Preparation of pH-dependent modified-release pellets of urapidil to improve its bioavailability

Objective: Modified-release pellets containing urapidil were developed and its in vivo bioavailability was investigated.

Methods: Lactose and MCC were used as the main fillers to prepare drug-layer pellets by the powder layering method using centrifugal granulation, and coated in a fluidized bed coater. Pellets with different drug release characteristics were prepared with a methacrylic acid copolymer aqueous dispersion.

Results: Using commercial German capsules as the reference (R), two coating formulations were selected for tests after optimization: pH-dependent pellets with a ratio of Eudragit^® NE30D/L30D55 of 10:1, a 3% coating level (T₁), and pH-independent pellets with a Eudragit^® NE30D coating level (T₂) of 3.5%. The bioavailability of the pellets (T₁, T₂, containing 30?mg urapidil) was determined in six healthy subjects after oral administration of a single dose, for a period of three weeks, in the form of a crossover design with a wash-out period of one week. The plasma concentrations of urapidil were determined by HPLC with UV detection. The C_max (maximum concentration), T_max, and MRT of T₁ were 311.7?ng/mL, 5.3?h and 8.3?h, respectively. T₁ was bioequivalent to R, with a relative bioavailability 110.9%. The C_max and T_max, of T₂ were 105.3?ng/mL and 13.3?h, respectively, and the relative bioavailability was 72.7%.

Conclusion: The pH-dependent urapidil pellets have a high bioavailability.