Metacetamol

Metacetamol (developmental code name BS-749), also known as 3-hydroxyacetanilide and AMAP, is a non-toxic regioisomer of paracetamol with analgesic and antipyretic properties, but has never been marketed as a drug.

Metacetamol is known to have several polymorphs. Form II is metastable, while form I is stable. Metacetamol polymorph II transforms to form I upon water moisture or direct contact with water and other popular solvents. Metacetamol II form may be obtained on cooling in narrow temperature regime.