Leflunomide

Introduction Overview

Generic Name

leflunomide

Brand Name

Arava

Dosage Form

oral tablet (10 mg; 20 mg)

Drug Class

Antirheumatics, Selective immunosuppressants

Pharmacokinetics

Absorption: Leflunomide is rapidly absorbed from the gastrointestinal tract after oral administration, with peak plasma concentrations of its active metabolite achieved within 1 to 4 hours. Its bioavailability is high, and absorption is not significantly influenced by food, allowing flexibility in dosing relative to meals. Following oral ingestion, leflunomide is extensively metabolized to its active metabolite, teriflunomide, which is responsible for the drug's therapeutic effects. The rapid conversion occurs via nonenzymatic and enzymatic hydrolysis. Distribution: Teriflunomide demonstrates extensive plasma protein binding, primarily to albumin (>99%). The volume of distribution is low to moderate, indicating limited tissue penetration beyond the vascular compartment and extracellular fluid. The drug crosses the placenta and can be found in breast milk, implying potential fetal and neonatal exposure. It does not accumulate significantly in the central nervous system, but caution is advised due to immune modulation. Metabolism: Leflunomide itself is a prodrug that undergoes rapid and extensive transformation to teriflunomide, primarily by hepatic cytochrome P450-independent mechanisms. Teriflunomide exhibits enterohepatic recirculation, which prolongs its half-life. The drug is stable and not further metabolized significantly, but its elimination is delayed due to reabsorption from the gastrointestinal tract. Elimination: The elimination half-life of teriflunomide is extremely long, averaging around 15 to 18 days but can extend up to several weeks due to enterohepatic cycling, which can maintain detectable plasma levels for months after cessation. Excretion occurs predominantly via biliary secretion into feces and renal elimination. Due to the prolonged half-life, a drug elimination protocol using cholestyramine or activated charcoal is recommended in overdose situations, prior to pregnancy, or when rapid drug clearance is medically necessary to reduce teriflunomide plasma levels rapidly. Regular monitoring of blood levels is essential in clinical practice to manage long-term exposure.

Dosage Forms

Available Dosage Forms: Leflunomide is available exclusively as oral tablets with strengths of 10 mg and 20 mg. These tablets are intended for oral administration and are coated to facilitate swallowing. Dosages for Adults and Adolescents: For the treatment of active rheumatoid arthritis in adults, the recommended dosing regimen begins with a loading dose of 100 mg orally once daily for three consecutive days to rapidly achieve therapeutic plasma concentrations. This is followed by a maintenance dose of 20 mg once daily. In patients who do not tolerate the 20 mg dose well, a reduced maintenance dose of 10 mg once daily may be employed to minimize adverse effects. Specific Patient Populations: Leflunomide use in elderly patients typically follows standard dosing guidelines; however, careful monitoring of liver function and hematologic parameters is advised due to altered pharmacodynamics associated with age. In patients with mild to moderate hepatic impairment, use with caution and intensified monitoring is warranted, whereas it is contraindicated in severe hepatic dysfunction. Safety and efficacy in pediatric populations have not been established. Given its teratogenic potential, leflunomide is contraindicated in pregnancy and requires enhanced preventive strategies including negative pregnancy testing before initiation and participation in a drug elimination program post-therapy if pregnancy is planned. Breastfeeding is not recommended during treatment due to unknown effects on the infant.

Mechanism Of Action

Leflunomide exerts its pharmacological action primarily through inhibition of dihydroorotate dehydrogenase (DHODH), a key mitochondrial enzyme involved in de novo pyrimidine synthesis. By blocking DHODH, leflunomide impedes the synthesis of uridine monophosphate, a critical precursor for RNA and DNA synthesis, thereby reducing nucleotide availability essential for cell proliferation. This mechanism particularly affects rapidly dividing cells, including activated lymphocytes, which are central to the pathogenesis of autoimmune diseases such as rheumatoid arthritis. At the cellular level, leflunomide's active metabolite, teriflunomide, disrupts the proliferation of activated T and B lymphocytes by arresting cells in the G1 phase of the cell cycle, leading to decreased clonal expansion and attenuation of the autoimmune response. Additionally, the drug exerts immunomodulatory effects by inhibiting tyrosine kinases and reducing the expression of cytokines such as interleukin-2 and tumor necrosis factor alpha, further dampening inflammation and tissue damage. Clinically, these effects translate to decreased joint swelling, pain, and progressive structural joint damage as evidenced by radiographic studies. Compared to other disease-modifying antirheumatic drugs (DMARDs) and biologics, leflunomide offers an oral immunosuppressive option with a distinct intracellular target and a long duration of action. Multiple clinical trials substantiate its efficacy and safety profile, highlighting its role in combination therapy protocols and as monotherapy in patients refractory to other agents. Ongoing research is assessing leflunomide's anti-proliferative effects in other immune-mediated conditions and potential antiviral properties linked to its inhibition of pyrimidine synthesis.

Pharmacological Actions

Selective inhibition of dihydroorotate dehydrogenase (DHODH), resulting in suppression of de novo pyrimidine synthesis.
Inhibition of activated T- and B-lymphocyte proliferation by inducing cell cycle arrest in G1 phase.
Immunomodulatory effects including reduced production of pro-inflammatory cytokines such as interleukin-2 and tumor necrosis factor-alpha.
Anti-inflammatory action leading to decreased joint swelling and improved physical function in rheumatoid arthritis.
Suppresses structural joint damage by inhibiting osteoclastogenesis and matrix metalloproteinase activity.
Exerts antiproliferative effects on rapidly dividing immune cells, thereby modulating autoimmune responses.
Potential antiviral activity linked to interference with nucleotide synthesis and viral replication.
Selective immunosuppressant with a prolonged half-life due to enterohepatic recirculation of its active metabolite.
Orally administered disease-modifying agent with systemic effects on immune cell dynamics.
Reduces markers of systemic inflammation, improving laboratory parameters and clinical symptoms.

Therapeutic Or Clinical Uses

Treatment of active rheumatoid arthritis to reduce signs and symptoms such as joint pain, swelling, and stiffness.
Inhibition of structural joint damage as measured by radiographic progression including erosions and joint space narrowing.
Improvement of physical function and patient quality of life in autoimmune arthritis conditions.
Alternative or adjunct to other disease-modifying antirheumatic drugs (DMARDs) in patients with inadequate response.
Used as a selective immunosuppressive agent in autoimmune disease management.
Potential off-label investigational use in psoriatic arthritis and other inflammatory rheumatologic disorders.
Management of chronic inflammation with intent to slow disease progression and minimize disability.
Employed to achieve long-term disease control in combination therapy regimens.
Reduction of systemic inflammatory markers in clinical and laboratory assessments.
May be considered in patients contraindicated or intolerant to biologic therapies.

Side Or Adverse Effects

Elevated liver enzymes and potential hepatotoxicity including severe or fatal liver damage.
Gastrointestinal symptoms such as nausea, diarrhea, and abdominal pain.
Headache and dizziness.
Hair thinning (alopecia) and rash including rare severe skin reactions such as Stevens-Johnson syndrome.
Hypertension and increased blood pressure requiring monitoring and management.
Myelosuppression leading to leukopenia, thrombocytopenia, and anemia increasing infection and bleeding risk.
Peripheral neuropathy manifesting as numbness, tingling, or burning sensation in hands and feet.
Increased susceptibility to infections due to immunosuppressive effects.
Respiratory symptoms including dry cough and wheezing.
Easy bruising and unusual bleeding from mucosal sites.
Fatigue, weakness, and malaise.
Hypersensitivity reactions including urticaria, angioedema, and anaphylaxis are rare but possible.
Potential teratogenicity necessitating strict contraceptive measures.
Possible interactions causing additive toxicities with concomitant hepatotoxic drugs.

Precautions

Avoid use in pregnancy and women of childbearing potential must have a negative pregnancy test before and avoid pregnancy during treatment and until drug elimination is confirmed.
Strict contraception is required during treatment and following discontinuation until drug elimination protocol is completed.
Baseline and periodic liver function tests are mandatory to detect hepatotoxicity early.
Regular hematological monitoring for blood cell counts to identify myelosuppression.
Avoid live vaccines during treatment due to immunosuppression increasing risk of infection.
Use cautiously in patients with pre-existing liver disease, hepatitis, or significant alcohol use.
Monitor blood pressure regularly as leflunomide may cause or worsen hypertension.
Use with caution in patients with impaired renal function due to potential altered excretion.
Avoid concomitant use with other hepatotoxic or immunosuppressive agents unless clinically necessary, with close monitoring.
Consider drug elimination procedure with cholestyramine or activated charcoal prior to planned pregnancy or in case of severe adverse effects.
Inform patients to report signs of infection, bleeding, or neurological symptoms immediately.
Avoid breastfeeding during therapy due to unknown excretion in human milk and potential risk to infant.
Monitor for hypersensitivity reactions and discontinue drug if severe allergic responses occur.
Caution in patients with a history of tuberculosis or latent infections; screen prior to initiation.

Warnings

Contraindicated in pregnancy due to teratogenicity and potential for fetal harm; discontinue immediately if pregnancy occurs.
Potential for severe or fatal liver injury requiring frequent liver function monitoring and potential discontinuation.
Risk of severe infections due to immunosuppression; avoid live vaccines and exposure to infectious agents.
May cause bone marrow suppression leading to anemia, leukopenia, and thrombocytopenia.
May induce or worsen peripheral neuropathy; neurological symptoms should prompt cessation.
Drug elimination procedure required in cases of overdose, before pregnancy, or prior to elective surgery to reduce drug concentration.
Use cautiously with concurrent medications that affect liver function or immune system to prevent enhanced toxicity.
Avoid use in patients with active serious infections or severe immunodeficiency states.
Potential for hypertension necessitates blood pressure monitoring and management.
Patients should avoid alcohol consumption to minimize liver damage risk.
Withdrawal symptoms possible; abrupt discontinuation should be medically supervised.
Risk of severe skin reactions including Stevens-Johnson syndrome and toxic epidermal necrolysis.
Close medical follow-up required due to the drug's long half-life and prolonged effects.
Not recommended in patients with severe hepatic impairment due to risk of accumulation and toxicity.

Contraindication

Known hypersensitivity to leflunomide or its active metabolite teriflunomide.
Pregnancy or planning pregnancy without prior drug elimination protocol completion.
Severe hepatic impairment or active liver disease.
Concurrent use of teriflunomide due to additive toxicity.
Severe immunodeficiency or untreated active infections.
History of serious allergic reactions to leflunomide or structurally-related compounds.
Concomitant use with other contraindicated drugs that increase risk of fatal hepatotoxicity unless under strict monitoring.
Breastfeeding due to potential risk to infant.

Drug Interactions

Increased risk of hepatotoxicity when combined with acetaminophen, NSAIDs (ibuprofen, naproxen, celecoxib), and other hepatotoxic agents.
Enhanced immunosuppression and infection risk when used with other immunosuppressive drugs including chemotherapy and corticosteroids.
Potential interaction with anticonvulsants such as carbamazepine, phenytoin, and valproic acid altering plasma levels.
Hormonal contraceptives (birth control pills) may increase risk of liver damage when taken concomitantly; consider alternative contraceptive methods.
Interactions with antibiotics, antifungals, sulfa drugs, antiviral and HIV medications may affect leflunomide metabolism and efficacy.
Cholesterol-lowering agents (statins like Crestor, Lipitor, Zocor) may increase risk of adverse hepatic events.
Heart and blood pressure medications may potentiate or be affected by leflunomide’s effects requiring close monitoring.
Concomitant use with methotrexate can increase toxicity, particularly bone marrow suppression and hepatotoxicity.
Drug elimination procedures may reduce efficacy of concomitant medications; timing coordination necessary.
Live vaccines contraindicated due to heightened infection risk with leflunomide-induced immunosuppression.
Potential reduction in teriflunomide plasma levels with cholestyramine or activated charcoal used in drug elimination protocols.
Interactions with performance-enhancing anabolic steroids (methyltestosterone) may impact liver toxicity risk.
Concomitant use of gold injections for gout or arthritis may enhance adverse effect profile.
Drugs that affect enterohepatic circulation may alter leflunomide pharmacokinetics.

Preparations Of The Drug

Oral tablet formulation available in 10 mg strength.
Oral tablet formulation available in 20 mg strength.
Coated tablets designed for oral administration to allow ease of swallowing and consistent absorption.
Supplied as blister packs or bottles depending on manufacturer and market.
No injectable or alternative formulations approved to date.
No fixed-dose combination products currently available containing leflunomide.
Tablets are stable under recommended storage conditions at room temperature away from moisture, heat, and light.
Available as brand name 'Arava' under prescription.
Generic forms may be available from various manufacturers adhering to strict quality control standards.
No pediatric formulations formulated or recommended.
No specialized extended-release or modified-release formulations available.
Dosing adjustments accomplished via tablet strength selection and daily administration schedule.
Packaging includes patient information leaflets detailing usage, side effects, and precautions.