Home COVID-19 test was positive; Interaction between the Paxlovid and tacrolimus; This spontaneous case was reported by a pharmacist and describes the occurrence of DRUG INTERACTION (Interaction between the Paxlovid and tacrolimus) and COVID-19 (Home covid-19 test was positive) in a male patient of an unknown age who received mRNA-1273 (Moderna COVID-19 Vaccine) for COVID-19 vaccination.    Co-suspect product included non-company product NIRMATRELVIR, RITONAVIR (PAXLOVID) for COVID-19 treatment.    The patient's past medical history included Kidney transplant on 02-Sep-2020. Previously administered products included for Product used for unknown indication: Janssen (Dose Number was 1. Batch/Lot No was unknown and not available/provided to reporter.) on 10-Mar-2021. Past adverse reactions to the above products included No adverse event with Janssen. Concurrent medical conditions included Gout, Hyperlipidemia and Hypertension. Concomitant products included ACETAMINOPHEN, ALLOPURINOL, CARVEDILOL, CHOLECALCIFEROL, FENOFIBRATE, FISH OIL, MULTIVITAMIN [VITAMINS NOS], MYCOPHENOLATE MOFETIL, PREDNISONE, SEMAGLUTIDE, SIMVASTATIN from an unknown date to 17-May-2022, TACROLIMUS from an unknown date to 19-May-2022 and TAMSULOSIN from an unknown date to 17-May-2022 for an unknown indication.   On 28-Oct-2021, the patient received second dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) 1 dosage form. On 18-Mar-2022, received third dose of mRNA-1273 (Moderna COVID-19 Vaccine) (unknown route) dosage was changed to 1 dosage form. On 17-May-2022, the patient started NIRMATRELVIR, RITONAVIR (PAXLOVID) (Oral) at an unspecified dose twice a day. In May 2022, the patient experienced DRUG INTERACTION (Interaction between the Paxlovid and tacrolimus). On an unknown date, the patient experienced COVID-19 (Home covid-19 test was positive). The patient was treated with PHENYTOIN on 21-May-2022 at a dose of 300 milligram, 2 doses. At the time of the report, DRUG INTERACTION (Interaction between the paxlovid and tacrolimus) and COVID-19 (Home covid-19 test was positive) outcome was unknown.      DIAGNOSTIC RESULTS (normal ranges are provided in parenthesis if available): In May 2022, Blood creatinine (1.5-1.8): 2.25 (High) SCr (Serum creatinine) on admit to the ED was 2.25 g/dL.. On 17-May-2022, SARS-CoV-2 test: positive (Positive) Home COVID-19 test was positive.. On 21-May-2022, Blood creatinine (1.5-1.8): 2.59 (High) Serum creatinine up to 2.59 g/dL.. On 21-May-2022, Drug level: 75.6 (abnormal) Tacrolimus level was 75.6 ng/mL.. On 23-May-2022, Blood creatinine (1.5-1.8): 2.48 (High) 2.48 g/dL..     For mRNA-1273 (Moderna COVID-19 Vaccine) (Unknown), the reporter did not provide any causality assessments.   Batch number/Lot number of Moderna COVID-19 Vaccine was unknown, not available/provided by the reporter. The patient was taking other medications/products within 2 weeks of starting COVID-19 treatment Paxlovid. Patient previously received COVID-19 Vaccine.  On 17-May-2022, tested positive for COVID-19. PCP prescribed Paxlovid as treatment for COVID-19. Patient picked up prescription and was told to hold his simvastatin and tamsulosin. Was not told to hold his tacrolimus. On May-2022 Tacrolimus level on admit to ED was not drawn. Discharged home from the ED with instruct to hold tacrolimus.   Hospitalization was not prolonged. Discharged from the hospital on 23-May-2022 and was instructed to hold tacrolimus, simvastatin, tamsulosin at discharge.  Treatment received for the adverse event included fluids, phenytoin to attempt to increase metabolism of Tacrolimus.  Company comment- This spontaneous case concerns a male patient of unknown age with relevant medical history of kidney transplant, who experienced unexpected, non-serious adverse event of special interest Covid-19 which occurred at an unknown time with regards to the mRNA-1273 vaccination. The patient tested positive on a home covid-19 test and was prescribed with Paxlovid (Nirmatrelvir/Ritonavir) 300/100 bid x 5 days. He was instructed to hold his simvastatin and Tamsulosin but was not advised to hold Histacrolimus. A few days after, he started feeling nauseous and weak. He was instructed to go to the emergency room where interaction between the Paxlovid and tacrolimus was identified. Serum creatinine was elevated but Tacrolimus level was not checked. He was discharged home from the emergency department with instructions to hold tacrolimus. A few days after, serum creatinine further increased, and tacrolimus level was elevated. The patient admitted for acute kidney injury secondary to tacrolimus toxicity. He started on fluids and was given 2 doses of phenytoin 300mg. He was discharged from the hospital; Sender's Comments: This spontaneous case concerns a male patient of unknown age with relevant medical history of kidney transplant, who experienced unexpected, non-serious adverse event of special interest Covid-19 which occurred at an unknown time with regards to the mRNA-1273 vaccination. The patient tested positive on a home covid-19 test and was prescribed with Paxlovid (Nirmatrelvir/Ritonavir) 300/100 bid x 5 days. He was instructed to hold his simvastatin and Tamsulosin but was not advised to hold histacrolimus. A few days after, he started feeling nauseous and weak. He was instructed to go to the emergency room where interaction between the paxlovid and tacrolimus was identified. Serum creatinine was elevated but Tacrolimus level was not checked. He was discharged home from the emergency department with instructions to hold tacrolimus. A few days after, serum creatinine further increased, and tacrolimus level was elevated. The patient admitted for acute kidney injury secondary to tacrolimus toxicity. He started on fluids and was given 2 doses of phenytoin 300mg. He was discharged from the hospital 2 days after with still elevated serum creatinine. He was instructed to hold tacrolimus, simvastatin, tamsulosin at discharge The outcome of the event was reported as unknown. The benefit-risk relationship of mRNA-1273 vaccine is not affected by this report.