Meclizine

Meclizine (also spelled meclozine) is a first-generation antihistamine belonging to the piperazine class of compounds. It has a diphenylmethyl piperazine core structure that confers lipophilicity, allowing passive absorption across the gastrointestinal tract and good oral bioavailability. Its long half-life and ability to cross cell membranes facilitate its distribution into tissues.

Originally marketed as an over-the-counter remedy for motion sickness and nausea, meclizine has attracted scientific interest as a repurposed agent. Research has identified additional pharmacological activities beyond histamine H1 receptor antagonism, including inhibition of FGFR3 signaling pathways relevant to skeletal dysplasias, modulation of cellular energy metabolism, and potential anticancer and antimicrobial properties, all accessible via oral administration.

Animal study: In transgenic mice carrying the achondroplasia-associated FGFR3 gain-of-function mutation, oral administration of meclizine significantly increased longitudinal bone growth, with longer cranium, radius, ulna, femur, tibia, and vertebrae compared to untreated ACH mice. Meclizine also increased bone growth in wild-type mice. (PMID 25456072)

Animal study: In transgenic achondroplasia mice, meclizine treatment at a clinically relevant exposure level significantly rescued short stature and also improved bone volume and metaphyseal trabecular bone quality. The study confirmed a preclinical proof of concept for meclizine in achondroplasia but noted that long-term toxicity requires further study. (PMID 28785080)

Animal study: In a mouse model of X-linked hypophosphatemia (Hyp mice), meclizine improved abnormal hypertrophic zone thickness of the growth plate, reduced cortical bone osteoid volume, and ameliorated osteoclast surface abnormalities. However, its effects on trabecular bone mineralization and plasma calcium and phosphate levels were only marginal. (PMID 36569439)

Laboratory study: In a lab study using rat and human chondrosarcoma cell lines and mouse chondrogenic cells, meclizine facilitated chondrocyte proliferation and differentiation by attenuating ERK phosphorylation downstream of abnormally activated FGFR3 signaling. Its efficacy was comparable to C-natriuretic peptide in suppressing FGFR3-related signaling cascades. (PMID 24324705)

Laboratory study: RNA-sequencing of murine chondrocytes and zebrafish experiments showed that meclizine reduced MAPK signaling enrichment in FGF2-treated chondrocytes and delayed vertebral ossification and reversed FGF2-induced craniofacial bone hyperossification in larval zebrafish. These findings provided additional mechanistic evidence for meclizine's inhibitory effect on FGF2-induced MAPK pathway activation. (PMID 35118060)

Laboratory study: A nutrient-sensitized screen of over 3,500 small molecules identified meclizine as an attenuator of mitochondrial respiration through a mechanism distinct from canonical inhibitors, shifting cellular energy metabolism toward glycolysis. In murine models, meclizine pretreatment conferred cardioprotection and neuroprotection against ischemia-reperfusion injury. (PMID 20160716)

Laboratory study: In a cell-based study, meclizine increased lactate production and was found to be a potent inducer of the PGC-1-related coactivator (PRC) stress program, which is linked to glycolytic energy metabolism. The authors suggested PRC activation may contribute to the cardio- and neuroprotective effects previously associated with meclizine. (PMID 23364789)

Laboratory study: Lab studies using human iPSC-derived hepatic organoids and cancer cell lines showed that meclizine, as an inhibitor of the phosphatidylethanolamine biosynthesis pathway, was selectively cytotoxic to early hepatoblasts. When combined with a glycolysis inhibitor, meclizine inhibited human liver carcinoma growth in vitro and in a xenotransplantation model, and showed activity against acute myeloid leukemia cells. (PMID 31760071)

Laboratory study: In a lab study using doxorubicin-resistant murine leukemia cells (P388/ADR), meclizine at non-growth-inhibitory concentrations was highly active in restoring sensitivity to doxorubicin, while having no synergistic effect in the drug-sensitive parent cell line. The mechanism did not correlate with calcium channel inhibition in synaptic vesicles. (PMID 6487516)

Laboratory study: A high-throughput screening study identified meclizine as an antivirulence agent against Clostridioides difficile, reducing TcdA and TcdB toxin protein levels, cytopathic potential, and toxin gene transcription in lab assays. Meclizine altered central carbon metabolism in C. difficile by upregulating carbohydrate transport and lactate-to-pyruvate conversion while downregulating glycolytic genes. (PMID 41405459)

Laboratory study: A screen of FDA-approved drugs against hydrogen peroxide-induced oxidant injury in neuroblastoma cells identified meclizine as one of 26 neuroprotective compounds. Gene expression profiling suggested its cytoprotective effects involve modulation of genes including TIMP1, clusterin, galanin, and GAP43. (PMID 12388792)

Human study: A phase Ia clinical trial in 12 children aged 5–10 years with achondroplasia found that meclizine was well tolerated with no serious adverse events after single and repeated oral administration. Drug exposure was higher in ACH children compared to adults, and food intake increased drug absorption. (PMID 32282831)

Limitations:

Animal study: Maternal administration of meclizine to pregnant mice carrying achondroplasia offspring produced a non-significant trend toward reduced premature synchondrosis closure, likely because placental transmission of the drug was low. The study concluded that meclizine has only a marginal effect on cranial base synchondrosis in this model. (PMID 27767902)

Open questions: It remains unclear whether meclizine's effects on FGFR3 signaling in animal models will translate into meaningful improvements in height or skeletal outcomes in humans with achondroplasia, as only early-phase safety and pharmacokinetic trials have been completed. The precise molecular target through which meclizine attenuates ERK phosphorylation downstream of FGFR3 has not been fully elucidated. Long-term safety of repeated administration in children, including effects on normal bone development and the central nervous system, has not been established.

Whether the anticancer synergy observed in cell and xenograft models will be reproducible and safe in human oncology settings is unknown, and the clinical relevance of meclizine's effects on Clostridioides difficile toxin biosynthesis in actual infections has yet to be tested.