Over a period of 5 years, a clinic in Los Angeles used a non-recommended preparation of penicillin to treat nearly 700 syphilis patients and their contacts, according a study released Thursday.

At least one of the patients may have progressed to a more serious form of the disease because of the mix-up.

The incorrect use of the drug was tracked to similarities in proprietary names and packaging of the different preparations, according to an article in the CDC’s Morbidity and Mortality Weekly Report.

The recommended drug, Bicillin L-A, contains 2.4 million units (MU) of benzathine penicillin G. The preparation that was used by mistake, Bicillin C-R, contains a mixture of 1.2 MU benzathine penicillin G and 1.2 MU procaine penicillin, lead author Dr. R. Bolan, of the Los Angeles Gay and Lesbian Center, and associates point out.

Bicillin C-R contains only half the recommended dose of benzathine penicillin G, and levels in the blood are maintained for up to 7 days. In contrast, Bicillin L-A produces effective concentrations for up to 30 days, according to an editorial comment by officials at the Centers for Disease Control and Prevention.

“Prolonged serum concentration is considered essential for treating syphilis effectively,” the CDC editors write.

Between 1999 and 2004, 429 patients with syphilis and 234 of their sexual contacts were incorrectly treated with Bicillin C-R.

Letters, telephone calls, and published press releases were used to reach the patients for re-testing and re-treatment.

Of the original syphilis patients, 282 were successfully contacted and 255 were retreated. One patient who was originally given the wrong drug developed neurosyphilis - that is, infection of the brain and nervous system, which can lead to dementia if untreated.

Among the 234 sexual contacts, 116 were re-contacted. Of these, 22 had serologic evidence of previous syphilis infection and 19 were re-treated.

The investigators are concerned that other facilities may have made the same mistake as the L. A. clinic. “Providers, STD clinics, and pharmacies should review their product records and tracking systems for ordering and delivering penicillin treatments for syphilis,” they advise.

As a result of the mix-up, the CDC and the US Food and Drug Administration have worked with the drugs’ manufacturer, King Pharmaceuticals, to change the product labeling and to print warnings on Bicillin C-R syringes and packaging.

SOURCE: Morbidity and Mortality Weekly Report, March 11, 2005.