Adsorption of Atenolol on Talc: An Indication of Drug Interference with an Excipient

Abstract

Talc is commonly used as an excipient for drug formulations. The general expectation is that the excipient should have only minimal interactions with the carrying drug. In this study, the adsorption of atenolol (AT), a β-blocker, on talc, a clay mineral of pH-dependent surface charge, was evaluated under different physicochemical conditions such as the initial AT concentration, equilibrium time, solution pH, ionic strength and temperature. Our experiments showed that talc had an AT adsorption capacity of 11 mmol/kg. In addition, adsorption of AT on talc was instantaneous, which suggests that the adsorption sites were located on the external surfaces or edges. Factors such as solution pH, ionic strength and temperature all had minimal influence on AT adsorption, although the adsorption process was exothermic and the free energy of adsorption was negative, indicating weak physical adsorption. The Fourier transform infrared results showed blue shifts of the bands corresponding to δ(C-OH) at 1410 and 1043 cm -1 , indicating hydrogen bonding for the uptake of AT on talc surfaces or edges.

Contrasting mechanisms of metoprolol uptake on kaolinite and talc

“…For talc, the contrast between AT and MT sorption was opposite with their sorption capacities of 11 [21] and 14 (this study) mmol/ kg, respectively. Considering the hydrophobic nature and lower charge density of talc, it would have a higher affinity for the less polar MT as confirmed by the K f of 15.4 mmol 1Àn L n /kg, in contrast to 6.1 mmol 1Àn L n /kg for AT uptake on the same talc [21].…”

“…In this study, we choose kaolinite, a common soil mineral found in warm and humid regions, and talc, a commonly used excipient, to study their interactions with MT. Together with our previous studies [17,21] on interactions between atenolol (AT), another commonly prescribed b-blocker, and kaolinite and talc, we anticipate to shed some light on elucidating mechanisms of interactions between clay minerals and b-blockers in the environment.…”

“…Considering the hydrophobic nature and lower charge density of talc, it would have a higher affinity for the less polar MT as confirmed by the K f of 15.4 mmol 1Àn L n /kg, in contrast to 6.1 mmol 1Àn L n /kg for AT uptake on the same talc [21]. The strong involvement of aromatic and aliphatic ether as revealed by the blue shift of these bands suggested significant contribution of -O-for the hydrogen bonding or hydrophobic interactions between MT and talc.…”

“…In contrast to kaolinite, the K L and S m values were 8.5 L/mmol and 15 mmol/kg based on the Langmuir isotherm, suggesting a higher affinity of MT for talc, although with a lower MT sorption capacity. The K L and S m values were 0.75 L/mmol and 11 mmol/kg for AT uptake on the same talc [21]. Thus, for talc the ether group in MT resulted in a slightly better MT uptake in comparison to the amide group for AT uptake on the same talc.…”

“…Sorption of MT on magnesium trisilicate resulted in a DG of -3.6 and -4.0 kJ/mol at 37 and 50°C with a DH value of À4 kJ/mol [1]. The lower negative values of DG for MT sorption on both minerals indicated physical sorption such as cation exchange or electrostatic interaction processes as observed in the case of ciprofloxacin and AT sorption on the same kaolinite [17,22], or hydrophobic interactions as observed in the case of sulfadiazene sorption [26], or hydrogen bonding for AT sorption on the same talc [21].…”