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: Enalapril and atenolol in essential hypertension: attenuation of hypotensive effects in combination. In 16 patients with essential hypertension the effects of enalapril 20 mg once daily were compared with those of atenolol 50 mg once daily, with the two drugs in combination and with placebo using a double-blind cross-over design with allocation of treatment order by randomised Latin squares. For each patient there were four treatment phases, each of four weeks duration, which together comprised a 2 x 2 factorial experiment. All blood pressure parameters were reduced in the three active treatment phases compared to placebo (p less than 0.001). Supine blood pressures ( group means ) were 171/97 ( placebo ) , 147/85 ( enalapril ) , 154/84 ( atenolol ) and 144/78 ( enalapril plus atenolol ) ( S.E.M. + /- 2/+/- 1-ANOVA ) , and standing blood pressures were 170/105 ( placebo ) , 146/92 ( enalapril ) , 154/92 ( atenolol ) and 147/86 ( enalapril plus atenolol ) ( S.E.M. + /- 3/+/- 1 ) . In the combination phase there was an additional hypotensive response but the potential fully additive effects of the two agents were attenuated by 30-50%. The mechanism of the attenuated hypotensive effect of the combined agents has not been determined. Plasma atrial natriuretic peptide (ANP) concentration was doubled in the presence of atenolol (P less than 0.01) suggesting that ANP may contribute to the hypotensive effect of the beta-blocker.

sentence: Supine blood pressures ( group means ) were 171/97 ( placebo ) , 147/85 ( enalapril ) , 154/84 ( atenolol ) and 144/78 ( enalapril plus atenolol ) ( S.E.M. + /- 2/+/- 1-ANOVA ) , and standing blood pressures were 170/105 ( placebo ) , 146/92 ( enalapril ) , 154/92 ( atenolol ) and 147/86 ( enalapril plus atenolol ) ( S.E.M. + /- 3/+/- 1 ) .
[["enalapril", "atenolol", "POS"]]