Therapeutic Classifications of Veterinary Drugs

Therapeutic Drug Classifications

  • Drugs are most commonly categorized based on their therapeutic use, meaning what conditions or symptoms they are intended to treat.
  • It is important to note that a drug's therapeutic classification does not dictate its physical form (e.g., tablet, liquid) or its route of administration (e.g., oral, injectable).
  • A single drug might be available in various forms and administered through different routes.

Key Points Regarding Therapeutic Drug Classifications

  • Many drugs possess more than one therapeutic application, leading to their inclusion in multiple drug classifications.
  • Different veterinary pharmacological sources may present varying classifications or organizational structures for drugs.
  • Understanding a drug's classification provides valuable insight into a patient's condition and allows for informed expectations regarding a medication's effects and anticipated outcomes.

Outline of Drug Categories

This lecture will cover the following therapeutic classifications, noting that analgesics will be discussed in a separate session:

  • Anti-infective/Antimicrobial Drugs
  • Antiparasitics
  • Gastrointestinal Drugs
  • Cardiovascular Drugs
  • Nervous System Drugs
  • Respiratory Drugs
  • Renal / Urinary Drugs
  • Endocrine/Hormonal/Reproductive Drugs
  • Immunologic Drugs

Anti-Infective Drugs

  • Also known as antimicrobials, these drugs are utilized to combat various types of infections:
    • Bacterial infections
    • Fungal infections
    • Protozoal infections
    • Viral infections
  • They function by either destroying (ending in "−cidal-cidal ") or inhibiting the growth (ending in "−static-static ") of specific infectious organisms.

Efficacy Requirements for Anti-Infective Drugs

For an anti-infective drug to be effective, two critical criteria must be met:

  • The drug must reach the site of infection in a sufficient concentration.
  • This sufficient concentration must be maintained for the required duration of time.
  • Failure to meet both criteria can lead to treatment failure, persistence of infection, or the development of antimicrobial resistance.

Antimicrobial Drugs for Bacterial Infections

  • Antimicrobial drugs targeting bacterial infections are commonly referred to as antibiotics or antibacterial drugs.
  • There are several hundred types of antibiotics, each designed to be effective against a particular group of bacteria.
  • Even antibiotics labeled as "broad spectrum" are not effective against every bacterial infection.
Classes of Antibiotics
  • Penicillins
  • Cephalosporins
  • Tetracyclines
  • Aminoglycosides
  • Quinolones
  • Macrolides
  • Lincosamides
  • Carbapenems
  • Sulfonamides
  • Other/Miscellaneous

Antifungal Drugs

  • Used to treat mycoses (fungal infections).
    • Dermatophytosis: Commonly known as ringworm.
    • Coccidioides: Causing conditions like valley fever.
  • Most preferred antifungal drugs are fungistatic, as fungicidal drugs can often be cytotoxic (toxic to cells) in the animal's or human's body.

Antiprotozoal Drugs

  • Treat infections caused by protozoa, such as giardia and coccidia.
  • Protozoa are single-celled organisms that most frequently cause gastrointestinal (GI) disease but are also capable of causing disease in numerous other organ systems.

Antiviral Drugs

  • Used to treat infections caused by viruses.
  • While research is continuously improving, there are currently very few FDA-approved antiviral agents specifically for veterinary use.
  • Even in human medicine, effective antivirals are relatively scarce.
  • Viruses are inherently more challenging to target and attack with drugs because they are not cellular organisms.

General Principles of Anti-Infective Action

  • Anti-infective drugs often do not completely eradicate an infection but rather suppress it to a level where the animal's own immune system can effectively clear the remaining pathogens.
  • Veterinarians will prioritize topical or local antimicrobials over systemic drugs whenever feasible. This approach benefits from reduced systemic side effects and provides more targeted treatment to the affected area.

Antiparasitic Drugs

  • Parasites are harmful organisms that live on (ectoparasites) or within (endoparasites) a host's body.
    • Ectoparasites: External parasites, including fleas, ticks, mites, and lice.
    • Endoparasites: Internal parasites, such as various types of worms or protozoa. These can invade the GI tract, blood, heart, lungs, muscle, brain tissue, and virtually any other organ system.

Classes of Antiparasitic Drugs

  • Anthelmintics: Drugs targeting worms.
    • Specifically effective against roundworms, whipworms.
  • Anticestodals: Drugs targeting tapeworms.
  • Antiprotozoals (mentioned as part of anti-infectives).
  • Insecticides
  • Preventives
Anthelmintics (Dewormers)
  • Dewormers are drugs used to treat infestations with nematodes (worms that are round in shape), particularly intestinal nematodes.
  • These drugs are generally considered safe and are often available over-the-counter (OTC) because they are difficult to overdose.
Classes of Anthelmintics
  • Piperazines
  • Benzimidazoles
  • Organophosphates
  • Tetrahydropyrimidines
  • Imidazolthiazoles
  • Milbemycins
  • Avermectins
Anticestodals
  • Anticestodals are drugs specifically designed to kill or facilitate the expulsion of tapeworms (cestodes).
Topical Insecticides
  • These are used to treat infestations by many types of ectoparasites, including fleas, ticks, mites, and lice.
Antiparasitic Preventives
  • Many types of preventive medications are available, administered regularly to prevent parasitic infections or infestations.
  • Examples include flea and tick products, dewormers, and heartworm preventatives.
  • Most preventives are given on a regular schedule, typically every one, three, or six months, depending on the specific product.

Gastrointestinal (GI) Drugs

Classes of GI Drugs

  • Emetics
  • Antiemetics
  • Adsorbents & Protectants
  • Bowel Stimulants
  • Antacids & Antiulcers
  • Appetite Stimulants
  • Antidiarrheals
Emetics and Antiemetics
  • Emetics: Drugs that induce emesis (vomiting).
  • Antiemetics: Drugs that control or prevent vomiting.
    • Typically administered parenterally (e.g., by injection) because the oral route is often compromised in vomiting patients.
Adsorbents & Protectants
  • These drugs form a coating that protects the stomach and intestinal lining from irritating substances.
  • They are sometimes deliberately used in cases of toxin ingestion to prevent absorption or reduce irritation.
Antacids and Antiulcer Drugs
  • Antacids: Work by neutralizing the stomach's acidity, which helps prevent the formation of gastric ulcers.
  • Antiulcer drugs: Are used to treat and help repair existing gastric ulcers by coating and protecting them from further exposure to stomach acid.
Bowel Stimulants and Appetite Stimulants
  • Bowel stimulants: Function by loosening bowel contents and/or directly encouraging the evacuation of feces in patients experiencing constipation or decreased gut motility (hypomotility).
  • Appetite stimulants: Are primarily used in anorexic (lack of appetite) patients.
    • A notable example is Diazepam, which can cause patients to become intensely hungry ("ravenous") immediately after injection.

Cardiovascular Drugs

  • Drugs affecting the cardiovascular system can impact the heart, blood vessels, blood pressure, and/or the blood itself.

Classes of Cardiovascular Drugs

  • Antiarrhythmics
  • Positive Inotropic Drugs
  • Vasodilators
  • Diuretics
  • Blood Modifiers
Positive Inotropic Drugs
  • These drugs are used to manage conditions such as congestive heart failure (CHF) and hypertension (high blood pressure) by increasing the force of contractility of the heart muscle.
Vasodilators
  • Vasodilators help manage congestive heart failure (CHF) and hypertension by causing the dilation (widening) of blood vessels, which reduces resistance to blood flow.
  • ACE-inhibitors are a common type of vasodilator.
Diuretics
  • Diuretics work by increasing the excretion of water and sodium via the urine, thereby removing excess cellular fluid from the body.
  • They are often prescribed to help manage CHF and/or hypertension because removing excess fluid reduces blood volume, eases the workload on the heart, and lowers blood pressure.
Common Blood Modifying Drugs
  • Hemantics: Promote blood oxygenation by increasing red blood cell production or hemoglobin levels.
  • Anticoagulants: Prevent blood from coagulating (clotting).
  • Hemostatics: Promote the formation of blood clots.
  • Fibrinolytics: Act to dissolve existing clots, embolisms, or thromboses.

Nervous System Drugs

Types of Nervous System Drugs

  • Opiates/Opioids
  • Sedatives & Tranquilizers
  • Anesthetics
  • Stimulants
  • Sympathomimetics
  • Analeptics
  • Muscle Relaxants
  • Behavior Modifiers
Opioids / Opiates
  • These are narcotic analgesics, primarily used as powerful pain relievers.
  • Further discussion on analgesic drugs will be covered in the Pain Management lecture.
Sedatives & Tranquilizers
  • These drugs induce a relaxed state of consciousness, reducing irritability or excitement.
  • It is crucial to understand that sedatives and tranquilizers typically do not possess analgesic properties; therefore, a tranquilized or sedated animal can still perceive pain.
Anesthetic Drugs
  • Anesthetic drugs are agents that provide a loss of consciousness and/or a loss of sensation, including pain, cold, heat, pressure, and touch.
Classes of Anesthetic Drugs
  • Barbiturates
  • Non-barbiturates
  • Dissociative anesthetics
  • Inhalants
  • Local anesthetics
  • Anesthetic drugs will be covered in more detail in the Principles of Anesthesia lecture.
Stimulants
  • Stimulants are used to increase nervous activity or to reverse central nervous system (CNS) depression caused by anesthetic or sedative agents.
  • They can achieve their effects through various mechanisms:
    • Promoting the release of excitatory neurotransmitters.
    • Delaying the reuptake of excitatory neurotransmitters from their receptors.
    • Inhibiting the release or facilitating the breakdown of inhibitory neurotransmitters.
Sympathomimetics
  • Sympathomimetics are drugs that mimic the effects of the sympathetic nervous system.
  • The sympathetic nervous system is responsible for regulating many homeostatic mechanisms, such as heart rate, respiration, and urination, often associated with the body's "$fight-or-flight$$" response (e.g., adrenaline-like effects).
Anticholinergics
  • Anticholinergics are a very common type of sympathomimetic drug.
  • They inhibit parasympathetic nerve impulses by blocking the binding of the neurotransmitter acetylcholine to its receptors.
  • Their effects include:
    • Increased heart rate and force of contraction.
    • Decreased salivation and respiratory secretions.
    • Dilation of pupils (mydriasis).
    • Decreased gut motility and reduction of gastrointestinal spasms.
Analeptics (Anticonvulsants)
  • Analeptics, also known as anticonvulsants, are drugs that help stop, reduce, or control seizures and seizure activity.
  • They typically achieve this by increasing the seizure threshold.
  • Some barbiturates (a class of anesthetic drugs) also function as analeptics.
Muscle Relaxants
  • Muscle relaxants are drugs primarily used to control or reduce muscle tightening and spasms by depressing neuromuscular activity.
  • They are highly beneficial for patients suffering from severe or chronic back pain.
  • Some anesthetics and anticonvulsant drugs can also exhibit muscle-relaxing properties.
Behavior Modifiers
  • Behavior modifiers are agents that alter the concentrations of specific neurotransmitters in the brain with the goal of decreasing or enhancing particular mental activities.
  • Behavior-modifying agents can be classified as:
    • Antipsychotic
    • Antidepressant
    • Antianxiety

Respiratory Drugs

Types of Respiratory Drugs

  • Expectorants & Mucolytics
  • Antitussives
  • Bronchodilators
  • Decongestants
Expectorants & Mucolytics
  • These drugs are used to break up or dilute mucous secretions within the respiratory tract.
  • They are primarily indicated when a productive cough (a cough that expels mucus) is present, facilitating the removal of respiratory secretions.
Antitussives
  • Antitussives are drugs that inhibit or suppress coughing.
  • They should only be used for non-productive coughs. Using them for productive coughs would prevent the necessary expulsion of mucus and debris from the airways.
  • Some narcotic analgesics also possess antitussive properties.
Bronchodilators
  • Bronchodilators work by dilating (widening) the airways, which decreases resistance to airflow and increases the amount of air reaching the lungs.
Decongestants
  • Decongestants reduce congestion and swelling within the nasal passageways.
  • They typically work by constricting nasal blood vessels, thereby reducing blood flow and swelling.

Endocrine Drugs

  • Most drugs that affect the endocrine system are either actual hormones or synthetic versions of hormones.
  • Endocrine drugs are administered to achieve one of two primary effects:
    • To correct a deficiency of a specific hormone within the body.
    • To obtain a desired physiological effect by leveraging hormonal activity (e.g., inducing ovulation).

Major Types of Endocrine Drugs

  • Steroids
  • Reproductive hormones
  • Thyroid hormones
  • Growth Promoters
  • Hyperglycemic agents (drugs that increase blood sugar)

Common Endocrine Disorders Treated

Endocrine drugs are used to treat a variety of common endocrine disorders, including:

  • Diabetes mellitus
  • Hypothyroidism and hyperthyroidism
  • Cushing's disease and Addison's disease
  • Reproductive disorders
Corticosteroids
  • Corticosteroids are hormones that possess strong anti-inflammatory effects and can suppress immune system responses.
  • They have a wide range of therapeutic uses but are also associated with many potentially harmful side effects.
  • Corticosteroids can delay wound healing, exacerbate existing infections, and lead to complications like diabetes with long-term use.
Anabolic Steroids
  • Anabolic steroids are used to promote appetite, encourage weight gain, and improve overall physical condition.
  • They are not considered safe for pregnant animals or animals intended for food production.
  • Due to their potential for human abuse, anabolic steroids are classified as a Schedule III controlled substance in many jurisdictions.
Reproductive Drugs
  • Reproductive drugs are primarily hormones given to supplement hormone deficiencies or to regulate reproductive processes.
  • Examples include:
    • Gonadotropins
    • Estrogen
    • Testosterone
    • Progesterone
    • Prostaglandin
    • Oxytocin
    • Corticosteroids (which can influence reproduction)
Blood Sugar Regulators
  • Diabetic drugs: Primarily treat diabetes mellitus, with insulin being a common example.
  • Hypoglycemic agents: Are administered to treat conditions characterized by low blood sugar.

Renal & Urinary Drugs

Types of Renal & Urinary Drugs

  • Antidiuretics
  • Urinary Incontinence Agents
  • Urinary pH Modifiers
Antidiuretics
  • Antidiuretics function by signaling the body to retain more water, thereby balancing fluid levels and reducing the production of urine.
  • They are used to treat conditions such as diabetes insipidus, which is characterized by excessive thirst and urination.
Urinary Incontinence Agents
  • These agents are prescribed to promote bladder control and enhance urine retention in incontinent animals.
  • Some of these drugs can also be categorized under the hormone and endocrine classification because they often interact with estrogen receptors on the bladder, influencing its function.

Immunologic Drugs

  • Immunologic drugs are designed to suppress the immune system.
  • They are used to treat immune-mediated disorders, which can include:
    • Conditions where the immune system is overactive (e.g., allergies, autoimmune diseases).
    • Conditions where a poorly responding immune system requires modulation.
Antihistamines
  • Antihistamines work by blocking the action of histamine, preventing it from binding to histamine receptors.
  • Histamine is one of the key chemicals released by the body that causes itching and other symptoms associated with allergies and allergic reactions.
Anti-inflammatory Drugs
  • Anti-inflammatory drugs suppress inflammation within the body, a process that is controlled and regulated by the immune system.
  • Corticosteroids: Can be used for their potent anti-inflammatory effects.
  • NSAIDs (non-steroidal anti-inflammatories): Are alternatives to corticosteroids that are widely used in treating pain and inflammation, often with a different side effect profile.

Miscellaneous Drugs

  • Antineoplastics (chemotherapy drugs)
  • Dermatological drugs (for skin conditions)
  • Ophthalmic drugs (for eye conditions)