If you are injecting novel pharmaceutical compounds, why would you risk your research by flushing them in with solutions of unknown quality? Heparin in particular has a notoriously “twisted” supply chain, starting with pig farms in China. Contaminated heparin harmed hundreds of patients in 2008, leading the FDA to require improved testing to receive the USP designation. And yet non-pharmaceutical-grade heparin remains readily available from Fisher Scientific and other suppliers.
AAALAC International states that using pharmaceutical-grade compounds is preferred in some situations and required in others, if available. If you are using non-pharmaceutical-grade flush or lock solutions, your IACUC should require a justification.
NIH's Office of Animal Welfare states: OLAW and USDA agree that pharmaceutical-grade substances, when available, must be used to avoid toxicity or side effects that may threaten the health and welfare of vertebrate animals and / or interfere with the interpretation of research results.
See their Guidelines for Use of Non-Pharmaceutical Grade Compounds in Laboratory Animals for additional details.
Read the Guide to Catheter Lock and Flush Solutions for Laboratory Animal Research