Discussion:
Metronidazole is an effective antimicrobial that was first used against
trichomonas infections in the late 1950s and then was found to have
effects on anaerobic bacteria and protozoal species. It is frequently
used and usually has gastrointestinal side effects of gastric upset and
metallic taste feeling. Its neurological adverse effects have been
infrequent and only reported in case reports; these include dizziness,
ataxia, encephalopathy, and seizure [2]. Ophthalmic side effects
have been rarely reported and only seen in case reports and are not
frequently recognized by healthcare providers. Here we described a case
report of 30-year-old lady who was medically free until around 20 days
before her admission when she had a bout of gastroenteritis and was
given a dose of Metronidazole 500 mg IV the next day. She noticed
progressively worsening vision in her right eye, which progressed to
complete vision loss in one-day duration. She did not seek medical
advice due to financial issues and stayed for around one week waiting
for spontaneous recovery of her vision. Upon admission, she was vitally
stable, and her physical examination was unremarkable apart from
complete vision loss in her right eye and right pupillary afferent
defect. Her Basic laboratory blood tests were normal, and her MRI
findings were consistent with left optic neuritis. CSF analysis showed
lymphocytic pleocytosis and elevated protein level but was negative for
culture, viral panel, and oligoclonal bands. Her hospital course has
been uneventful, and she was started on IV Methylprednisolone 1000 mg
daily for five days. She showed a slight improvement in her right eye
vision from complete vision loss to hand movement at 50 cm distance
which then did improve to only counting fingers at 50 cm distance.
An extensive literature review was done, and we found 10 case reports
and 1 case report with a literature review discussing the
neuro-ophthalmic profile of Metronidazole. The age of patients ranged
from 6 to 67 years, 8 were males, and 9 were females. All of the cases
we could extract data for were administered Metronidazole orally. The
dose ranged between 250 mg to 1500 mg per day, and the duration of drug
administration to symptom development was from one dose of 250 mg up to
chronic use of 2 years. 15 patients developed optic neuritis, three
patients developed aseptic meningitis, one patient developed myelitis,
and two patients had cerebellar involvement. All the patients were
managed with the withdrawal of Metronidazole, except one patient with
aseptic meningitis who was treated with a 3rd generation intravenous
cephalosporin for one week, and another patient with optic neuritis who
was initiated on coenzyme Q10 for 3 months in addition to cessation of
metronidazole. Most patients fully recovered their vision, but one whose
damage was irreversible, and seven other patients had 71% reversibility
of their sight (Please see table 1 for the summary and comparison of
literature review and our case).