API Leflunomide

Leflunomide More Info

1. Overview

Leflunomide is an isoxazole immunomodulatory agent primarily used for the treatment of rheumatoid arthritis (RA) and psoriatic arthritis. It acts as a selective inhibitor of pyrimidine synthesis, thereby exerting anti-inflammatory and antiproliferative effects.

2. Mechanism of Action

Leflunomide functions as a selective inhibitor of dihydroorotate dehydrogenase (DHODH), a key enzyme in the de novo synthesis of pyrimidine nucleotides. By inhibiting DHODH, leflunomide reduces the synthesis of DNA in rapidly dividing cells, particularly activated lymphocytes. This leads to:

Immunomodulation: Suppression of T-cell activation and proliferation.

Anti-inflammatory Effects: Reduction in the production of inflammatory cytokines such as IL-1β and TNF-α.

Antiproliferative Activity: Inhibition of fibroblast proliferation in synovial tissue .

3. Indications

Leflunomide is primarily indicated for:

Rheumatoid Arthritis (RA): To reduce joint damage and improve symptoms.

Psoriatic Arthritis: As a therapeutic option for patients who require disease-modifying treatment .

4. Dosage & Administration

Loading Dose: Typically, a loading dose of 100 mg once daily for the first three days is administered to achieve therapeutic plasma levels more rapidly .

Maintenance Dose: Followed by a daily maintenance dose of 10 mg or 20 mg (most commonly 20 mg) once daily. The dose may be adjusted based on tolerability and clinical response.

Administration: Oral tablets; may be taken with or without food .

5. Pharmacokinetics

Metabolism: Leflunomide is rapidly metabolized in the liver to its active metabolite, A771726 (teriflunomide), which is responsible for the drug’s therapeutic effects .

Half-Life: The active metabolite has a long elimination half-life (approximately 2 weeks), leading to a prolonged duration of action and necessitating a washout procedure if rapid drug elimination is required (e.g., before pregnancy).

Excretion: Primarily excreted via biliary and renal routes.

6. Safety Profile & Contraindications

Common Side Effects: Diarrhea, nausea, abdominal pain, alopecia (hair loss), rash, and elevated liver enzymes. These are generally mild to moderate in severity.

Serious Risks:

Hepatotoxicity: Potential for severe liver injury; regular monitoring of liver function tests is mandatory.

Teratogenicity: Leflunomide is highly teratogenic and contraindicated in pregnant women or women of childbearing potential unless an effective contraception method is used. A washout procedure is required to eliminate the drug from the body before conception.

Hematologic Effects: Potential for leukopenia, anemia, and thrombocytopenia.

Infections: Increased susceptibility to infections due to immunosuppression.

Contraindications: Known hypersensitivity to leflunomide, severe hepatic impairment, severe immunodeficiency, severe bone marrow dysfunction, and pregnancy.

7. Drug Interactions & Precautions

Drug Interactions:

Cholestyramine: Significantly reduces plasma concentrations of leflunomide and its metabolites; should be avoided or timed appropriately.

Methotrexate: Concurrent use may increase the risk of severe hepatic or marrow toxicity.

Cytochrome P450 Enzymes: Rifampicin can increase the clearance of leflunomide.

Precautions:

Avoid alcohol and hepatotoxic drugs.

Monitor blood pressure, as hypertension may be aggravated.

Caution in patients with renal impairment, as drug elimination may be prolonged.

Conclusion

Leflunomide is a valuable therapeutic option for managing rheumatoid and psoriatic arthritis, offering the convenience of oral administration and a unique mechanism of action. However, due to its potential for severe hepatotoxicity and teratogenicity, careful patient selection, regular monitoring, and adherence to contraindications are essential for its safe and effective use.