Document gbZjyDLy8yzzJraLrXR84QB5a

Toxicology, 8 (1977) 3-11 Elsevier/North-Holland Scientific Publishers, Ltd. THE FATE OF 2,4-DICHLOROPHENOXYACETIC ACID (2,4-D) FOLLOWING ORAL ADMINISTRATION TO MAN M.W. SAUERHOFF *, W.H. BRAUN *, G.E. BLAU ** and P.J. GEHRING * Health and Environmental Research* and Computation Laboratory **, The Dow Chemical Co,, Midland, Michigan 48640 (U.S.A.) (Received November 9th, 1976) (Accepted January 4th, 1977) SUMMARY The pharmacokinetic profile of 2,4-D is defined in man. Five male human volunteers ingested a single dose of 5 mg/kg 2,4-D without detectable clinical effects. Concentration of 2,4-D were determined in plasma in 3 of 5 subjects and in urine in all subjects at intervals after ingestion. The elimination of 2.4- D from plasma in all subjects occurred by an apparent first-order rate process with an average half-life (t1/2) of 11.6 h. All subjects excreted 2,4-D in the urine with an average t1/2 of 17.7 h. Excretion occurred mainly as 2.4- D'(82.3%) with smaller amounts excreted as a 2,4-D conjugate (12.8%). Essentially all of the 2,4-D was absorbed from the gastrointestinal tract in man. Clearance of 2,4-D from the plasma and excretion from the body are first-order rate processes. There was no evidence that 2,4-D would accumu late following repeated administration. INTRODUCTION 2,4-DichIorophenoxyacetic acid (2,4-D) is a chlorophenoxy acid herbicide. Following oral administration to rats, pigs, calves and chickens, 2,4-D is readily absorbed, distributed and eliminated in the urine [1]. The half-life values for the apparent first-order clearance of 2,4-D from plasma were reported to be 3 h for rats, 8 h for calves and chickens and 12 h for pigs. The fate of 2,4-D following ingestion by man has not been reported. A AH correspondence to: M.W. Sauerhoff, Toxicology Research Laboratory, Health and 'Environm ental Research, The Dow Chemical Company, 1803 Building, Midland, Michigan 48640 (U .S.A.). Abbreviation: 2,4-D, 2,4-dichlorophenoxyacetic acid. macokinetic study of 2,4-D in man would provide critical information 've to the potential for 2,4-D to accumulate in the body. This report es the pharmacokinetic profile and metabolism of 2,4-D following oral nistration to 5 human male volunteers. ERIALS AND METHODS ects >e healthy male volunteers aged 29--40, weighing 70--90 kg, particid in the study. The medical history of each individual was reviewed and ysical examination conducted prior to the study. Included in the examion were blood pressure, pulse rate, pulmonary function, electrocardioi, chest X-ray, hemoglobin, packed cell volume, red and white blood cell its including differential, and sedimentation rate, serum concentration of 1 calcium, cholesterol, triglycerides, glucose, inorganic phosphate, .min, total protein, uric acid, bilirubin, glutamicoxaloacetic transaminase, ic dehydrogenase, alkaline phosphatase activities, as well as urinary proand sugar. All values were in the normal range. age and sample collection for analysis ''ive subjects ingested 5 mg/kg analytical grade 2,4-D (sample AGR 53C, Dow Chemical Co.). Two subjects ingested the free acid of 2,4-D i slurry in milk and 3 ingested it directly from a weighing paper followed a few swallows of water. All subjects ingested 2,4-D between 8:00 and 5 a.m. Subjects were not fasted prior to ingestion of the dose. Rood samples, 10 ml, were collected from 3 subjects in tubes containing ag of potassium oxalate at 1, 4, 8, 12, 24, 36, 48, 72, 96,120 and 144 h ir ingestion. Following collection, the whole blood samples were centried, the plasma separated and placed in tared vials and frozen for subuent analysis of 2,4-D. 411 the urine voided by each subject during successive 12-h intervals post ing was collected and the volume recorded. The urine collected during h 12-h interval was thoroughly mixed and aliquots were frozen until subuently analyzed for 2,4-D. Samples of plasma and urine were analyzed for 2,4-D by gas chromatog'hy-mass spetrometry. Urine and plasma samples (5 ml) were acidified -h 1 ml of 1.0 N HC1 and extracted twice with 5 ml of diethyl ether. To ermine whether hydrolyzable conjugates of 2,4-D may be present, addinal samples of urine (5 ml) from the 0--12-, 12--24- and 24--36 h collecn intervals were acidified with 1 ml of concentrated hydrochloric acid and ated at 80C for 1 h. Subsequently, these samples were extracted twice :h diethyl ether and analyzed for 2,4-D together with non-hydrolyzed ne samples. The ether extracts were methylated with diazomethane, iporated to dryness and redissolved in 0.5 ml of hexane. A 2 il aliquot of :tromi i.d.) id 238 symample th the of the expe stane Phar d rate ist the were RESI i funcin the and 3 .e subline tic ject 30 1C ' 1.0 O.C QOl QOOl Fig. CT) TABLE I RATE CONSTANTS AND H A L F-L IFE VALUES FOR ABSORPTION AND CLEARANCE OF 2,4-D FROM PLASMA IN 3 MALE SUBJECTS GIVEN A SINGLE ORAL DOSE 5 mg/kg 2,4-D Subject Model Absorption ---------------------------------------- Rate consLant Half-life Elimination ---------------------------------------------------------- -- Rate consLant Half-life Distribution Vlt (ml/kg) K ill--1) l W2 (M tic 0 " 1) Ll/2 (M 1 2 Com partm ent 0.165 i: 0.055 4.20 :: 1.40 J'*.a12 = 0.013 t 0.009 ^'*21 = 0.048 0.007 v f - 83.6 : 28.4 Vv 2c = 218 : 15.7 /'? = 0.145 0.04 9 Oc = 0.163 0.048 4.25 !l 1.25 p c = 0.043 - 0.012 16.2 j! 4.31 2 1 Com partm ent 0.202 ;: 0.0-17 3.43 :i 0.80 0.0G2 - 0.002 1 1.2 i; 0.36 283 : 42 3 1 Compnrtrnenl 0.4 1ft i! 0.082 1.67 !i 0.33 0.095 ! 0.003 7.29 ; 0.23 294 i 39 a ^12> ^21 ( First-order distribution constants between the plasma and slow exchange compartments. b kf . First-order rate constant for overall elimination from the central compartment. c a, 0, hybrid raLc constants for a and 0 portions of plasma clearance curve. d Vj, Volume of central compartment. e V2, Volume of slow exchange com partm ent. V 2,Volume of slow exchange compartment. t a b u -; II PERCENTAGES OF 2,4-D (FREE AND CONJUGATE) EXCRETED IN URINE DURING SUCCESSIVE TIME INTERVALS FOLLOWING A SINGLE ORAL DOSE OF 5 mg/kg 2,4-D Subject 1 2' 3 4 5 Free Conjugate Free Conjugate Free Conjugate Free Conjugate Free Conjugate 0-12 12-24 24-36 36-48 48-60 60-72 72-84 84-96 96-108 108-120 120-132 132-144 14.3 13.9 31.6 15.9 5.07 1.10 0.86 0.93 0.27 0.11 0.08 ' 0.07 2.50 8.80 10.8 29.9 33.9 9.18 8.78 3.91 1.10 0.49 0.22 0.06 0.05 0.03 0.01 -- -- -- 40.6 17.3 8.64 2.33 0.68 0.31 0.16 0.12 0.02 0.04 0.01 0.01 10.5 11.8 4.76 21.0 17.1 14.1 11.0 9.98 7.15 4.04 2.97 -- 3.10 1.70 24.7 13.8 10.7 10.0 8.99 7.90 6.03 1.25 5.70 3.00 1.10 Total 84.2 22.1 87.6 0.00 70.1 27.1 86.3 4.8 83.4 9.8 Total " 106.3 87.6 97.2 91.1 93.2 Free + conjugate. parameters for 3 subjects were calculated using a nonlinear parameter estima tion program [2]. Parameters for a 2-compartment model were calculated for subject 1. They are reported in Table I with their linearized standard deviations. Comparing the parameter estimates reveals the importance of characterizing each subject individually. For example, the absorption constant (/?0) for subjects 2 and 3 are significantly different at the 95% confidence levels as are the elimination rate constants (ke). A lack of fit test was performed for all compartmental models based on the know analytical error [3]. Each model was shown to be inadequate to describe the data at the 95% confidence level. The volume of distribution (Vd) was calculated for all subjects (refer to Table I). The Vd for subjects 2 and 3 were 238 and 294 ml/kg, respectively. The Vd for subject 1, Y x and V3, were 83 and 218 ml/kg. This indicates 2,4-D is not extensively distributed to tissues. The urinary excretion of 2,4-D expressed as a percentage of the dose excreted during each collection interval is presented in Table II and represented graphically in Fig. 2. Subjects were modeled individually using a 1-compartment linear pharmacokinetic model. The pharmacokinetic param eters determined using a nonlinear parameter estimation program are presented in Table III [2]. The half-life of elimination ranged from 10.2 to Fig. 2. Excretion of 2,4-D in urine expressed as percentage of dose excreted during successive time intervals following a single oral dose of 5 mg/kg 2,4-D. 8- Q.C33. O' H3* in" >T0O-1i TO o ST sa o' PS 5inT XTO) O s<r. L vT 7(D7 TO ctO TO o 5 aEli CTOL in ,qto O' C P KTO S ' CL rt- O O3 3r"*- Eli tr to to Ol rtor 3 p> a o a01* O 3w3 -3 o C". to o' 3 O>-*i 5. 5to' CL irPn*J- 3a R2. t-T1oO o B. o w* ST TABLE III RATE CONSTANTS AND HALF-LIFE VALUES FOR THE ELIMINATION OF 2,4-D IN THE URINE OF INDIVIDUALS FOLLOW ING A SINGLE ORAL DOSE OF 5 mg/kg Subject 1 2 3 4 5 Estimated fraction of dose eliminated a 71.4 i 18.9 84.3 i 14.5 47.8 i 15.5 96.5 t 4.67 88.4 i 18.5 Absorption cons tan t /`" ,, ( l" 1) - 0.108 i 0.052 0.192 t 0.098 -- 0.522 t 4.67 -- l l/2 (*'5 absorption 6.42 i 3.09 3.61 t 1.84 -- 1.33 i 1.44 -- Elimination constant 0 ~ l) 0.0566 i 0.0060 0.0678 i 0.0023 0.0638 t 0.0029 0.0244 i 0.0020 0.0290 t 0.0065 l l/2 (h) elimination 12.2 i 1.3 10.2 * 0.44 10.9 * 0.50 28.4 * 2.38 23.9 5.42 a Estimated fraction of sode eliminated as free 2,4-D. b Meaningful estimate of absorption constant could not be obtained from these two subjects. to 28.5 h for subjects 2 and 4, respectively. Recovery of 2,4-D ranged from 87.6 to 106.3% of the administered dose. DISCUSSION These data demonstrated that orally administered 2,4-D was well absorbed in man and excreted in urine, at the dose provided, mainly as 2,4-D. A frac tion of administered 2,4-D was also excreted in the urine as a conjugate. The average recovery of 2,4-D and conjugate was 95.1%. Recovery of greater than 90% in human studies reflects quantitative excretion of the administered chemical. After ingestion of 5 mg/kg 2,4-D, plasma concentrations increased and reached a peak of approximately 25 /ig/ml at 4 h. Clearance of 2,4-D from the plasma of subjects 2 and 3, as well as the excretion in urine from all 5 subjects, was monophasic. The plasma data for subject 1 exhibited a biphasic clearance phenomenon. The explanation for this is not avialable. It is inter esting to note that this biphasic clearance in subject 1 is accompanied by the delayed peak in the urine excretion data. The slow clearance phase param eter for the plasma data of subject 1 is only slightly slower than the monophasic clearance for subjects 2 and 3. This suggests that the overall clearance characteristics of subjects 1, 2 and 3 will not be markedly different. Statistical tests [3] performed to determine the suitability of the com partmental models to characterize the 2,4-D plasma data based on a combined analytical and sampling error of 10.2%, indicates that there was a significant lack of fit between the models and the experimental data. A significant lack of fit implies either that a more complex model (i.e., one having more parameters such as a 2-compartment model) is required or that the data are sufficiently precise to reveal deviations from the linear approximations inherent to compartment models. In this case, the latter situation is occurring. If, for example, the experimental error had been 15% rather that 10.2%, no significant lack of fit would have been detected. This means that the differences between data points and the line draw through the plasma data in Fig. 1 are real differences and not random scatter. Moreover, these differences represent real departures from the assumed first-order rate processes. Excretion data are presented for 5 subject ingesting 5 mg/kg 2,4-D. It is not reasonable to pool the individual subject data because of the difference in the pattern of excretion. One of the 5 subjects did not form the conjugate of 2,4-D while other subjects excreted between 4.8 to 27.1% of the administered dose as 2,4-D conjugate. Modeling of the data was based on the excretion of 2,4-D and not the conjugate. The data presented in Table II and Fig. 2 show significance between subject variation in the excretion of 2,4-D from th body. The slower excre tion of 2,4-D in subjects 4 and 5 may be attributable to such factors as increased protein binding, decreased capability of the kidney to excrete 2,4-D or differences in reabsorption from the tubular filtrate. (In addition, 10 0 ranged from ^ B I I I 1 as well absorbed 1 as 2,4-D. A frac- '^B a conjugate. The j^B y of greater than .he administered ^ B is increased and 'j^B :e of 2,4-D from ^ B urine from all 5 ^ B libited a biphasic -^B liable. It is inter- ^ B mpanied by the ^ B ice phase param- ^ B r than the mono- ^ B overall clearance fferent. .^B y of the compart- '^B d on a combined ^^B was a significant ^ B A significant lack one having more ^ B that the data are ^ B * approximations <S liter situation is n 15% rather that ^ B i. This means that ^ B rough the plasma ^ B \ Moreover, these ^ B 1 first-order rate ^ B ng/kg 2,4-D. It is ^ B of the difference ^ B orm the conjugate to 27.1% of the ^ B i was based on the ^ B rificance between ^ B The slower excre- j^B o such factors as cidney to excrete ^ B rate. (In addition, the urine samples from subjects 4 and 5 were stored refrigerated for 18 months before they were analyzed.) Data presented in this report indicated first-order excretion of 2,4-D The pooled data half-life values for clearance of 2,4-D from plasma was 11.6 h. It may be useful to compare this data with pooled data from human 2 4,5-T pharmacokinetic studies. Gehring et al. [4] reported that the plasma clearance t I/2 of 2,4,5-T was 23.1 h. Decreasing the number of chlorines from 3 to 2 on the phenoxy ring apparently increased the rate of clearance of these chlorophenoxy acids from the body. A practical question is: What will be the concentration of a chemical in The plasma or other tissues after repeated administration? Assuming the firstorder elimination process following a single dose does not change, is not induced or saturated, the cumulative concentration in plasma may be deter mined by addition of the concentrations attributable to each exposure. In practical terms, the time required to attain 90% of the steady-state value is about 3.5 times the biological half-life; for 99% of steady-state value it requires about 7 times the biological half-life. Steady-state concentrations of 2,4-D would be reached by approximately 3 days. No additional accumula tion would occur after this time. Based on our analysis of the data collected in this study, 2,4-D would not accumulate in the body with repeated administration. In conclusion, 2,4-D is well absorbed following oral administration to man and eliminated as unchanged 2,4-D (82.3%) and 2,4-D conjugate (12.8%) in urine. Clearance of 2,4-D from plasma and elimination from the body occur by apparent first-order rate processes. No evidence of nonlinear kinetics was observed following the 5 mg/kg oral dose of 2,4-D. REFERENCES 1 K. Erne, Acta Vet. Scand., 7 (1966J 240. 2 Y.J. Bard, Nonlinear Parameter Estimation, Academic Press, New York, 1974 3 P.M. Riley and G.E. Blau, Can. J. Chem. Eng., 52 (1974) 289. 4 P.J. Gehring, C.G. Kramer, B.A. Schwetz, J.Q. Rose and V.K. Rowe, Toxicol. Appl. Pharmacol., 26 (1973) 352. 11