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Sub-antimicrobial Doxycycline — MFDS Part 1 MCQ

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HardPharmacologySub-antimicrobial DoxycyclineMFDS Part 1

Although current UK guidance does not recommend host-modulation therapy for the routine management of periodontitis, sub-antimicrobial-dose doxycycline has been studied as an adjunct to professional mechanical plaque removal. Which pharmacological action principally accounts for its proposed periodontal effect at this dose?

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Correct answer: A — Downregulation of host-derived matrix metalloproteinases, reducing collagenolysis

The correct answer is A. At sub-antimicrobial exposure, doxycycline acts principally as a host-modulating agent by downregulating or inhibiting matrix metalloproteinases, including collagenases such as MMP-8. These host-derived enzymes contribute to extracellular-matrix and collagen breakdown in periodontitis. The dose is not intended to suppress periodontal organisms through 30S ribosomal inhibition, so B does not explain the proposed benefit. Doxycycline does not principally act by directly stimulating osteoblast differentiation or enhancing neutrophil bacterial killing, excluding C and D. Direct cyclo-oxygenase inhibition is characteristic of NSAIDs rather than doxycycline, excluding E. Current SDCEP guidance does not recommend systemic sub-antimicrobial doxycycline for routine periodontal care; this question tests its proposed pharmacological mechanism, not a current treatment recommendation.

Reference: Preshaw PM et al. Subantimicrobial dose doxycycline as adjunctive treatment for periodontitis: a review. Journal of Clinical Periodontology. 2004;31:697–707. https://pubmed.ncbi.nlm.nih.gov/15312090/