Monosodium [1-hydroxy-2-(1H-imidazol-3-ium-4-yl)ethane-1,1-diyl]bis(phosphonate) tetrahydrate (monosodium isozoledronate).

The title compound, Na(+).C(5)H(9)N(2)O(7)P(2)(-).4H(2)O, is an isomer of zoledronate, a potent bone antiresorptive bisphosphonate drug having significant activity against several parasitic protozoa. The crystal structure of isozoledronate consists of bisphosphonate dimers coordinated by two Na(+) ions. The dimers are held together through an extensive hydrogen-bonding network. The crystals exhibit non-merohedral twinning that roughly superimposes the a and b axes, and inverts the c axis.