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: Atenolol-nifedipine combinations compared to atenolol alone in hypertension: efficacy and tolerability. 1. In a double-blind, randomised, three-way-crossover study, 25 patients with sitting diastolic blood pressure between 95 and 120 mm Hg (Phase V) after 4 weeks' run-in on atenolol 50 mg twice daily, received atenolol 50 mg twice daily alone, atenolol 50 mg plus nifedipine 20 mg each twice daily and atenolol 50 mg plus nifedipine 40 mg each twice daily in three treatment periods each lasting 4 weeks. 'Washout' periods were not included. 2 . The two combination treatment regimes lowered the 12 h post-dose blood pressure more effectively than did atenolol alone , but the high dose nifedipine combination was no more effective than the low dose nifedipine combination . Sitting systolic BP (+/- s.e. mean) at the end of each period was 174 +/- 5 mm Hg after the atenolol run-in, 170 +/- 5 mm Hg with atenolol alone, 156 +/- 5 mm Hg with the low dose combination and 158 +/- 4 mm Hg with the high dose combination. Corresponding diastolic BP readings were 106 +/- 2 mm Hg, 106 +/- 2 mm Hg, 97 +/- 2 mm Hg and 99 +/- 2 mm Hg respectively. 3. Side-effects tended to occur less commonly with the low dose of the fixed combination than with atenolol alone. An increased number of side-effects occurred with the 40 mg twice daily doses of nifedipine, particularly flushing/erythema, oedema of the ankles/feet, and a hot feeling in the legs. These differences did not reach significance. 4. Overall compliance was good (98 +/- 0.7 s.e. mean %) and was similar within the different treatment regimes.(ABSTRACT TRUNCATED AT 250 WORDS)

sentence: 2 . The two combination treatment regimes lowered the 12 h post-dose blood pressure more effectively than did atenolol alone , but the high dose nifedipine combination was no more effective than the low dose nifedipine combination .
[["atenolol", "nifedipine", "POS"]]