Leflon (Leflunomide)

Leflunomide is a disease-modifying antirheumatic drug used to manage inflammatory joint diseases.

• Rheumatoid arthritis: decreases disease activity and prevents joint damage.
• Psoriatic arthritis: alleviates joint inflammation and skin involvement.
• Active disease in adults: offers an oral alternative when other DMARDs are insufficient.

• Leflunomide is converted to its active metabolite teriflunomide, which selectively inhibits dihydroorotate dehydrogenase, a key enzyme in de novo pyrimidine synthesis. By limiting pyrimidine availability, the drug suppresses proliferation of activated lymphocytes, particularly T cells, thereby reducing the autoimmune inflammatory response that drives joint damage in rheumatoid and psoriatic arthritis. The inhibition is reversible and preferentially affects rapidly dividing immune cells while sparing resting cells, contributing to its disease‑modifying properties.

Leflunomide may cause a range of adverse reactions, varying from mild to serious.

Common Side Effects

• Diarrhea: loose stools or increased frequency.
• Nausea: feeling of sickness or urge to vomit.
• Elevated liver enzymes: increased ALT/AST levels.
• Hypertension: raised blood pressure.
• Rash: mild skin irritation or itching.
• Headache: persistent or intermittent head pain.

Serious or Rare Side Effects

• Severe liver injury: jaundice, hepatic failure.
• Bone marrow suppression: anemia, leukopenia, thrombocytopenia.
• Pulmonary toxicity: interstitial lung disease, dyspnea.
• Severe skin reactions: Stevens‑Johnson syndrome, toxic epidermal necrolysis.
• Infections: opportunistic infections due to immunosuppression.
• Pregnancy complications: teratogenic effects, fetal malformations.

Before initiating Leflunomide therapy, several precautions should be observed to minimize risk.

• Baseline liver assessment: obtain ALT/AST and bilirubin levels before treatment.
• Pregnancy avoidance: drug is contraindicated in pregnancy; effective contraception required for women of childbearing potential.
• Renal function monitoring: adjust use in patients with severe renal impairment.
• Infection vigilance: screen for active infections and monitor for new signs during therapy.
• Hematologic monitoring: regular CBC to detect bone marrow suppression.
• Store at ambient temperature: keep tablets below 25 °C in the original container, protect from moisture and light.

Leflunomide can interact with other medicines, altering efficacy or safety.

Major Interactions (Avoid)

• Warfarin: increased anticoagulant effect, risk of bleeding.
• Statins (e.g., simvastatin): heightened risk of myopathy and rhabdomyolysis.
• Live vaccines: reduced vaccine efficacy and potential infection.

Moderate Interactions (Monitor Closely)

• Methotrexate: additive hepatotoxicity, monitor liver enzymes.
• Azathioprine or cyclophosphamide: combined bone marrow suppression.
• Oral contraceptives: reduced hormonal efficacy, consider alternative contraception.