Are there any drug interactions between infliximab and denosumab?

No Clinically Significant Drug Interactions Between Infliximab and Denosumab

There are no documented drug-drug interactions between infliximab and denosumab, and they can be safely used together in patients requiring both therapies.

Evidence Base

Direct Safety Data

The combination of denosumab with biologic DMARDs (including TNF inhibitors like infliximab) has been directly studied. A retrospective evaluation of 28 patients receiving both a biologic DMARD and denosumab compared to 49 matched controls on biologic DMARD alone found:

• No difference in safety profile including local, systemic, or serious adverse events 1
• No difference in efficacy of the biologic DMARD when combined with denosumab 1
• No impact on treatment persistence over 2 years of evaluation 1
• The combination did not predict disease flare or treatment withdrawal 1

Pharmacokinetic Considerations

Denosumab does not interact with cytochrome P450 systems. Studies demonstrate that denosumab did not affect the pharmacokinetics of midazolam (a CYP3A4 substrate), indicating it should not alter drug metabolism 2. This is mechanistically consistent with both agents:

• Infliximab: Monoclonal antibody cleared via reticuloendothelial system, not hepatic metabolism 3
• Denosumab: Monoclonal antibody with mean half-life of 25.4 days, cleared independently of hepatic/renal function 2

Immunosuppression Considerations

While both agents affect immune function through different mechanisms, the FDA labeling for infliximab notes that concomitant immunosuppressant agents actually reduce infusion reactions and antibody formation 3. However, denosumab is not classified as an immunosuppressant—it specifically inhibits RANK ligand to prevent osteoclast formation.

Clinical Caveats

Infection Risk

Both medications carry infection warnings in their labeling:

• Infliximab increases risk of serious infections including tuberculosis, opportunistic infections, and bacterial infections 3
• While denosumab's primary concern is hypocalcemia, not infection risk per se

When combining these agents, maintain vigilance for:

• Tuberculosis screening before infliximab initiation
• Monitoring for respiratory tract infections, urinary tract infections
• Prompt evaluation of any fever or signs of infection

Hypocalcemia Monitoring with Denosumab

Recent disproportionality analysis identified that denosumab-induced hypocalcemia may be more common in real-world practice than clinical trials 4. When used with other medications:

• Monitor calcium levels, particularly in first weeks after denosumab administration
• Ensure adequate calcium and vitamin D supplementation
• Be aware of additive hypocalcemia risk if patient takes loop diuretics, proton pump inhibitors, or other calcium-lowering agents 4

Osteonecrosis of the Jaw (MRONJ)

Denosumab carries risk of MRONJ, particularly with dental procedures 5. This risk is independent of infliximab use but warrants:

• Dental evaluation before initiating denosumab
• Timing invasive dental procedures during the "window of opportunity" when denosumab effect is waning (typically months 4-6 of the 6-month dosing cycle) 5

Practical Algorithm

For patients requiring both infliximab and denosumab:

1. Initiate as clinically indicated - no dose adjustments needed for either medication
2. Screen for tuberculosis before starting infliximab (standard practice)
3. Obtain baseline calcium level and ensure adequate supplementation before denosumab
4. Complete dental evaluation before first denosumab dose
5. Monitor calcium 2 weeks after each denosumab dose
6. Maintain infection surveillance as per standard infliximab monitoring
7. Continue both medications without concern for pharmacokinetic interaction

The combination does not require special monitoring beyond what is already indicated for each individual agent.