Pump port maint/refill with pt bringing in own drug

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A patient picks up his 5-FU cassette at a local pharmacy, pays for it and then comes to the hospital to have the cassette placed in the pump for delivery of the drug. CPT 96521 and RX- heparin flush is on the claim, but the claim will edit since the drug is not on the claim. What is the appropriate way to charge for this drug or bypass the edit? Thanks!