Applied Pharmacology

Applied Pharmacology

Pharmacology is integral to dental hygiene practice, encompassing the management of dental pain, prevention of systemic infections, and response to medical emergencies. A thorough understanding of drug mechanisms, side effects, and clinical protocols is required for board examinations and clinical practice.

Analgesics in Dentistry

Analgesics are categorized into non-opioid (non-narcotic) and opioid (narcotic) agents. In dental practice, non-opioids are the first-line therapy for mild-to-moderate inflammatory pain, while opioids are reserved for severe pain.

Non-Steroidal Anti-inflammatory Drugs (NSAIDs)

• Examples: Ibuprofen (Advil, Motrin), Naproxen (Aleve).
• Mechanism of Action: Reversible inhibition of the cyclooxygenase (COX-1 and COX-2) enzymes. This blocks the conversion of arachidonic acid to prostaglandins, which are key mediators of pain, fever, and inflammation.
• Adverse Effects:
  • Gastrointestinal Distress: COX-1 inhibition reduces the synthesis of prostaglandins that maintain the mucosal lining of the stomach, leading to gastritis, peptic ulcers, and GI bleeding.
  • Bleeding Tendency: Reversible inhibition of platelet aggregation (via thromboxane A2 inhibition).
  • Nephrotoxicity: Decreased renal blood flow due to inhibition of renal prostaglandins, potentially causing acute kidney injury or worsening chronic hypertension.
• Contraindications: Active peptic ulcer disease, severe renal impairment, late pregnancy (causes premature closure of the ductus arteriosus in the fetus), and NSAID-sensitive asthma (where COX inhibition shunts arachidonic acid to the lipoxygenase pathway, leading to bronchoconstrictive leukotriene production).

Acetaminophen (APAP)

• Example: Tylenol.
• Mechanism of Action: Inhibits prostaglandin synthesis primarily in the central nervous system (CNS), with minimal peripheral activity. As a result, it exhibits analgesic and antipyretic (fever-reducing) properties but lacks anti-inflammatory action.
• Adverse Effects:
  • Hepatotoxicity: Metabolized by the liver. In therapeutic doses, a small toxic metabolite (NAPQI) is safely conjugated by glutathione. In overdose or liver compromise, glutathione is depleted, and NAPQI causes hepatic necrosis.
• Dosing Limits: The maximum daily dose for healthy adults is 4,000 mg (4g) per 24 hours. For patients with hepatic dysfunction, chronic alcohol use, or geriatric status, the limit is reduced to 3,000 mg or lower.
• Contraindications: Severe hepatic impairment, active liver disease, or chronic alcoholism.

Opioid Analgesics

• Examples: Codeine, Hydrocodone, Oxycodone. (Often combined with acetaminophen, e.g., Vicodin, Percocet).
• Mechanism of Action: Act as agonists at mu (μ), kappa (κ), and delta (δ) opioid receptors in the CNS. This inhibits the transmission of nociceptive signals and alters the perception of pain.
• Adverse Effects: Respiratory depression (most dangerous; primary cause of death in overdose), sedation, dizziness, nausea/vomiting, miosis (pupil constriction), and severe constipation (due to decreased GI motility).
• Reversal Agent: Naloxone (Narcan) is a competitive opioid antagonist used to reverse respiratory depression in acute opioid overdose.

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Antibiotics & Antimicrobial Therapy

Antibiotics are prescribed in dentistry to treat odontogenic infections or as prophylaxis.

• Tooth Staining Note: Tetracyclines chelate calcium ions and become incorporated into developing teeth and bone. Contraindicated in pregnant women (second and third trimesters) and children under 8 years of age.

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AHA/ADA Infective Endocarditis Premedication Guidelines

Infective endocarditis (IE) is a life-threatening infection of the cardiac valves or endocardium. Antibiotic prophylaxis is recommended only for dental procedures involving manipulation of gingival tissue, the periapical region of teeth, or perforation of the oral mucosa, and only in patients at the highest risk for adverse outcomes from IE.

Indications for Antibiotic Prophylaxis

1. Prosthetic cardiac valves (including transcatheter-implanted valves and homografts).
2. Prosthetic material used for cardiac valve repair (such as annuloplasty rings, clips, and chords).
3. A history of infective endocarditis.
4. Unrepaired cyanotic congenital heart disease (CHD), including palliative shunts and conduits.
5. Completely repaired CHD with prosthetic material or device (placed surgically or via catheter) during the first 6 months after the procedure (allows endothelialization).
6. Repaired CHD with residual defects at the site or adjacent to the site of a prosthetic patch or device.
7. Cardiac transplant recipients who develop cardiac valvulopathy.

[!IMPORTANT] No Longer Recommended: Prophylaxis is NOT recommended for mitral valve prolapse, bicuspid valve disease, rheumatic heart disease, or calcified aortic stenosis. Furthermore, routine antibiotic prophylaxis is not recommended for patients with prosthetic joint replacements unless specified by the patient's orthopedic surgeon due to severe immunocompromised status.

Standard Prophylaxis Regimens (Administered Orally 1 Hour Prior to Procedure)

• Standard First-Line Regimen (No Penicillin Allergy):
  • Amoxicillin: 2g (2,000 mg) orally (Pediatric: 50 mg/kg).
• Penicillin-Allergic Regimens:
  • Cephalexin: 2g (2,000 mg) orally (Pediatric: 50 mg/kg) - Note: Avoid if the patient's penicillin allergy involved anaphylaxis, bronchospasm, or angioedema.
  • Azithromycin or Clarithromycin: 500 mg orally (Pediatric: 15 mg/kg).
  • Doxycycline: 100 mg orally (Pediatric: 2.2 mg/kg for children <45 kg; 100 mg if >= 45 kg).
• Non-Oral Administration (If unable to take oral medication):
  • Ampicillin: 2g IM or IV (Pediatric: 50 mg/kg IM/IV) 30-60 minutes before.
  • Cefazolin or Ceftriaxone: 1g IM or IV (Pediatric: 50 mg/kg IM/IV) 30-60 minutes before.

[!WARNING] Clindamycin (600mg) is NO LONGER recommended by the American Heart Association (AHA) as an alternative for dental premedication due to its high incidence of severe adverse reactions, particularly Clostridioides difficile infection.

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Dental Office Emergency Drugs

Every dental setting must maintain an updated emergency drug kit. Clinicians must recognize the indications, contraindications, and physiological actions of these core agents.

1. Epinephrine (1:1,000 concentration, Autoinjector):
   • Indications: Severe anaphylaxis or acute bronchospasm/asthma attack unresponsive to albuterol.
   • Action: Direct-acting sympathomimetic. Stimulates alpha-1 (vasoconstriction to reverse hypotension), beta-1 (increases heart rate and cardiac output), and beta-2 (bronchodilation) receptors.
2. Diphenhydramine (Benadryl):
   • Indications: Mild, localized, non-anaphylactic allergic reactions (urticaria, pruritus).
   • Action: Histamine H1-receptor antagonist. Blocks histamine-mediated capillary permeability and smooth muscle contraction.
3. Nitroglycerin (Sublingual Spray or Tablets):
   • Indications: Acute angina pectoris (chest pain due to transient ischemia).
   • Action: Direct smooth muscle relaxant and vasodilator. Decreases venous return (reduces preload) and dilates coronary arteries, lowering myocardial oxygen consumption.
   • Contraindications: Systolic blood pressure < 90 mmHg or use of phosphodiesterase-5 (PDE-5) inhibitors (e.g., sildenafil, tadalafil) within 24 to 48 hours (risk of severe, life-threatening hypotension).
4. Albuterol (Inhaler):
   • Indications: Acute asthma attack or bronchospasm.
   • Action: Selective beta-2 adrenergic agonist. Relaxes bronchial smooth muscle, causing rapid bronchodilation with minimal cardiac effects.
5. Aspirin (Chewable Tablets):
   • Indications: Suspected acute myocardial infarction (heart attack).
   • Action: Irreversible cyclooxygenase inhibitor. Prevents thromboxane A2 formation, inhibiting platelet aggregation and reducing clot enlargement. Dose: 162 mg to 325 mg (chewed to facilitate rapid absorption).
6. Glucose (Oral Gel or Tablets):
   • Indications: Hypoglycemia in a conscious patient (diabetic emergency).
   • Action: Elevates blood glucose levels rapidly. Note: Unconscious patients must receive intravenous dextrose or intramuscular glucagon; do not administer oral glucose to an unconscious patient due to aspiration risk.
7. Oxygen (Positive Pressure Delivery):
   • Indications: Most medical emergencies characterized by respiratory distress, syncope, or chest pain.
   • Contraindications: Hyperventilation, as it worsens hypocapnia (loss of carbon dioxide).