A series of 250 patients with filariasis due to periodic type of Brugia malayi was selected for the mass treatment with diethylcarbamazine from two areas in Cheju-Do.

Two types of dosage schedules have been employed: the one was the conventional dosage schedule (uninterrupted dose of 6 mg/kg once daily 6 times repeated with an interval of one or two month totaling 72 mg/kg), and the other was the low dosage schedule (uninterrupted dose of 0.5, 1, 2, 4, 6 mg/kg body weight given once a day with an additional 6 mg/kg once daily totaling the maximum 37.5 mg/kg).

The relative effectiveness of those two schedules was evaluated under the basis of the effects on microfilaria counts and the results of analysis of side-reactions observed. The results obtained in this experiment are summarized as it follows.

In the conventional dosage treatment, 118 out of 141 microfilaria positives treated (83.7%) became negative and microfilaria reduction rate was about 99%. However, in the low dosage treatment, 35 out of 43 positives treated (85.4%) became negative and reduction rate of microfilaria, 99.5% in average.

Total dose and duration of treatment were 72 mg/kg and about 60 days in the former schedule but it were maximum 37.5 mg/kg and 10 days in the latter. The recurrence of filariasis after treatment in both conventional and low dosage was negligible.

Comparative analyses regarding the resulting side-reactions between the two schedules were made on their frequency, severity, onset and duration and relationship with microfilaria density.

The febrile reaction was most frequently observed in 80.5% in the conventional, 43.9% in the low dosage schedule. The main side-reactions usually appeared within 6 to 10 hours and lasted 48 to 72 hours in the former threament, however they occurred in 7 to 8 hours and lasted 24 to 43 hours in the latter dosage schedule.

It is assumed that the side-reactions are not directly related with the microfilaria count. However, the febrile reaction seems to be correlated with microfilaria density if it is above a certain limit. The presence of adult worm in a lymphnode involved with local reaction was ascertained from the biopsy specimens performed and local reactions such as lymphangitis and lymphadenitis after drug administrations were assessed from clinical and pathological point of view.

It was conclusively indicated that the chemotherapeutic response to low dosage schedule within shorter length of treatment was equal to that of larger doses in long term medication from the point of the reduction in microfilaria, and particularly the resulting side-reactions were also reduced in the low dosage schedule.