Mechanism of Action

The mechanism of action of thalidomide is not fully understood. Thalidomide possesses immunomodulatory, antiinflammatory and antiangiogenic properties. Available data from in vitro studies and clinical trials suggest that the immunologic effects of this compound can vary substantially under different conditions, but may be related to suppression of excessive tumor necrosis factor-alpha (TNF-α) production and down-modulation of selected cell surface adhesion molecules involved in leukocyte migration.^3-6 For example, administration of thalidomide has been reported to decrease circulating levels of TNF-α in patients with erythema nodosum leprosum (ENL)³, however, it has also been shown to increase plasma TNF-α levels in HIV-seropositive patients.⁷ Other antiinflammatory and immunomodulatory properties of thalidomide may include suppression of macrophage involvement in prostaglandin synthesis, and modulation of interleukin-10 and interleukin-12 production by peripheral blood mononuclear cells. Thalidomide treatment of multiple myeloma patients is accompanied by an increase in the number of circulating natural killer cells, and an increase in plasma levels of interleukin-2 and interferon-gamma (T cell-derived cytokines associated with cytotoxic activity). Thalidomide was found to inhibit angiogenesis in a human umbilical artery explant model in vitro. The cellular processes of angiogenesis inhibited by thalidomide may include the proliferation of endothelial cells.

Pharmacokinetics and Drug Metabolism

Absorption

The absolute bioavailability of thalidomide from THALOMID® (thalidomide) Capsules has not yet been characterized in human subjects due to its poor aqueous solubility. However, the capsules are 90% bioavailable relative to an oral PEG solution. In studies of both healthy volunteers and subjects with Hansen's disease, the mean time to peak plasma concentrations (Tmax) of THALOMID® (thalidomide) ranged from 2.9 to 5.7 hours indicating that THALOMID® (thalidomide) is slowly absorbed from the gastrointestinal tract. While the extent of absorption (as measured by area under the curve [AUC]) is proportional to dose in healthy subjects, the observed peak concentration (Cmax) increased in a less than proportional manner (see Table 1 below). This lack of Cmax dose proportionality, coupled with the observed increase in Tmax values, suggests that the poor solubility of thalidomide in aqueous media may be hindering the rate of absorption.

Table 1: Pharmacokinetic Parameter Values for THALOMID® (thalidomide) Mean (%CV)

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