Pharmacokinetic Features
The pharmacokinetics of Leflunomidum are based on the prodrug concept. Upon administration, the parent molecule is pharmacologically inactive. To exert therapeutic activity, the drug must undergo mandatory metabolic transformation.
The liver is the primary organ responsible for this transformation. Chemical modification of the drug structure within hepatic tissue yields the active metabolite. This metabolite subsequently enters the systemic circulation and interacts with cellular targets to produce the desired clinical effects.
Cellular Mechanism of Action
The mechanism of action of the active metabolite occurs at the biochemical level and involves highly specific enzyme inhibition. The process unfolds in several sequential steps:
- Enzyme Blockade: The primary target of the drug is the enzyme dihydroorotate dehydrogenase. The drug acts as a potent inhibitor.
- Halting Pyrimidine Synthesis: Inhibition of this enzyme stops cellular pyrimidine production.
- Cell Division Arrest: Because pyrimidines are critically required for cell division, their deficiency makes this process impossible.
- Inhibition of Lymphocyte Proliferation: The pyrimidine shortage primarily affects immune system cells, causing marked inhibition of lymphocyte proliferation and interrupting the pathological immune response.
Pharmacodynamics and Clinical Application
Pharmacodynamic effects follow logically from the mechanism of action. By suppressing excessive lymphocyte activity, the drug exerts a multifaceted effect on the body:
- Anti-inflammatory Action: Reducing the pool of active immune cells decreases the severity of inflammation.
- Analgesic Effect: Amelioration of inflammation leads to secondary pain reduction.
- Slowing Joint Destruction: The drug protects joint surfaces from degradation. This structural-modifying effect is achieved by suppressing osteoclast activity.
In clinical practice, this agent is versatile. It can be prescribed as monotherapy or in combination therapy—for example, combined with methotrexate to achieve a more robust therapeutic response.
Adverse Reactions and Contraindications
Therapy carries a risk of adverse effects affecting various organ systems, categorized as follows:
- Gastrointestinal Tract: Patients frequently experience dyspeptic symptoms, most notably nausea and diarrhea.
- General Disorders: Systemic drug exposure may manifest as headache, unexplained weight loss, and alopecia.
- Immune System: There is a continuous risk of allergic reactions of varying severity.
Absolute and strict contraindication for use is pregnancy. The drug has a proven teratogenic effect, meaning it disrupts embryonic development; therefore, its use in pregnant women is strictly prohibited.