Blanchard J, Conrad K A, Garry P J
Department of Pharmaceutical Sciences, University of Arizona, Tucson 85721.
Eur J Clin Nutr. 1990 Jun;44(6):447-60.
The pharmacokinetics of vitamin C following a 500 mg oral tablet dose were compared in a group of fourteen healthy young women whose age was 26.0 +/- 2.8 years (mean +/- s.d.), and in a group of fourteen healthy elderly women aged 68.1 +/- 2.6 years. The body composition of each subject was assessed using several anthropometric measurements in order to help explain any observed differences in the pharmacokinetic behavior of vitamin C. The vitamin C doses were characterized with the subjects in two states of vitamin C nutriture: a 'depleted' state which was achieved by 4-5 weeks on a vitamin C-restricted diet of less than 10 mg/d and a 'supplemented' state in which the subjects were given daily doses of 500 mg of vitamin C for 3 weeks. Plasma and urine samples were collected for 72 h following the dose of vitamin C from subjects in a 'depleted' state and for 24 h from subjects in a 'supplemented' state and analysed for their vitamin C content. None of the pharmacokinetic parameters measured differed significantly between the two age groups. In contrast, the vast majority of these parameters were significantly different in depleted and supplemented subjects. The peak times (tmax) were greater in the depleted state in both young and elderly groups whereas the peak concentrations (Cmax) were greater in the supplemented state. The absorption rate constant (Ka) was significantly larger in the supplemented state compared to the depleted state in the young group and the absorption half-life (t 1/2, Ka) was significantly greater in the depleted state in the young group only. The absorption lag time (tlag) did not differ with respect to age or nutritional status. The elimination half-life (t 1/2, Ke) was significantly longer in supplemented subjects. Although the apparent high volume of distribution (Vd) was not significantly different within each age group the Vd was significantly greater in the depleted state when the two age groups were combined. The clearance (CL), and the nonrenal clearance (CLNR) were significantly greater in the depleted state. The renal clearance (CLR) and the amounts of vitamin C excreted in the 0- to 12- and 12- to 24-h intervals were significantly larger in the supplemented state. The urinary excretion data also indicate that, in supplemented subjects, an average of about 40 percent of the administered dose is excreted as unchanged vitamin C in the first 12 h after dosing, with very little being excreted thereafter.
对一组14名年龄为26.0±2.8岁（均值±标准差）的健康年轻女性和一组14名年龄为68.1±2.6岁的健康老年女性，比较了口服500毫克维生素C片后的药代动力学。为了帮助解释观察到的维生素C药代动力学行为的差异，使用多种人体测量方法评估了每个受试者的身体组成。维生素C剂量在维生素C营养状况的两种状态下对受试者进行了表征：一种是“缺乏”状态，通过4-5周摄入低于10毫克/天的维生素C限制饮食来实现；另一种是“补充”状态，在此状态下受试者每天服用500毫克维生素C，持续3周。在给予维生素C剂量后，从处于“缺乏”状态的受试者收集72小时的血浆和尿液样本，从处于“补充”状态的受试者收集24小时的血浆和尿液样本，并分析其中维生素C的含量。两个年龄组之间测量的药代动力学参数均无显著差异。相比之下，这些参数中的绝大多数在缺乏和补充状态的受试者中存在显著差异。年轻组和老年组在缺乏状态下的达峰时间（tmax）均更长，而在补充状态下的峰浓度（Cmax）更高。年轻组中，补充状态下的吸收速率常数（Ka）显著大于缺乏状态，仅年轻组在缺乏状态下的吸收半衰期（t 1/2, Ka）显著更长。吸收滞后时间（tlag）在年龄或营养状况方面没有差异。补充状态下受试者的消除半衰期（t 1/2, Ke）显著更长。尽管每个年龄组内的表观分布容积（Vd）没有显著差异，但将两个年龄组合并时，缺乏状态下的Vd显著更大。清除率（CL）和非肾清除率（CLNR）在缺乏状态下显著更高。补充状态下的肾清除率（CLR）以及在0至12小时和12至24小时间隔内排泄的维生素C量显著更大。尿液排泄数据还表明，在补充状态的受试者中，给药后前12小时平均约40%的给药剂量以未改变的维生素C形式排泄，此后排泄量很少。
