Sixty-two women with signs and symptoms compatible with lower urinary tract infections were randomized to receive single-dose tetracycline (2 g), multi-dose tetracycline (500 mg four times per day for 10 days), or single-dose amoxicillin (3 g). Urine cultures were obtained upon entry into the study and on days 4, 14, and 28 after therapy. Single-dose tetracycline cured 12 of 16 (75%) of women with documented urinary tract infections, compared with 15 of 16 (94%) in the multi-dose tetracycline group and 7 of 13 (54%) receiving single-dose amoxicillin. Mild nausea in 3 of 20 patients (15%) was the only complication in the single-dose tetracycline group. Two grams of single-dose tetracycline is as effective as other reported regimens regardless of the susceptibility of the initial pathogen and has minimal toxicity.Symptomatic lower urinary tract infections (UTI) in women are a common problem in the United States. It affects approximately 20% of women during child-bearing years and generates approximately 6 million office visits annually. In recent years, numerous studies have attempted to define an effective, easily administered, nontoxic, inexpensive therapeutic regimen, deliverable in a single oral dose (2, 5-7, 9, 14-16, 18, 19, 23). Although these studies tested a variety of single-dose agents, tetracycline (TCN) has certain properties that make it particularly attractive as a singledose regimen. TCN is active against most common bacterial urinary pathogens (17) and is also one of the most effective antimicrobial agents available for treatment of Chlamydia trachomatis, the etiological agent in perhaps 20% of women with the acute urethral syndrome (22). TCN is inexpensive ($0.16 for 2 g at our pharmacy), has a low incidence of toxicity in nonpregnant adults, and is largely excreted through urine (12). TCN has been used successfully without significant toxicity in single-dose regimens for shigellosis (4, 13) and gonorrhea (3,11). We previously evaluated the efficacy of a 2.5-g single-dose TCN (SDT) in uncomplicated UTI and reported that although it was efficacious, frequent gastrointestinal toxicity limited its use (unpublished data). In this study, we compared the efficacy and adverse side effects of a 2-g SDT in the therapy of UTI to single-dose amoxicillin (SDA) (3 g) and to 10 days of TCN (500 mg mented UTI in the preceeding 2 years, or allergy to penicillin or TCN. Informed consent was obtained from all patients.At the initial visit, the following specimens were obtained: a urethral swab, two cervical swabs, and a clean-catch midstream urine (MSU) sample. The MSU was examined chemically by dipstick (N-Multistix-C; Ames Co., Elkhart, Ind.) and cultured by standard microbiological techniques. Antimicrobial susceptibility testing was determined by the Kirby-Bauer disk method. Positive MSU cultures had colony counts greater than or equal to 1,000 organisms per ml of a single isolate (20). The MSU sediment was prepared in duplicate by centrifuging 10-ml portions for 10 min at 1,500 x g. One sediment was suspende...