Introduction: Mepolizumab is a high-cost biologic therapy for conditions like severe asthma and CRSwNP. The Pharmaceutical Benefits Scheme (PBS) is intended to provide equitable national access, but it is unknown if significant geographic variation in its utilisation exists or if this is driven by public versus private prescribing. Aim: To quantify and compare the average per capita prescription rates of Mepolizumab across Australian jurisdictions and to determine if observed variation is driven by public or private prescribing patterns. Methods: A retrospective, cross-sectional analysis of 30 months of national PBS prescription data (per 100,000 capita) was performed. Data was stratified by funding source (Public vs. Private). Three separate One-Way ANOVAs with Tukey's post-hoc tests were used to compare the mean prescription rates for Total, Public-only, and Private-only scripts across all eight jurisdictions. Results: A significant difference in the Total mean prescription rate was found between states (ANOVA, p < 0.0001). This variation was not confined to one sector; significant differences were identified in both the Private system (ANOVA, p < 0.0001) and the Public system (ANOVA, p < 0.0001). Notably, the Australian Capital Territory (ACT) and Northern Territory (NT) had significantly lower prescribing rates overall (p<0.05). Conclusion: Mepolizumab prescribing exhibits significant geographic variation. Our analysis shows this variation is present in both public and private patients. The observed differences are system-wide and may be driven by factors such as differing state-level formulary policies, regional differences in specialist access, or patient-driven demand. These findings provide a basis for reviewing prescribing guidelines to support equitable access for all eligible patients.