# Optimized Milling Approaches for Scalable Production of Ritonavir Nanocrystals: from Process Design to Bioperformance Evaluation

## TL;DR

This paper describes a scalable method to produce ritonavir nanocrystals, which improve drug solubility and performance through optimized milling and drying techniques.

## Contribution

The study introduces an optimized and scalable milling approach for ritonavir nanocrystals with enhanced bioperformance and physical stability.

## Key findings

- Ritonavir nanocrystals achieved a particle size of ~300 nm using bead milling and spray-drying.
- Nanocrystals showed improved dissolution in a discriminative medium and retained Form II ritonavir structure.
- Biodistribution and pharmacokinetic studies revealed formulation-dependent effects on hepatic stress and metabolism.

## Abstract

The development of nanoformulations aims to overcome
the biopharmaceutical
limitations associated with conventional drug delivery. Reducing the
particle size to the nanometric scale enhances drug solubility, dissolution
rate, and bioavailability. In this study, the development and quality
control of ritonavir nanocrystals are described by using applied experimental
milling approaches. Ritonavir nanosuspensions were initially prepared
at a small scale using an Ultra-Turrax Tube Drive, in which 200 and
500 μm beads were identified as the most efficient for particle
size reduction. The process was then successfully scaled up by using
a bead mill, achieving particle sizes of approximately 300 nm within
30 min, followed by spray-drying. Solid-state characterization by
XRD, TGA, DSC, and hot-stage microscopy confirmed that the nanocrystals
retained Form II ritonavir throughout processing. The resulting nanocrystals
were physically stable and exhibited a marked improvement in dissolution,
particularly in a discriminative dissolution medium (0.04 M POE10LE).
Process optimization was achieved by balancing bead sizes and steric
stabilizers, such as PVP K30 and HPMC. Biodistribution studies using
[99mTc] radiolabeling (labeling efficiency >90%) showed
uptake in the liver, kidneys, and intestines, with notable differences
in the cardiac distribution between nanocrystals and nanosuspensions.
Pharmacokinetic analysis indicated similar overall distribution profiles,
with a transient 4 h peak in blood levels for the nanocrystals. Biochemical
analyses suggested formulation-dependent hepatic stress, reflected
by increased GGT for the nanosuspension, and alterations in carbohydrate
metabolism, including elevated glucose and amylase levels, for the
nanocrystal formulation. Overall, ritonavir nanocrystals significantly
improved dissolution, and the optimized milling and spray-drying approach
represents a robust and scalable strategy to enhance the performance
of Class II or IV drugs.