Aliphatic amine polymers are useful as active pharmaceutical ingredients for use in pharmaceutical compositions. A particularly interesting aliphatic amine polymer is Sevelamer, a polymeric phosphate binder intended for oral administration. Sevelamer hydrochloride is a poly(allylamine hydrochloride) crosslinked with epichlorohydrin in which forty percent of the amines are apparently protonated. It is known chemically as poly(allylamine-co-N,N′-diallyl-1,3-diamino-2-hydroxypropane) hydrochloride. Sevelamer hydrochloride is hydrophilic, but insoluble in water. The reported structure of Sevelamer HCl is represented below:

Sevelamer HCl is currently being marketed as RENAGEL®, for the treatment of patients with Chronic Kidney Disease (CKD) which are on hemodialysis1. According to the prescribing information RENAGEL® is indicated for the control of serum phosphorus in such CKD patients. In general, commercially available Sevelamer tablets also contain the following inactive ingredients; hypromellose, diacetylated monoglyceride, colloidal silicon dioxide, and stearic acid. 1Renagel® is sold by Genzyme Corporation. The Prescribing Information is available from www.renagel.com/docs/renagel_pi.pdf which describes the 400 mg and 800 mg tablets as containing the following inactive ingredients: hypromellose, diacetylated monoglyceride, collodial silicon dioxide and stearic acid.
The method of producing a direct compressible composition of a polymer tablet core is described in U.S. Pat. No. 6,733,780 B1 and U.S. Patent Application 2005/0260236 A1. These references describe Sevelamer HCl as a product which compressibility is strongly dependent upon the degree of hydration. Apparently, hydrating the polymer to the desired moisture level is considered by those inventors as an essential first step in manufacturing the finished product.
Further, Sevelamer HCl is known to be very hygroscopic and swell upon contact with water. Such swelling of the aliphatic amine polymer Sevelamer complicates formulating the active pharmaceutical ingredient in a pharmaceutical composition. Thus although compressibility is apparently dependant on the degree of hydration, simply adding water to sevelamer results in a swollen material which swollen material is impossible to use to press tablets. The present invention overcomes this problem of swelling of the active pharmaceutical ingredient by providing a more compressible sevelamer formulation within which the water content of sevelamer is not significantly increased compared to the commercially available sevelamer raw material. Even when using a wet granulation method with the present sevelamer formulation, the active pharmaceutical ingredient sevelamer has not swollen significantly. It is noted that commercially available sevelamer raw material is similarly impossible to compress.