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Journalof AnalyticalToxicology,Vol. 25, May/June2001
Severe Intoxication with the Veterinary Tranquilizer
Xylazine in Humans
U. Hoffmann 1,*, C.M. Meister 2, K. Golle2, and M.
Zschiesche 1
1Departrnentof Pharmacology, Ernst-Moritz-Arndt University Greifswald, Friedrich-Loeffler-Str.23 d, D-17489 Greifswald, Germany
and 2Departmentof 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 analysesof xylazine were done by thin-layer
chromatography, gas chromatography-massspectrometry, 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 poisoningand present a review of
xyl;~zine toxicity in humans.
Introduction
Xylazine hydrochloride is the generic name for [2-(2.6dimethylphenylamino)-4-H-5.6-dihydro- 1.3]thiazine hydrochloride, which is extensively used in veterinary practice either
alone as a sedative or in combination with other drugs for sedation, 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 containing 500 mg per vial. Chemical structure and pharmacological 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 respiratory depression. Plasma levels of norepinephrine, epinephrine, insulin, and non-esterified fatty acids are decreased, and
9Author tOwhom correspondenceshould be addressed: Dr. Ulrich Hoffmann, Depanrnentof
Pharmacology,Ernst-Moritz-AmdtUniversily, 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 frequently associated with marked hypotension, and therefore its
use is restricted to veterinary medicine. In humans, toxicity consists 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 consequence 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 charcoal, and cathartics. He was placed on a ventilator and received
intensive therapy including intravenous fluid therapy and urinary, 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
Xylazlne
Figure1. Structuresof xylazineand clonidine.
Reproduction(photocopying)of editorialcontentof thisjournalis prohibitedwithoutpublisher'spermission.
H
CI
Clonldlne
245
Journal of Analytical Toxicology, Vol. 25, May/June 2001
the course of the two days, to 50 bpm and 100/40mm Hg, respectively, 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 temperature 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 extubated 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.
Analytical Methods
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).
Methods
Gas chromatography-massspectrometry (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 selectivedetector. The chro2 0 . O0 T
matographic columns (HP 1) were 15-m x 0.25mm i.d. capillary columns with 0.25-1Jm film
thickness. The oven temperature was programmed from 100 to 300~ at 20~
The
injector temperature was 270~ the transfer line
was held at 300~ Helium was used as carrier gas
I,' "
'I''
ata flowrate of 2 mL/min. The injection was made
i|
i
in the splitless mode with 1 min hold time, and
-3 9
e . O0
2.00
'
4'.aa
6'.oe
~e~ee
*2:ee
8~.e8
the
mass range scanned was 50-550 ainu.
T I ~ (rain)
Xylazine was detected in samples and compared
Figure2. Liquid chromatogram of an extract from plasma sample after xylazine intoxication. Xylazine,
with reference spectra obtained from commercial
3.21 min; midazolam, 10.95 min.
xylazine solution. Quantitation was carried out
using xylazine standards in urine and gastric fluid.
Table I. Cases of Xylazine Intoxications in Humans
Thin-layer chromatography (TLC). Xylazine
was also analyzed by thin-layer chromatography
Volume/dose
Concentration
(TLC) using Toxi-Lab| drug detection system
Gender* Age
Usage + Application* (mL) resp. (mg)
(mg/t)
References
(Analytical Systems, Laguna Hills, CA).The substance
was isolatedfrom urine and gastric fluid in
M
34
S
i.m.
10
1000
Carruthers et al.
Toxi-Tubes
A by liquid-liquid extraction at pH 9.
1979 (3)
After solvent evaporation, the chromatogram was
F
20
S
oral
4
400
plasma: neg. Gallanosa et al.
developed and the spots detected by sequentially
urine: pos.
1981 (4)
F
39
A
i.m.
--Lewis et al.
dipping in sulfuric acid, water, viewing under UVserum: 0.03
urine: 1.7
1983 (5)
light, and dipping in Dragendorffs reagent. The
M
36
S
i.v.
--serum: 0.2
Poklis et al.
xylazine spot was identifiedby comparing with the
urine: 7.0
1985 (6)
spot of the parent substance.
F
29
--
i.m.
I
40
(0.73 mg/kg)
F
37
S
i.m.
24
F
M
29
19
-S
i.v.
s.c.
-2
2400
(22 mglkg)
-200
F
23
H
--
--
M
33
H
M
27
S
i.m.
75
m
--
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
1500
serum: 4.6 mg/L
this work
(13 mg/kg)
urine: 194 mg/L
2000
stomach: 446 mgiL
--
* M: Male, F: Female.
* A: accidental intoxication; S: suicide attempt; H: homicide.
* i.m.: intramuscular; s.c.: subcutaneous; i.v.: intravenous.
246
Spoerke et al.
1986 (7)
High-performance liquid chromatography
(HPLC).The HPLCfrom Merck-Hitachiconsisted
of an L-2000 pump, an AS-2000autosampler, 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 flowrate 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 evaluatedby the
internal standard method using peak-height
ratios for calculation. Relative retention time and
Journal of Analytical Toxicology, Vol. 25, May/June 2001
5000
4000
ff
8
3000
o
o
~9
2000
m
>.
X
1000
T
r
2
4
6
8
10
Time (hours after ingestion)
12
curve.
Figure 3. Plot of xylazine plasma concentrations versus time in humans after intoxication. Plasma halflife t,h = 4.9 h after i.m. adminstration of about 1.5 g xylazine.
i
plasma
xylazlne
cholesterol
7.03
11.85
UV spectrum were used for qualitative identification.
Sample extraction. Plasma samples were collected every 2 h for a period of 12 h. One milliliter
of plasma was spiked with 20 pL midazolam (0.1
rag/L), and 1 mL borate buffer (pH 9.5) was added.
The sample was vortex mixed and extracted twice
with 3 mL ether. After centrifugation, the organic
phases were combined, dried under a gentle
stream of nitrogen and redissolved in 3 ml
hexane/ethanol (10:4, v/v). After the addition of
200 lJL of water, the upper hexane phase was discarded, the rest evaported completely under
nitrogen at 80~ and the extract resolved in 140
IJL mobile phase for injection into the LC. When
necessary, plasma samples were diluted to yield
concentrations within the limits of the calibration
In the case of GC-MS analysis, the urine and
gastric juice extracts were resolved in 50 IJL
methanol, and 1 IJL was injected into the GC.
A
Results
Time (mln)
B
TIC:M-037-T1,D
ooo(x)oo
stomach
6.71 IIdocaine
7 , 1 4 xylazlne
7oc<)cr
notxxmo
f,t x ~
40ooooo
3 o ~
2000000
IO~OOO
~o" ' ' ~..6o"
" ;~.~
" " ~.6o" " ' ~ . ~
" ' ++.~"
/+.,~
" " ~'.~
" " ~'.~d " " / + . ~
" ' t+.,~ ' ' ~.6d
' "/+.~
"
Tlme (mln)
9.+.oo~176176
C
la~or
urine
CH~
205
1r
=M
+
c
,a
+- .........i..I, ,1, ![ ~II
~
~J
~-
,,.l .-
d
'
] :!.
:1:. II1-
.,.,,,
.....
!~,
[
m/z
Figure 4. Total ion chromatogram of xylazine in plasma (A) and gastric fluid (B) and mass spectrum
o f xylazine p e a k in urine (C).
The HPLC system described was suitable for the
analysis of xylazine in serum. The recovery was
75%. The linear relationship calculated from the
peak-height ratio and the xylazine concentration in
plasma up to I mg/L was R = -0.16 + 0.0069x (r >
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 precision 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 calculated 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
Journal of Analytical Toxicology, Vol. 25, May/June 2001
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 colorless; 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 animals 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-receptors 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, serotonergic, dopaminergic, r
histaminergic, or opiate
mechanisms (12).
Xylazine causes profound respiratory depression, and the present 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 maintaining respiratory function and blood pressure and was symptomatic. Based on the information from the literature, the
e
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 administered dose being eliminated in the urine as unchanged substance (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 retention 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 metabolites 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.
r
e
A
B
k
1
2 3
Stage 1
4
1
2 3
Stage 2
4
1
2 3
Stage 3
4
1
2 3
Stage 4
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
Journal of AnalyticalToxicology,Vol. 25, May/June2001
Various antagonists have been used as a therapy. Tolazoline
may be administered in unresponsive bradycardia and hypotension 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 antagonize 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 bradycardia and hypotension in humans (4). Naloxone was adminstered without effect (7,8).
Conclusions
Xylazine is a hazardous drug in humans. The plasma concentration 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 pharmacological 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, phenothiazines, 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 pharmacology 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