1381 m 1351 s 1331 m 1255 m 1201 w 1156 m 1121 vs 1048 w 995 w 823 w 767 w 744 s 724 d 630 w where w weak intensity m medium intensity s strong intensity vs very strong intensity fig2 represents the infrared spectrum of the crystalline polymorph 2 of bilastin in a potassium bromide tablet recorded in a fourier perkin elmer spectrum one transformer spectrophotometer the crystalline polymorphic form 3 of bilastin is also characterised by its infrared absorption spectrum in potassium bromide that has the following characteristic absorption bands expressed in reciprocal centimetres 3430 s 3053 w 2970 s 2932 s 2868 s 2804 w 1921 w 1708 m 1614 m 1568 m 1508 s 1461 vs 1380 m 1351 m 1330 m 1271 m 1255 m 1201 w 1156 m 1121 vs 1048 w 995 w 823 m 767 w 744 s 724 w 630 w where w weak intensity m medium intensity s strong intensity vs very strong intensity fig3 represents the infrared spectrum of the crystalline polymorph 3 of the bilastin in a potassium bromide tablet recorded in a fourier perkin elmer spectrum one transformer spectrophotometer we have discovered that in selected experimental conditions the mixture of the polymorphic forms 2 and 3 obtained according to u s pat no 5 877 187 is surprisingly transformed into polymorph 1 we have also discovered that polymorph 1 of bilastin is very stable and is not transformed into any of the other polymorphs 2 and 3 similarly in the same experimental.