Lackluster sales of NitroMed's ( NTMD) congestive heart failure drug for African-Americans -- a result of high copayments charged by managed care organizations and low salesforce productivity -- contributed to a fourth-quarter loss that tripled from a year earlier. The Lexington, Mass.-based company said Thursday that efforts to improve sales of the drug BiDil include stepping up negotiations with insurers and converting the contract salesforce to an in-house salesforce. BiDil has been available since mid-July. A combination of two generic drugs, BiDil is the first drug approved by the Food and Drug Administration on the basis of race . "Prescription growth, while steady, has remained below expectations, leaving many patients without access to BiDil," said Michael D. Loberg, NitroMed's chief executive. "It is a primary objective of the company to ensure that patient copayments are affordable for the 750,000 blacks with symptomatic heart failure in the United States. ... It is important that we continue to make progress in moving BiDil to Tier II on managed care plans." Many managed care plans have three tiers of coverage. The lowest patient copayments are assigned to Tier I generic drugs, higher copayments are for Tier II preferred brand-name drugs, and the highest copayments accompany Tier III brand-name drugs. Insurers place the highest copayments on Tier III to encourage patients to use generics or brand-name drugs on their preferred lists. NitroMed executives told analysts Thursday that the difference between Tier II and Tier III copayments can mean the difference between filling and not filling a prescription. Some Tier III copayments can be as high as $100 and "raise the question of affordability," Loberg said during a telephone conference call. NitroMed has encountered "more affordability issues than we anticipated." Dr. Lawrence E. Bloch, the chief financial officer, said NitroMed's research shows that a filled BiDil prescription has an average copayment of $39, while an unfilled prescription has an average copayment of $73.