What is the usual starting dose of methotrexate for rheumatoid arthritis and moderate‑to‑severe plaque psoriasis?

Methotrexate Starting Dose for Rheumatoid Arthritis and Psoriasis

For rheumatoid arthritis, start methotrexate at 15 mg orally once weekly and escalate by 5 mg every 2–4 weeks to reach 20–25 mg weekly; for moderate-to-severe plaque psoriasis, start at 10–15 mg orally once weekly and escalate by 5 mg every 4 weeks to a maximum of 25 mg weekly. 1

Rheumatoid Arthritis Dosing Protocol

Initial Dose and Escalation Strategy

• Begin with 15 mg orally once weekly rather than lower starting doses (7.5–10 mg), as this provides superior early disease control without compromising safety. 1, 2

• Escalate by 5 mg every 2–4 weeks until reaching a target of 20–30 mg weekly, depending on clinical response and tolerability. 1, 3

• The faster escalation schedule (5 mg monthly) demonstrates greater clinical efficacy than slower escalation (5 mg every 3 months), though with a modest increase in gastrointestinal adverse events. 1, 3

• Wait at least 4 weeks after each dose increase before assessing clinical response, as therapeutic benefit requires this interval. 3

• Starting doses of 12.5–20 mg weekly yield better disease control than 5–10 mg weekly without increasing toxicity rates. 1

When to Switch to Subcutaneous Administration

• If inadequate response occurs at 15–20 mg oral weekly or gastrointestinal intolerance develops, switch to subcutaneous methotrexate at the same milligram dose before further dose escalation. 1, 3

• Subcutaneous methotrexate provides higher bioavailability than oral dosing at doses exceeding 15 mg weekly because intestinal absorption becomes saturable. 1, 3

• A randomized trial demonstrated that 15 mg subcutaneous weekly produced superior clinical response compared with 15 mg oral weekly in early rheumatoid arthritis. 3

• However, in longstanding rheumatoid arthritis after oral methotrexate failure, switching to intramuscular methotrexate at 15 mg weekly with subsequent escalation did not improve efficacy. 1, 3

Mandatory Folic Acid Supplementation

• Prescribe at least 5 mg folic acid per week to reduce gastrointestinal side effects, mucosal ulcers, and hepatotoxicity without compromising methotrexate efficacy. 1, 3

• Administer folic acid on a different day than methotrexate (e.g., methotrexate Monday, folic acid Thursday) to avoid competing for cellular uptake. 1, 3

• Use folic acid rather than folinic acid (leucovorin); folinic acid offers no efficacy advantage and is substantially more expensive. 1, 3

Psoriasis Dosing Protocol

Initial Dose and Escalation Strategy

• Start at 10–15 mg orally once weekly for moderate-to-severe plaque psoriasis. 1

• The FDA label recommends 10–25 mg per week as the starting range, with gradual adjustment to achieve optimal clinical response. 4

• Escalate by 5 mg every 4–6 weeks if improvement is less than 25–50% of baseline PASI, up to a maximum of 25 mg weekly. 1

• In patients with normal renal function, a more aggressive starting dose of 15 mg once weekly may be considered. 1

• In elderly patients or those with renal impairment, reduce the initial dose to 2.5 mg. 1

• Do not ordinarily exceed 30 mg weekly. 4

Alternative Dosing Schedules

• Methotrexate may be administered as a single weekly dose or divided into 3 doses given every 12 hours over 24 hours (Weinstein schedule). 1, 4

• Split dosing may reduce gastrointestinal side effects in some patients. 1

• Subcutaneous or intramuscular administration should be considered if oral therapy produces inadequate response or intolerance. 1

Folic Acid Supplementation

• Prescribe 5 mg folic acid daily except on the day methotrexate is taken, or 5 mg once weekly on a different day. 1

• Folic acid supplementation decreases mucosal and gastrointestinal side effects and may protect against hepatotoxicity. 1

• If gastrointestinal side effects or early bone-marrow toxicity develop despite folic acid, increase the folic acid dose. 1

Pre-Treatment Work-Up (Both Conditions)

• Obtain complete blood count with differential, liver function tests (AST, ALT, albumin), serum creatinine with calculated clearance, and chest radiograph (within the previous year). 1, 3

• Screen for hepatitis B/C serology, HIV (consider), fasting glucose, lipid profile, and pregnancy test where appropriate. 1, 3

• Assess clinical risk factors for methotrexate toxicity, including alcohol intake, renal impairment, advanced age, diabetes, obesity, and history of liver disease. 1

Monitoring Requirements

Initial Phase

• During the first month or until a stable dose is reached, check CBC, liver enzymes (ALT ± AST), and creatinine every 1–2 weeks. 1, 3

• Perform CBC before dosing in week 2 to detect early bone-marrow suppression. 1

• Watch for downward trends in blood counts even when absolute values remain normal, as this may signal toxicity. 1, 3

Maintenance Phase

• Once the dose is stable, repeat CBC, liver enzymes, and creatinine every 2–3 months. 1, 3

• Patients with risk factors (renal insufficiency, advanced age, lack of folate supplementation) require closer monitoring. 1, 3

When to Hold or Reduce Methotrexate

• Temporarily withhold methotrexate if WBC < 3.5 × 10⁹/L, neutrophils < 2 × 10⁹/L, platelets < 100 × 10⁹/L, or transaminases > 2 × upper limit of normal on repeat testing. 3

• Discontinue methotrexate if confirmed ALT/AST exceeds 3 × upper limit of normal; the drug may be restarted at a lower dose after normalization. 1, 3

• If ALT/AST remains ≤ 3 × upper limit of normal but persistently elevated, reduce the methotrexate dose. 1

Dose Adjustments for Renal Impairment

• Reduce the methotrexate dose by 50% when creatinine clearance is 20–50 mL/min. 3

• Avoid methotrexate entirely if creatinine clearance is < 20 mL/min. 3

• Use the standard dose when glomerular filtration rate > 90 mL/min. 3

Test Dose Consideration

• An optional test dose of 2.5–5 mg with a CBC 5–7 days later may be used to assess individual susceptibility to bone-marrow suppression. 1, 3

• Test dosing is mandatory in patients with decreased glomerular filtration rate or other significant risk factors for hematologic toxicity (advanced age, drug interactions, hypoalbuminemia). 1

• Alternatively, it is reasonable to begin at a therapeutic dose (15 mg weekly for rheumatoid arthritis, 10–15 mg for psoriasis) with subsequent laboratory evaluation, reserving test doses only for high-risk patients. 1

Common Pitfalls to Avoid

• Do not prescribe methotrexate for daily administration; accidental daily dosing can cause fatal toxicity. 3

• Do not start below 10 mg weekly in rheumatoid arthritis, as lower doses delay therapeutic benefit without reducing toxicity risk. 1, 2

• Do not continue escalating once adequate disease control is achieved at a lower dose; use the minimum effective dose to minimize cumulative toxicity. 1, 3

• Do not administer folic acid on the same day as methotrexate, as concurrent dosing may compete for cellular uptake and reduce therapeutic effect. 1, 3

• Avoid trimethoprim-sulfamethoxazole, as it can precipitate severe bone-marrow suppression. 3

• NSAIDs reduce renal clearance of methotrexate and increase toxicity risk; use with caution and monitor closely. 3

• Methotrexate must be discontinued at least 3 months before planned pregnancy in both men and women due to high teratogenicity. 1, 3