Case Report: Severe Antibiotic-Associated Diarrhea and Perianal Dermatitis Secondary to Amoxicillin

Case at a Glance

A 46-year-old male with a history of type 2 diabetes and obesity was prescribed a 7-day course of amoxicillin for a dental infection. He subsequently developed severe, frequent, watery diarrhea and significant perianal burning. This case illustrates a severe adverse reaction to a commonly prescribed antibiotic and the recommended course of action.

Patient's Story

A 46-year-old male presented with a toothache and was prescribed a standard 7-day course of amoxicillin by his dentist. The day after initiating treatment, he began experiencing severe gastrointestinal distress. He described the onset of frequent, entirely liquid stools, occurring up to six times per day and as often as every 60-90 minutes while awake. A significant complaint was an intense burning sensation in the perianal region following each bowel movement, which he reported lasted for approximately 10 minutes. By day four of the antibiotic course, the symptoms were debilitating, causing significant anxiety about leaving his home and potential fecal incontinence, which jeopardized a scheduled follow-up dental appointment. The patient noted he had been taking a probiotic for the first three days but had discontinued it based on information he had read. He was concerned about the volume of stool despite having a poor appetite.

Initial Assessment

History of Present Illness: The patient's clinical presentation was highly suggestive of antibiotic-associated diarrhea (AAD). The timeline, with symptoms beginning within 24 hours of starting amoxicillin and escalating in severity, strongly supported this link. The primary symptoms were high-frequency, non-bloody, watery diarrhea and severe perianal irritation secondary to the stool's composition and frequency. Medications: Metformin, Insulin, Amoxicillin. Past Medical History: Type 2 Diabetes Mellitus (managed with metformin and insulin), Class III Obesity (Weight: 420 lbs / 190.5 kg). Social History: Non-smoker, non-drinker, no use of recreational drugs.

The Diagnostic Journey

The diagnosis was primarily clinical, based on the clear temporal relationship between the initiation of amoxicillin and the onset of symptoms. The patient's description of severe watery diarrhea raised the differential diagnosis of Clostridioides difficile (C. diff) infection, a more serious complication of antibiotic use, particularly in patients with comorbidities. However, the immediate step was to address the offending agent. Following the advice to contact the prescriber, the patient called his dentist to report the severe adverse effects. The dental office acknowledged the symptoms as a likely side effect of the amoxicillin.

Final Diagnosis

Severe Amoxicillin-Induced Diarrhea with secondary Irritant Perianal Dermatitis.

Treatment Plan

Based on the consultation with the prescribing dentist, the following plan was implemented:

1. Discontinuation of Offending Agent: The patient was instructed to immediately cease taking the amoxicillin.
2. Alternative Antibiotic: The dentist prescribed an alternative antibiotic from a different class to treat the underlying dental infection while minimizing the risk of similar gastrointestinal side effects.
3. Symptomatic Care:
   • Hydration: The patient was advised to increase his fluid intake to prevent dehydration, a critical consideration given his diabetic status.
   • Dietary Modification: A bland diet (e.g., BRAT diet: bananas, rice, applesauce, toast) was recommended to reduce bowel stimulation.
   • Perianal Care: To manage the severe burning, the patient was advised to use gentle cleansing with warm water (e.g., using a sitz bath or bidet) instead of abrasive wiping, to pat the area dry, and to apply a zinc oxide-based barrier cream to protect the inflamed skin.
4. Monitoring: The patient was instructed to monitor for any signs of worsening, such as fever, blood in the stool, or symptoms of dehydration (dizziness, decreased urination), and to seek immediate medical care if these occurred.

Outcome and Follow-up

After discontinuing the amoxicillin, the patient's diarrheal symptoms began to improve within 24-48 hours. The frequency of bowel movements decreased, and the stool consistency gradually returned to normal. The perianal burning resolved as the diarrhea subsided and with the implementation of gentle skin care and a barrier cream. The patient was able to tolerate the new antibiotic, complete his dental treatment successfully, and achieve a full recovery from the gastrointestinal side effects. An allergy/adverse reaction to amoxicillin was noted in his medical records to prevent future prescription.