7.3 Antimicrobial Prescribing, BNF/DPF Guidance & Stewardship

7.3 Antimicrobial Prescribing, BNF/DPF Guidance & Stewardship

Antimicrobial resistance (AMR) is a major global public health threat. Primary care dental prescribing accounts for approximately 10% of all NHS oral antibiotic prescriptions in the UK. Dental practitioners have an ethical and clinical responsibility to adhere strictly to guidelines issued by the Scottish Dental Clinical Effectiveness Programme (SDCEP), the College of General Dentistry (CGDent / FGDP), and the Dental Practitioners' Formulary (DPF) contained within the British National Formulary (BNF).

Principles of Dental Antimicrobial Stewardship

The Fundamental Rule of Dental Prescribing

Systemic antibiotics are never a substitute for operative clinical intervention.

Odontogenic infections are primarily contained within avascular tooth structures or localized soft tissue spaces. Antibiotics cannot penetrate necrotic dental pulp tissue or an undrained abscess cavity effectively. The primary management of acute dental conditions requires prompt mechanical drainage or surgical elimination of the source:

• Pulpitis / Apical Periodontitis: Pulpectomy, root canal debridement, or tooth extraction.
• Acute Dental Abscess: Incision and drainage of soft tissue swelling, or drainage via the root canal.
• Pericoronitis: Operative debridement, irrigation with warm saline or 0.2% chlorhexidine, and removal of the opposing tooth if impinging.
• Alveolar Osteitis (Dry Socket): Gentle irrigation with warm saline, packing with dressed socket dressings (e.g., Alvogyl), and analgesia.

Conditions Where Antibiotics Are NOT Indicated

According to SDCEP guidelines, systemic antibiotics are strictly contraindicated for:

• Irreversible pulpitis
• Symptomatic apical periodontitis
• Localized acute apical abscess without systemic involvement
• Dry socket (alveolar osteitis)
• Uncomplicated pericoronitis without systemic signs
• Periodontal abscess without systemic involvement

Valid Indications for Systemic Antibiotics

Systemic antibiotics are indicated only as an adjunct to operative treatment when there is clear evidence of:

1. Spreading Infection: Progressive facial swelling, cellulitis, or Ludwig's angina.
2. Systemic Manifestations: Elevated body temperature (fever > 38°C), systemic malaise, chills, tachycardia, cervical lymphadenopathy, or severe trismus (< 20 mm mouth opening).
3. Immunocompromised Patients: Patients undergoing chemotherapy, poorly controlled diabetes, advanced HIV infection, or taking systemic immunosuppressants who present with acute odontogenic infection.

---

Antibacterial Agents in Dental Practice (BNF / DPF)

Beta-Lactam Antibiotics

Amoxicillin

• Mechanism of Action: Moderate-spectrum aminopenicillin. Inhibits penicillin-binding proteins (PBPs), which catalyze the transpeptidation step in bacterial cell wall synthesis. This weakens the peptidoglycan layer, leading to cell lysis and bacterial death (bactericidal).
• Spectrum: Active against oral Gram-positive aerobes (Streptococcus mutans, viridans group streptococci) and facultative oral anaerobes.
• Standard Dosing (BNF/DPF): 500 mg three times daily (TDS) for 5 days. In severe spreading infections, a high-dose regimen of 1 g TDS may be prescribed.
• Hypersensitivity: IgE-mediated Type I anaphylaxis occurs in ~0.05% of patients. Cross-reactivity with cephalosporins is estimated at 1–5%.

Phenoxymethylpenicillin (Penicillin V)

• Standard Dosing: 500 mg four times daily (QDS) for 5 days.
• Clinical Status: Narrower spectrum than amoxicillin. Amoxicillin is generally preferred in UK dental practice due to superior oral bioavailability and lower dosing frequency.

Nitroimidazoles: Metronidazole

• Mechanism of Action: Prodrug that selectively enters anaerobic bacteria. Bacterial nitroreductase enzymes reduce the nitro group of metronidazole into cytotoxic free radical intermediates that disrupt helical bacterial DNA, causing strand breakage and cell death (bactericidal).
• Spectrum: Highly active against obligate anaerobic oral pathogens, including Porphyromonas gingivalis, Prevotella intermedia, Fusobacterium nucleatum, and Treponema denticola.
• Indications: First-line agent for Acute Necrotising Ulcerative Gingivitis (ANUG), acute pericoronitis, and as first-line therapy for dental abscesses in penicillin-allergic patients.
• Standard Dosing: 400 mg three times daily (TDS) for 5 days.
• Critical Drug Interactions:
  • Alcohol Interaction: Inhibits hepatic aldehyde dehydrogenase, causing a severe disulfiram-like reaction characterized by violent facial flushing, throbbing headache, nausea, vomiting, tachycardia, and hypotension.
  • Warfarin Interaction: Inhibits CYP2C9 metabolism of warfarin, producing marked elevation of INR and severe bleeding risk.

Macrolides (Clarithromycin, Erythromycin, Azithromycin)

• Mechanism of Action: Reversibly bind to the 50S ribosomal subunit of susceptible bacteria, inhibiting translocation during protein synthesis (bacteriostatic).
• Indications: First-line alternative for patients with confirmed IgE-mediated penicillin allergy.
• Standard Dosing: Clarithromycin 250–500 mg twice daily (BD) for 5 days; Azithromycin 500 mg once daily (OD) for 3 days.
• Drug Interactions: Clarithromycin and erythromycin are potent inhibitors of hepatic CYP3A4. They significantly elevate plasma levels of co-administered drugs including simvastatin/atorvastatin (inducing rhabdomyolysis), carbamazepine, and warfarin. They also prolong the QT interval.

Lincosamides: Clindamycin

• Pharmacological Profile: Potent activity against oral anaerobes and staphylococci.
• MHRA Drug Safety Alert: Clindamycin carries a high risk of inducing Clostridioides difficile (formerly Clostridium difficile) pseudomembranous colitis by eradicating normal colonic microflora. Clindamycin is NO LONGER recommended for routine primary care dental prescribing in the UK.

Tetracyclines: Doxycycline

• Mechanism of Action: Reversibly binds to the 30S ribosomal subunit, blocking binding of aminoacyl-tRNA to the mRNA-ribosome complex (bacteriostatic).
• Periodontal Host Modulation: Sub-antimicrobial dose doxycycline (Periostat 20 mg BD for 3 months) is used as an adjunct in periodontitis. At this low dose, it does not exert antibacterial activity but directly inhibits host matrix metalloproteinases (MMPs), specifically tissue-destructive collagenase (MMP-8).
• Contraindications: Contraindicated in children under 12 years of age and pregnant/breastfeeding women due to chelation with calcium ions, causing intrinsic tooth discolouration (yellow-brown staining) and enamel hypoplasia.

---

Summary of Dental Antibacterial Prescribing (BNF/DPF)

---

Antifungal Therapeutics in Dental Practice

Oral candidiasis presents clinically as acute pseudomembranous candidiasis (thrush), acute/chronic erythematous candidiasis (denture stomatitis), or angular cheilitis, primarily caused by Candida albicans.

Nystatin

• Mechanism of Action: Polyene antifungal. Binds to ergosterol in fungal cell membranes, forming transmembrane pores that leak intracellular potassium and essential metabolites, causing fungal cell death.
• Formulation & Dosing: Nystatin oral suspension 100,000 units/mL. 1 mL four times daily (QDS) after food for 7–14 days. The suspension should be retained in contact with lesions for several minutes before swallowing.
• Pharmacokinetics: Nystatin is not absorbed systemically from the gastrointestinal tract; its action is purely topical.

Miconazole

• Mechanism of Action: Imidazole antifungal. Inhibits the fungal cytochrome P450 enzyme 14α-demethylase, blocking the conversion of lanosterol to ergosterol, disrupting fungal membrane integrity.
• Formulation & Dosing: Miconazole 2% oral gel. 2.5 mL four times daily (QDS) applied to oral lesions after meals for 7–14 days.
• CRITICAL MHRA DRUG SAFETY WARNING — WARFARIN INTERACTION:
  • Miconazole oral gel, despite topical administration, is absorbed systemically in significant amounts and acts as a potent inhibitor of hepatic CYP2C9.
  • In patients taking Warfarin, miconazole dramatically inhibits warfarin breakdown, causing massive INR spikes, severe uncontrolled bleeding, and potentially fatal internal hemorrhages.
  • Miconazole oral gel is strictly CONTRAINDICATED in patients taking Warfarin.

Fluconazole

• Systemic Triazole: Prescribed for extensive or refractory candidiasis in non-warfarinized patients. 50 mg daily for 7–14 days. Potent CYP2C9 inhibitor.

---

Antiviral Therapeutics in Dental Practice

Primary Herpetic Gingivostomatitis and Recurrent Herpes Labialis (cold sores) are caused by Herpes Simplex Virus Type 1 (HSV-1).

Aciclovir (Acyclovir)

• Mechanism of Action:
  1. Selective Phosphorylation: Aciclovir is converted to aciclovir monophosphate specifically by viral thymidine kinase (present only in HSV-infected cells).
  2. Cellular Phosphorylation: Host cellular kinases convert the monophosphate to active aciclovir triphosphate.
  3. DNA Polymerase Inhibition & Chain Termination: Aciclovir triphosphate competitively inhibits viral DNA polymerase and is incorporated into the growing viral DNA chain. Lacking a 3'-hydroxyl group, it causes irreversible DNA chain termination.

Aciclovir → Aciclovir-MP → Aciclovir-TP → Chain Termination

• Dosing Regimen: Systemic Aciclovir 200 mg 5 times daily (every 4 hours while awake) for 5 days. (In immunocompromised patients, 400 mg 5 times daily). Topical 5% aciclovir cream is applied 5 times daily starting during the prodromal phase (tingling/erythema).