What is the best course of treatment for a patient with anal pruritus, skin crawling sensations, and gastrointestinal symptoms, who has been prescribed ivermectin (antiparasitic medication) and now presents with excessive bowel movements and potential parasites in her feces, despite a normal psych eval?

Diagnostic and Treatment Approach for Suspected Intestinal Parasitic Infection

Immediate Next Steps

You should continue ivermectin therapy and add albendazole 400 mg as a single dose to provide broader helminthic coverage, while simultaneously collecting stool specimens for proper parasitological examination using concentration techniques. 1, 2

Diagnostic Workup

Stool Examination Requirements

• Collect at least three stool specimens over the next few days and submit for concentrated stool microscopy using Baermann concentration method, as standard examination has poor sensitivity for many helminths including Strongyloides 3, 2
• The "rice-like" structures in stool suggest possible pinworm (Enterobius vermicularis) segments or proglottids from tapeworm infection 4, 5
• Request fecal PCR if available, as it offers higher sensitivity than microscopy alone 2
• The thread-like material she brought in a jar warrants direct microscopic examination to identify larvae or adult worm morphology 3

Additional Testing Based on Travel History

• Screen for Loa loa infection if the patient has traveled to Central or West Africa before continuing ivermectin, as co-infection can cause fatal encephalopathy 2, 3
• Consider serologic testing for Strongyloides given the skin crawling sensations, though this has lower specificity 6
• Check complete blood count for eosinophilia, which supports helminthic infection 4, 7

Treatment Protocol

Current Ivermectin Dosing Assessment

• The 12 mg dose appears appropriate if the patient weighs 60-80 kg (standard dosing is 200 mcg/kg for strongyloidiasis) 1, 3
• Ensure the patient takes ivermectin on an empty stomach with water to optimize bioavailability 1, 3
• The excessive bowel movements following ivermectin are consistent with parasite die-off and intestinal clearance 3

Recommended Combination Therapy

• Add albendazole 400 mg orally as a single dose to provide coverage for pinworm, hookworm, roundworm, and other common helminths that ivermectin alone may not adequately treat 2, 1
• For suspected pinworm infection (based on anal pruritus and rice-like structures), treat all household contacts simultaneously with albendazole 400 mg due to high contagiousness 2

Follow-Up Dosing Strategy

• Repeat stool examinations at 3-4 weeks post-treatment to document clearance, as recrudescence can occur up to 106 days after ivermectin 3
• If larvae reappear in stool, retreatment with ivermectin 200 mcg/kg is indicated 3
• Consider a second dose of albendazole in 2 weeks if pinworm infection is confirmed 1

Specific Parasite Considerations

Strongyloidiasis (Thread-like Worms, Skin Crawling)

• The skin crawling sensation and thread-like appearance strongly suggest Strongyloides stercoralis 7, 8
• Single-dose ivermectin achieves 83-100% cure rates for uncomplicated strongyloidiasis 3
• If the patient is immunocompromised, she may require repeated courses at 2-week intervals (ivermectin 200 mcg/kg on days 1,2,15, and 16) 1, 3

Enterobiasis/Pinworm (Anal Pruritus, Rice-like Structures)

• The anal pruritus and rice-like structures in stool are classic for Enterobius vermicularis 4, 5
• Pinworm can cause severe diarrhea and eosinophilic colitis in some patients, contrary to the common belief that it only causes perianal itching 4
• Perform cellophane tape test on perianal skin in the morning before bathing to recover eggs for definitive diagnosis 5
• Mebendazole 100 mg is an alternative treatment if albendazole is unavailable 4, 9

Hookworm or Whipworm (Diarrhea, Anemia Risk)

• If hookworm is confirmed, extend albendazole to 400 mg daily for 3 days rather than single dose 2
• For whipworm, consider mebendazole 100 mg twice daily PLUS ivermectin 200 mcg/kg once daily for 3 days 2

Critical Safety Precautions

Loa Loa Screening

• Always exclude Loa loa infection before giving ivermectin to anyone with significant exposure to West or Central Africa, as hypermicrofilaremic patients can develop severe encephalopathy, seizures, coma, or death 3, 2
• Pretreatment assessment and careful post-treatment follow-up are mandatory in at-risk patients 3

Monitoring for Complications

• Watch for signs of Strongyloides hyperinfection if the patient develops paralytic ileus or worsening symptoms despite treatment 8
• Monitor for aggravation of symptoms in the first 3 days post-treatment, which can occur with microfilaricidal drugs 3

Prevention of Reinfection

• Counsel on hand hygiene with soap before eating and after defecation 2
• Recommend simultaneous treatment of all household contacts for pinworm given high contagiousness 2
• Advise washing bedding and clothing in hot water to eliminate pinworm eggs from the environment 5

When to Seek Specialist Consultation

• Consult infectious disease specialist if the patient is immunocompromised, as cure may not be achievable with standard therapy and suppressive monthly treatment may be needed 3
• Seek specialist advice if symptoms persist despite appropriate treatment or if unusual ectopic manifestations develop 6, 9