Stability of extemporaneous suspensions of carbamazepine

The stability of carbamazepine in four suspending vehicles is reported. Suspensions of carbamazepine 200 mg/5 ml in sorbitol 70%, simple syrup, modified Hospital of the University of Pennsylvania Suspending Vehicle (HUP), and diluted HUP (HUP-A) were prepared. The first three suspensions were stored in amber glass bottles and oral syringes at 4, 25, and 37 degrees C, and the HUP-A suspension was stored at 4 degrees C. Physical stability was assessed by visual inspection of sedimentation, ease of pouring, and foaming upon shaking. Carbamazepine concentrations were determined periodically over 90 days by an enzyme-multiplied immunoassay. The assay was validated by acid-heat degradation of the drug, separation of breakdown products by thin-layer chromatography, and confirmation of non-reactivity of the breakdown products with the assay. The concentration of carbamazepine in sorbitol 70%, simple syrup, and HUP-A was at least 90% of the prepared concentration at all sampling times. Although separation occurred, the simple syrup suspensions could be redispersed. The suspension in HUP-A remained homogeneous, was easy to pour, and produced less foam than the HUP suspension. Extemporaneously compounded suspensions of carbamazepine in HUP-A or in simple syrup can be used for patients who require a liquid dosage form. Even though sorbitol 70% produced a pharmaceutically acceptable product, its use is not recommended because it has been reported to cause intractable diarrhea.