Pharmacology in Dentistry Flashcards

What is the mechanism of action of bisphosphonates and why are they relevant in dental practice?

Answer: Inhibit osteoclast function by blocking the mevalonate pathway, reducing bone resorption — dental relevance: MRONJ (medication-related osteonecrosis of the jaw) is a rare but serious complication after extractions

Bisphosphonates inhibit osteoclasts, reducing bone turnover. MRONJ (medication-related osteonecrosis of the jaw) is a rare but serious complication, especially with IV bisphosphonates (used in metastatic cancer), manifesting as exposed, necrotic jaw bone, often triggered by extractions.

Which antibiotic can reduce the efficacy of the combined oral contraceptive pill?

Answer: Current evidence suggests ONLY enzyme-inducing antibiotics (e.g., rifampicin) reduce OCP efficacy — broad-spectrum antibiotics no longer considered to do so per FSRH 2019 guidance

FSRH updated guidance (2019): non-enzyme-inducing antibiotics (amoxicillin, metronidazole, etc.) do not significantly reduce OCP efficacy. Only enzyme inducers (rifampicin, some anticonvulsants) require additional contraceptive precautions.

What is chlorhexidine's mechanism of action and why is it used in dentistry?

Answer: Cationic bisbiguanide that binds to bacterial cell membranes, disrupting integrity at bactericidal concentrations — used as antimicrobial mouthwash, irrigation, and periodontal gel

Chlorhexidine binds to negatively charged bacterial cell walls, disrupting membrane permeability. At low concentrations it is bacteriostatic; at higher concentrations bactericidal. It has broad-spectrum activity and substantivity (binds to oral surfaces, releasing slowly).

A patient with a known penicillin allergy (anaphylaxis) requires a dental antibiotic. Which antibiotic should be avoided?

Answer: All cephalosporins (due to cross-reactivity risk — approximately 1–2% with true anaphylaxis history, though generally amoxicillin is clearly contraindicated)

In a patient with confirmed anaphylactic penicillin allergy: amoxicillin (penicillin) and cephalosporins (cross-reactivity ~1–2%) should be avoided. Safe alternatives for dental infections include metronidazole, clarithromycin, or clindamycin.

What is the rationale for prescribing dexamethasone before lower third molar surgery?

Answer: Prophylactic corticosteroid reduces post-operative trismus, swelling, and pain by suppressing inflammatory mediators before surgical trauma occurs

Pre-operative dexamethasone (4–8 mg IM or IV) reduces post-surgical trismus, facial swelling, and pain by pre-emptively suppressing the inflammatory cascade. It is used in third molar surgery and other oral surgical procedures.

What is the dental significance of long-term steroid therapy?

Answer: Adrenal suppression may cause an 'adrenal crisis' under surgical stress — doubling of steroid dose ('steroid cover') or consultation with medical team required before invasive procedures

Long-term systemic steroids suppress the HPA axis (adrenal suppression). Surgical stress cannot trigger the normal cortisol surge, risking Addisonian crisis (hypotension, collapse). Historically, 'steroid cover' was applied; current guidance is more nuanced and patient-specific.