  The digital transformation of the medical sector requires solutions that are
convenient and efficient for all stakeholders while protecting patients'
sensitive data. One example that has already attracted design-oriented research
are medical prescriptions. However, current implementations of electronic
prescription management systems typically create centralized data silos,
leaving user data vulnerable to cybersecurity incidents and impeding
interoperability. Research has also proposed decentralized solutions based on
blockchain technology, but privacy-related challenges have often been ignored.
We conduct design science research to develop and implement a system for the
exchange of electronic prescriptions that builds on two blockchains and a
digital wallet app. Our solution combines the bilateral, verifiable, and
privacy-focused exchange of information between doctors, patients, and
pharmacies through verifiable credentials with a token-based, anonymized
double-spending check. Our qualitative and quantitative evaluations as well as
a security analysis suggest that this architecture can improve existing
approaches to electronic prescription management by offering patients control
over their data by design, a high level of security, sufficient performance and
scalability, and interoperability with emerging digital identity management
solutions for users, businesses, and institutions. We also derive principles on
how to design decentralized, privacy-oriented information systems that require
both the exchange of sensitive information and double-usage protection.
