Page 105 - JCBP-3-1

Journal of Clinical and
Basic Psychosomatics Serotonin syndrome unexpected medication

of action has the greatest potential for lethality. Duloxetine (101 bpm), and a fever of 98.4°F following admission.
2
is a SNRI widely used for its combined antidepressant and Laboratory tests revealed a creatine phosphokinase level
neuropathic pain reduction properties, whereas bupropion of 995 U/L. Physical examination was notable for clonus,
is a norepinephrine and dopamine reuptake inhibitor with nystagmus, and tremors.
weak serotonergic activity. 4
A psychiatrist was consulted for investigating possible
Metaxalone, an oxazolidinone analog used as a muscle serotonin syndrome. The neurological examination
relaxant, has been less extensively investigated but may demonstrated ocular vertical nystagmus, inducible clonus
possess serotonergic activity. Although its mechanism on the right foot, jerkiness, tremors, and akathisia but no
of action remains unknown, it is hypothesized that brachial or patellar hyperreflexia. The patient discontinued
metaxalone acts as a reversible MAOI due to its comparable his psychotropic medications 2 days before admission, as
structure. According to a previous case report, serotonin he believed that they were the cause of his symptoms. He
5
syndrome is caused by metaxalone overdose alone or was unable to provide additional information due to acute
metaxalone overdose along with a therapeutic dose of an mental status changes.
SSRI. Serotonin syndrome has been reported to manifest The patient’s wife reported that 5 days before admission,
6
in a patient with cirrhosis receiving venlafaxine and he began experiencing tremors, diaphoresis, diarrhea,
quetiapine, upon initiation of metaxalone. 7
abdominal pain, and temperature dysregulation and was
Phentermine is a sympathomimetic medication “tense” while driving. Two days before admission, the patient
employed for suppressing appetite and facilitating weight experienced deterioration, as evidenced by increased
loss. Although there are no published cases of serotonin restlessness and tremors, decreased sleep, diaphoresis,
8
syndrome associated with phentermine, the drug is known altered mental status, hypertension, and tachycardia, as
to inhibit serotonin metabolism through monoamine determined by blood pressure measurement at home.
9
oxidase. Overall, the literature on metaxalone and/or Tremors were described as the patient’s hands rhythmically
phentermine-induced serotonin syndrome is limited. oscillating up and down while holding the steering wheel
However, there appears to be significant potential for as he was driving. The patient’s wife, however, was unaware
increasing serotonergic activity through monoamine of the specific medications that the patient had received in
oxidase pathways. the weeks preceding this event.
This case report describes a patient on duloxetine, A review of the patient’s medication regimen included
bupropion, and phentermine who developed serotonin duloxetine 60 mg daily, bupropion XL 150 mg daily,
syndrome following the administration of metaxalone. gabapentin 600 mg QID, metaxalone 800 mg BID PRN,
Several factors that potentially contributed to the pantoprazole 40mg daily, hydrochlorothiazide 12.5 mg
development of serotonin syndrome in this patient will be daily, nilotinib 150 mg BID, cyclobenzaprine 10 mg
reviewed. TID PRN, oxycodone 15mg q4h PRN, and phentermine

2. Case presentation 37.5 mg daily.
The patient fulfilled Hunter’s criteria for serotonin
A 56-year-old male with moderate, recurrent major syndrome by exhibiting ocular clonus, inducible clonus,
depressive and adjustment disorders presented to the and use of serotonergic medications (such as duloxetine,
emergency department due to a 1-week history of metaxalone, and phentermine). Cyproheptadine
progressive restlessness, abdominal pain, diaphoresis, administration was initiated after a psychiatric consultation.
nausea, and vomiting. He also had a history of medical After 2 days of treatment with a 12 mg loading dose and a
comorbidities, including chronic myelogenous leukemia, 2 mg Q2H dose of cyproheptadine for a maximum dose of
peripheral neuropathy, chronic lumbar back pain (for 32 mg/day, the patient’s mental status markedly improved.
which he was receiving oxycodone), and hypertension. He acknowledged receiving phentermine “sparingly” but
Upon admission, he was conscious and oriented, afebrile,
and hemodynamically stable but was restless, tremulous, had resumed daily doses 5 days before symptom onset.
and demonstrated akathisia. The urine drug screen was Metaxalone was another agent he used PRN; however,
positive for oxycodone and negative for illicit substances. he had also resumed taking this medication twice a day
He was administered morphine (2 mg/mL) intravenous for 2 days before symptom onset. These two PRN agents
(IV) q6h for pain and lorazepam (0.5 mg/0.25 mL) IV q4h were being used in addition to his regular scheduled
medications.
for acute agitation. Due to concerns regarding serotonin
syndrome, he was admitted to the intensive care unit. He On day 4, evaluation revealed that the vital signs were
developed hypertension (159/89 mmHg), tachycardia within normal limits. Neurological examination revealed

Volume 3 Issue 1 (2025) 99 doi: 10.36922/jcbp.4490