Biomedical subjects

N A Daabis

Publications and source records attributed to N A Daabis.

7 recordsLinked to original sources

PubMed1978

Aspirin stability in solid dispersion binary systems.

The stability of aspirin in its solid dispersion with urea or povidone was investigated at two accelerated storage conditions. The observed aspirin degradation in both systems followed the first-order rate equation. The water sorption ability of the two carriers as well as the alkalinity imparted by urea could possibly be the most important factors responsible for the observed acceleration of aspirin decomposition. The results also showed that the temperature effect was more pronounced than the humidity effect. Generally, coprecipitated samples exhibited slightly higher degradation rates than physically mixed ones.

Aspirin↗

PubMed1977

The effect of dihydroxypropyl theophylline on the solubility and stability of menadione (vitamin K3).

The effect of dihydroxypropyl theophylline on the solubility and stability of menadione was investigated. An increase of about 4-fold in the solubility of menadione with 0.1 m dihydroxypropyl theophylline was observed at 30 degrees C. Thermodynamic paremeters were calculated by conducting the experiments at different temperatures. The rate of base-catalyzed degradation of menadione in the presence and absence of dihydroxypropyl theophylline was found to be first order with respect to the vitamin at all conditions of pH, temperature and concentration. Dihydroxypropyl theophylline leads to an accelerated rate of decomposition of the drug at relatively high pH values. This adverse effect decreases considerably as the pH of the solution approaches neutrality. At pH = 7.5, dihydroxypropyl theophylline exerts a rather stabilizing effect on menadione solution. The enhancement of the rate of base-catalyzed degradation is directly proportional to the concentration of dehydroxypropyl theophylline at pH = 9.2. The base-catalyzed degradation of menadione in the absence and presence of dihydroxypropyl theophylline follows Arrhenius' equation for the thermal activation of molecules. No noticeable variation in the energy of activation of both systems was detected. The addition of 4% dihydroxypropyl theophylline to menadione solution nearly completely suppressed the aerobic photodegradation of menadione.

Catalysis↗

PubMed1976

The effect of some additives on the adsorption of tetracycline hydrochloride on magnesium trisilicate and milk.

The effect of various additives on the adsorption of tetracycline hydrochloride on magnesium trisilicate or milk was investigated. Adsorption-elution, dialysis and sedimentation volume measurements were used in the present investigation. Citric acid was found to exert the highest adsorption suppressing effect of the antibiotic on both antacids. The nonionic surfactants, polyoxyethylene-23-lauryl ether (Brij 35) and polysorbate 80, had an intermediate action, while polyethylene glycol 6000 (PEG-6000), polyvinylpyrrolidone (PVP), sodium carboxymethylcellulose (CMC) and urea had only a slight effect. On the other hand, the effect of sodium benzoate and sodium salicylate varied with concentration. Results of the elution study showed that the efficiency of the additives, as eluting agents, was more or less parallel with their influence on adsorption. The presence of citrate or Brij 35, having the highest adsorption-suppressing effect, was found to have a negligible effect on the chemical stability or microbiological activity of tetracycline. Conclusions were made that the incorporation of some of these additives may possibly reduce tetracycline-antacids interactions and consequently improve the antibiotic availability when co-administered with antacids.

Adjuvants, Pharmaceutic↗

PubMed1976

The in vitro adsorption of some antibiotics on antacids.

The adsorption of oxytetracycline hydrochloride, tetracycline hydrochloride, doxycycline hyclate, triacetyloleandomycin, chloramphenicol, ampicillin, and cloxacillin sodium was studied on various antacids namely, magnesium trisilicate, magnesium oxide, calcium carbonate, bismuth oxycarbonate, aluminium hydroxide, and kaolin. The adsorption of the various antibiotics by milk was also tested as milk is frequently used as an antacid. Charcoal was included in the present study as a model adsorbent having a large hydrophobic surface. The adsorption of the various antibiotics on the different antacids and other adsorbents in most cases obeyed the Freundlich adsorption isotherm. Magnesium trisilicate and magnesium oxide showed the highest adsorptive capacity, relative to other antacids used, for most antibiotics. Calcium carbonate and aluminium hydroxide and intermediate power while kaolin and bismuth oxycarbonate had the least adsorptive power. Charcoal exhibited a marked adsorption for all antibiotics tested. Tetracyclines were found to be more highly adsorbed than other antibiotics studied. Triacetyloleandomycin and chloramphenicol had intermediate values. Ampicillin was only adsorbed to a slight extent while cloxacillin was not adsorbed on the antacids used. The extent of adsorption was correlated to the structure of both the adsorbent and adsorbate, the pH of the adsorbent suspension, and to the polarity of the antibiotic in such pH. The reversibility of the adsorption process was studied in different media and at pH values similar to those of the gastrointestinal tract. The extent of elution was found to be inversely proportional to the adsorptive capacity of the different adsorbents. In general, 0.0143 n NaHCO3 solution was found to possess higher eluting properties than 0.01 n HCl. An exception to this pattern was observed with tetracyclines adsorbed on aluminium hydroxide where the elution with acid resulted in a higher degree of desorption. Careful in vitro and in vivo testing of drug availability is advisable prior to the concomitant administration of antibiotics with antacids or other adsorbents.

Adsorption↗

PubMed1976

The in-vitro adsorption of some antirheumatics on antacids.

The adsorption of sodium salicylate, salicylamide, acetylsalicylic acid, paracetamol, mefenamic acid, flufenamic acid, phenylbutazone, oxyphenbutazone, phenazone, aminophenazone, indometacin and methiazinic acid on some antacids was studied. The antacids used were magnesium trisilicate, magnesium oxide, aluminium hydroxide, bismuth oxycarbonate, calcium carbonate and kaolin. Magnesium oxide, followed by aluminium hydroxide and bismuth oxycarbonate showed a fairly high adsorptive capacity for salicylates, mefenamic acid, flufenamic acid, methiazinic acid, indometacin and to a lesser extent for phenylbutazone and oxyphenbutazone. On the other hand, magnesium trisilicate exhibited a tendency to adsorb phenazone, aminophenazone, indometacin and methiazinic acid. Kaolin was found to be a good adsorbent for anthranilic acid derivatives, indometacin and methiazinic acid. Calcium carbonate showed a weak adsorptive capacity for all drugs tested. The adsorption of phenylbutazone and salicylates on magnesium oxide, aluminium hydroxide and/or bismuth oxycarbonate obeyed the Freundlich adsorption isotherm. Elution study showed that salicylates and anthranilic acid derivatives were tenaciously held by magnesium oxide while magnesium trisilicate showed an intermediate retention power for phenazone and aminophenazone. Sodium hydrogen carbonate solution gave, in general, a higher eluting power than hydrochloric acid solution. A marked reduction in the apparent partition coefficients of all drugs tested was observed in the presence of magnesium trisilicate or aluminium hydroxide. Careful in vitro and in vivo testing of drug availability is advisable prior to the concomitant administration of antirheumatics with antacids or other adsorbents.

Adsorption↗

PubMed1975

Physicochemical study of drug binary systems. Part 3: Tolbutamide-urea and tolbutamide-mannitol systems.

The phase diagram of the tolbutamide-urea system, constructed by data obtained from the microheating table apparatus, was a peritectic type. It showed the possibility of the formation of two molecular compounds with incongruent m. p. at 112 degrees C and 123 degrees C. Metastable and stable eutectic points were observed at 63 degrees C and 92 degrees C respectively. The phase diagram of tolbutamide-mannitol system revealed that in addition to eutectic liquefaction at 102 degrees C and 6% (w/w) mannitol, there was a region [40--80% (w/w) mannitol] in which the two components were not completely miscible in the liquid state. Solubility studies showed an increase of about 2.5 fold in the solubility of tolbutamide with 0.5 g% urea and suggested the possibility of the formation of a low-solubility complex in addition to a soluble higher complex of the two components. No obvious increase in the solubility of tolbutamide was detected in the presence of mannitol. A full description of the nature and composition of the final solidified melts of the two present systems could prove to be helpful in the explanation of the dissolution behaviour of the different studied samples and their corresponding physical mixtures. The fused 90% urea and mannitol solid dispersions showed a fast rate of dissolution in the order of 15 and 10 times (respectively) greater than pure tolbutamide.

Chemical Phenomena↗

PubMedDate not supplied

Effect of magnesium trisilicate and citric acid on the biovailability of tetracycline in man.

Oral absorption of tetracycline hydrochloride by human subjects was compared with its absorption when coadministered with magnesium trisilicate, citric acid or magnesium trisilicate-citric acid mixture. Evaluation of the absorption rate was done by means of urinary excretion measurements. The concomitant administration of magnesium trisilicate with tetracycline hydrochloride resulted in a dramatic reduction of the excretion rate of the drug. Ingestion of citric acid with tetracycline showed no significant effect on its absorption. Citric acid administration simultaneously with tetracycline hydrocloride-magnesium trisilicate combination failed to improve the absorption of tetracycline in the presence of magnesium trisilicate contrarily to preveious in vitro results. Conclusions were made that in vitro experiments are not always successful in the prediction of in vivo findings.

Adult↗