A polymeric biguanide composition comprising less than 18 mol % of terminal amine groups as measured by 13C NMR. The polymeric biguanide composition also is characterized by a relative increase in the molar concentration of terminal guanidine groups or terminal cyanoguanidino groups. The invention is also directed to ophthalmic compositions comprising the polymeric biguanide compositions. The polymeric biguanide compositions can be used as an antimicrobial component in an ophthalmic lens care solution, or as a preservative to in a pharmaceutical composition or other health care product.