What's the usual methotrexate dose for kids with arthritis?

What dose do doctors normally start with?
Most pediatric rheumatologists give 10 – 15 mg of methotrexate per square‑meter of body surface area (BSA) once a week. If the child is very small, the dose is often rounded to 0.4 – 0.6 mg per kilogram of body weight, but it never exceeds 15 mg per week. [1]

How is the dose tied to a child’s weight or height?
Because methotrexate is cleared proportionally to body size, dosing uses BSA or weight. A 20‑kg child typically receives about 10 mg, while a 40‑kg child gets around 20 mg. The calculation follows the same formula used for adults: dose = BSA × mg/m². [2]

When do doctors bump the dose up?
If a child shows no improvement after 6–12 weeks, the dose may be increased by 2–4 mg/m² or 1 mg/kg per week, up to a maximum of 25 mg/m² (≈ 25 mg) weekly. The step‑up is usually done cautiously, monitoring for side‑effects. [1]

How often is methotrexate taken?
In children, methotrexate is almost always given orally or subcutaneously once a week. Oral dosing requires a folic acid supplement (5‑10 mg daily or every other day) to reduce nausea and liver toxicity. [3]

What forms are available for kids?
- Oral tablets (often 5 mg or 10 mg)
- Oral liquid suspensions for younger patients
- Subcutaneous injections for patients who have trouble swallowing tablets or need faster absorption
The same weekly dose applies regardless of route, but injections may allow a higher weekly maximum. [2]

What laboratory tests do children need while on methotrexate?
Routine monitoring includes a complete blood count (CBC), liver enzymes (AST/ALT), and kidney function (creatinine) before starting therapy and then every 4–6 weeks. If the dose is increased, labs are checked sooner. [3]

What side‑effects should parents watch for?
- Mild nausea, especially after oral doses
- Mouth sores or sore throat
- Low blood counts (rare but serious)
- Elevated liver enzymes
- Fatigue or flu‑like symptoms
If any of these appear, the clinician may adjust the dose or add folic acid. [3]

When might a child need a higher dose than the usual range?
In cases of aggressive juvenile idiopathic arthritis, a dose up to 25 mg/m² (≈ 25 mg) weekly may be justified. Teenagers with higher BSA or who have reached puberty may also require the upper limit. The decision rests on disease severity and lab safety. [1]

What if methotrexate alone does not control the arthritis?
If symptoms persist after 3–6 months at the maximum safe dose, doctors often add a biologic agent (e.g., adalimumab, etanercept) or switch to a different disease‑modifying drug. [2]

How do dosing rules change as a child grows into an adult?
When a teenager turns 18 or when their BSA exceeds the pediatric range, dosing may shift to adult guidelines: 15 mg weekly up to a maximum of 25 mg, usually still once a week. Transition plans are individualized. [2]