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: The antinociceptive effects of systemic administration of tramadol, gabapentin and their combination on mice model of acute pain. The aim of the present study was to investigate the possible antinociceptive effects of systemic administration of tramadol and gabapentin either alone or in combination on acute pain models in mice. ### methods After obtaining the approval of Animal Ethics Committee; 96 BALB/c albino male mice were divided into 12 groups: (I) control without injection, (II) control treated with saline, (III)-(IV) mice treated with tramadol 10 mg/kg or 30 mg/kg, (V)-(VIII) mice treated with gabapentin; 30, 100, 200, 300 mg/kg respectively. In order to determine possible interactions between tramadol gabapentin and; mice received four different combinations of tramadol + gabapentin (30+30, 30+100, 30+200 and 30+300 mg/kg) (Groups IX-XII respectively). Mice received 0.1 ml solution for every 10 g of their weight. The drug was injected into peritonea. Thirty minutes after the drug injection, tail-flick and hot-plate tests were conducted. ### results Ten and 30 mg/kg tramadol produced dose dependent antinociceptive effect in tail-flick and hot plate tests. gabapentin had no antinociceptive effect in the tail flick test except 300 mg/kg dose, and had dose dependent antinociceptive effect in hot-plate test. In both tests, various combinations of tramadol and gabapentin produced an antinociceptive effect that is greater than that produced by tramadol and gabapentin alone. But, just 30 mg/kg tramadol + 300 mg/kg gabapentin combination caused statistically significant increase in both tests (p<0.05). ### conclusion When gabapentin and tramadol were used in combination, gabapentin had no additive antinociceptive effect except for 300 mg/kg in tail-flick and hot-plate tests. Tail-flick test showed that tramadol produced better antinociceptive effect than gabapentin .

sentence: Tail-flick test showed that tramadol produced better antinociceptive effect than gabapentin .
[]