Correspondence 890 www.thelancet.com/infection Vol 16 August 2016 have given preference to efavirenz over nevirapine in recognition of the inferior efficacy of the tenofivir and nevirapine combination, and although 30% of patients in low- income and middle-income countries in the TeNoRes study received nevirapine, most countries no longer recommend nevirapine in first- line ART. The association between lamivudine use and increased risk of resistance is less compelling. In the TeNoRes study, only four of 30 studies found a statistically significant association between lamivudine and tenofovir resistance, while the remainder found no difference, which is consistent with data from randomised trials. 6 Although the TeNoRes study provides important data for resistance patterns among ART failures, and therefore informs optimal selection of subsequent regimens, we do not think that these data warrant reconsideration of tenofovir as a preferred first-line agent, the interchangeability of lamivudine and emtricitabine, or the need for resistance testing for patient monitoring. WHO’s recommended surveillance of HIV resistance to drugs used in first line regimens, including tenofovir, is intended to gain a better understanding of the extent of pre-treatment drug resistance. 7 Present rates do not justify a move away from current policy and practice, but WHO will continue to assess the latest data and incorporate these data into future ART guideline revisions. We declare no competing interests. *Nathan Ford, Marco Vitoria, Meg Doherty, Silvia Bertagnolio fordn@who.int Department of HIV, World Health Organization, Geneva, Switzerland 1 WHO. Consolidated guidelines on the use of antiretroviral drugs for treating and preventing HIV infection: Recommendations for a public health approach. 2015. http://www.who.int/ hiv/pub/arv/arv-2016/en/ (accessed July 1, 2016). Tenofovir resistance and first-line antiretroviral therapy Since 2013, WHO guidelines have recommended a single regimen of tenofovir combined with efavirenz and either lamivudine or emtricitabine for treatment of HIV in adults and adolescents. This recommended regimen has been widely adopted by countries and is maintained in WHO’s updated 2016 guidelines. 1 The TeNoRes study group showed that a high proportion of patients who failed a tenofovir-containing antiretroviral therapy (ART) regimen carry an HIV virus that is resistant to this drug, which is concerning. 2 These findings raise questions around the suitability of the recommended first-line regimen and the need for affordable drug resistance testing for patient care in low-income and middle-income countries. 3 Although this study is important in providing data for the nature of acquired drug resistance, the choice of first-line regimens should be based on levels of drug resistance among individuals who have yet to start ART, known as pre-treatment drug resistance. Although updated data are needed, available data up to 2013 suggest that rates of transmitted tenofovir resistance remain low, at 0·4% in sub-Saharan Africa. 4 In the TeNoRes study, risk of acquired tenofovir resistance was associated with late presentation at start of ART and the use of nevirapine compared with efavirenz, and lamivudine compared with emtricitabine, as partner drugs. Although baseline CD4 cell count at start of ART is increasing over time, late presentation-to-care persists. 5 WHO recommends that ART should be started at any CD4 cell count as this approach will help reduce the proportion of people starting ART late. 1 Since 2013, WHO guidelines to use serial procalcitonin measure- ment, 1 which provides substantially more information than a single measure ment. Daily procalcitonin is a valuable additional laboratory measurement that helps improve the quality of the decision whether to continue or discontinue antibiotics, but no more than that. Therefore, when a stopping criterion was reached, the algorithm explicitly provided advice—but not an order— to stop. The freedom of the attending physician to take other factors into account is underscored by the large number of patients for whom antibiotics were continued after advice to discontinue was provided by the algorithm. 1 We believe that the potential in reducing inappropriate antibiotic use in the intensive care unit is large. With its limitations, the SAPS trial showed that daily procalcitonin measurements facilitated a safe reduction in antibiotic duration. In many patients, 5 days of antibiotic treatment are sufficient. In view of the global health threats posed by increasing antibiotic resistance, this is a fact that should not be ignored. University Medical Centre Utrecht, as part of the steering group of the SAPS study, received financial compensation for the online case record forms from Thermo Fisher. *Evelien de Jong, Jos A van Oers, Albertus Beishuizen, Armand R Girbes, Maarten W Nijsten, Dylan W de Lange ev.dejong@vumc.nl VU University Medical Center, 1081 HV Amsterdam, Netherlands (EdJ, AB, ARG); Medisch Spectrum Twente, Enschede, Netherlands (AB); Elisabeth Tweesteden Hospital, Tilburg, Netherlands (JAvO); University Medical Centre, University of Groningen, Groningen, Netherlands (MWN); and University Medical Centre Utrecht, Utrecht, Netherlands (DWdL) 1 de Jong E, van Oers JA, Beishuizen A, et al. Efficacy and safety of procalcitonin guidance in reducing the duration of antibiotic treatment in critically ill patients: a randomised, controlled, open-label trial. Lancet Infect Dis 2016; 16: 819–27. 2 Kip MM, Kusters R, IJzerman MJ, Steuten LM. A PCT algorithm for discontinuation of antibiotic therapy is a cost-effective way to reduce antibiotic exposure in adult intensive care patients with sepsis. J Med Econ 2015; 18: 944–53.