Fosinopril and hydrochlorothiazide combination versus individual components: lack of a pharmacokinetic interaction.

OBJECTIVE: To evaluate the pharmacokinetic interaction and bioequivalence of a combination formulation of the angiotensin-converting enzyme inhibitor fosinopril and the diuretic hydrochlorothiazide (HCTZ). METHODS: In an open-label, balanced, randomized incomplete block, three-way crossover fashion, healthy men received single doses of three of four regimens in one of two independent studies. Regimens for study A (36 subjects): (1) fosinopril 10-mg tablet, (2) HCTZ 12.5-mg tablet, (3) a combination tablet of fosinopril 10 mg plus HCTZ 12.5 mg, or (4) coadministered tablets of fosinopril 10 mg and HCTZ 12.5 mg. Study B (40 subjects) received: (1) fosinopril 20-mg tablet, (2) HCTZ 12.5-mg tablet, (3) a combination tablet of fosinopril 20 mg plus HCTZ 12.5 mg, or (4) coadministered tablets of fosinopril 20 mg and HCTZ 12.5 mg. RESULTS: There was no evidence of any significant effect of HCTZ on the pharmacokinetics of fosinoprilat, based on maximum concentration value, AUC, or cumulative urinary recovery over 24 hours. Fosinoprilat had no clinically important effect on the pharmacokinetics of HCTZ only slightly decreasing its AUC by 14% in study A. Coadministration was well tolerated; no new adverse events were reported with the combination tablet. CONCLUSIONS: Fosinopril and HCTZ in a combination tablet display pharmacokinetic profiles similar to those achieved when either drug is administered alone or when coadministered in separate tablets. When used with HCTZ, the favorable pharmacokinetic feature of fosinopril, dual and compensatory pathways of renal and hepatic elimination, is preserved.

A specific radioimmunoassay for the measurement of gadoteridol, a contrast agent for magnetic resonance imaging in biological fluids.

Gadoteridol, a nonionic gadolinium chelate, is currently being evaluated for contrast-enhanced magnetic resonance imaging. A radioimmunoassay (RIA) has been developed for the measurement of gadoteridol in biological fluids. The RIA has a range of 0 to 25 micrograms/mL and has the sensitivity to detect 0.05 microgram/mL of gadoteridol. Satisfactory zero binding and sensitivity were obtained after an overnight incubation at 4 degrees C. Separation of the antibody-bound and free radiolabel was achieved with 12.5% polyethylene glycol. A quantitative recovery of the exogenous analyte was obtained at all concentrations of gadoteridol tested. Linearity in both serum and urine was satisfactory. Intraassay coefficients of variation were 6.4 and 2.8% for the low and medium controls, respectively. Interassay coefficients of variation were 5.4, 3.8, and 12.2% for the low, medium, and high controls, respectively. Cross reactivities of the ligand 5 and the calcium salt 6 were 37 and 29%, respectively. Clinical samples from the ascending dosage studies were analyzed by the gadoteridol RIA. The results obtained from the serum specimens demonstrated an excellent linear proportionality between drug concentration in blood and administered dosage of gadoteridol. Cumulative urinary excretion data showed that 94% of the drug was excreted in the urine within 24 h.