Severe Intoxication with the Veterinary Tranquilizer Xylazine in ...

Journal of Analytical Toxicology, Vol. 25, May/June 2001
Severe Intoxication with the Veterinary Tranquilizer
Xylazine in Humans
U. Hoffmann 1,*, C.M. Meister 2, K. Golle 2, and M. Zschiesche 1
1Departrnent of Pharmacology, Ernst-Moritz-Arndt University Greifswald, Friedrich-Loeffler-Str. 23 d, D-17489 Greifswald, Germany
and 2Department of Anaesthesiology, Central Hospital, Wollweber Str. 21, D- 17109 Demmin, Germany
Abstract[
Xylazine (Rompun | Proxylaz | is a veterinary tranquilizing agent.
A case of self-injection of 1.5 g xylazine by a 27-year-old farmer is
reported. He subsequently became comatose, hypotensive,
bradycardic, and mildly glycemlc. An intensive supportive therapy
including intubation and ventilation was required. The patient
made a full recovery over the next 30 h. The largest concentrations
measured were 4.6 mg/L in plasma, 446 mg/L in gastric fluid, and
194 mg/L in urine. The calculated plasma half-life was 4.9 h.
Kinetic data correlated with clinical symptoms. Qualitative and
quantitative analyses of xylazine were done by thin-layer
chromatography, gas chromatography-mass spectrometry, and
high-performance liquid chromatography. These methods allow the
detection "of small amounts substance in stomach, plasma, and
urine. Liquid-liquid extraction was used for the isolation of drug.
The sensitvity is high, and with these methods, a rapid analysis is
possible. Xylazine intoxications in humans are rare. We describe
the management of acute poisoning and present a review of
xyl;~zine toxicity in humans.
Introduction
Xylazine hydrochloride is the generic name for [2-(2.6-
dimethylphenylamino)-4-H-5.6-dihydro- 1.3]thiazine hydro-
chloride, which is extensively used in veterinary practice either
alone as a sedative or in combination with other drugs for seda-
tion, analgesia, or general anesthesia. It is marketed under the
trade names Rompun (Bayer) and Proxylaz (Prodivet/Atarost)
and is available in 2, 5, and 10% solutions or as dry product con-
taining 500 mg per vial. Chemical structure and pharmacolog-
ical properties are similar to the phenothiazines and the
antisympathonic agent clonidin (Figure 1). Xylazine acts by
stimulat~ofi of r in the central and peripheral nervous
system. CNg-mediated actions include strong sedation and res-
piratory depression. Plasma levels of norepinephrine, epin-
ephrine, insulin, and non-esterified fatty acids are decreased, and
9 Author tO whom correspondence should be addressed: Dr. Ulrich Hoffmann, Depanrnent of
Pharmacology, Ernst-Moritz-Amdt Universily, F.-L~effler-Str. 23 d, D- 17487 Greifswald, Germany.
E-mail: jaki@rnaihuni-gceil'swald.de.
glucose is increased. The therapeutic index is relatively small (1),
and two- to threefold overdose can lead to collapse or death of the
animal due to circulatory and respiratory depression (2).
Xylazine has also been investigated in humans, but was fre-
quently associated with marked hypotension, and therefore its
use is restricted to veterinary medicine. In humans, toxicity con-
sists of fainting, bradycardia, hypotension, hyperglycemia,
apnoe, and coma (3-9). Effects of xylazine are discussed by
Mittleman et al. (9) and Fyffe (10).
We present a case of severe xylazine intoxication with suicidal
intention and report on some laboratory and pharmacokinetic
parameters and the clinical management of poisoning.
Case History
The patient, a 27-year-old farmer, attempted to commit suicide
by self-administration of about 75 mL 2% aqueous solution
xylazine (Proxylaz/Atarost) by intramuscular injection as a con-
sequence of a conflict situation in his family. He was found to be
comatose with narrow pupils and no response to light and pain
stimuli. His initial heart rate was 88 bpm; blood pressure was
180/100 mm Hg. Two hours after ingestion, he was transported
to the Intensive Care Unit of the hospital. After endotracheal
intubation, the patient received gastric lavage, activated char-
coal, and cathartics. He was placed on a ventilator and received
intensive therapy including intravenous fluid therapy and uri-
nary, gastric, and central venous catheters.
The patient received 20 mg etomidate i.v., 200 mg propofol i.v.,
0.25 mg orciprenaline i.v., 10 mg metoclopramide i.v., and 50 mg
ranitidine i.v. The heart rate and the blood pressure decreased in
H H CI
Xylazlne Clonldlne
Figure 1. Structures of xylazine and clonidine.
Reproduction (photocopying) of editorial content of this journal is prohibited without publisher's permission. 245

the course of the two days, to 50 bpm and 100/40 mm Hg, respec-
tively, recovering later gradually. There were hypotensive
episodes that responded to intravenous fluid infusion. After
admission, plasma glucose was slightly increased, 9.8 mmol/L,
but subsequent glucose estimations were normal. The patient
had increased bronchial secretion and decreased body tempera-
ture of 35.6~ The electrocardiogram showed no abnormalities,
and no evidence of myocardial damage was observed. His status
gradually improved, and he exhibited episodes of spontaneous
movements. The patient regained consciousness and was extu-
bated 20 h after admission. He was discharged four days later and
referred to an ambulatory psychiatric attendance.
Blood, urine, and gastric secretion were taken immediately
after admission to the hospital for laboratory investigations.
20. O0 T
-3 9
I,' " 'I''
e. O0 2.00 ' 4'.aa 6'.oe
TI~ (rain)
i|
8~.e8
i
~e~ee *2:ee
Figure 2. Liquid chromatogram of an extract from plasma sample after xylazine intoxication. Xylazine,
3.21 min; midazolam, 10.95 min.
Table I. Cases of Xylazine Intoxications in Humans
Volume/dose Concentration
Gender* Age Usage + Application* (mL) resp. (mg) (mg/t) References
M 34 S i.m. 10 1000
F 20 S oral 4 400
F 39 A i.m. -- --
M 36 S i.v. -- --
F 29 -- i.m. I 40
(0.73 mg/kg)
F 37 S i.m. 24 2400
(22 mglkg)
F 29 -- i.v. -- --
M 19 S s.c. 2 200
F 23 H -- -- --
M 33 H
M 27 S i.m. 75 1500
(13 mg/kg)
* M: Male, F: Female.
* A: accidental intoxication; S: suicide attempt; H: homicide.
* i.m.: intramuscular; s.c.: subcutaneous; i.v.: intravenous.
246
plasma: neg.
urine: pos.
serum: 0.03
urine: 1.7
serum: 0.2
urine: 7.0
m
Analytical Methods
Journal of Analytical Toxicology, Vol. 25, May/June 2001
Materials
All chemicals were of analytical reagent grade9 Xylazine
hydrochloride reference standard was generously supplied by
Prodivet Pharmaceuticals (Eynatten, Belgium). The internal
standard, midazolam, was obtained from Hoffmann-La Roche
(Basel, Switzerland).
Carruthers et al.
1979 (3)
Gallanosa et al.
1981 (4)
Lewis et al.
1983 (5)
Poklis et al.
1985 (6)
Spoerke et al.
1986 (7)
-- Samanata et al.
1990 (8)
liver: 42 mglkg Mittleman et al.
kidney: 28 mg/kg 1997 (9)
brain: 19 mglkg
liver: 0.26 mglkg
kidney: 0.15 mglkg
brain: 0.16 mglkg
serum: 4.6 mg/L this work
urine: 194 mg/L 2000
stomach: 446 mgiL
Methods
Gas chromatography-mass spectrometry (GC--MS). Xylazine
was initially detected during drug screening in gastric fluid,
serum, and urine. The screening was performed on an HP 5890
GC with a 5972 mass selective detector. The chro-
matographic columns (HP 1) were 15-m x 0.25-
mm i.d. capillary columns with 0.25-1Jm film
thickness. The oven temperature was pro-
grammed from 100 to 300~ at 20~ The
injector temperature was 270~ the transfer line
was held at 300~ Helium was used as carrier gas
ata flow rate of 2 mL/min. The injection was made
in the splitless mode with 1 min hold time, and
the mass range scanned was 50-550 ainu.
Xylazine was detected in samples and compared
with reference spectra obtained from commercial
xylazine solution. Quantitation was carried out
using xylazine standards in urine and gastric fluid.
Thin-layer chromatography (TLC). Xylazine
was also analyzed by thin-layer chromatography
(TLC) using Toxi-Lab | drug detection system
(Analytical Systems, Laguna Hills, CA). The substance
was isolated from urine and gastric fluid in
Toxi-Tubes A by liquid-liquid extraction at pH 9.
After solvent evaporation, the chromatogram was
developed and the spots detected by sequentially
dipping in sulfuric acid, water, viewing under UVlight,
and dipping in Dragendorffs reagent. The
xylazine spot was identified by comparing with the
spot of the parent substance.
High-performance liquid chromatography
(HPLC). The HPLC from Merck-Hitachi consisted
of an L-2000 pump, an AS-2000 autosampler, and
an L-4500 diode-array detector. The separation
was performed on a LiChroCart 125-4, RP select B
column at 25~ The eluent was monitored at 220
nm. The mobile phase, consisting of triethylammonium
phosphate (0.02M, pH 3)/acetonitrile
(77:23), was pumped at a flow rate of 1 mL/min.
Analyses. A 1-mg/mL xylazine stock solution
was prepared in methanol. Calibration curves
were constructed by means of linear regression
using the peak-height ratio between xylazine and
midazolam as internal standard from spiked
serum blanks of the concentration from 25 to 800
ng/mL. The patient samples were evaluated by the
internal standard method using peak-height
ratios for calculation. Relative retention time and

Journal of Analytical Toxicology, Vol. 25, May/June 2001
ff
5000
4000
8 3000
o
o
~ 9 2000
m >.
X
1000
T r
2 4 6 8 10 12
Time (hours after ingestion)
Figure 3. Plot of xylazine plasma concentrations versus time in humans after intoxication. Plasma half-
life t, h = 4.9 h after i.m. adminstration of about 1.5 g xylazine.
c
,a
ooo(x)oo
7oc
0.99). The relative error of the calibration was
between -9.5 and 1 9%. The quantitation limit
(LOQ) was 25 ng/mL, the detection limit (LOD)
was 5 ng/mL using plasma samples larger than 1
mL. Statistical evaluation of accuracy and preci-
sion were not performed. Figure 2 shows a typical
chromatogram.
Xylazine was detected in all samples analyzed.
The toxicological results are presented in Table I.
The plot of plasma xylazine concentration versus
time after i.m. application is shown in Figure 3.
The level of drug concentration declined over 12 h.
Further plasma samples were not taken. These data
were well fitted by a one-compartment model with
an exponential decline. The plasma half-life calcu-
lated was t]/2= 4.9 h.
Gastric fluid, plasma, and urine samples were
also analyzed by GC-MS (Figure 4).
Xylazine was found in all samples, even in the
stomach contents. The retention time and mass
spectra were matched with a standard and found to
be identical. The parent ion of xylazine is registered
at m/z 220. Further ingredients of the original
xylazine solution as 4-hydroxy benzoic acid
methyl- and -propylester were also found in urine.
Xylazine metabolites were not identified.
The characteristics of xylazine detected by TLC
247

are shown in Figure 5. The Rf value amount was 0.75. The color
results were as follows: stage I was rose-brown; stage 2 was col-
orless; stage 3 was faint blue; and stage 4 was brown.
Discussion
Xylazine is extensively used in veterinary practice as a sedative
with analgesic and muscle relaxant properties. The dose in ani-
mals is 0.5-5.0 mg/kg i.v. or i.m. and produces bradycardia and
respiratory depression. This usually begins within a few minutes
and lasts up to 4 h (11).
Xylazine produces its effects by stimulation of central (z2-recep-
tors and depression of norepinephrine release from peripheral
nerve terminals. As evidenced by the paradoxical blood pressure
changes, xylazine possess also peripheral action causing an initial
blood pressure increase. The predominating central oe-properties
produce inhibitory effects by interneural blockade resulting in
long-lasting hypotension, bradycardia, and decreased cardiac
output. Xylazine actions may also involve cholinergic, seroton-
ergic, dopaminergic, r histaminergic, or opiate
mechanisms (12).
Xylazine causes profound respiratory depression, and the pre-
sent patient, as well as earlier ones (3,4,7,8), required assisted
ventilation. The hypotension could be managed by fluid infusion
with Sterofundin and Ringer-Lactat solution under the control of
electrolytes. Further toxicological signs are sedation, coma,
bradycardia, and hyperglycemia. Arrhythmias were not seen. The
thermoregulation was disturbed, and body temperature was
decreased in the initial phase. Treatment was directed to main-
taining respiratory function and blood pressure and was symp-
tomatic. Based on the information from the literature, the
e
e
k
1 2 3 4
Stage 1
r
1 2 3 4
Stage 2
Journal of Analytical Toxicology, Vol. 25, May/June 2001
dosages known to produce toxic effects in humans vary from 40
mg up to 2000 mg (Table I).
Xylazine is metabolized in the liver and is excreted to 70% renal
and to 30% biliary in dogs (2). Studies showed that the drug is
metabolized to nearly 20 metabolites, with only 8% of the admin-
istered dose being eliminated in the urine as unchanged sub-
stance (13). The major metabolite is 2,6-dimethylaniline. In spite
of the high dose administered, we did not find any metabolites in
the urine of the patient. The xylazine metabolites, especially the
aniline derivative, are very volatile substances with short reten-
tion times. Our solvent delay time after injection is 3 rain.
Therefore, the metabolites might elute together with the solvent
before the mass spectrometer was turned on. Because the urine
sample was collected very early, the concentration of the metabo-
lites was too small.
Pharmacokinetic studies in animals found an exponential
decline of xylazine concentration after i.m. dosage. The data were
described by an open one-compartment model with a transient
absorption phase followed by an elimination phase. Half-life of
absorption was short (3--6 rain) during the elimination half-life
varied between 30 and 60 min depending on the species (14).
We measured plasma concentrations as a function of time and
found that the half-life calculated is much larger than in animals
if the data were fitted by a first order kinetic model. However,
other also models correlate with the experimental data, so an
explanation is difficult. Nevertheless, the pharmacokinetic result
obtained in the present case is in good agreement with clinical
symptoms.
Although the substance was self-administered by i.m. injection,
a substantial amount was found in gastric fluid, supporting the
fact that alkaloids are excreted in the stomach, and a gastric
lavage is therefore important.
1 2 3 4 1 2 3 4
Stage 3 Stage 4
Figure 5. Thin-layer chromatogram of xylazine was dipped into four reagents sequentially. Lane 1, substances for comparison; lane 2, urine; lane 3, gastric fluid; and
lane 4, 100 lag xylazine. A, lidocaine and B, xylazine.
248
A
B

Journal of Analytical Toxicology, Vol. 25, May/June 2001
Various antagonists have been used as a therapy. Tolazoline
may be administered in unresponsive bradycardia and hypoten-
sion in doses of 10 mg i.v. over an hour up to a maximum of 40
mg (7). On the other hand, tolazoline has been associated with
hypertension, arrhythmias, and tachycardia and should be
reserved for cases unresponsive to other interventions.
Yohimbine, an other c~2-antagonist, has been shown to antago-
nize the sedative effects of xylazine in humans in doses up to
0.125 mg/kg. It can be used as i.m. injection, which is effective
after 15-20 rain, or i.v. injection, after which the effects begin in
1-2 rain (15). Atropine has been used and may reverse brady-
cardia and hypotension in humans (4). Naloxone was admin-
stered without effect (7,8).
Conclusions
Xylazine is a hazardous drug in humans. The plasma concen-
tration in our case is consistent with a fatal overdose and causes
coma, respiratory depression, and hypotension. Compared with
other human poisonings the clinical findings were similiar and
because of the severity of intoxication more pronounced.
Intensive supportive therapy is usually necessary.
For the detection of xylazine in body fluids both a GC-MS
system and an LC method are suitable. TLC is also a convenient
and quick screening method for the detection of xylazine. This
finding confirmed the results of GC-MS in screening for the
drug.
The substance can be isolated by liquid-liquid extraction from
samples with satisfying cleanliness. The drug is excreted largely
by the kidneys.
We recommend the need for an awareness of the pharmacolog-
ical effects of xylazine in humans, especially because of its
widespread use in veterinary medicine.
Acknowledgment
We are grateful to Anja Moll and Gitta Schumacher for skillful
technical assistance in the analytical procedures.
References
1. Hagers Handbook, part 9, 5th ed., F. von Bruchhausen, G.
Dannhardt, S. Ebel, A.W. Frahm, E. Hackenthal, and U. Holzgrebe,
Eds. Springer Verlag Berlin, Germany, 1993, pp 1215-1216.
2. E. Rector, K. Otto, M. Kietzmann, I. Nolte and W. Lehmacher.
Pharmacokinetics and effects of xylazine (Rompun | in dogs. BerL
M~nch. ?ier~rztl. Wschr. 109:18-22 (1996).
3. S.G. Carruthers, M. Nelson, H.R. Wexler, and C.R. Stiller. Xylazine
hydrochloridine (Rompun | overdose in man. Clin. Toxicol. 15:
281-285 (1979).
4. A.G. Gallanosa, D.A. Spyker, J.R. Shipe, and D.L. Morris. Human
xylazine overdose: a comparative review with clonidine, phenoth-
iazines, and tricyclic antidepressants. Clin. ToxicoL 18:663-678
(1981 ).
5. S. Lewis and C.L.P. O'Calaghan. Clinical curio: self medication with
xylazine. Br. Meal. J. 287:1369 (1983)
6. A. Poklis, M.A. Mackell, and M.E.S. Case. Xylazine in human tissues
and fluids in a case of fatal drug abuse. J. AnaL ToxicoL 9:234-236
(1985).
7. D.G. Spoerke, A.H. Hall, M.J. Grimes, B.N. Honea, and B.H.
Rumack. Human overdose with veterinary tranquilizer xylazine.
Am. ]. Emerg. Med. 4:222-224 (1986).
8. A. Samanta, C. Roffe, and K.L. Woods. Accidental self administration
of xylazine in a veterinary nurse. Postgrad. Med. J. 66:244-245
(1990).
9. R.E. Mittleman, W.L. Hearn, and G.W. Hime. Xylazine toxicity--
literature review and report of two cases. J. Forensic $cL 43:400-402
(1998).
10. J.J. Fyffe. Effects of xylazine on humans: a review. Aust. Vet. J. 71:
294-295 (1994).
11. S.A. Greene and J.C. Thurmon. Xylazine--a review of its pharma-
cology and use in veterinary medicine. J. Vet. Pharmacol. Ther. 11:
295-313 (1988)
12. J.V. Kitzman, N.H. Booth, and R.C. Hatch. Antagonism of xylazine
sedation by 4-aminopyridine and yohimbine in cattle. Am. J. Vet.
Res. 43:2165-2169 (1982).
13. A.E. Mutlib, Y.C. Chui, L.M. Young, and F.S. Abbott. Characterisation
of metabolites of xylazine produced in vivo and in vitro by
LC/MS/MS and by GC/MS. Drug Metab. Dispos. 20:840-848
(1992).
14. R. Garcia-Villar, RL. Toutain, M. Alvinerie, and Y. Ruckebusch. The
pharmacokinetics of xylazine: an interspecific study. J. Vet.
PharmacoL Ther. 4:87-92 (1981).
15. C. Macintosh. Potential antidote for Rompun | (xylazine) in humans.
NZMed.J. 98:714-715 (1985).
Manuscript received July 25, 2000;
revision received October 27, 2000.
249