Abstract: Four trials that randomised a total of 268 participants met the inclusion criteria. In all four studies antibiotic was administered orally. One study conducted in Brazil in both adults and children compared trimethoprim-sulfamexacocol over 20 months to no treatment and was judged to be at high risk of performance, detection, and attrition bias. The other three studies compared antibiotic treatment to placebo. We judged these three studies to be at a mixture of low or unclear risk of bias due to poor reporting. One study conducted in the US in adults studied pyrimethamine-trisulfapyrimidine for eight weeks; one study conducted in the UK in children and adults evaluated pyrimethamine for four weeks; and one study conducted in Brazil in adults investigated trimethoprim-sulfamethoxazole for 12 months. In the last study, all participants had active retinochoroiditis and were treated with antibiotics for 45 days prior to randomisation to trimethoprim-sulfamethoxazole versus placebo. Only the study in Brazil of trimethoprim-sulfamethoxazole over 12 months, in participants with healed lesions, reported the effect of treatment on visual acuity. People treated with antibiotics may have a similar change in visual acuity compared with people treated with placebo at one year (mean difference -1.00 letters, 95% confidence interval (CI) -7.93 to 5.93 letters; 93 participants; low-quality evidence). Treatment with antibiotics probably reduces the risk of recurrent retinochoroiditis compared with placebo (risk ratio (RR) 0.26, 95% CI 0.11 to 0.63; 227 participants; 3 studies; I2 = 0%; moderate-quality evidence); similar results were seen for acute and chronic retinochoroiditis. The UK study of pyrimethamine for four weeks reported an improvement in intraocular inflammation in treated compared with control participants (RR 1.76, 95% CI 0.98 to 3.19; 29 participants; low-quality evidence). The study in Brazil of trimethoprim-sulfamethoxazole for 12 months stated that the severity of inflammation was higher in the comparator group when compared to the antibiotic-treated group but did not provide further details. In the US study of pyrimethamine-trisulfapyrimidine for eight weeks intraocular inflammation had almost completely resolved by eight weeks in all participants, however in this study all participants received steroid treatment. Two studies (UK and US studies) reported an increased risk of adverse events in treated participants. These were a fall in haemoglobin, leucocyte, and platelet count, nausea, loss of appetite, rash, and arthralgia. Treatment with antibiotics probably reduces the risk of recurrent toxoplasma retinochoroiditis, but there is currently no good evidence that this leads to better visual outcomes. However, absence of evidence of effect is not the same as evidence of no effect. Further trials of people with acute and chronic toxoplasma retinochoroiditis affecting any part of the retina are required to determine the effects of antibiotic treatment on visual outcomes.

Plain-language summary: We found four studies with a total of 268 participants. These studies were conducted in Brazil, the UK, and the US. The evidence is current to 22 February 2016. Only one of the four studies compared the effect of antibiotic treatment for 12 months with placebo on visual acuity and found similar changes in both groups. Three studies examined the effect of antibiotics on reducing the number of recurring episodes of the disease. Two of these three studies were conducted in Brazil in adults infected with the more aggressive South American strains of the parasite, which can cause frequently recurring eye symptoms. The studies from Brazil found that the long-term antibiotics over 14 and 12 months, respectively, reduced the number of recurrent episodes of retinochoroiditis. The other study did not find that short-term (eight weeks) treatment with antibiotics made any difference. Two studies reported an improvement in intraocular inflammation in antibiotic-treated compared with untreated participants, and one study reported no changes. Two studies investigated side effects of giving antibiotics such as decreased white blood cells, loss of appetite, rashes and other allergic reactions and found only weak evidence that antibiotics increase the risk of side effects. There were problems with the design, conduct, and analyses of all of the studies, which could have biased the results. There was a lack of evidence about whether antibiotics (short or long term) prevent vision loss. More trials are needed, including trials of newer antibiotics.