Findlay J W, Butz R F, Welch R M
Clin Pharmacol Ther. 1977 Oct;22(4):439-46. doi: 10.1002/cpt1977224439.
Radioimmunoassay (RIA) was used to determine several pharmacokinetic parameters of codeine in man, including the relative bioavailability after oral and intramuscular administration. The study followed a crossover design in 6 healthy, young (18 to 21 yr), male volunteers. Three subjects received 65 mg codeine phosphate orally in an analgesic mixture which also contained aspirin, phenacetin, and caffeine. At the same time a similar group received an equivalent dose of codeine phosphate in a single intramuscular injection. Two weeks later the study was repeated so that each group received the alternate treatment. Plasma samples were collected at various times after drug administration, and codeine concentrations were determined by a specific RIA procedure. The procedure can detect less than 50 pg of codeine. Following intramuscular administration, peak plasma concentrations (194 to 340 ng/ml) were observed between 0.25 to 1 hr; after oral dosing, peak codeine plasma concentrations (102 to 140 ng/ml) appeared within 0.75 to 1 hr. The mean plasma t1/2 and volume of distribution of codeine following intramuscular injection were 3.32 hr and 5.1 L/kg, respectively. Oral, relative to intramuscular, bioavailability of codeine, based on areas under the codeine plasma curves, was 42% to 71% (mean, 53%).
采用放射免疫分析法（RIA）测定可待因在人体中的几个药代动力学参数，包括口服和肌肉注射后的相对生物利用度。该研究采用交叉设计，选取了6名健康、年轻（18至21岁）的男性志愿者。3名受试者口服含阿司匹林、非那西丁和咖啡因的镇痛合剂中的65毫克磷酸可待因。与此同时，另一组受试者单次肌肉注射等量的磷酸可待因。两周后重复该研究，使每组接受交替治疗。给药后在不同时间采集血样，并通过特定的放射免疫分析程序测定可待因浓度。该程序可检测到低于50皮克的可待因。肌肉注射后，在0.25至1小时之间观察到血浆峰值浓度（194至340纳克/毫升）；口服给药后，可待因血浆峰值浓度（102至140纳克/毫升）在0.75至1小时内出现。肌肉注射后可待因的平均血浆半衰期和分布容积分别为3.32小时和5.1升/千克。基于可待因血浆曲线下面积，可待因口服相对于肌肉注射的生物利用度为42%至71%（平均53%）。
