You will be shown a paragraph from a biomedical research article. Your task is to extract all drug combinations appearing in a specific sentence within in the paragraph. Each drug combination should be assigned to one of the following three categories:

- POS: Indicates a positive interaction between the drugs in the combination; for instance, drugs that have an additive or synergistic effect.
- NEG: Indicates a negative interaction between the drugs in the combination; for instance, combining these drugs might result in adverse side effects, or might reduce their efficacy.
- COMB: Indicates that the drugs are given in combination, but the type of interaction between the drugs cannot be determined based on the provided context.

Please format your answer as a json array. Each entry in the array should itself be an array formatted as [<drug_1>, <drug_2>, ..., <drug_n>, <category>] where <category> is one of the three categories listed above and <drug_1>, ..., <drug_n> are drug names copied verbatim from the input sentence. Different combinations may involve different numbers of drugs; in other words, the `n` in <drug_n> may vary.

As an example, the following output describes two extracted drug combinations; one between two drugs, and one between three drugs:

[["artesunate", "artemether", "COMB"], ["Nifedipine", "Labetalol", "Prazosin", "POS"]]

The paragraph and specific sentence are below. You should only extract relationships expressed in the specific sentence; the paragraph is provided for context.

In your output, return only the json array and no other text. If no drug combinations appear, return an empty array `[]`.

paragraph: Where are We with current therapy? Despite intensive research and widely publicized recommendations from consensus meetings in different continents, the public and primary care physicians are relatively slow in picking up the impact of Helicobacter pylori infection and identifying optimal therapies. The treatment of H. pylori infection has evolved from bismuth-containing regimens, 2-week proton pump inhibitor (PPI)-dual therapies, and now, the widely accepted PPI/ranitidine bismuth citrate (RBC) single week triple therapies. There is a wealth of evidence showing that these regimens are highly efficacious and well tolerated by patients. The MACH-2 studies have confirmed that the addition of a PPI to two antimicrobials has significantly improved the cure rate of H. pylori infection and reduced the impact of antimicrobial resistance. Attempts to use shorter regimens ranging from 1 to 3 days should be resisted because of their unacceptably low therapeutic efficacy. In the United States, there are some indications that 10-14 days of treatment may be required. While the first-line therapies for H. pylori infection is well established, we are still struggling with the choice of optimal regimen in retreatment after the first attempt fails. Quadruple therapy combining PPI with bismuth, metronidazole and tetracycline has achieved a respectable success of around 85%. Switching between metronidazole and clarithromycin seems to be a sensible strategy as these two are the most effective anti-Helicobacter agents . Changing between PPI and RBC in the triple therapy would not make much difference without replacing some of the antimicrobials. rifabutin-containing regimens and high-dose PPI-amoxicillin dual therapy deserve more studies with large-scale studies. Data on anti-Helicobacter therapy for children are few. Most studies based on bismuth derivatives in combination with amoxicillin or tinidazole and were limited by the small number of cases. Recent studies showed 1-week bismuth-based triple therapy and 2-week PPI-based triple therapy are highly efficacious. Reinfection in children > 5 years of age after successful cure is rare. It is worthwhile to refine the optimal therapy for children as the treatment of this group would, theoretically, prevent the development gastric cancer in the long term.

sentence: Switching between metronidazole and clarithromycin seems to be a sensible strategy as these two are the most effective anti-Helicobacter agents .
[]