INCIDENCE OF PROCAINAMIDE-INDUCED LUPUS ANTICOAGULANT
Isolated cases of lupus anticoagulants (LA) in association with procainamide have been reported. This study was done to estimate the frequency of LA in patients taking procainamide. Two groups of patients were evaluated: Group A: 110 hospitalized patients (84 males, 26 females, ages 51-78, mean age 74.3) and Group B: 80 ambulatory patients (54 males, 26 females, ages 36-89, mean 67.5 years). The latter group of patients was on this drug for a period of two-five years, while the former group hadbeen on drug at least two full days. All patients were screened with baseline laboratory data including activated partial thromboplastin time (APTT) and prothrombin time (PT) which were performed using Auto APTT® and Simplastin® on a Coagulamate X2® (General Diagnostics/Organon Teknika). Patients taking drugs known to alter the APTT and PT were excluded. All patients were followed with daily (hospital patients) or weekly (ambulatory patients) APTT and PT. Prolongation of the APTT of 5 sec or PT of 3 sec over baseline was considered as a positive LA screening test. Patients with a positive screening test were further evaluated with tissue thromboplastin inhibitor assay (TTI), platelet neutralization procedure (PNP, anti-nuclear antibodies (ANA) and blood serology (RPR). In Group A. 11 out of 110 (1096) developed prolonged APTT while on procainamide . Of these, 9 developed abnormal TTI and 2 had positive PNP. The ANA was positive (titers of 1:320-1:2560) in 10 patients with the only positive RPR test, being in the patient with the highest ANA titer. In Group B, 12 out of 80 (1596) developed prolonged APTT, 11 had positive TTI. The ANA titer was elevated in all positive cases, although one patient's titer was 1:30. The PNP was positive in 1/12. All blood serologies were negative in this group. The difference in incidence between Groups A and B may reflect longer exposure to drug in the latter group. This difference is not statistically significant. This study indicates that the incidence of procainamide-induced lupus antocoagulant is between 10-1596 when the APTT (or PT) is used as a screening test. The TTI and ANA seem to have equal sensitivity in this syndrome when taking this drug. The failure of the PNP to be sensitive to LA may be due to the minimal prolongation of the APTT arbitrarily chosen as representing a positive screening test.