Is it safe to use methotrexate together with allergy medication?

SKĐS – People using methotrexate to treat chronic diseases often worry about the risk of interactions when they have to use additional antihistamine medications...

1. In what cases is the immunosuppressant methotrexate used?

Methotrexate is a folic acid antagonist that has anticancer effects at high doses and acts as a potent immunosuppressant and anti-inflammatory agent at low doses. As an immunosuppressant, methotrexate reduces the activity of overreactive immune cells, thereby preventing the immune system from attacking healthy tissues. However, drug interactions should be considered when using methotrexate to ensure safety and effectiveness in treatment.

The specific cases in which methotrexate is indicated for immunosuppressive purposes are:

Autoimmune bone and joint diseases:

Rheumatoid arthritis : This is the most common indication; the medication helps slow the progression of joint damage, reducing swelling, pain, and stiffness in adults and children.

Psoriatic arthritis: Reduces inflammation in both the skin and joints.

Ankylosing spondylitis: Used in cases where patients do not respond to conventional anti-inflammatory drugs.

Autoimmune and proliferative dermatological diseases:

Severe psoriasis : Used for cases of widespread psoriasis, pustular psoriasis, or psoriatic arthritis that are not controlled by topical treatments.

Atopic dermatitis or lupus erythematosus : Considered as an indication when corticosteroid therapies are ineffective or when corticosteroid dosage reduction is necessary.

The immunosuppressant methotrexate may interact with antihistamine medications.

Chronic inflammatory bowel disease:

Crohn's disease: Helps maintain remission and reduce inflammation in the digestive tract.

Ulcerative colitis: Use alternative treatment when the patient's body is resistant to or dependent on steroids.

Preventing bone marrow rejection:

Using low doses to suppress the recipient's immune system helps prevent graft-versus-host disease after bone marrow transplantation.

Note: Methotrexate, used to treat autoimmune/immunosuppressive diseases, is usually taken only once a week (not daily). Taking the wrong daily dose can lead to acute, life-threatening poisoning. The drug can cause serious birth defects and should absolutely not be used by pregnant women or women planning to become pregnant.

2. Common allergy medications currently available

Allergy medications are now widely used by people for conditions such as allergic rhinitis caused by weather changes, persistent sneezing, runny nose, and itchy eyes; chronic urticaria, rashes, and skin itching due to food or chemical allergies; and to soothe itching from insect bites.

The most commonly used anti-allergy medications today are H1 antihistamines, especially those belonging to the second and newer generations. These drugs work by blocking histamine receptors (a mediator that causes allergic reactions), thereby rapidly reducing symptoms such as itching, hives, sneezing, and runny nose.

Commonly used active ingredients include chlorpheniramine, promethazine, diphenhydramine (classic) and cetirizine, loratadine, fexofenadine, desloratadine (newer generation).

Additionally, some corticosteroids are also used to treat allergies in certain cases, especially when the allergic reaction is moderate or severe, or when antihistamines do not control the symptoms.

If you are taking methotrexate, consult your doctor before taking any additional allergy medication.

3. Is it safe to use methotrexate with other allergy medications?

Simultaneous use of the immunosuppressant methotrexate with anti-allergy medications is generally quite safe, with few serious pharmacokinetic interactions that alter drug concentrations. However, the extent of the impact depends greatly on the specific allergy medication chosen by the patient. Because methotrexate is a highly toxic drug, incorrect combination with other allergy medications can indirectly increase side effects or mask signs of toxicity.

- First-generation antihistamines such as chlorpheniramine, promethazine, and diphenhydramine generally do not have dangerous chemical interactions. However, the sedative and sleep-inducing side effects of this group can be combined with the fatigue and lethargy already caused by methotrexate. Patients may experience extreme drowsiness, dizziness, and severely reduced concentration.

- For second-generation antihistamines (newer generation that cause little or no drowsiness) such as cetirizine, loratadine, and fexofenadine, they are more often chosen because this combination is safer.

- Oral corticosteroids such as prednisolone, methylprednisolone, and dexamethasone are not preferred for allergy treatment due to the higher risk of interactions and side effects. Simultaneous use with methotrexate increases the immunosuppressive effect, making the body more susceptible to serious opportunistic infections. Furthermore, corticosteroids can mask early symptoms of methotrexate toxicity such as fever, sore throat, or general fatigue. This group of drugs should only be used in short courses and under strict medical supervision.

- For combination cold/allergy medications that are widely available on the market, many people have a habit of buying these pills to treat runny noses and seasonal allergies. Be especially cautious because if the pill contains NSAIDs (such as ibuprofen, aspirin) for pain relief, these substances will reduce the kidneys' ability to excrete methotrexate, causing the drug to accumulate in the blood and leading to bone marrow toxicity, mouth ulcers, and kidney failure.

- For cold and flu medications containing pseudoephedrine (which causes vasoconstriction and nasal decongestant effects), consult a doctor as it may increase the metabolic burden on the body.

To use allergy medication safely while taking methotrexate, topical allergy medications such as nasal sprays or eye drops are preferred because they are less absorbed into the bloodstream and less likely to interact with methotrexate. If oral allergy medication is used, a second-generation antihistamine should be chosen. When purchasing allergy medication, patients should inform their pharmacist or doctor that they are taking weekly methotrexate to ensure the most appropriate medication is selected for their treatment plan.

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