General Pharmacology Principles for Dental Practice: Guide

Pharmacology is the science of how drugs act on the body, and dental practice runs on it: dentists prescribe antibiotics, painkillers, and local anaesthetics almost daily. Dose calculations, interactions, and special-group precautions separate safe prescribing from dangerous guesswork.

This matters because the commonest dental prescriptions are the most misused: unfinished antibiotic courses breed resistance, NSAIDs on an empty stomach cause ulcers, and a drug safe in adults can stain a child's teeth for life.

Key Concepts

• Pharmacokinetics (ADME): what the body does to the drug: Absorption, Distribution, Metabolism (liver), Excretion (kidneys). Liver or kidney disease changes dosing.
• Pharmacodynamics: what the drug does to the body via receptors: agonists activate, antagonists block.
• Therapeutic index (TI): a safety margin; higher TI means a wider gap between effective and toxic dose.
• First-line dental drugs: amoxicillin (odontogenic infections), metronidazole (anaerobes), ibuprofen (pain plus inflammation), paracetamol (pain and fever, gentler on the stomach).
• Key interactions: metronidazole + alcohol causes a disulfiram-like reaction; NSAIDs + warfarin raises bleeding risk; tetracyclines in pregnancy/children permanently discolour developing teeth.
• Special groups: children need weight-based dosing, pregnancy restricts drug choice, the elderly need lower doses as kidneys decline.

Formulas

• Child's dose = weight (kg) x dose per kg. Standards: paracetamol 15 mg/kg; ibuprofen 10 mg/kg per dose.
• TI = TD50 / ED50 (toxic dose in 50% divided by effective dose in 50%). Larger TI means a safer drug.
• Syrup volume: (required mg / mg per 5 mL) x 5. Example: 300 mg from 120 mg/5 mL syrup = (300/120) x 5 = 12.5 mL.

Worked Example

A 20 kg child needs paracetamol for dental pain; the syrup is 120 mg per 5 mL.

1. Dose: 20 x 15 = 300 mg.
2. Volume: (300/120) x 5 = 12.5 mL, measured with a syringe, never a kitchen spoon.
3. Frequency: every 6 hours as needed, maximum 4 doses per 24 hours (1,200 mg/day), within the paediatric ceiling.

Common Misconceptions

• "A stronger antibiotic works better." Broad-spectrum overkill breeds resistance; narrow-spectrum first-line drugs cure most dental infections with less collateral damage.
• "Painkillers are safe on an empty stomach." NSAIDs like ibuprofen should be taken with food to avoid gastritis.
• "Leftover antibiotics are fine to reuse." Wrong drug, wrong dose, wrong duration: the perfect recipe for resistant bacteria.

Real-World Applications

• Dentists apply weight-based dosing for every child and screen adults for interactions.
• Pharmacists double-check dental prescriptions, catching dose errors and allergy conflicts.
• Patients who understand why the full course matters become partners against resistance.

Dental pharmacology is arithmetic plus caution: ADME tracks the drug's journey, the therapeutic index describes its safety margin, children are dosed by weight (15 mg/kg paracetamol, 10 mg/kg ibuprofen), and interactions like metronidazole with alcohol must be screened every time. Right drug, calculated dose, full course: safe dental prescribing in one sentence.