What is the role of Diethylcarbamazine (DEC) in treating eosinophilia?

Role of Diethylcarbamazine (DEC) in Treating Eosinophilia

DEC is the treatment of choice for eosinophilia caused by lymphatic filariasis and loiasis, but requires mandatory pre-treatment screening for onchocerciasis and quantification of Loa loa microfilarial load to prevent life-threatening complications including blindness and fatal encephalopathy. 1, 2

Critical Pre-Treatment Screening Algorithm

Before administering DEC for eosinophilia, you must complete this screening sequence:

1. Screen for Onchocerciasis Co-infection

• Obtain skin snips for microscopy and perform slit lamp examination in patients from co-endemic regions 1, 2
• If these tests are unavailable, administer a test dose of DEC 50 mg—this will precipitate a mild Mazzotti reaction (pruritus and erythema) if onchocerciasis is present 1, 2
• DEC is absolutely contraindicated in onchocerciasis as it causes severe reactions including blindness, hypotension, pruritus, and erythema 1

2. Screen for Loa loa and Quantify Microfilarial Load

• Obtain daytime blood microscopy (10 am to 2 pm) using 20 ml citrated blood samples 1, 3
• If microfilariae are detected, determine the exact count—patients with >1000/ml are at highest risk of fatal encephalopathy 2, 3
• DEC can cause encephalopathy with high mortality in high Loa loa loads 1, 2

3. Screen for Strongyloidiasis

• Complete this before using corticosteroids in patients requiring pre-treatment with prednisolone 1, 3

Treatment Regimens Based on Etiology

Lymphatic Filariasis (W. bancrofti, B. malayi, B. timori)

Primary regimen: DEC 6 mg/kg PO in 3 divided doses for 14 days PLUS doxycycline 200 mg PO daily for 6 weeks 1, 2

• This combination is more effective than DEC alone, with doxycycline targeting the Wolbachia endosymbiont 1, 4
• DEC is both microfilaricidal and macrofilaricidal (kills adult worms), with higher total dosages and spaced dosing schedules showing better long-term results 5
• Alternative in onchocerciasis co-endemic areas: Ivermectin 200 μg/kg single dose plus albendazole 400 mg single dose 2, 4

Loiasis (Loa loa)

For microfilarial load >1000/ml:

• Start prednisolone (after screening for strongyloidiasis) 1, 3
• Administer albendazole 200 mg PO twice daily for 21 days 1, 3
• Check daytime blood microscopy at day 28 and repeat albendazole courses until microfilarial count <1000/ml 1, 3
• Then proceed with DEC regimen below with prednisolone cover 1, 3

For microfilarial load <1000/ml or negative blood film:

• DEC escalating regimen without steroid cover: 1, 3
  • Day 1: 50 mg single dose
  • Day 2: 50 mg three times daily
  • Day 3: 100 mg three times daily
  • Day 4: 200 mg three times daily
  • Days 5-25: 200 mg three times daily

Tropical Pulmonary Eosinophilia (TPE)

• DEC 6 mg/kg PO in 3 divided doses for 14 days 6
• Some patients require inhaled or systemic corticosteroids for symptomatic relief 6
• Approximately 15-20% of patients relapse and require a second course of DEC 6

Expected Eosinophil Response to DEC Treatment

DEC paradoxically increases eosinophilia acutely before reducing it:

• Eosinophil counts rise significantly within 8 days of starting treatment, peaking at 2-4 weeks at levels 2.5-3 times baseline 7
• The degree of post-treatment eosinophilia correlates directly with pre-treatment worm burden (r=0.727, P<0.001) 7
• This represents an immune response to dying parasites, with plasma IL-5 and RANTES peaking 1-2 days post-treatment, followed by peripheral eosinophil peak at day 4 8
• Clinical symptoms (fever, lymphadenitis, lymphangitis) occur within 24 hours as microfilariae are killed 4, 8

Monitoring Requirements

• Monitor full blood counts and liver function tests every 2 weeks for 3 months, then monthly if normal 2, 4
• Repeat blood microscopy at 6 and 12 months after last negative sample to monitor for relapse in loiasis 1, 3
• Follow-up serological testing at 3-6 months may be warranted to ensure complete parasite clearance in lymphatic filariasis 2

Special Populations

• Pregnancy: Avoid DEC and seek expert consultation 2, 4
• Breastfeeding: DEC safety data is limited; ivermectin is excreted in very low levels in breast milk and is likely compatible 4
• Children 12-24 months: Discuss with expert before treatment 2, 4
• Children >24 months: Standard dosing can be used 4

Critical Pitfalls to Avoid

1. Never administer DEC without screening for onchocerciasis and Loa loa in patients from endemic regions—this is the most common cause of preventable severe adverse events 1, 2
2. Do not use nocturnal blood microscopy for Loa loa—microfilariae circulate during daytime hours (10 am to 2 pm) 1, 3
3. Do not assume eosinophilia worsening after DEC indicates treatment failure—this is an expected immune response to dying parasites 7, 8
4. Avoid alcohol during treatment as it may worsen side effects 2, 4
5. Exercise caution with azithromycin co-administration as it significantly increases serum ivermectin concentrations 2, 4