**6. Antibiotic therapy**

Therapy regimens used over the past decade are declining in efficacy being the *Hp* treatment affected by drug-resistant strains. New treatment strategies are under study worldwide. The knowledge of the local susceptibility to the antibiotics in a single geographical area is crucial in order to establish a correct therapy. For instance as far as CLA susceptibility is concerned, it is stated that in those regions that show a resistance percentage > 15%, this antibiotic should not be used [30]. Indeed it would be possible to predict the efficacy of any treatment knowing the prevalence of antibiotic resistance for a regimen or even for a specific patient. As a matter of fact empiric therapy that takes into consideration the regional and mostly the local resistance patterns may be superior to the tailored therapy in predicting the efficacy of any regimen [40]. Hence, the regional resistance patterns and the eradication rates in the context of local environment are crucial for a correct establishment of *Hp* cure in real-world settings [41].

The old triple therapy (PPI=Proton Pump Inhibitors + clarithromycin and either amoxicillin or metronidazole) should be considered only in areas where the resistance to CLA is low (<15%) or where a high eradication success with these regimens (>85%) is well known. In general, in Western countries, clarithromycin-containing triple and sequential therapy should be considered obsolete as empiric therapies.

The resistance to CLA is reported to be increasing all over the world, and in some countries, it depends on the local seropositivity rate [42]. As far as LEV is concerned, there is a more limited number of studies evaluating susceptibility to LEV. In Italy LEV resistance has been reported to be 22–24% as well as in Portugal [43]. MZ shows a high rate of resistance (50–80%) in almost all the studied countries achieving a rate of 80% especially in developing areas [26]. Nevertheless in spite of its high resistance in vitro, it is included in the BQT (Bismuth Quadruple Therapy). This discrepancy between in vitro MZ resistance and treatment outcome may partially be explained by changes in oxygen pressure in the gastric environment, as MZ-resistant *Hp* isolates become MZ susceptible under low oxygen conditions in vivo [44]. The Bismuth Quadruple Therapy (PPI + Bismuth +MZ + TE] for 14 days has proven high efficacy in spite of MZ resistance in Europe bypassing also the quinolone resistance [29].

The new guidelines for the cure of *Hp* recommend to prolong the therapy from 10 to 14 days [45]. As first line therapy a concomitant non-bismuth quadruple therapy (PPI + AMX + MZ + CLA) may be used in those countries where the resistance to CLA is <15% otherwise the traditional bismuth quadruple therapy unaffected by CLA resistance, should be used. The BQT (PPI + Bismuth+MZ + TE, PBMT) results as being very useful in the countries where particular *Hp* high resistance is detected and when the AST (Antimicrobial Susceptibility Testing) is complicated to perform. In contrast if a bismuth-based quadruple therapy is used in these different situations, it is not recommended to perform AST because a risk of having a TE-resistant strain is extremely low and it was shown that MZ-resistance has no impact in the treatment of patients [29]. Recommended rescue therapy includes LEV as a second line of treatment ie PPI, AMX, LEV (PAL) [45] these therapeutic options are reported in **Table 3**.


*Notes: The therapy should be prolonged for 14 days.*

*PPI = proton pump inhibitor, CLA = clarithromycin, MZ = metronidazole; TE = tetracycline; AMX = amoxicillin, RIF = rifabutin.*

*\*Obsolete therapy.*

*\*\*Used in the countries where CLA – resistance is <15%.*

*\*\*\*Unaffected by CLA - resistance.*

*Virulence Markers, Genotypic versus Phenotypic Resistance and New Treatment Strategies... DOI: http://dx.doi.org/10.5772/intechopen.97026*
