Which statement about penicillins for post-exposure prophylaxis of anthrax is correct?

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When selecting post-exposure prophylaxis for Anthrax, you need a regimen that will be reliably effective against the strains people might have been exposed to. If there is documented variability in beta-lactam resistance among Bacillus anthracis isolates, penicillins cannot be relied upon to provide universal protection. That uncertainty means penicillins should not be used as the initial PEP choice, because some strains could evade their activity during the crucial early period after exposure. Instead, first-line PEP regimens use agents with proven, consistent activity against B. anthracis in this context, such as fluoroquinolones or doxycycline, to ensure broad coverage while exposure investigations continue. Penicillins may be considered later only if susceptibility testing confirms effectiveness or in specific, guideline-directed scenarios, but they are not the initial universal option.