A rapid, simple, specific and quantitative assay for trapidil in the serum was developed by reversed-phase high-performance liquid chromatography. Only 20μl of the serum is required. Serum proteins are precipitated with 100μl of methanol. After the centrifugation, 90μl of the supernatant is injected into the chromatograph equipped with a Model U6K injector, a 3.9 mm×30 cm μBondapak C
18 column, a Model M-45 Solvent Delivery System (Waters Assoc. Inc., ) and a Model S-310A ultraviolet detector (Soma optics Co., Ltd.) set at 0.01 AUFS (307 nm). The flow rate of the mobile phase of 28% acetonitrile solution containing 0.01 M sodium acetate (pH 7.0) is 1.0 ml/min. The retention time for trapidil is about 13 min. The amount of trapidil is determined by measuring its peak height. Within-run and day-to-day reproducibilities for 1.0μg/ml are ±0.01 (±S.D. : n=10) and ±0.02 (n=10), respectively and those for 4.0μg/ml are ±0.03 (n=10) and ±0.11 (n=10), respectively. The recovery of added trapidil is 95.3-102%. The limit of detection is 0.5μg/ml of serum. The proposed method can be completed in less than 15 min. Pharmacokinetics of trapidil was studied on asthmatic patients. Trapidil was administered at a dose of 1.32-2.33 mg/kg by a constantrate intravenous infusion for 30 min. The level of trapidil in the serum was analyzed by using a one-compartment open model. The mean elimination rate constant (K
e) was 0.476±0.198 h
-1, biological half-life (t
1/2) was 1.72±0.768 h, K
0/V was 6.20±4.13 (μg/ml)·h
-1, D/V was 3.10±2.06μg/ml, C
ss was 18.9±19.3μg/ml, volume of distribution (V) was 0.826±0.426 l/kg, AUC
240 min0 was 6.85±5.89 (μg/ml)·h, AUC
∞240 min was 3.14±3.98 (μg/ml)·h, and total AUC was 10.0±8.83 (μg/ml)·h. All average data are given as mean±S.D. These data would be useful for determining precise dosage requirement for trapidil in asthma.
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