THE FATE OF ACETANILIDE IN MAN'

         BERNARD B. BRODIE AND JULIUS AXELROD
i:zacnrch Service, Third (New York University) Medical Division, Goldwa@r Memorial
Hospital, and Department of Biochemistry, New York University College of Medicine
       and Laboratory of Industrial Hygiene, New York, New York
           Received for publication May 11, 1948
Therapeutic agents, in general, undergo chemical alteration in the body to
form derivatives of the parent compound.  Isolation and pharmacological assay
of the various transformation products may yield valuable information in the
Senrch for better therapeutic agents, in studies on the mechanism of drug action
:,*d in the elucidation of norm+l metabolic processes.
The therapeutic effect of a drug could be limited by a chemical change which
results in a less active or an inactive product.  Knowledge of the nature of this
metabolic product may suggest the introduction of substituents in the parent
drug that would prevent the transformation and thereby enhance its activity.
On the other hand, it is possible that the parent drug itself is inert but produces
:I therapeutic effect incidental to the formation of a highly active metabolic
product. Knowledge of the structure of this derived product may suggest a
synthesis of more effective derivatives.  Again, the toxicity of the drug could
reside in a derived product the formation of which, if its structure be known,
may be blocked by an appropriate modification of the parent drug.
Fundamental studies on the mechanism of drug action attempt to correlate
the effect of a drug on ensymatic activity with its pharmacological activity. The
compound possessing the pharmacological action may be a product derived in
the body from the parent drug.  It is obvious in this case that the studies should
be made not with the parent drug but with the active derived product.
It is unlikely that special ensymes exist in the body for the chemical transfor-
mation of each drug. Rather, it is likely that a drug undergoes chemical change
by becoming involved in biochemical reactions whic,h ordinarily handle normally
occurring substances.  The presence of a particular ensyme system within the
animal is indicated by the transform&on of' the foreign compound.  Knox used
the transformation of quinine to 2-hydroxy quinine by various tissues as an indi-
cator in the isolation in-relatively pure form of the so-called quinine oxidase.
He found this enzyme normally to be involved in the metabolism of nicotin-
amide (1).
The study of drugs fr,om the above points of view has been considerably fa-
cilitated by two recent developm&ts: .I, a scheme whereby simple and sensitive
analytical methods for nitrogenous bases in biological material may readily be
devised; included in thii scheme is a technique for identifying the substance
measured by means of its solubility &aracteristics (2, 3) ; 2. the technique of
counter-current distribution which has been applied to the fractionation and iso-
lation of substances from biological material (4).
' This work was supported by a grant from the Institute for the Study of Analgesic and
Sedative Drugs.
                          29


30            BERNARD B. BRODIE AND JULIUS AXELROD

The aniline analgesics were selected for study because of their relatively simple
chemical structure. The present investigation is concerned with the fate of
tietanilide in the body.  Studies on other drugs will follow.
A recent monograph on acetanilide presents the conflicting views of various

investigators concerning the metabolism of acetanilide (5).  It is generally be-
lieved, however, that acetanilide owes both its therapeutic and its tosc action to
its conversion in the body to p-aminophenol which is then conjugated with sul-
furic or glucuronic acid.

Recent work, reported since the publication of the above monograph, indicated
that in the human, 70-90 per cent of administered acetanilide is excreted in the
urine as conjugated p-aminophenol (6).  Neither free p-aminophenol nor aniline
was found. N-acetyl p-aminophenol and hydroxyl-conjugated N-acetyl p-
aminophenol were found in the blood and plasma, but no free p-aminophenol(7).
The compounds found were identified only on the basis of non-specific chemical
methods without proof that a single substance WM being measured identical with
an authentic compound.  The same studies also showed that the occurrence of
methemoglobin after the administration of acetanilide was not due to the forma-
tion of p-aminophenol (8).

METHODS AND I~~ATERL~L.  Acetanilide and its metabolites were identified and estimated
by the methods described in the previous paper (9).

Methemoglobin was determined by a slight modification of the method of Evelyn and
Malloy (10).  The subjects used for the experiments described below were normal subjects
or patients with various chronic diseases without renal or liver involvement.

EXPERIMENTAL. A single lot of acetanilide was used for the entire study.
This w&9 a commercially available sample which was assayed for purity by the
counter-current distribution technique using a procedure involving 25 plates
(4).  The results indicated that the acetanilide was at least 99.5 per cent pure.
,4bsorption and excretion of acetanilide.  Information was obtained relative
to the absorption .from the gastrointestinal tract and the renal excretion of
acetanilide, and the part that each of the& processes plays in t,he physiological
disposition of the drug after the oral dosage.  Human subjects received 2 grams
of t,he drug daily, in two doses,% hours apart, over a period of G days.  Urine and
stool collections were made during the last 72 hours of administration.  The drug
recovered in the stools in each instance amounted to about 0.1 per cent of the
administered dose, indicating almost complete absorption from the gastrointes-
tinal tract.  Previous experiments had shown that the drug was not destroyed
aftfter incubatioa in stool suspensions for 24 hours at 37oC.  The urinary excre-
tion, in these a,s well as b single dose experiments, account.ed for only 0.1-0.2
per cent of the administered acetanilide; Therefore, almost all the drug under-
went metabolic alteration in the body.    .
Plasma concentration-time curves. The plasma concentrations of acetanilide

and the per cent methemoglobin after the administration of single oral doses of
1 and 2 grams to man, in the post-absorptive state, are shown in table I.  The
results shown here are typical of 15 such experiments.  As a rule, the absorption
was rapid and maximal plasma levels mere reached within 1 to 2 hours.  The


ACETANILIDE METABOLISM               31

,,lasma level fell rapidly, the drug being almost completely metabolized in about
; hours.  The methemoglobin followed a similar curve but with some time-lag.
-&eta&de and its transformation products found in urine.  Information con-
cerning the metabolic products of acetanilide was obtained in the urine of sub-
jects given 1 gram orally.  The urines were secured for the succeeding 24 hours
:,nd examined for the drug and its transformation products.  The urinary excre-
tion of acetSanilide and its transformation products subsequent to this time, was
ll&igible.  About 80 per cent of the drug was accounted for as conjugated X-


                       TABLE I

~`~(~sIIL(I acctanilide and per cent methemoglobin following oral administration of one and tuyo
              gram doees of acetanilide to man

hrs.

0
1
2
4
7

-

snspn D

I

1 gram

    ! Methemo-
Acetnnilide / gl,,bin
      I

T

WQW./L. I par cent
-     1.4
5.6     3.9

2 grams

Acetanilide

mgm./L.

-
17.0
12.0
6.8
1.6

-


_

Methemo-
globin

par cart
0.3
7.2
12.0
13.2
6.0

sosJEcT E

1 gram

A&Glide

mgm./L.

-
9.0
7.2
5.0
1.1

per cent
1.5
4.5
7.7
8.0
4.3




.

2 gmms

Acetanilide

mgm./L.

-
11.0
19.0
11.5
4.2

M;;~de~-

per cent
2.2
5.0
10.0
17.5
13.5

TABLE II

            The metabolic fate of acelanilide in man
Recovery of acetsnilide and its metabolic products from the urine of subjects given
single oral doses of acetanilide.

The urine was collected over a period of 24 hours.  The proportion of the various me-
tabolites is ertxessed in percentage of the amount of acetanilide administered.

ACETANTLIDE       *cETmlllDE        N-ACETW.    co*JucATEo N-ACEM
`WmNIsTEPED                   p4YINOPHENOL     p4MIHOPriEXOL


  g,lW?U          per cent         fier cent        ph cent
  1.0         0.11          3.9          82
  1.0      ,    0.19          3.8           50
  2.0         0.10          3.4      I     78
  2.0         0.10   .        3.2     I     86

ANILINE


jcr cent
0.95
0.05
0.05
0.03

acetyl p-aminophenol,z about 4 per cent as free N-acetyl p-aminophenol, and
traces as aniline.
changed.    Less than 0.2 pe! cent of the parent drug was excreted un-
    The results shown in table II are representative of 10 simiiar experi-
ments. That the conjugated p-&mophenol also J&S, acetylated was surmised
from the absence of free amino groups in plasma or urine other than that due to
the small amount of aniline present.  The conjugated N-acetyl p-aminophenol

z The conjugated N-acetyl p-aminophenol is the total conjugated p-aminophenol less

the N-acetyl p-aminophenol.


32            BERNARD B. BRODIE AND JULIUS AXELROD

has been shown to be esterified at the OH group, partly with sulfuric and partly
with glucuronic acid (7).  Free p-aminophenol was not detected,  An attempt
was made to demonstrate the presence of a substance in urine or plasma capable
of converting hemoglobin to methemoglobin.  Urine or plasma from subjects
receiving acetanilide was added to hemolyzed red cells.  One hour incubation of
t,his solution at 37oC. failed to result in the formation of methemoglobm.

It is to be noted that the above substances were not analyzed merely on the
basis of non-specific chemical reactions but by methods which identified the ma-
terial measured as a single substance identical with the authentic compound (9).

Additional evidence that the apparent p-aminophenol resulting from the hy-
drolysis of its conjugated derivatives in urine was a single substance rather than
a mixture, and the actual isolation and precise identification of this substance
was gained with the aid of Craig's counter-current distribution technique.  The
urine was acidified by the addition of 3 volume of concentrated HCl and heated
in an autoclave at 15 pounds for 1.5 hours. The urine was now adjusted to pH
i by the addition of KzHPO4 and the apparent p-aminophenol extracted with
ether. The apparent p-aminophenol was then returned to 0.1 N HCl. The
material was then subjected to a counter-current distribution involving 8 trans-
fers, according to the method of Craig (4).  The distribution was effected in a
series of separatory funnels, between the immiscible solvent pair: isoamyl alcohol
and pH 5.8 phosphate buffer.  The partition coefficients of the apparent p-am-
inophenol in each separatory funnel was then determined by measuring the con-
centration in each phase.  The partition coefficients were found to be the same,
within analytical error, for the apparent p-aminophenol in each separatory fun-
nel.  It was concluded, therefore, that the material which reacted chemically as
p-aminophenol was not a mixture but a single substance.

The aqueous phases of the middle three separatory funnels were acidified with
HCl.  The total apparent p-arninophenol in each separatory funnel was trans-
ferred to the aqueous phases by shaking.  The three aqueous phases were com-
bined and the pH adjusted to 7.  The apparent p-aminophenol was extracted
into ether and then returned to dilute HCl. , This latter phase was evaporated
to dryness on a water bath.  The residue was taken up in 30 per cent acetic
acid, and benzaldehyde added to form a benzylidene derivative.  After two re-
crystallizations from 30 per cent ethyl alcohol, crystals melting at 179-183oC.
were obtained.  The mixed melting point with the benzylidene derivative of
pure p-aminophenol was unchanged.  This showed that the apparent p-amino-
phenol isolated from urine was identical with the known substance.

Acefanilide and.@ transformation products found in plaamo.  The plasma levels
of acetanilide and its transformation products after the oral administration of 1
gram doses of the drug are shown in table III.  These results are representative
of 13 similar experiments.  It is seen that the acetanilide levels declined rapidly
vhile those of N-acetyl p-ammophenol increased, suggesting that acetanilide
was quickly oxidized to the latter compound.  The plasma levels of acetanilide
and N-acetyl p-aminophenol permitted an estimate of the amounts of these sub-
stances in the body.  The calculation was based on the experimental finding for


                   ACETANILIDE METABOLISM               33

dogs that both compounds are distributed fairly uniformly throughout total
body water. Thus in the casa of subject D, if the acetanilide were distributed
in 70 per cent of the body weight, the amount of administered acetanilide which
remained in the subject would correspond to 28 per cent in 2 hours and 2.5 per
cent in 7 hours. The corresponding amounts for N-acetyl paminophenol in
terms of the administered acetanilide would be 41 per cent in 2 hours and 11 per
cent in 7 hours. A rise in conjugated N-acetyl paminophenol was coincident

                     TABLE III

ptaema acetanili&, N-out&p-aminophenol, conjugated N-acetyl-p-aminophenol and aniline
      after the oral administration of 2 gram of acetanilid.e to man
                                    I

rmx Acttanside w   cwj.
     E&j   AQiIiie Acetaniu?

     ----
hrr.    w-4.   31r.b.   yrr.P.   nlr./L.   mm&.
1     9.3 7.9 2.1 0.06    14.0
2     5.8 9.4 6.6 0.04     9.3
4     2.7 0.2 10.4 0.02     6.6
7     0.5 2.0 7.0 0.01     1.2


                   TABLE IV

--
fW=.fL.   yr.b.
7.0    6.9
7.9     9.7
6.6    12.8
3.0 * 11.5

rYr.lL.
0.09
0.08
0.05
0.02

        Distribution of acetanilide and aniziru in the dog
The distribution of acetanilide and aniline WM examined in dog tissues.  The studies
were made 4 hours after the oral administration of 2.9 grams of acetanilide. The dog
weighed 23 kiloqam~.

            nnuz              -NW-   -TIOHWAlWJW

                            nlrr.llln.           -PLfk=.
Plasma...............................        70              11.4
Whole blood. . . . . . . . . . . . . . . . . . . . . . . . . . .        63              15.0
Kidney.. . . . . . . . . . . . . . . . . . . : . . . . . . . . . .        59              11.2
Heart................................        60              10.3
Muscle . . . . . . . . . . . . . . . . . . . _ . . . . _ . . . . . .        57               11.2
Lung.................................        58               12.1
Liver.................................        73              15.2
Cerebrospinal f&d. . . . . . . ;. . . . . . . . . . .        68               7.3
Brain.. . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . .        60               5.8

with a fall in free N-ace&y1 p-aminophenol as the latter compound is conjugated.
Aniiie levels were low in compa&on with the other substances, suggesting that
only a minor fraction of the acetanilide was dea&tylated.  However, as will be
shown later, this small amount of aniline plays a significant role in the toxicity
of acetanilide. No free p-aminophenol was demonstrated.
Acefanilide and its transformation pro&z& found in tissues.  The distribution
of acetanilide and aniline 4 hours after the oral adminiitration of acetanilide to
a dog, is shown in table IV.  The concentration of acetanilide in most organ


34            BEBNARD B. BRODIE AND JULIUS AXELROD

tissues was about 80 per cent of that in plasma.  The extent to which acetanilide
was bound to the non-diBusible constituents of plasma, presumably plasma al-
bumen, was determined by dialysis against isotonic phosphate buffer of pH 7.4
and at 37oC. for 18 hours.  Visking membranes were utilised for the dialysis
bags.  None of the acetanilide was found to be bound in plasma.  These results
indicated that acetanilide was distributed uniformly throughout most body
fluids with negligible localiaation in cellular tissues.  Even in the cerebrospinal
fluid and the brain the levels were such as to indicate little if any hindrance by the
blood-brain barrier to the passage of the drug.  In the above respects the acet-
anilide behaved like urea.

Aniline levels in various tissues were fairly uniform, although the cerebro-
spinal fluid and brain levels were distinctly lower than those in the other tissues.
Here again, there was little if any localization of the compound in body tissues.
Free p-aminophenol was not demonstrated in any tissue.

Site and rate of the transformation of acetanilide in the body.  The role of the
kidney and the liver in the transformation of acetanilide in the body was studied.
The rate of the disappearance of acetanilide from the blood was compared with
that of bromsulfalein, a compound presumed to be removed chiefly by the liver
(11). Acetanilide and bromsulfalein were administered simultaneously to normal
individuals in 3 experiments by means of a constant intravenous infusion at such
a rate that the concentration of the substances in the peripheral blood remained
unchanged.  Under these conditions, the rate of the transformation of acetani-
lide by the body may be assumed to equal the infusion rate since urinary excre-
tion of acetanilide is negligible.  The concentration of acetanilide in the periph-
eral blood was compared with that in the blood leaving the kidney and the liver.
The blood draining the organs was obtained by the venous catheterization tech-
nique (11).

The concentration of acetanilide in the renal vein blood did not differ signifi-
cantly from that in the peripheral venous blood indicating that little, if any, role
was played by the kidney in the transformation of acetanilide in uivo.  On the
other hand, the concentration of acetaniliae in the hepatic vein blood was found
to be considerably lower than that in the peripheral venous blood, indicating
that considerable amounts of ac&anilide had been transformed by the liver.  If
it is assumed that the drug was removed only by the liver, then the hepatic

blood flow per minute would be X  L
                     X where L is the removal rate per minute
                           1- 9,

of the compound by the liver (equal to the infusion rate), Xi is the peripheral
blood concentration and X? is the concentration in the blood leaving the organ.
The hepatic blood flow estimated from the data for bromsulfalein and acetanilide
were in good agreement.  This is in accord with the belief that the removal of
acetanilide is also limited for the most part to the liver.  The details of this work
will be published subsequently.'

Fate of aniline and N-act@ p-amdnophend in the body.  The important role
of aniline and N-acetyl p-aminophenol in the overall pharmacological action of
acetanilide prompted a study of their fate in the organism.  One hundred mgm.
s Berliner, R. W., and Kennedy, T. W.: To be published.


ACETANlXIDE YETABOLISM              35

of aniline hydrochloride were administered orally to 6 human subjects.  Urine
,,,ss c&&d for a period of 24 hours.  About 80 per cent of the aniline was
found in the urine aa conjugated N-acetyl p-aminophenol.  The absence of free
nmino groups other than that which could be ~CCOU.II~~ for as aniline was taken
aa an indication that the conjugated p-aminophenol was also acetylated.  No
free p-aminophenol was demonstrated. Only about 0.6 per cent of the adminis-
tered aniline WSB excreted unchanged.  It is of interest that in the dog, the con-
jugated paminophenol resulting from the administration of aniline contained a
free amino group.  This fits the ~dl-kn~~n observation that the dog does not
acetylate amino groups.
One gram doses of N-mtyl p-aminophenol were administered fo 6 human sub-
jects. About 85 per cent of the administered compound was fo&d in the urine
a~ total conjugated p-aminophenol.  No free aniline was demonstrated in plasma
OP urine. About 3 per cent of the compound was recovered unchangd  The
remainder could not be accounted for.

The rok of andine in the? fomurtion of methemoglobin.  Both methemoglobin and
aniline were found in the blood of man after the administration of acetanilide.

TABLE V

Correlation of aniline and m&hemoglobin levels in the blood after the adminietratiok of aniline
                  and acelcrnilide to man

Acetanilide .............................
Acetmilide .............................
Aniline hydrochloride. ..................
Aniline hydrochloride. ..................

lr-
2.0
2.0
0.10
0.10

PLMxAhnnlnx
-LavxL

=6-P.
0.07
0.05
0.07
0.05

nuxMSN
-IN


  ww
  13.5
  9.0
  11.5
  10.0

Methemoglobm was also found after the oral administration of aniline.  This
suggested that the methemog,lob& in the blood after the $gestion of acetanilide
might have been forrped as a result of the aniline present.  The evidence for
this was that the amount of methemoglobin is-correlated with the plasma aniline
concentration subsequent to the administration of either acetanilide or aniline
(table V).  A similar relationship between the aniline and methemoglobin levels
held also in the case of the dog.  About 20 times as much acetanilide aa aniline
was required to produce the same amounts of methemoglobm in man.  This
indicated that only a small fra@ion of the acetanilide was deacetylated to form
aniline. Whole blood, incubated for 1 Mur at -37oC. with either drug at a con-
centration of 100 micrograms per ml. of blood showed no' accumulation of met-
hemoglobin.  It is concluded from this that the hemoglobk in the body was not
oxidized to methemoglobin directly by aniline; but by some product derived from
it in the organism.
The nature of the actual methemoglobin-forming agent is not known.  It has
been considered to be p-aminophenol.  This hypothesis is made unlikely since
free p-aminophenol was not demonstrated in the blood after the administration


36            BERNARD B. BRODIE AND JULIUS AXELROD

of either acetanilide or aniline.  In addition, both in Vito and in vitro experiments
have shown that considerable concentrations of free p-aminophenol in blood
were required to promote the formation of a measurable amount of methemoglo-
bin (8).  It is possible that phenylhydroxylamine is the actual methemoglobin
forming agent.  One mgm. per kilo of this compound administered intravenously
to a dog resulted in the conversion of 45 per cent of its hemoglobin to methe-
moglobin.  This is a considerably greater quantity of methemoglobm than would
be expected on the basis of a stoichiometric reaction between `phenylhydroxyl-
amine and hemoglobin.  This suggests that phenylhydroxylamine is involved in
a cyclic reaction in which the oxidizing compound is being reformed.  Concern-
ing the fate of phenylhydroxylamine in the body, a considerable fraction of the
administered compound rearranges in the organism to p-aminophenol which is
then excreted in the conjugated form.

TABLE VI

A comparison of plasma N-ace&l p-aminophenol levels ajter oral administration of equima-
        lecular doses of N-a&g1 p-aminopbnol and acetanilide
The dose of N-acetyl p-aminophenol was 1 gram, and that of scetanilide was 0.9 gram.

2.9          1.1          5.8          3.5
8.2          3.1         10.9          4.1
4.6          6.5          7.5          4.8
2.6          3.0          2.9         3.9
0           1.0          0           2.7

The characteristic, toxic symptoms of acetanilide overdosage may be largely
explained in terms of the anemic anoxia reklting from the formation of methe-
moglobii, and anemia due to the destruction of red cells (12).  Aniline poisoning
also results in methemoglobin formation and the destruction of red cells (12).  It
is probable that the overall toxicity of acetanilide is derived mainly from the
small amount of aniline produced in the body.

The role of N-acetyl p-aminophenol in the analgesic action of acetanilide.  N-
acetyl p-aminophenol, which is found in both plasma and urine after the admin-
istration of acetanilide, appears to be the ilrst step in the major route of the me-
tabolism of the drug. The high concentration of this metabolite in the plasma
prompted an appraisal of its analgesic effect. Studies conducted on human
subjects, utilizing the Wolff-Hardy technique, showed N-acetyl p-aminophenol
to be, dose for dose, about equal in analgesic activity to acetanilide (13).  Plasma
levels of N-acetyl p-aminophenol achieved after the administration of equimo-
lecular doses of acetanilide and N-acetyl p-aminophenol were of the same order
of magnitude, but those obtained after acetanilide persisted longer (table VI).


ACETAh7LIDE METABOLISM              37

llowever, the peak levels of N-acetyl p-aminophenol, when this drug itself was
given, were higher and were reached more rapidly, as is to be expected.  The
results are compatible with the assumption that acetanilide exerted its action
mainly through N-aoetyl;b-aminophenol.  Further studies are planned to ascer-
tain whether acetanilide has any analgesic activity per ae or whether its activity
is predicated solely upon its conversion to N-acetyl p-aminophenol.  The lat-
ter compound, administered orally, WAS not attended by the formation of methe-
moglobin nor, at least in vitro, did it destroy red cells.  It is possible, therefore,
that it may have distinct advantages over acetanilide as an analgesic, and it may
~vell serve as a starting point for the synthesis of more effective agents.

Preliminary work in this laboratory has shown that acetophenetidin (p-ethoxy-
acetanilide), a webknown analgesic, is also transformed in the body to N-acetyl
p-aminophenol.
DISCUSSION. The following scheme for, the route of metabolism of acetamhde
in the human is suggested by the observations described previously.
HyCOCHs      HYoCH3      HYoCHs

Acetamhde \,

R = Glucuronic
   Acid

Aniline        Phenylhydroxylamine

The main route of metabolism appears to involve two serial steps.  The first
of these is oxidation with the replace&$ of .the hydrogen atom in the para posi-
tion of the benzene nucleus by a hydroxy group to form N-acetyl p-aminophenol,
an active analgesic.  The second step is conjugation of this compound at the
hydroxyl group with sulfuric or glucuronic acid.  A minor channel of metabolism
also involves several serial steps.  Part of the acetanilide deacetylates to yield
aniline. This compound then adds oxygen to the benzene nucleus to form p-ami-
nophenol which is rapidlj; conjugated at both the amino and the hydroxy groups.
Aniline is also the precursor of the substance, probably phenylhydroxylamine
which is responsible for the formation of methemoglobin.

The route of metabolism of acetanilide in the organism differs from that ex-
pected on the basis of studies with animal tissues in vitro.  It has been demon-
strated that acetanilide is rapidly hydrolyzed to aniline when it is incubated with
rat liver and kidney tissue (14). Yet the intact organism hydrolyzes only a


38            BEBNABD B. BBODIE AND JULIUS AXELROD

minor fraction of the drug to aniline, while the major fraction is oxidized to
N-acetyl p-aminophenol.  Results (unpublished) with other compounds make
it apparent that studies in v&o concerning the fate of a drug may describe a
pathway of metabolism which is of minor importance only, in the intact organ-
ism.  Many factors come into play in the intact animal which may be eliminated
in the simpler experimental conditions in z&o.  This is not meant to imply that
work with isolated tissues is not important.  Such work can do much to clarify
reactions which first have been shown to occur significantly in the whole animal.

SUMMARY

The route of metabolism of acetanibde in man was shown to be as follows: a
minor fraction of the drug deacetylates to form aniline; this compound was shown
to be the precursor of the substance which oxidizes hemoglobin to methemoglo-
bin; the major fraction of the drug is oxidized to N-acetyl p-aminophenol; this
compound is excreted in a conjugated form. `The analgesic action of acetanilide
is exerted mainly through N-acetyl p-aminophenol which is an active analgesic.
The oxidation of acetanilide occurs mainly in the liver.

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3. BBODIE, B. B., UDENFIUEND, S., AND BAEE, J. E.: J. Biol. Chem., 168: 299, 1947.
4. CEAIQ, L. C.: J. Biol. Chem., 166: 619,1Q44.
5. GEOSS, M.: Acetanilide, Chapter 3, Hillhouee Press, New Haven, 1946.
6. GBEENBEBQ, L. A., AND LESTEB, D.: THIS JOIJENAL, 88: 87,1Q46.
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