Effect of Ca (II) ion on the in vitro availability and protein binding of Amlodipine besylate

Background

The present study explicates the effect of metals ion (Ca²⁺) on the in vitro availability of Amlodipine besylate owing to drug–metal interaction.

Methods

Spectral studies were performed in an aqueous system at a fixed temperature (37 ± 0.5)°C and under different pH by UV spectrophotometric method at various concentrations of drug and metal. A Job plot was used to determine the stoichiometry of a binding event and The Ardon's method confirmed the complexation. An in vitro study of protein binding of Amlodipine besylate and their 1:1 mixture with Ca²⁺ ion had been conducted by equilibrium dialysis method at (37 ± 0.5)°C and at pH 7.4 by using Bovine Serum Albumin (BSA).

Results

Spectral studies detected the initial complexation. By Job's plot it was found that the interaction of Amlodipine besylate with metal ion (Ca²⁺) form one complex with metal at composition of 1:1. The Ardon's spectrophotometric method confirmed the 1:1 complexation and the value of stability constant was higher at pH 7.4 (0.11). The percentage of protein binding of Amlodipine besylate with BSA was found to be 86% and 42% at high and low concentration range respectively. In presence of Ca²⁺ the percentage of protein binding of drug increased 46% at lower concentration range and 94% at higher concentration zone. The results were statistically significant (p < 0.05).

The Scatchard plots showed that in class I binding sites, the value of affinity constant and number of binding sites of 1:1 complexes with Ca²⁺ was 1.04 and 20.8 respectively.

Conclusion

Drug–metal complex might, therefore, decrease the free drug in plasma and tissue systems. This may change the pharmacokinetic properties of the drug and may affect the pharmacological effects. It is thus inferred that care and monitoring must be taken during combination therapy of Amlodipine besylate and Ca²⁺.