How Methotrexate Affects Your Immune System
Methotrexate (MTX) is a powerful medication used to treat various inflammatory and autoimmune conditions, including rheumatoid arthritis (RA) and psoriasis. Its primary mechanism of action involves slowing down the body's immune system to reduce inflammation. In higher doses used for chemotherapy, MTX is cytotoxic and works by inhibiting the proliferation of rapidly dividing cells. In the lower, weekly doses used for inflammatory conditions, it is thought to work through different anti-inflammatory mechanisms, such as increasing extracellular adenosine levels. While this immune-modulating effect is key to treating the underlying disease, it also makes the body more vulnerable to infections. The risk of infection is a trade-off for controlling the autoimmune disease.
Impact on Immune Cells
Low-dose MTX may lead to a reduced number of white blood cells (leukopenia), which are crucial for fighting off pathogens. This bone marrow suppression means the body may not be able to mount a robust immune response against an invading infection, leading to delayed recovery or more severe illness. In addition, MTX can affect other components of the immune system, such as reducing the production of certain immunoglobulins.
Increased Risk and Common Infections
The immunosuppressive effect of methotrexate means users are more susceptible to infections than the general population. While serious infections are not common, the risk is elevated, particularly for certain types of infections. For example, some studies have shown a modestly increased rate of bacterial respiratory and skin infections in patients with RA on low-dose MTX. Opportunistic infections, which take advantage of a weakened immune system, are rarer but can be life-threatening and have been reported in patients on low-dose MTX.
Common sites and types of infections to be aware of include:
- Respiratory Infections: Including colds, flu, and pneumonia. A persistent cough or shortness of breath is a particular concern.
- Urinary Tract Infections (UTIs): Symptoms can include pain or difficulty urinating.
- Skin Infections: Wounds that do not heal, cellulitis, or shingles (herpes zoster).
- Oral Infections: Severe mouth ulcers or sores can be a sign of toxicity or infection.
Recognizing the Signs of Infection
Prompt recognition of an infection is essential for patients on methotrexate. Symptoms that might be a minor inconvenience for a healthy person can signal a more serious problem for someone who is immunosuppressed. It is also important to note that methotrexate toxicity can sometimes mimic the symptoms of an infection, including causing a fever. This makes consulting a healthcare professional crucial for accurate diagnosis.
Watch for the following signs and symptoms:
- Fever, especially if it exceeds 101°F
- Chills or night sweats
- A sore throat or cough
- General feeling of being unwell, malaise, or unusual tiredness
- Pain, redness, or swelling in any area
- Unexplained bruising or bleeding
- Pain or burning during urination
What to Do If You Suspect an Infection
If you believe you have an infection while on methotrexate, do not attempt to self-treat. Contact your healthcare provider immediately for advice. The standard procedure is to temporarily stop taking methotrexate until the infection has cleared and you have completed any course of antibiotics.
Steps to take:
- Contact your care team immediately: Report all symptoms, even if they seem minor. Include details about fever, chills, cough, sore throat, or any wounds that don't heal.
- Temporarily stop methotrexate: Your doctor will likely advise you to withhold your weekly dose of methotrexate until the infection resolves. Do not restart without your doctor's approval.
- Complete antibiotic courses: Finish the entire course of any prescribed antibiotics. Do not restart methotrexate until you are fully recovered.
- Be mindful of medication interactions: Inform any prescribing doctor or pharmacist that you are taking methotrexate. Certain antibiotics, especially trimethoprim-sulfamethoxazole, should be avoided as they can increase methotrexate toxicity.
Infection Management and Special Considerations
Comparison of Minor vs. Severe Infection Management
| Feature | Minor Infection (e.g., common cold) | Severe Infection (e.g., pneumonia, sepsis) |
|---|---|---|
| Symptom Severity | Mild, such as a runny nose, mild cough. | High fever, severe cough, breathing difficulties, confusion, severe pain. |
| Doctor's Action | May recommend temporarily holding MTX dose and supportive care. | Urgent medical evaluation, possibly hospitalization, IV antibiotics, and cessation of MTX. |
| MTX Dose | Temporarily hold the weekly dose until symptoms resolve. | Stop MTX immediately. Only restart on a doctor's orders. |
| Duration of Hold | Typically until symptoms are gone, often about one week. | Dependent on the severity of the illness and doctor's judgment. |
| Monitoring | Less intensive. May not require blood tests. | Regular monitoring of blood counts and organ function is necessary. |
Important Drug Interactions
As mentioned, some antibiotics can interact dangerously with methotrexate. Trimethoprim-sulfamethoxazole (Bactrim) is a significant concern as it can increase methotrexate toxicity due to overlapping side effects and competition for removal by the kidneys. Other drugs, including some penicillin antibiotics, NSAIDs, and proton pump inhibitors, can also affect how your body processes methotrexate and should be discussed with your doctor.
Proactive Prevention Strategies
Taking proactive measures can significantly reduce your risk of infection while on methotrexate.
Lifestyle and Hygiene
- Practice good hand hygiene: Wash your hands frequently with soap and water or use an alcohol-based hand sanitizer.
- Avoid sick contacts: Stay away from people who are clearly unwell, especially during cold and flu season.
- Be aware of food safety: Some health services advise avoiding certain foods like unpasteurized milk and soft cheeses that can carry bacteria.
Vaccinations
- Get appropriate vaccinations: Staying up-to-date with your vaccinations is crucial. Inform your doctor that you are on methotrexate before receiving any vaccine.
- Avoid live vaccines: Patients on immunosuppressants should not receive live vaccines, such as the nasal flu spray, live shingles vaccine (Zostavax), MMR, or yellow fever vaccine. The injectable flu vaccine and the non-live shingles vaccine (Shingrix) are safe and recommended.
Conclusion
Being on methotrexate requires heightened awareness regarding the risk of infection. By understanding how the medication affects the immune system, recognizing the signs of an infection promptly, and knowing the appropriate steps to take, patients can manage their health safely. The most critical actions involve immediate communication with your healthcare provider upon suspecting an infection and following their instructions regarding temporarily holding the medication. While the risk of serious infection is relatively low with standard low-dose regimens, vigilance and a proactive approach are key to preventing complications and maintaining overall health.
Authoritative Outbound Link
For more detailed patient information on methotrexate, visit the NHS guide on common questions about methotrexate.
