Which drug is effective against amoebae and is commonly used to treat periodontitis?

Metronidazole is a nitroimidazole antibiotic that is highly effective against anaerobic bacteria and protozoa, particularly amoebae. It disrupts the DNA of these organisms, preventing their proliferation. In the context of treating periodontitis, metronidazole is advantageous due to its effectiveness against certain anaerobic pathogens that are often implicated in periodontal infections. Its ability to specifically target these bacteria helps in managing and reducing the inflammation associated with periodontitis, making it a commonly prescribed medication for this condition.

In contrast, other options have different roles or are less effective against the specific pathogens associated with periodontitis. Tetracycline, while an antibiotic, is primarily effective against a broader range of bacteria but does not target the anaerobic organisms as effectively as metronidazole. Ciprofloxacin is a fluoroquinolone antibiotic that is more suited for aerobic bacterial infections, rather than the anaerobic bacteria often involved in periodontal disease. Cephalexin, a cephalosporin antibiotic, is used for various infections but is not specifically indicated for amoebic infections or the anaerobes commonly involved in periodontitis.