Respiratory Drugs and Pharmacology

RESPIRATORY DRUGS PHARMACOLOGY

Vocabulary
  • Antitussive: A drug that suppresses coughing.
  • Dyspnea: Difficulty in breathing.
  • Expectorate/Expectorant: To cough up mucus from the lungs; an agent that aids in this process.
  • Extravasation: The leakage of fluid out of its container, particularly important in the context of intravenous drug administration.
  • Mucolytic: A substance that breaks down mucus.
  • Parturition: The act of giving birth.
  • Purulent: Containing or consisting of pus.
  • Sympathomimetic: A substance that mimics the effects of sympathetic nervous system activation.
  • Transient: Temporary, not lasting.
Respiratory Actions of Drugs
  • Expectorant: Helps in expectoration, enabling patients to cough up mucus from the lungs.
  • Mucolytic: Breaks down mucus to facilitate clearance from the airways.
  • Bronchodilators: Medications that relax and open the airways (bronchioles).
  • Antitussives: Drugs that inhibit or suppress coughing.
  • Respiratory Stimulants: Drugs that stimulate the respiratory centers of the brain.
  • Decongestants: Agents that relieve nasal congestion.
  • Antihistamines: Medications that inhibit the release of histamine, thus fighting allergic responses.
  • Corticosteroids: Anti-inflammatory agents that reduce airway swelling and mucus production.
Common Drugs

  • Expectorants:
      - Guaifenesin

  • Mucolytics:
      - Acetylcysteine

  • Bronchodilators:
      - Albuterol
      - Epinephrine
      - Methylxanthines

  • Antitussives:
      - Butorphanol: suppresses coughs.
      - Hydrocodone: opiate that suppresses coughs.
      - Temaril - P: combination of antihistamine and corticosteroid.

  • Respiratory Stimulants:
      - Doxapram

  • Decongestants: Not typically useful in animals.

  • Antihistamines

  • Corticosteroids

Guaifenesin (Expectorant)
  • Trade Name: Unknown
  • Class: Muscle relaxant with expectorant properties.
  • Controlled Drug Status: Not controlled.
  • Uses: As a mild analgesia adjunct in anesthesia and helps in clearing phlegm from the lungs (especially in horses).
  • Administration: IV (Intravenous), PO (by mouth).
  • Action: Relaxation of skeletal muscle with minimal effect on respiratory function.
  • Pharmacokinetics: Generally excreted through urine.
  • Time: Induces recumbency in horses within 2 minutes and lasts for 6 minutes.
  • Adverse Effects: Generally transient and mild, possible hypotension and increased heart rate.
  • Contraindications: None noted.
  • Caution: Significant tissue damage can occur with perivascular administration; always administer IVC (Intravenous catheter).
  • Calculation Example: 545 kg x 30-50 mg/kg x 1 ml/50 mg = 327 ml Guaifenesin.
Acetylcysteine (Mucolytic)
  • Trade Name: Unknown
  • Class: Mucolytic agent and antidote.
  • Controlled Drug Status: Not controlled.
  • Uses: Breaks down mucus; antidote for Tylenol toxicity.
  • Administration: Via nebulizer (slow IV for 15-20 minutes; PO for Tylenol toxicity).
  • Action: Alters the chemical composition of mucus, both purulent and nonpurulent.
  • Pharmacokinetics: Converted into cysteine in the liver.
  • Excretion: Not specified.
  • Time: Half-life is 0.8 hours (IV), 1.3 hours (PO).
  • Adverse Effects: Few adverse effects; may cause vomiting if given PO and possible bronchospasms.
  • Contraindications: None specified.
  • Caution: Administer oral doses on an empty stomach.
Bronchodilators
Albuterol
  • Trade Name: Ventolin, Proventil.
  • Class: Beta-2 adrenergic agonist.
  • Controlled Drug Status: Not controlled.
  • Uses: For bronchodilation and to alleviate bronchospasm or cough.
  • Administration: Inhalation, PO.
  • Action: Relaxes smooth muscle fibers at receptor sites.
  • Pharmacokinetics: Metabolized in the liver.
  • Excretion: Not specified.
  • Time: Effects occur within 5 minutes.
  • Adverse Effects: Transient, mild sympathomimetic reactions (e.g., increased heart rate, tremors, CNS excitement).
  • Contraindications: May delay labor; caution in dogs with cardiac issues.
  • Calculation Examples: For cats, one puff every 30 minutes as needed.
Epinephrine
  • Class: Alpha & beta adrenergic agonist.
  • Controlled Drug Status: Not controlled.
  • Uses: For anaphylaxis and cardiac resuscitation; bronchodilation only in life-threatening situations.
  • Administration: IM (Intramuscular), SC (Subcutaneous), IV.
  • Action: Non-selective agonist leading to vasoconstriction and bronchodilation.
  • Pharmacokinetics: Does not cross the blood-brain barrier; can cross the placenta.
  • Excretion: Metabolized in liver and tissues.
  • Time: Immediate effects when given IV, 5-10 minutes for SC.
  • Adverse Effects: Anxiety, excitability, vomiting, hypertension, arrhythmias, significant tachycardia.
  • Contraindications: Numerous drug interactions exist.
  • Caution: Confusion between concentrations (1 mg/mL and 0.1 mg/mL) may lead to overdose.
Methylxanthines
Theophylline & Aminophylline
  • Trade Names: Theophylline (PO), Aminophylline (IV).
  • Class: Bronchodilator.
  • Controlled Drug Status: Not controlled.
  • Uses: For bronchodilation in feline asthma, dogs, and horses.
  • Administration: PO (timed release) intravenous or intramuscular.
  • Action: Inhibits an enzyme in smooth muscle to allow for relaxation.
  • Pharmacokinetics: Crosses placenta; metabolized in the liver.
  • Excretion: Not specified in detail.
  • Time: Half-life of 5.7 hours in dogs, 7.8 hours in cats.
  • Adverse Effects: Gastrointestinal upset, mild stimulation of heart and respiratory muscles.
  • Contraindications: Induces diuresis; increases gastric acid secretion, caution in neonatal and geriatric patients due to altered clearance.
  • Calculation Examples: For a patient weighing 34.4 kg, doses range from 3-11 mg/kg, which translates to approximately 15.1 mL of the solution.
Antitussives
Butorphanol
  • Trade Name: Torbutrol, Torbugesic, Stadol.
  • Class: Opioid antitussive.
  • Controlled Drug Status: Class IV.
  • Uses: Treats dry, non-productive coughs (such as kennel cough), provides mild to moderate visceral pain relief and acts as an antiemetic.
  • Administration: Oral, IV, IM, SQ.
  • Action: Agonist (kappa & sigma) and antagonist (mu) activity.
  • Pharmacokinetics: Crosses the placenta.
  • Excretion: Metabolized by the liver.
  • Time: Sedative effect lasts 2-4 hours, with analgesic effects lasting less than 1 hour.
  • Adverse Effects: Lesser sedation, possible dysphoria, and respiratory depression compared to other opioids.
  • Contraindications: Use caution if the patient has the MDR1 mutation or is experiencing severe pain.
  • Caution: Antagonistic action can displace other opioids from the mu receptor; monitoring for misuse is essential.
  • Calculation Examples: Dosage to reverse mu-agonist opiates suggested at 0.05-0.1 mg/kg IV.
Hydrocodone
  • Trade Names: Tussigon, Hycodan.
  • Class: Opiate agonist.
  • Controlled Drug Status: Class II.
  • Uses: For dry, nonproductive coughs (kennel cough), collapsing trachea, and bronchitis in dogs.
  • Administration: PO.
  • Action: Depresses the cough center in the brain.
  • Pharmacokinetics: Not detailed.
  • Excretion: Not detailed.
  • Time: Peak effects occur in approximately 45 minutes.
  • Adverse Effects: Sedation, constipation, gastrointestinal upset.
  • Contraindications: Caution with products containing acetaminophen in cats.
  • Caution: High potential for abuse; vigilance required for drug-seeking behavior.
  • Calculation Examples: Dosage for a 34.4 kg patient ranges from 0.2-0.5 mg.
Combination Drugs
Temaril-P
  • Trade Name: Temaril-P.
  • Class: Combination drug (Phenothiazine antihistamine + corticosteroid).
  • Controlled Drug Status: Not controlled.
  • Uses: Antitussive, antipruritic, particularly for allergic conditions.
  • Administration: PO.
  • Action: Antitussive, antipruritic, anti-inflammatory, and mild sedative properties.
  • Pharmacokinetics: Not in detail studied; expected to be metabolized by the liver.
  • Excretion: Not specified.
  • Time: Duration of effect not specified.
  • Adverse Effects: Sedation, depression, hypotension, polyuria/polydipsia, vomiting/diarrhea.
  • Contraindications: Similar to corticosteroids.
  • Caution: Taper dosing to avoid withdrawal; can induce parturition in pregnant patients.
  • Calculation Examples: For a patient weighing 34.4 kg, the medication is dosed based on weight.
Doxapram (Respiratory Stimulant)
  • Trade Name: Dopram.
  • Class: CNS respiratory stimulant.
  • Controlled Drug Status: Not controlled.
  • Uses: To stimulate respiratory function in anesthesia and neonates; assess laryngeal function.
  • Administration: IV.
  • Action: Stimulates central nervous system mediated respiratory centers.
  • Pharmacokinetics: Rapidly metabolized; increases respiratory rate but does not improve arterial oxygenation.
  • Excretion: Urine.
  • Time: Onset within 15-30 seconds, lasting about 2 minutes.
  • Adverse Effects: Potential for hypertension, arrhythmias, hyperventilation, seizures; controversial effects on cerebral blood flow in neonates.
  • Contraindications: Avoid in cases of airway obstruction, pneumothorax, acute asthma, or severe dyspnea.
  • Caution: Care to avoid IV extravasation and monitor ventilation closely.
  • Calculation Examples: Dosing for a patient weighing 34.4 kg would be calculated carefully depending on the situation.
Laryngeal Function Examination
  • Normal Laryngeal Function: Refers to the adequate lateral movement (abduction) of arytenoids during inspiration.
  • Abnormal Laryngeal Function: Signified by paralysis or improper adduction of arytenoids, resulting in potential breathing difficulties and obstruction during inhalation.