Influence of food on the bioavailability of diltiazem and two of its metabolites following the administration of conventional tablets and slow-release capsules

The influence of food on the bioavailability of a conventional tablet and of a slow‐release capsule of diltiazem was investigated in two separate groups of 24 healthy volunteers in two open crossover studies. Diltiazem, as a conventional tablet (2 × 30 mg, first group) or as a slow‐release capsule (120 mg SR, second group), was administered in a fasting condition and 30 min after a breakfast of 784 kcal (23 per cent proteins, 55 per cent lipids, and 22 per cent of carbohydrates). Multiple blood samples were withdrawn during the next 24 h and diltiazem, desmethyldiltiazcm, and dcacctyldiltiazcm were assayed by HPLC. Neither the rate of absorption, assessed by the rate constant of absorption, the peak plasma concentration, and the time required to reach the peak, nor the amount of drug reaching the systemic circulation, assessed by the area under the plasma concentration time curve (AUC∞) were influenced by food, and that independently of the formulation. Compared to the fasting experiment, food did not affect either the rate of formation or the AUC∞ of desmethyldiltiazem or deacetyldiltiazem. The results of the present study show that the relative bioavailability of the single dose of diltiazem administered as a slow‐release capsule is significantly higher (69 per cent) than that estimated after the administration of diltiazem in a conventional tablet. It was concluded that food does not influence the bioavailability of diltiazem administered as a conventional tablet or as a slow‐release formulation.