A 1-year retrospective analysis was undertaken to discern the economic utility of providing prescription coverage for the sustained-release (SR) formulation of diltiazem, a calcium-channel antagonist, under the state of South Carolina's Medicaid program. Data for this analysis were derived from the state of South Carolina's Medicaid computer archive. The study population consisted of 347 ambulatory beneficiaries diagnosed with hypertension for whom either the SR or immediate-release (IR) formulation of diltiazem was prescribed. Multivariate regression analysis was used to discern the incremental influence of selected demographic characteristics, use of medical services prior to diagnosis for hypertension, and prescribed formulation of diltiazem on health care expenditures 1-year postdiagnosis. Patients for whom the SR formulation of diltiazem was prescribed achieved a significant (P < or = 0.05) increase in the medication possession ratio, an index of compliance (SR, 0.63 +/- 0.17) relative to patients for whom the IR formulation was prescribed (IR, 0.44 +/- 0.13). Results indicate that receipt of diltiazem in an SR formulation was associated with a significant decrease in aggregate health care expenditures over the 1-year study period ($258.80, P < or = 0.05). Receipt of the SR formulation was associated with an increase in expenditures for antihypertensive therapy ($109.26, P < or = 0.05), and a decrease in financial commitments for physician ($128.70, P < or = 0.05), hospital ($211.84, P < or = 0.05), and laboratory ($27.52, NS) services. At the managerial and policy levels, these data argue for an increased use of therapeutic alternatives that facilitate a reduction in the patient's daily dosing schedule for antihypertensive therapy.