The Use of 13C Labeling to Enhance the Sensitivity of 13C Solid-State CPMAS NMR to Study Polymorphism in Low Dose Solid Formulations

13C labeling was used to enhance the sensitivity of 13C solid-state NMR to study the effect of tabletting on the polymorphism of a steroidal drug. The steroidal drug Org OD 14 was 13C labeled and formulated into tablets containing only 0.5-2.5% active ingredient. The tablets were subsequently studied by solid-state 13C CPMAS NMR. The crystalline form present in tablets could readily be analyzed in tablets. No change in crystalline form was observed as a result of formulation or in subsequent stability studies. Solid-state NMR in combination with 13C labeling can, in suitable cases, be used as a strategy to study the effect of formulation on the polymorphism of low dose drugs. © 2004 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 94:458-463, 2005