Data are available such that choice of Helicobacter pylori therapy for an individual patient can be reliably predicted. Here, treatment success is defined as a cure rate of 90% or greater. Treatment outcome in a population or a patient can be calculated based on the effectiveness of a regimen for infections with susceptible and with resistant strains coupled with the knowledge of the prevalence of resistance (ie, based on formal measurement, clinical experience, or both). We provide the formula for predicting outcome and we illustrate the calculations. Because clarithromycin-containing triple therapy and 10-day sequential therapy are now only effective in special populations, they are considered obsolete; neither should continue to be used as empiric therapies (ie, 7- and 14-day triple therapies fail when clarithromycin resistance exceeds 5% and 15%, respectively, and 10-day sequential therapy fails when metronidazole resistance exceeds 20%). Therapy should be individualized based on prior history and whether the patient is in a high-risk group for resistance. The preferred choices for Western countries are 14-day concomitant therapy, 14-day bismuth quadruple therapy, and 14-day hybrid sequential-concomitant therapy. We also provide details regarding the successful use of fluoroquinolone-, rifabutin-, and furazolidone-containing therapies. Finally, we provide recommendations for the efficient development (ie, identification and optimization) of new regimens, as well as how to prevent or minimize failures. The trial-and-error approach for identifying and testing regimens frequently resulted in poor treatment success. The described approach allows outcome to be predicted and should simplify treatment and drug development. Data are available such that choice of Helicobacter pylori therapy for an individual patient can be reliably predicted. Here, treatment success is defined as a cure rate of 90% or greater. Treatment outcome in a population or a patient can be calculated based on the effectiveness of a regimen for infections with susceptible and with resistant strains coupled with the knowledge of the prevalence of resistance (ie, based on formal measurement, clinical experience, or both). We provide the formula for predicting outcome and we illustrate the calculations. Because clarithromycin-containing triple therapy and 10-day sequential therapy are now only effective in special populations, they are considered obsolete; neither should continue to be used as empiric therapies (ie, 7- and 14-day triple therapies fail when clarithromycin resistance exceeds 5% and 15%, respectively, and 10-day sequential therapy fails when metronidazole resistance exceeds 20%). Therapy should be individualized based on prior history and whether the patient is in a high-risk group for resistance. The preferred choices for Western countries are 14-day concomitant therapy, 14-day bismuth quadruple therapy, and 14-day hybrid sequential-concomitant therapy. We also provide details regarding the successful use of fluoroquinolone-, rifabutin-, and furazolidone-containing therapies. Finally, we provide recommendations for the efficient development (ie, identification and optimization) of new regimens, as well as how to prevent or minimize failures. The trial-and-error approach for identifying and testing regimens frequently resulted in poor treatment success. The described approach allows outcome to be predicted and should simplify treatment and drug development. Similar to other infectious diseases, the factors responsible for effective antimicrobial therapy of a Helicobacter pylori infection as well as those responsible for treatment failure are both straightforward and easily discoverable. Poorly designed or executed regimens rarely produce good results. Treatment success depends on the details of the regimen including choice of drugs, doses, formulations, duration of therapy, administration in relation to meals, number of administrations/day, the use of adjuvants such as antisecretory drugs or mucolytics, and so forth.1Graham D.Y. Helicobacter pylori eradication therapy research: ethical issues and description of results.Clin Gastroenterol Hepatol. 2010; 8: 1032-1036Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar Results can be defined in terms of treatment success.2Graham D.Y. Fischbach L.A. Empiric therapies for Helicobacter pylori infections.CMAJ. 2011; 183: E506-E508Crossref PubMed Scopus (15) Google Scholar, 3Rimbara E. Fischbach L.A. Graham D.Y. Optimal therapy for Helicobacter pylori infections.Nat Rev Gastroenterol Hepatol. 2011; 8: 79-88Crossref PubMed Scopus (165) Google Scholar For exploratory studies the primary outcome generally is expressed per protocol (PP), which controls for compliance and other variables and thus provides an indication of the potential maximum success of the regimen in clinical practice.1Graham D.Y. Helicobacter pylori eradication therapy research: ethical issues and description of results.Clin Gastroenterol Hepatol. 2010; 8: 1032-1036Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar For the information to be useful and to be used to predict success in other groups, regions, and populations, the results also should be provided as the outcomes with both susceptible and resistant strains (see later). In addition, the data also should be expressed as both modified intention to treat (MITT) (which is the outcome of all who received a dose and for whom an outcome measure is available), and as intention to treat (ITT), in which those lost to follow-up evaluation typically are scored as treatment failures. ITT and MITT provide estimates of a regimen’s actual success in clinical practice. PP and MITT are the most useful for the development of new regimens, whereas for large multicenter randomized comparisons most authorities prefer ITT.4Sheiner L.B. Rubin D.B. Intention-to-treat analysis and the goals of clinical trials.Clin Pharmacol Ther. 1995; 57: 6-15Crossref PubMed Scopus (259) Google ScholarConsidering that H pylori is a common infectious disease and 100% success is obtainable, outcome (eg, PP or ITT) also is scored in terms of efficacy (ie, as excellent, good, borderline acceptable, or unacceptable) because efficacy is the most important measure for patient care. For evaluating new therapies we score success (PP with susceptible strains) as excellent (≥95% success), good (≥90 success), borderline acceptable (85%–89% success), or unacceptable (<85% success). The most common causes for reliably good or excellent regimens to fail are the presence of organisms resistant to one or more of the antimicrobials used, poor compliance with therapy, or both. A number of studies have suggested a variety of miscellaneous factors that might be important including age, presentation (eg, nonulcer dyspepsia vs duodenal ulcer), and CagA status.5Broutet N. Marais A. Lamouliatte H. et al.cagA Status and eradication treatment outcome of anti-Helicobacter pylori triple therapies in patients with nonulcer dyspepsia.J Clin Microbiol. 2001; 39: 1319-1322Crossref PubMed Scopus (70) Google Scholar, 6Scaccianoce G. Hassan C. Panarese A. et al.Helicobacter pylori eradication with either 7-day or 10-day triple therapies, and with a 10-day sequential regimen.Can J Gastroenterol. 2006; 20: 113-117Crossref PubMed Scopus (73) Google Scholar, 7Suzuki T. Matsuo K. Ito H. et al.Smoking increases the treatment failure for Helicobacter pylori eradication.Am J Med. 2006; 119: 217-224Abstract Full Text Full Text PDF PubMed Scopus (147) Google Scholar However, these candidates typically have been discovered in data-dredging studies in which resistance was not assessed, and most of the studies lacked biologic plausibility. Although some of these factors (eg, nonulcer dyspepsia vs duodenal ulcer) have proven to be surrogates for differences in the prevalence of resistant strains,8Taneike I. Nami A. O'Connor A. et al.Analysis of drug resistance and virulence-factor genotype of Irish Helicobacter pylori strains: is there any relationship between resistance to metronidazole and cagA status?.Aliment Pharmacol Ther. 2009; 30: 784-790Crossref PubMed Scopus (32) Google Scholar, 9Zullo A. Perna F. Hassan C. et al.Primary antibiotic resistance in Helicobacter pylori strains isolated in northern and central Italy.Aliment Pharmacol Ther. 2007; 25: 1429-1434Crossref PubMed Scopus (102) Google Scholar none of the clinical correlates other than resistance and compliance has proven to be important in studies in which compliance and resistance have been assessed.Therapy ChoiceSimilar to other infectious diseases, treatment results are best when reliably excellent regimens are used to treat patients with organisms susceptible to the antimicrobials chosen. Pretreatment susceptibility testing, either by culture of the organism or indirectly by molecular testing of stools of infected patients or fluorescent in-situ hybridization using paraffin-embedded gastric biopsy specimens, allows one to select a regimen tailored by antimicrobial susceptibility (ie, tailored therapy).3Rimbara E. Fischbach L.A. Graham D.Y. Optimal therapy for Helicobacter pylori infections.Nat Rev Gastroenterol Hepatol. 2011; 8: 79-88Crossref PubMed Scopus (165) Google Scholar However, in many instances, one must choose therapy empirically and, in this instance, the best approach is to use regimens that have been proven to be reliably excellent locally.2Graham D.Y. Fischbach L.A. Empiric therapies for Helicobacter pylori infections.CMAJ. 2011; 183: E506-E508Crossref PubMed Scopus (15) Google Scholar That choice should take advantage of knowledge of resistance patterns obtained from local or regional antimicrobial surveillance programs and/or based on local clinical experience with regard to which regimens are effective locally. Finally, the history of the patient’s prior antibiotic use and any prior therapies will help identify which antibiotics are likely to be successful and those for which resistance is probable (Figure 1).All other things being equal, data from any area or region regarding the effects of resistance on outcome can be used reliably to predict outcome in any other area. Thus, strains with similar patterns of resistance in Italy, the United States, Iran, China, and so forth should be expected to respond alike such that, if one knows the results with susceptible and with resistant strains in one place, one reasonably can predict the outcome of therapy anywhere.Using Available Data to Predict Treatment SuccessAn optimized regimen is defined as one that reliably achieves 95% or greater cures in patients with susceptible organisms. Although the effectiveness of any regimen can be undermined by antimicrobial resistance, the effect of resistance is not random and the effect of any particular level of resistance can be estimated based on studies with that combination elsewhere, for example, use of the optimized regimen (14-day concomitant therapy, consisting of a proton pump inhibitor [PPI], clarithromycin, metronidazole, and amoxicillin, given twice a day for 14 days).10Molina-Infante J. Romano M. Fernandez-Bermejo M. et al.Optimized non-bismuth quadruple therapies cure most patients with Helicobacter pylori infection in populations with high rates of antibiotic resistance.Gastroenterology. 2013; 145: 121-128Abstract Full Text Full Text PDF PubMed Scopus (153) Google Scholar The regimen contains 4 drugs, but for the purpose of understanding the effects of resistance can best be considered as the simultaneous administration of 2 triple therapies plus a dual therapy (eg, a PPI–amoxicillin-clarithromycin plus a PPI–amoxicillin-metronidazole plus a PPI-amoxicillin dual therapy). Both triple regimens individually will reliably achieve 95% or greater success PP with susceptible strains whereas the dual component will achieve approximately 50% success with clarithromycin- and metronidazole-resistant strains (ie, the strains are only susceptible to amoxicillin). If resistance to clarithromycin or metronidazole was not present, there would be no indication to use the 4-drug regimen. However, when resistance results in unacceptably low treatment success rates when either is used empirically, the 4-drug combination might be considered.Unless there is an interaction between the antibiotics, the treatment population can be visualized as 4 separate subgroups: one group with organisms susceptible to all antibiotics, one group with only clarithromycin-resistant organisms, another group with only metronidazole-resistant organisms, and the final group with organisms resistant to both (here, we assume an absence of resistance to amoxicillin). The subgroups without resistance and those resistant to a single drug will each receive an optimized triple therapy for their infection and most will be cured, and the overall success thus will depend entirely on the success of the PPI-amoxicillin therapy for those with dual clarithromycin-metronidazole resistance.In this example, both triple therapies achieve 97% treatment success and the dual therapy achieves 50% success (Table 1). One can calculate that treatment success will remain at or above 90% until dual resistance exceeds 15%. That calculation is based on the following formula: (% success with all-susceptible strains) (proportion with all-susceptible infections) + (% success with clari-susceptible strains) (proportion with clari-susceptible infections) + (% success with met-susceptible strains) (proportion with met-susceptible infections) + (% success with dual resistant strains) (proportion with dual resistant strains) = 90%. Because the success with organisms susceptible to all antibiotics and single-drug resistances is the same, the 2 triple therapies can be combined to simplify the calculation (eg, where X = the proportion with dual resistance, the formulas is 0.97 (1 − X) + 0.5 X = ∼0.90, and thus X = 14.9%). Table 1 lists the approximate success rates with a number of common therapies.Table 1Approximate Treatment Success PP With Susceptible Strains (Western Results)TherapyDaysSuccess rateClarithromycin triple therapy794%Clarithromycin triple therapy1497%Sequential therapy1094%Sequential therapy1497%Hybrid therapy1497%Fluoroquinolone triple therapy7<80%Fluoroquinolone triple therapy10<90%Fluoroquinolone triple therapy1496%PPI + amoxicillin therapyaEquals triple therapies but with clari-, met-, or fluoroquinolone-resistant infections.510%PPI + amoxicillin therapyaEquals triple therapies but with clari-, met-, or fluoroquinolone-resistant infections.715%PPI + amoxicillin therapy1020%PPI + amoxicillin therapyaEquals triple therapies but with clari-, met-, or fluoroquinolone-resistant infections.1450%PPI metronidazole triple therapy794%PPI metronidazole triple therapy1497%PPI-bismuth tetracycline, metronidazole therapy14>95%a Equals triple therapies but with clari-, met-, or fluoroquinolone-resistant infections. Open table in a new tab Resistance EffectsTriple therapies containing a PPI and amoxicillin plus clarithromycin, metronidazole, a fluoroquinolone, or rifabutin all are extremely sensitive to resistance to the third drug. Resistance to clarithromycin, fluoroquinolones, and rifabutin cannot be overcome by increasing the dose or duration. By using the earlier-described formula one can calculate that 7-day clarithromycin-containing triple therapy will decrease to less than 90% success when clarithromycin resistance exceeds 5% (or 15% when the regimen is given for 14 days).The 4-drug nonbismuth clarithromycin-containing sequential and concomitant therapies are extremely sensitive to dual clarithromycin-metronidazole resistance, which reduces the regimens to contain only the PPI-amoxicillin component. Because the prevalence of dual resistance has such a great effect, it is important to consider how dual resistance might be acquired and what clinical factors might help predict its prevalence. Probably the most important variable is whether dual resistance is acquired from one encounter with both drugs or from separate encounters. For example, the prevalence of metronidazole resistance in many developing countries is greater than 40%, and often is 80% or greater. In these countries both drugs are rarely given together and the prevalence of dual resistance depends primarily on the prevalence of clarithromycin resistance such that the proportion of patients with dual resistance will be approximately the same as the prevalence of clarithromycin resistance. In Nicaragua, the prevalence of metronidazole resistance is at least 80%, and thus dual resistance would exceed 15% whenever clarithromycin resistance exceeded 19% (ie, 80% of 19 = 15.2%).11Graham D.Y. Gonzalez C. Palacios C. et al.Importance of determining the pattern of H. pylori resistance in countries with a high prevalence of gastric cancer such as Nicaragua.Helicobacter. 2011; 11: 136Google Scholar In Southern Europe, metronidazole resistance is approximately 30% (Supplementary Figure 1),12Megraud F. Coenen S. Versporten A. et al.Helicobacter pylori resistance to antibiotics in Europe and its relationship to antibiotic consumption.Gut. 2013; 62: 34-42Crossref PubMed Scopus (665) Google Scholar and if acquisition of resistance to each drug were truly independent, clarithromycin resistance would need to exceed 50% to undermine 14-day concomitant therapy. However, even in low metronidazole resistance prevalence countries, pockets of high prevalence of metronidazole resistance often exist in which dual resistance may exceed 15% (eg, in women in whom metronidazole is used for trichomonas infections, immigrants from developing countries, and patients who previously failed sequential or PPI-clarithromycin-metronidazole triple therapy). For such high-risk groups, empiric concomitant or sequential therapies likely would be poor choices.Current Recommended RegimensCaveatIt should be recognized that the data pool from which the outcomes of various therapies with susceptible and resistant organisms are available is not large, making the numbers we have used in our calculations imprecise, and our calculations are only approximations (Table 2). Sadly, the lack of data is related to the fact that resistance is not collected in most trials. Nonetheless, the results shown provide reasonable estimates of what can be expected, and the appendix to the recent article by Liou et al13Liou J.M. Chen C.C. Chen M.J. et al.Sequential versus triple therapy for the first-line treatment of Helicobacter pylori: a multicentre, open-label, randomised trial.Lancet. 2013; 381: 205-213Abstract Full Text Full Text PDF PubMed Scopus (205) Google Scholar provides additional details, comparisons, and sensitivity analyses, as well as a useful online calculator (https://hp-therapy.biomed.org.tw/) based on data from their comparison of 10- and 14-day sequential therapy and 14-day triple therapy in Taiwan.Table 2H pylori Therapies Recommended for Empiric Therapy in Western CountriesFor general use 14-day concomitant therapy 14-day bismuth quadruple therapy 14-day hybrid sequential-concomitant therapyAreas where there is clarithromycin-metronidazole dual resistance <5% 14-day sequential therapyWith fluoroquinolone resistance 14-day fluoroquinolone triple therapy <13% 14-day fluoroquinolone bismuth therapy <25% 5-day fluoroquinolone concomitant therapy <20%Salvage therapies (after ≤2 failures with different drug combinations) Dependent on background rates of resistance and prior drug use by subjectOne of the earlier-mentioned regimens14-day furazolidone bismuth quadruple therapyA rifabutin regimen, preferably for 14 daysObsolete regimens for use only in special low-resistance populations 14-day clarithromycin-containing triple therapy 14-day metronidazole-containing triple therapy 10-day sequential therapyNOTE. These are recommendations for populations. See text for details of therapies and for modifications when considering an individual patient. Open table in a new tab The most variable results are probably those regarding the expected outcomes of PPI-amoxicillin dual therapies. However, this group generally represents only a small proportion of cases. The data used here primarily are derived from Western studies that have shown that 14-day dual therapy yields approximately 50% success, and results greater than 50% are uncommon when using the doses and durations typically used with common therapies, and success decreases as the duration decreases. The actual results will depend in part on the effectiveness of the PPI in increasing the intragastric pH to high levels (eg, pH 6). PPI effectiveness depends in part on the PPI used, its dose and frequency of administration, the effects of CYP2C19 on the metabolism of the PPI14Furuta T. Graham D.Y. Pharmacologic aspects of eradication therapy for Helicobacter pylori infection.Gastroenterol Clin North Am. 2010; 39: 465-480Abstract Full Text Full Text PDF PubMed Scopus (88) Google Scholar (and potentially some antibiotics), as well as the ability of the stomach to produce acid. The results reported here probably err slightly on the optimistic side but are consistent with the use of the formulas described previously with data from clinical trials.Concomitant TherapyMeta-analyses have shown that the outcome of concomitant therapy (PPI-amoxicillin 1 g, clarithromycin 500 mg, metronidazole/tinidazole 500 mg, all twice daily for 14 days) is duration dependent,15Essa A.S. Kramer J.R. Graham D.Y. et al.Meta-analysis: four-drug, three-antibiotic, non-bismuth-containing “concomitant therapy” versus triple therapy for Helicobacter pylori eradication.Helicobacter. 2009; 14: 109-118Crossref PubMed Scopus (189) Google Scholar, 16Gisbert J.P. Calvet X. Review article: non-bismuth quadruple (concomitant) therapy for eradication of Helicobacter pylori.Aliment Pharmacol Ther. 2011; 34: 604-617Crossref PubMed Scopus (139) Google Scholar which was confirmed in a recent head-to-head comparison of 5- and 10-day concomitant therapies in Thailand, where 5-day therapy proved unsatisfactory,17Kongchayanun C. Vilaichone R.K. Pornthisarn B. et al.Pilot studies to identify the optimum duration of concomitant Helicobacter pylori eradication therapy in Thailand.Helicobacter. 2012; 17: 282-285Crossref PubMed Scopus (39) Google Scholar and by failure of 5-day concomitant therapy in Central and South America (ie, regions with known high levels of metronidazole resistance).18Greenberg E.R. Anderson G.L. Morgan D.R. et al.14-day triple, 5-day concomitant, and 10-day sequential therapies for Helicobacter pylori infection in seven Latin American sites: a randomised trial.Lancet. 2011; 378: 507-514Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar The Achilles' heel of concomitant therapy is dual metronidazole-clarithromycin resistance. Fourteen-day concomitant therapy is a preferred initial empiric therapy for areas and patient groups in whom dual resistance is unlikely, but is not recommended as a first-line empiric regimen where metronidazole resistance is likely greater than 60%, such as China, Iran, India, central and South America, or in populations at high risk of dual resistance (ie, after clarithromycin or metronidazole treatment failures).Hybrid TherapyHybrid therapy (PPI, amoxicillin 1 g for 14 days with amoxicillin 1 g, clarithromycin 500 mg, metronidazole/tinidazole 500 mg given for the final 7 days, all twice a day) combines sequential and concomitant therapy because all 4 drugs are given together. This is a new regimen with only a few published studies.10Molina-Infante J. Romano M. Fernandez-Bermejo M. et al.Optimized non-bismuth quadruple therapies cure most patients with Helicobacter pylori infection in populations with high rates of antibiotic resistance.Gastroenterology. 2013; 145: 121-128Abstract Full Text Full Text PDF PubMed Scopus (153) Google Scholar, 19Sardarian H. Fakheri H. Hosseini V. et al.Comparison of hybrid and sequential therapies for Helicobacter pylori eradication in Iran: a prospective randomized trial.Helicobacter. 2013; 18: 129-134Crossref PubMed Scopus (78) Google Scholar, 20Hsu P.I. Wu D.C. Wu J.Y. et al.Modified sequential Helicobacter pylori therapy: proton pump inhibitor and amoxicillin for 14 days with clarithromycin and metronidazole added as a quadruple (Hybrid) therapy for the final 7 days.Helicobacter. 2011; 16: 139-145Crossref PubMed Scopus (140) Google Scholar In a head-to-head comparison with 14-day concomitant therapy they appeared to be equivalent, albeit hybrid therapy was more complicated. Further studies are needed to identify if there are important differences in relation to success in the face of different patterns of resistance. It could be considered in the same populations in whom concomitant therapy is recommended; 14-day hybrid therapy is expected to decrease to less than 90% when clarithromycin-metronidazole resistance exceeds 9%.Bismuth Quadruple TherapyBismuth quadruple therapy (PPI twice daily, bismuth 4 times daily, tetracycline HCl 500 mg 4 times daily, metronidazole 500 mg 3 times daily for 14 days) is the oldest effective therapy and still one for which we do not yet know the optimal dose. With attention to detail regarding the dose and duration, the primary Achilles' heel is compliance. Tetracycline resistance is rare but currently many countries are experiencing a general unavailability of tetracycline. Generally, doxycycline is not an adequate substitute.By using this regimen at full doses and for 14 days one can expect 95% or greater treatment success irrespective of the level of metronidazole resistance.21Salazar C.O. Cardenas V.M. Reddy R.K. et al.Greater than 95% success with 14-day bismuth quadruple anti-Helicobacter pylori therapy: a pilot study in US Hispanics.Helicobacter. 2012; 17: 382-389Crossref PubMed Scopus (37) Google Scholar, 22Liang X. Xu X. Zheng Q. et al.Efficacy of bismuth-containing quadruple therapies for clarithromycin-, metronidazole-, and fluoroquinolone-resistant Helicobacter pylori infections in a prospective study.Clin Gastroenterol Hepatol. 2013; 11: 802-807Abstract Full Text Full Text PDF PubMed Scopus (120) Google Scholar Therapy for 7 and probably for 10 days is very susceptible to metronidazole resistance; however, the prevalence of resistance, which results in a decrease in outcome to less than 90%, is probably approximately 30%.23Fischbach L. Evans E.L. Meta-analysis: the effect of antibiotic resistance status on the efficacy of triple and quadruple first-line therapies for Helicobacter pylori.Aliment Pharmacol Ther. 2007; 26: 343-357Crossref PubMed Scopus (308) Google ScholarThis regimen also has the most unanswered questions regarding the optimal doses and frequency of drug administration. For example, in Italy, dosing only with the mid-day and evening meals was effective despite a dose reduction to half of the recommend dose.24Dore M.P. Farina V. Cuccu M. et al.Twice-a-day bismuth-containing quadruple therapy for Helicobacter pylori eradication: a randomized trial of 10 and 14 days.Helicobacter. 2011; 16: 295-300Crossref PubMed Scopus (44) Google Scholar, 25Dore M.P. Maragkoudakis E. Pironti A. et al.Twice-a-day quadruple therapy for eradication of Helicobacter pylori in the elderly.Helicobacter. 2006; 11: 52-55Crossref PubMed Scopus (23) Google Scholar Treatment with resistant strains was less effective when administered at breakfast and the evening meal.26Graham D.Y. Belson G. Abudayyeh S. et al.Twice daily (mid-day and evening) quadruple therapy for H. pylori infection in the United States.Dig Liver Dis. 2004; 36: 384-387Abstract Full Text Full Text PDF PubMed Scopus (0) Google Scholar Recent studies from China in a population with essentially universal metronidazole resistance also used twice-daily bismuth and full 4 times daily doses and dosing intervals for the antibiotics with excellent results.22Liang X. Xu X. Zheng Q. et al.Efficacy of bismuth-containing quadruple therapies for clarithromycin-, metronidazole-, and fluoroquinolone-resistant Helicobacter pylori infections in a prospective study.Clin Gastroenterol Hepatol. 2013; 11: 802-807Abstract Full Text Full Text PDF PubMed Scopus (120) Google ScholarBecause of the relative high rate of side effects, optimization is needed in terms of formulations, forms of bismuth, doses, and dosing intervals, as well as effectiveness in relation to the minimal inhibitory concentrations of metronidazole. Two caveats: the Etest overestimates the prevalence of metronidazole resistance such that resistance always should be confirmed (eg, by agar dilution) for an accurate estimation of effectiveness in the presence of resistance.27Osato M.S. Reddy R. Reddy S.G. et al.Comparison of the Etest and the NCCLS-approved agar dilution method to detect metronidazole and clarithromycin resistant Helicobacter pylori.Int J Antimicrob Agents. 2001; 17: 39-44Crossref PubMed Scopus (106) Google Scholar, 28Osato M.S. Graham D.Y. Etest for metronidazole susceptibility in H. pylori: use of the wrong standard may have led to the wrong conclusion.Am J Gastroenterol. 2004; 99: 769Crossref PubMed Scopus (8) Google ScholarTherapies Generally Recommended Only for Geographic Areas With a Low Prevalence of ResistanceClarithromycin-Containing Triple TherapyDespite the Maastricht IV recommendations, clarithromycin-containing triple therapy (PPI, amoxicillin 1 g, clarithromycin 500 mg, all twice a day for 14 days) is an obsolete therapy whether given for 7, 10, or 14 days.29Malfertheiner P. Megraud F. O'Morain C.A. et al.Management of Helicobacter pylori infection–the Maastricht IV/ Florence Consensus Report.Gut. 2012; 61: 646-664Crossref PubMed Scopus (1844) Google Scholar The Achilles' heel is clarithromycin resistance, with success depending on clarithromycin