OBJECTIVE: The decision to prescribe one drug instead of another within the same therapeutic class may be influenced by a variety of drug-related, direct, or indirect factors; but little is known about which considerations are most important in such choices. The low-molecular-weight heparins (LMWHs) represent a class of drugs that are commonly used and for which therapeutic equivalence has been debated in the literature. The purpose of this study was to identify and compare factors perceived by physicians and clinical pharmacists to be influential in prescribing decisions among LMWHs. METHODS: Physicians and clinical pharmacists were interviewed to elicit information and rank factors that influence the prescribing and use of LMWHs in community hospitals. For each factor, the mean and median of the rating was determined along with the frequency distribution across ratings. The nonparametric Mann-Whitney U test was used to examine differences between physicians and clinical pharmacists. RESULTS: Both groups considered efficacy, formulary status, and policies restricting drug use to be highly influential in the decision to use one LMWH versus another. Compared to clinical pharmacists, physicians rated personal experience as more influential, whereas they rated drug cost and prescribing guidelines lower. CONCLUSIONS: These findings suggest that physicians and clinical pharmacists differentiate between LMWHs based on differences between products and because of hospital administrative programs (such as drug formularies). This information may be of value in designing programs to alter medication use in community hospitals.