Our observations are consistent with the hypothesis that dissociation or destruction of complement C1 eliminates the prozone effect. Addition of EDTA to serum of highly immunized patients is the easiest way to avoid false-negative results in SAB testing caused by a prozone effect.

A controlled, double-blind, double-placebo, crossover clinical trial was carried out in 24 mild to moderate hypertensives of either sex to compare the anti-hypertensive and other effects of indapamide (2.5 mg) and pindolol (15 mg). After a 2-week run-in placebo period the patients were randomly assigned to one of the drugs in the study for 6 weeks. After a second 2-week placebo period, the subjects received the alternative drug for an additional 6 weeks. Both drugs produced a significant and similar decrease in arterial blood pressure (averaging 19 mmHg for systolic and 15 mmHg for diastolic blood pressure; p less than 0.05), with minimal differences between the drugs in this respect (p greater than 0.10). Pulse, rate, however, was significantly reduced (from 76 to 67 beats/min; p less than 0.05) only with pindolol. The laboratory data did not change appreciably, and few side-effects were reported. It is concluded that indapamide and pindolol at the dosage levels used are drugs of comparable antihypertensive activity.