Development of a stable powdered herbal formulation suitable for capsule filling

Abstract

Herbal bioactive compounds hold significant therapeutic potential but often face formulation challenges due to hygroscopicity, stickiness, and poor flowability. This study aimed to develop a stable, free-flowing powdered formulation from a highly hygroscopic polyherbal extract for oral capsule delivery while ensuring safety, flowability, and stability. The polyherbal extract was prepared using hot water extraction of an equal weight of four different plant parts. Initial crude extracts exhibited a gummy consistency and extreme hygroscopicity, which remained even after conventional drying techniques (rotary evaporation, vacuum/oven drying, flash drying). Freeze-drying at −80°C produced a fine powder, but it still absorbed moisture easily, requiring the application of a suitable excipient mixture to stabilize. The flowability of the formulations prepared with different excipients was assessed using the angle of repose (angle determined by the fixed funnel method/ θ) and Carr's compressibility Index (calculated from the difference between bulk and tapped densities divided by tapped density, expressed as a percentage). Initial trials with corn starch alone as an excipient failed to improve flow, whereas pharmaceutical-grade Nano silica (Aerosil®) at 20% exhibited reduced hygroscopicity, passable flowability (θ = 41° 65′) and fair compressibility (17.7%), but led to excessive puffiness which cause to difficulties in the capsule filling process. Then the excipient mixtures containing Aerosil® (5–15%), talc (0.5%), and magnesium stearate (0.25–0.5%) were applied, which have reduced hygroscopicity and puffiness, but it still exhibited poor flowability (θ = 47°–55°). However, incorporating anhydrous lactose instead of talc, notably improved flow properties and the optimized formulation (9% Aerosil®, 20% lactose, 1% magnesium stearate), has achieved fair flowability (θ = 40°35′) and good compressibility (15.9%), producing a stable, non-hygroscopic, puffiness reduced powder, suitable for capsule filling. This study shows that excipient selection plays an important role in overcoming herbal extract formulation challenges. The optimized excipient mixture effectively mitigated hygroscopicity and improved flow properties, enabling scalable capsule production. These results revealed that adding suitable excipients could enhance the flow characteristics and reduce the hygroscopicity of highly hygroscopic herbal products to overcome the challenges associated with hygroscopicity and gummy nature.