BACKGROUND: Dental pain can have a detrimental effect on quality of life. Symptomatic apical periodontitis and acute apical abscess are common causes of dental pain and arise from an inflamed or necrotic dental pulp, or infection of the pulpless root canal system. Clinical guidelines recommend that the first-line treatment for teeth with these conditions should be removal of the source of inflammation or infection by local, operative measures, and that systemic antibiotics are currently only recommended for situations where there is evidence of spreading infection (cellulitis, lymph node involvement, diffuse swelling) or systemic involvement (fever, malaise). Despite this, there is evidence that dentists frequently prescribe antibiotics in the absence of these signs. There is concern that this could contribute to the development of antibiotic-resistant bacterial colonies within both the individual and the community. This review is an update of the original version that was published in 2014. OBJECTIVES: To evaluate the effects of systemic antibiotics provided with or without surgical intervention (such as extraction, incision and drainage of a swelling, or endodontic treatment), with or without analgesics, for symptomatic apical periodontitis and acute apical abscess in adults. SEARCH METHODS: Cochrane Oral Health's Information Specialist searched the following databases: Cochrane Oral Health's Trials Register (to 26 February 2018), the Cochrane Central Register of Controlled Trials (CENTRAL; 2018, Issue 1) in the Cochrane Library (searched 26 February 2018), MEDLINE Ovid (1946 to 26 February 2018), Embase Ovid (1980 to 26 February 2018), and CINAHL EBSCO (1937 to 26 February 2018). The US National Institutes of Health Ongoing Trials Register (ClinicalTrials.gov) and the World Health Organization International Clinical Trials Registry Platform were searched for ongoing trials. A grey literature search was conducted using OpenGrey (to 26 February 2018) and ZETOC Conference Proceedings (1993 to 26 February 2018). No restrictions were placed on the language or date of publication when searching the electronic databases. SELECTION CRITERIA: Randomised controlled trials of systemic antibiotics in adults with a clinical diagnosis of symptomatic apical periodontitis or acute apical abscess, with or without surgical intervention (considered in this situation to be extraction, incision and drainage or endodontic treatment) and with or without analgesics. DATA COLLECTION AND ANALYSIS: Two authors screened the results of the searches against inclusion criteria, extracted data and assessed risk of bias independently and in duplicate. We calculated mean differences (MD) (standardised mean difference (SMD) when different scales were reported) and 95% confidence intervals (CI) for continuous data. A fixed-effect model was used in the meta-analysis as there were fewer than four studies. We contacted study authors to obtain missing information. MAIN RESULTS: We included two trials in this review, with 62 participants included in the analyses. Both trials were conducted in university dental schools in the USA and compared the effects of oral penicillin V potassium (penicillin VK) versus a matched placebo when provided in conjunction with a surgical intervention (total or partial pulpectomy) and analgesics to adults with acute apical abscess or symptomatic necrotic tooth. The patients included in these trials had no signs of spreading infection or systemic involvement (fever, malaise). We assessed one study as having a high risk of bias and the other study as having unclear risk of bias.The primary outcome variables reported in both studies were participant-reported pain and swelling (one trial also reported participant-reported percussion pain). One study reported the type and number of analgesics taken by participants. One study recorded the incidence of postoperative endodontic flare-ups (people who returned with symptoms that necessitated further treatment). Adverse effects, as reported in one study, were diarrhoea (one participant, placebo group) and fatigue and reduced energy postoperatively (one participant, antibiotic group). Neither study reported quality of life measurements.Objective 1: systemic antibiotics versus placebo with surgical intervention and analgesics for symptomatic apical periodontitis or acute apical abscessTwo studies provided data for the comparison between systemic antibiotics (penicillin VK) and a matched placebo for adults with acute apical abscess or a symptomatic necrotic tooth when provided in conjunction with a surgical intervention. Participants in one study all underwent a total pulpectomy of the affected tooth, while participants in the other study had their tooth treated by either partial or total pulpectomy. Participants in both trials received oral analgesics. There were no statistically significant differences in participant-reported measures of pain or swelling at any of the time points assessed within the review. The MD for pain (short ordinal numerical scale 0 to 3) was -0.03 (95% CI -0.53 to 0.47) at 24 hours; 0.32 (95% CI -0.22 to 0.86) at 48 hours; and 0.08 (95% CI -0.38 to 0.54) at 72 hours. The SMD for swelling was 0.27 (95% CI -0.23 to 0.78) at 24 hours; 0.04 (95% CI -0.47 to 0.55) at 48 hours; and 0.02 (95% CI -0.49 to 0.52) at 72 hours. The body of evidence was assessed as at very low quality.Objective 2: systemic antibiotics without surgical intervention for adults with symptomatic apical periodontitis or acute apical abscessWe found no studies that compared the effects of systemic antibiotics with a matched placebo delivered without a surgical intervention for symptomatic apical periodontitis or acute apical abscess in adults. AUTHORS' CONCLUSIONS: There is very low-quality evidence that is insufficient to determine the effects of systemic antibiotics on adults with symptomatic apical periodontitis or acute apical abscess.