The steady-state pharmacokinetics of ceftibuten, an orally active cephalosporin were investigated in 12 healthy male volunteers (19--38 years) and in 12 geriatric volunteers (65--76 years). Each received one 200-mg ceftibuten capsule every 12 h on days 1--3 and one capsule in the morning on day 4. Plasma and urine samples were collected at various times on days 1--4 and assayed by high-pressure liquid chromatographic method for ceftibuten and ceftibuten-trans, a conversion product. The T(max) for ceftibuten and ceftibuten-trans occurred at about 2 and 3 h, respectively, in both populations. The C(max) and AUC((0--12 h)) ranged from 10.8 to 12.4 &mgr;g ml(minus sign1) and from 47.5 to 55.1 &mgr;g h ml(minus sign1), respectively, for normal volunteers compared to 12.9--17.5 &mgr;g ml(minus sign1) and 62.3--87.1 &mgr;g h ml(minus sign1), respectively, for geriatric volunteers. The respective values for ceftibuten-trans in normal and geriatric volunteers were 1.3 and 1.3 &mgr;g ml(minus sign1), respectively, and 6.9--8.2 and 5.9--9.8 &mgr;g h ml(minus sign1). At steady state, the C(max) and AUC((0--12 h)) of ceftibuten-trans were about 10--11% and 13--16% those of ceftibuten in normal volunteers and about 8--9% and 9--11% those of ceftibuten, respectively, in geriatric volunteers. The accumulation factor of ceftibuten in normal volunteers was 1.1 as compared to 1.3 in geriatric volunteers. The terminal phase half-life was 2.5 h in healthy volunteers and 3.2 h in geriatric volunteers. Urinary excretion appeared to be the major route of elimination in both populations accounting for more than 90% of the dose recovered in the urine during the dosing interval. The results of this study demonstrate that ceftibuten, 200 mg given twice a day, is safe and well tolerated, is well absorbed, and that steady-state is achieved on days 3 and 4. There is some accumulation in the elderly, but dosage regimen based on age is not warranted.