Oranges and grapefruit

Something in grapefruit juice inhibits an isoform, CYP3A4, of cytochrome P450, causing drug interactions. That is why terfenadine was last year removed from over the counter sales: grapefruit juice inhibits its metabolism, and that can lead to dangerous cardiac arrhythmias. The active ingredient in the grapefruit is unknown, although at least one of the flavonoid glycosides that citrus fruits contain, naringin, seems to have been exonerated. Now if you thought that “naringin” was reminiscent of another member of the citrus family, “orange,” you would be right, and here's why.

The indefinite article takes two forms, “a” and “an.” Originally it was “an,” a weak …