Amoxapine in Human Overdose

Journal of Analytical Toxicology, Vol. 8, May/June 1984

Amoxapine in Human Overdose J.J. Tasset and A.J. Pesce

Toxicology Laboratory, Department of Pathology and Laboratory Medicine University Hospital, University of Cincinnati 234 Goodman Street, Cincinnati, Ohio 45267

gested Ioxapine, which is converted to amoxapine, and the fifth had taken both amoxapine and loxapine. Abstract Amoxaplne, a trlcyclic antidepressant, is metabolized to 8-hydroxyamoxapine and 7.hydroxyamoxaplne. There are few reports on the metabolism of this drug and correlation of clinical symptoms in overdose patients. Five such patients admitted to the Emergency Unit of the University of Cincinnati Hospital were studied. Clinically, all had seizures and evidence of altered cardiac function. The amounts of the parent drug and the 7- and 8-hydroxy metabolltea were measured and, in all cases, the parent and 8-hydroxy metabollte were present in both urine and serum, in contrast, the 7-hydroxysmoxaplne was found in trace amounts in the serum of only two patients, but in the urine of all the patients observed. These observations were confirmed by gas chromatographic/mass spectroscopic analysis. The pattern of metabolism was analogous to that found in patients on maintenance doses of the drug. In two overdose patients, it was possible to monitor the levels as a function of time. The elimination curve of parent and metabollte was first order with a half-life of 8.5 to 15.0 and 48 hr, respectively.

Introduction

Amoxapine [Asendin | 2-chloro-I I-(1-piperazinyl) dibenz [b,f] [1,4] oxazepine] is a dibenzoxazepine class of antidepressant introduced by Lederle Laboratories in 1980 (Figure 1). It is metabolized to 8-hydroxyamoxapine and 7-hydroxyamoxapine, both of which are psychoactive and have serum half-lives of 30 and 6.5 hr, respectively (1). In general, 8-hydroxyamoxapine is the major metabolite observed. A therapeutic daily dose is 200 to 300 mg (2). A 200 to 400 ng/mL serum level of amoxapine plus 8-hydroxyamoxapine is associated with patient response (3). Adverse effects in overdose may include seizure (4) and cardiotoxicity (5). it is important to analyze for both parent and metabotite, since the ~atter is the dominant form of the drug present in the patient, Five overdose patients were admitted to this institution's Emergency Department, and these cases offered the opportunity to study the effects of high levels of amoxapine on cardiac function and observe the metabolism of the drug. Three of the patients had taken amoxapine while another in-

124

Materials and Methods Reagents Pure standards of amoxapine, 8-hydroxyamoxapine, 7-hydroxyamoxapine, and 8-methoxyloxapine were obtained from Lederle Laboratories. The SKF 525A was obtained from Smith Kline and French Laboratories. All reagents were of analytical grade and were purchased from Fischer Scientific. Qualitative Analytical Procedures Gas chromatography (GC). Qualitative screening was performed using a Hewlett Packard 5830A gas chromatograph with a flame ionization detector (GC/FID), and a 1.83 m • mm i.d. glass column packed with 3% OV-17 on Chromosorb W HP 80/100 mesh. Nitrogen was used as a carrier gas at a flow rate of 30 mL/min. Temperature programming was performed from 150~ to 270~ at 15~ after an initial hold time of 0.5 min. Final temperature was held for 12 rain. Urine extraction procedures were followed as described by Davidow (6), utilizing a dichloromethane:isopropanol (90:10) extraction solvent. The retention time of amoxapine was 9.97 min, and that of the metabolite 14.81 min, as confirmed by gas chromatography/mass spectrometry (GC/MS). Thin layer chromatography (TL C). Qualitative screening was also performed by TLC using the Davidow method (6). This procedure used the dichloromethane: isopropanol (90:10) extraction solvent. The extracts were spotted on a 20-cm • 20-cm silica plate and developed utilizing ethyl acetate:methanol:concentrated ammonium hydroxide (85: 10:5) to a height of 15 cm. The plate was sprayed with iodoplatinate and dragendorff sprays. Gas chromatography/mass spectrometry (GC / MS). Qualitative findings were confirmed with GC/MS. A Finnigan m~del (GC/MS) 4021 was employed using a 1.83 m x 2 mm i.d, glass column packed with 3~ OV-I (hromosorb W H P 80/100 mesh. Helium was used as the carrier gas at a flow rate of 30 mL/min. Temperature programming lrom 100~ to 270~C at 12~C/min was used, and the final temperature ~as maintained for 10 rain. The

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mass spectrometer v~as in the electron ionization mode at an electron voltage of 70 V. Other parameters of operation x~erc as described by }:inkle (7). Again, SKI: 525A was used as chromatographic standard for relative retention time calculations.

Quantitative Analysis

High performance liquid chromatography (HPLC). Quantitative analysis was performed by H P L ( . This assay was a slight modification of an earlier method (8). The extraction procedure used a I-mL plasma sample on a ClinElut extraction column (Analytichem International) buffered with 0.2 mL saturated sodium carbonate. The drug v,as eluted with two 4-mL aliquots o f hexane:butanol (5:1) extraction solvent. The eluent was extracted into 1.0 mL o f 0. IN HCI and then back-extracted into

2.0 mL of the original extraction solvent. The sample was concentrated at 55~ In this updated procedure, a C8 radial compression column (Waters Associates) was substituted for a #Bondapak C,8 column (Waters) to increase column life. Also, 5 mL of 10M Tris buffer was added to an acetonitrile:water (85:15) and 300 # L / L n-butylamine mobile phase to achieve a pH of 9.0. Because the radial compression column could not be heated, the flow rate was increased to 4.0 m L / m i n . All of the other parameters associated with the assay were the same. Samples were drawn in tubes without preservatives and the serum was removed and frozen within one hour after the phlebotomy. Appropriate dilution of patient specimens was performed to insure a linear response.

Toxicological Findings and Case Histories Amoxapine

8-Hydroxyamoxapine

7-Hydroxyamoxapine

LoxaDine

,H

CH,

9

Figure 1, Molecularstructures of amoxapine,8-hydroxyamoxapine,7-hydroxy-

amoxapine, and Ioxapine.

The result o f toxicological analysis of the five cases is seen in Table I. The toxicological samples analyzed were obtained upon admission to the emergency room. The elimination profiles were described as time post admission since no reliable ingestion time was available. The major point of interest in Case 1 is the presence of 7-hydroxyamoxapine in serum, which has a very short half-life and does not accumulate during therapeutic dosing pattern. Also, the patient sustained esophageal burns due to a previous suicide attempt which made lavage impossible. Amoxapine was the only drug ingested and serum analysis yielded a toxic amount. While the patient was in a coma and seized, the only cardiac abnormality was sinus tachycardia and a slight prolonged QT segment. The second case evaluated was a patient ingesting amoxapine, propoxyphene, and zomepirac. The amount of amoxapine taken was toxic, but was the lowest serum level of amoxapine and metabolite of all five cases. The patient was comatose, seized, and exhibited sinus tachycardia. The third case is the most unique as only amoxapine, ethanol, and acetaminophen were ingested. A serum ethanol level of 2133

Table I. Summary of Data in Amoxapine Overdose Amount Amoxaplne Ingested*

Case

Age (yr)

Sex

1

28

F

--

2

26

F

800 mg

3

42

F

2000 mg

4

40

F

1330 mg

5

22

F

1000 mg

Drugs Ingested

Highest Serum Amoxapine (~g/L)

Highest Serum 8.Hydroxyamoxapine (~OIL)

Clinical Notes

Amoxapine

625

640

Amoxapine Propoxyphene Zomepirac Amoxapine Acetaminophen Ethanol Loxapine Phenytoin Doxepin Chlordiazepoxide Caffeine Nicotine Loxapine Amoxapine Phenylpropanolamine Phenmetrazine Caffeine Nicotine

308

405

2900

900

Coma and seizure, ventricular tachycardia

1560

1480

Coma and seizure, ventricular fibrillation, death

475

685

Coma and seizure, sinus tachycardia. Lavage impossible due to esophagealscarring Coma and seizure, sinus tachycardia

Coma and seizure, sinus tachycardia

9By history

125


#g/mL and serum acetaminophen level of 59 #g/mL were detected. An extremely large amount of amoxapine was ingested and yielded a combined parent and metabolite serum concentration of 3800 ng/mL. A serum elimination pattern was obtained over a two-day period (Figure 7A). This change in drug blood concentration can be related to changes in patient status. Upon admission, the patient was in a coma and showed atrial flutter with ST segments and T wave changes. At 8 hr post admission, the patient presented with a compensated metabolic acidosis, 114/70 mm Hg blood pressure, and a pulse rate of 164 beats/ rain. The patient was transferred to MICU at 16 hr post admission and had a seizure that was controlled by oxazepam. One day into hospitalization, the patient began to respond to pain and had a QRS interval of 0.8 m sec. There was also blood pressure of 130/90 mm Hg and pulse of 104 beats/min. In the following 8 hr, there were similar vital signs, and the patient began to respond to voice commands. The final 8 hr were marked by a blood pressure of 130/90 mm Hg and a pulse of 109 beats/rain with no ectopic foci present. The patient was on a dosage regimen of 100 mg/day before the overdose. The fourth case died shortly following admission to the emergency room. This patient ingested a variety of drugs which the coroner's office later quantified. These drugs consisted of loxapine (500 ng/mL), phenytoin (16.0 #g/mL), doxepin (4400 ng/ mL), chlordiazepoxide (12.0 #g/mL), nicotine, and caffeine. Amoxapine is the metabolite of loxapine. This patient exhibited the most severe cardiac dysfunction which may, in part or entirely, be attributed to the large amount of doxepin ingested. The large amounts of different types of drugs present makes interpretation of the patient's symptoms difficult. The final patient also ingested a variety of medications. Most notably, these drugs included loxapine, amoxapine, phenylpropanolamine, and phenmetrazine. The amount of amoxapine present was in the toxic range (>500 #g/L), but the patient showed little toxicity with the exception of tachycardia. The comparison of these cases to other cases in the literature reinforces the minimal amount of cardiotoxicity exhibited by amoxapine in overdose. Seizure is common and, in contrast to other findings each case exhibited, 8-hydroxyamoxapine was present in blood and urine.

9 o

9

9

O

o

9

O

~8 9 Q

o

9

0

o

o

9

. . . . . .

9

A B C D E F G H

A ~

~"

Figure 2 Thin layer chromatographic comparison of urine from Case 4 (G and H) with standards of doxepin (A), desmethyldoxepin (t3). Ioxapine (C), amoxapine (D). 8-hydroxyamoxapine (E). and 7-hydroxyamoxapine (F)

~

Results

The summary of the five patients is given in Table 1. The maximum amount of drug present in serum of each case ranged from a total of 713 to 3800 ng/mL of both amoxapine and 8-hydroxyamoxapine. All the patients had seizures and cardiac abnormalities. Indeed, in Case 4 cardiotoxicity was responsible for death. All of these cases had amoxapine and both metabolites present in urine as evidenced by TLC and GC. For example, in Case 4, TLC data suggested the presence of loxapine, amoxapine, 8-hydroxyamoxapine, 7-hydroxyamoxapine, doxepin, and desmethyldoxepin (Figure 2). When injected into the GC, the same specimen gave peaks with the same retention time as amoxapine and amoxapine metabolites (Figure 3) as confirmed by GC/MS. The reconstructed ion chromatogram by total ion analysis of the patient's urine is seen in Figure 4. The mass spectrum of scan number 259 was obtained, yielding a mass spectrum with a base ion of 56 and a molecular mass of 313 (Figure 5). This data was in agreement with the amoxapine standard. The same procedure was used to confirm the presence of metabolites. The 126

C

o

Figure 3. Gas chromatographic comparison of urine from Case 4: (A) peak 1.53 nicotine, 5.68 caffeine, 7.01 doxepin, 7.29 desmethyldoxepin, 9.29 Ioxapine, 9.55 chlordiazepoxide, 9.97 amoxapine, and 14.81 amoxapine hydroxylated metabolites; (B) standard of amoxapine; and (C) both 8- and 7-hydroxyamoxapine, with the same retention time.


mass spectrum of scan 306 in Case 4 is shown in Figure 5 with base peak ion of 56 and a molecular ion of 329. A comparison of the spectrum of the reference standards of 8-hydroxyamoxapine and 7-hydroxyamoxapine (Figure 6) against the unknown confirmed the presence of amoxapine metabolite. In addition, serial blood levels were obtained in Cases 3 and S. The changes in the concentration of the parent and 8-hydroxyamoxapine over time are reported in Figures 7A and 7B. The half-life of amoxapine and 8-hydroxyamoxapine in therapeutic concentrations is 7.7 and 30 hr, respectively (4). In Case 3, amoxapine and 8-hydroxyamoxapine have half-lives of 15 and 48 hr, while in Case 5 the respective values were 8.5 and 48 hr.

261 300p

100.0. ss

I

j~ 50.0 20g

10007

50.0 85

Discussion

100

150 M/E

200

250

350

400 M/E

450

500

329

300

Five cases of suspected amoxapine overdose were followed. The drugs involved in these cases were determined by GC and TLC analyses, with confirmation by GC/MS. These methods supported the fact that amoxapine metabolites were present in

Jill273

Figure 6. Mass spectrum of scan 306 from urine of Case 4.

A

3000 I"

254 259

206 167

4270

~

306

119 1 ~

~.

1000. "~ 9oo a,-_ \ 8oo - - . -_ \ 700 "i-. o

~J ~

"'-.~.

soo

8 soo E

400

o~

300

~281//321 v ~ 353374403 430

200

Figure 4. Reconstructedionization chromatogram of the urine of Case 4: peak 42 nicotine; peak 167 caffeine; peak 206 doxepin and desmethyldoxepin; peak 254 chlordiazepoxide;peak 259 amoxapine; and peak 306 hydroxyamoxapine.

100

ll2

2~4

3=2

418

Hours Post Admission

B

1000 I:

100.0

245

,

8OOl70016oo I-

5,0X

500 IA 400-J 300

v c 200 o --

100

== u 90 70

~500 313

25;" 69

164

50

40 30 20

228

42

O S ca

'

i i

29

;

10

50

1O0

150

200

250

M/E

Figure 5. Mass spectrum of scan 259 from urine of Case 4.

300

1'8

2',

3'2

4'0

4'8

Hours Post Admission

Figure 7. Changes in concentration of amoxapine (e) and 8-hydroxyamoxapine (11) over time: (A) Case 3, (B) Case 5.

127

Journal of Analytical Toxicology. Vol. 8, May/June 1984

overdose situations. This finding is in contrast to an earlier report (9). In Cases 1 and 3, high levels of 8-hydroxyamoxapine were observed. This compound is reported to be pharmacologically active and possess 50% greater ability to inhibit norepinephrine uptake than amoxapine (10). These observations reinforce the importance of monitoring metabolite concentrations, particularly 8-hydroxyamoxapine after a nonfalal overdose as it was present and uas presumably the agent precipitating the tachycardia. While seizures and coma are commonly reported in amoxapine overdose (2,3), cardiotoxicity was reported as minimal (3). The cardiotoxicity experienced in Case 3 could be clearly attributed to amoxapine. The rate of elimination of the parent drug and metabolite in the overdose situations appears to follow first order kinetics. In these limited observations, the rates were slower than previously reported for therapeutic doses.

Acknowledgments

The authors are grateful to F.M. Hassan for his technical assistance and support. We also would like to thank Lederle Laboratories for providing the purified compounds, and the Document Processing Area of the Department of Pathology for their assistance in the preparation of this manuscript.

128

References 1. T.B. Cooper and K.G. Kelly. GLC Analysis of Ioxapine, amoxapine, and their metabolites in serum and urine. J. Pharm. Sci. 68:216-19 (1979). 2. Physicians' Desk Reference. 37th Ed. Ohio, Medical Economics, 1983, p. 1071. 3. W. Boutelle. Clinical response and blood levels in the treatment of depression with a new antidepressant drug amoxapine. Neuropharmaco/ogy 19: 1229-231 (1980). 4. K. Kulig, B. Rurnack, and J. Sullivan. Amoxapine overdose J. Am. Med. Assoc. 248:1092-094 (1982). 5. S. Zavodnick. Atrial flutter with amoxapine: A case report. Am. J. Psychiatry 138:1503-504 (1981). 6. B. Davidow, N.L. Petri, and B. Quame. A thin-layer chromatographic procedure for detecting drug abuse. Am. J. C/in. Patho/. 38:714-19 (1968). 7. B.S. Finkle, RL. Foltz, and D.M. Taylor. A comprehensive GC-MS Reference Data System for toxicological and biomedical purposes. J. Chro. matogr. Sci. 12:304-28 (1974). 8. J.J. Tasset and F.M Hassan. Liquid chromatographic determination of amoxapine and 8-hydroxyamoxapine in human serum. C/in. Chem. 28: 2154-157 (1882). 9. P. Sedgewich, V. Spiehler, and D. Lowe. Toxicological findings in amoxapine overdose,J. Anal. Toxicol. 6:82-84 (1982). 10. J. Couput, C. Rauch, V. Suer-Meyers, et aL 2-Chloro-11-(1-piperaxinal) [b,l] [1,4}oxazepine (amoxapine), an antidepressant with antipsychotic properties--A possible role for 7-hydroxyamoxapine. Biochem. Pharmacol. 28: 2514-515 (1979).

Manuscript received April 28, 1983; revision received September 14, 1983.