Co-administration of Paxlovid and Tamiflu

Pharmacokinetic Rationale for Safety

Oseltamivir is primarily metabolized by hepatic esterases to its active form, oseltamivir carboxylate, with approximately 80% excreted renally via glomerular filtration and tubular secretion through the anionic pathway, which supports its safe co-administration with Paxlovid 1
The lack of interaction between oseltamivir and Paxlovid is due to their distinct metabolic pathways, with oseltamivir not undergoing CYP3A4 metabolism and therefore not affected by ritonavir's inhibitory effects 1
Oseltamivir is not a substrate, inhibitor, or inducer of P-glycoprotein, eliminating another potential interaction pathway with Paxlovid 1

The American College of Physicians and other guideline societies, as reported by the Advisory Committee on Immunization Practices (ACIP), identify no contraindications to the combination use of influenza antiviral drugs, including oseltamivir and Paxlovid, although they note that no published data are available concerning the safety or efficacy of using combinations of these drugs 2, 3, 4, 5
The only documented drug interaction with oseltamivir is probenecid, which reduces oseltamivir carboxylate clearance by approximately 50% through competition for renal tubular secretion, as stated by the Centers for Disease Control and Prevention (CDC) 2, 3, 4, 5, 1

Neither Paxlovid nor Tamiflu requires dose modification when used together, according to the guideline recommendations from the Infectious Diseases Society of America 1
Renal function monitoring is necessary for both drugs, with oseltamivir requiring a reduced dose to 75 mg once daily for creatinine clearance 10-30 mL/min, as recommended by the National Kidney Foundation 6, 1
Administering oseltamivir with food can reduce gastrointestinal side effects, such as nausea and vomiting, without affecting absorption, as suggested by the American Gastroenterological Association 6, 1, 7
Initiate oseltamivir within 48 hours of influenza symptom onset for maximum benefit, as recommended by the CDC 7