicillin by some commonly used antacids were measured; these are bismuth carbonate, magnesium trisilicate and aluminium hydroxide. The adsorption of ampicillin by bismuth carbonate followed the Langmuir adsorption isotherm, which suggests chemisorptions. It was characterized by a strong adsorption at a low adsorbate (ampicillin) concentration but the % adsorption decreased with increase in adsorbate concentration, which is a feature of a saturated monolayer adsorption. On the other hand, the adsorption by magnesium trisilicate and aluminium hydroxide followed the Freundlich adsorption isotherm characterized by a low adsorption at a low adsobate concentration but this increased slightly with increase in adsorbate concentration, suggesting a weak physical adsorption. The adsorption capacities (mg/g) of the adsorbate were 1.64 (bismuth carbonate) 0.04 (magnesium carbonate) and 0.03 (aluminium hydroxide). Bismuth carbonate thus gave by far the highest degree of adsorption. The conclusion is that the co-administration of ampicillin and bismuth carbonate in the treatment of certain peptic ulcers is erroneous.
Highlights
Antacids and anti diarrhoeas are potent adsorbents and they impair the bioavailability of concomitantly administered drugs
With the other two adsorbents the extent of adsorption was weak at the low adsorbate concentration, for instance there was no measurable adsorption at the adsorbate concentration, O.5mglmlI but the adsorption increased slightly as the adsorbate concentration increased and 20%
The values of the correlation coefficients for the various adsorbents were as follows: 0.980, 946, and 0.749. These results show that aluminium hydroxide and magnesium trisilicate conformed with Freundlich adsorption while bismuth carbonate deviated
Summary
Ampicillin trihydrate (a product of Sigma, U.S.A.) was the test drug. It is sparingly soluble in water dissolving one part in 150 parts of water (i.e. about 7mglml) at 20°C. Adsorbate concentration increased and 20% (magnesium up to a maximum of 15% allumimum hydrate) These results suggest that the adsorptive surface area was not readily saturated, as was the case with bismuth carbonate. - 2mglml) bismuth carbonate conformed with Freundlich adsorption with a correlation coefficient, 0.966. The linear correlation coefficients by this Langmuir analysis for the three adsorbents were 0.9705 (bismuth carbonate), 0.8152 (aluminium hydroxide) and 0.6273 (magnesium trisilicate), indicating that only bismuth carbonate conformed to the Langmuir adsorption isotherm. The K value is a measure of the extent of adsorption as adsorbate concentration tends to zero bismuth carbonate displayed a stronger adsorptive capacity compared with the other two adsorbents. The affinity index values were 2.5 (bismuth carbonate), 0.66 (aluminium hydroxide), and 0.62 (magnesium trisilicate); which means that bismuth carbonate displayed the strongest affinity for the adsorbate. Note: - no measurable adsorption, the percentages represent the proportion of the initial amount of ampicillin (in the test solution) which was adsorbed
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