Design and Evaluation of a New Fixed-Dose Immediate Release Capsule of Atenolol, Enalapril Maleate and Hydrochlorothiazide

Aim and Objectives: To design, formulate and perform in vitro studies of a fixed dose combination (FDC) immediate release solid dosage form of the antihypertensive drugs atenolol, enalapril and hydrochlorothiazide. The objectives of the study were to perform pre-formulation studies, design an immediate-release FDC capsule dosage form, and evaluate the prepared dosage form.

Methods: Differential Scanning Calorimetric (DSC) analysis of physical mixtures of drugs and drug-excipient combinations was used to assess compatibility. Binary mixtures of atenolol and enalapril form a eutectic mixture indicating that a tablet dosage form, in which the drugs would be highly compressed together, may not be stable. Hard gelatin shell encapsulation was therefore employed. Atenolol and enalapril were separately dry-granulated with hydrochlorothiazide and excipients and mixed together at appropriate therapeutic proportions and encapsulated in size 1 hard gelatin capsules (HGC). Preliminary screening produced five formulations each with similar proportions of the 3-drug FDC but with 5 different levels of disintegrant. Capsule weight variation, disintegration time and dissolution rate were determined as output variables, following USP procedures. For the dissolution studies, a reverse phase high-pressure liquid chromatographic (RP-HPLC) method was developed for simultaneous analysis of the three drugs.

Results: Granules possessed good fluidity (compressibility index 8.53 to 11.63 and tapped bulk density 1.09 to 1.132). Capsule disintegration time was generally £ 2 minutes while 80% of each drug dissolved within 20 minutes. Capsules showed no sign of physical instability or adverse effect during a period of 1 year shelf storage at room temperature (average temperature 25°C).

Conclusions: Granules possess adequate fluidity and compressibility for filling into HGC. Results generally indicated that an immediate release FDC capsule of atenolol, enalapril and hydrochlorothiazide was stable for more than 1 year of observation. Capsule disintegration time and dissolution rate were generally within the USP specification.