Proto, Fungal, Endo, Ecto

Anticoccidials

Are drugs used to prevent or treat coccidiosis, an intestinal protozoal disease primarily caused by Eimeria species. They are heavily used in poultry and livestock because coccidiosis spreads easily and can cause severe economic losses through diarrhea, poor growth, and mortality.

Antibabesia and Antitheilerial Drugs

Are drugs used against Babesia and Theileria, blood parasites transmitted by ticks. Because these protozoa invade red blood cells, infection commonly results in anemia, weakness, jaundice, and reduced productivity.

Antigiardial Drugs

Are drugs that treat Giardia infections of the small intestine. Giardia interferes with nutrient absorption and often causes chronic diarrhea. Control of environmental contamination is important because reinfection is common.

Antitrypanosomal Drugs

Are drugs that target Trypanosoma species, protozoa transmitted by insect vectors. Trypanosome infections can affect blood and tissues, causing chronic disease, weight loss, anemia, and decreased production in livestock.

Antileishmanial Drugs

Are drugs used against Leishmania species transmitted by sandflies. Infection is often chronic and may involve the skin, lymphoid tissues, and internal organs. Dogs are important reservoirs in endemic areas, giving the disease zoonotic importance.

ANTIPROTOZOAL MECHANISMS OF ACTION

• Folate Antagonism - Prevents folic acid synthesis, which protozoa need to produce DNA and divide.

• DNA Damage - Directly damages protozoal genetic material, preventing replication and survival.

• Inhibition of Protozoal Metabolism - Blocks essential biochemical pathways needed for energy production and growth.

• Interference with Mitochondrial Function - Disrupts ATP production, depriving the parasite of energy.

• Thiamine Antagonism - Prevents utilization of vitamin B1, leading to impaired parasite metabolism.

• Membrane Disruption - Damages cell membranes, causing loss of cellular integrity and death.

ANTIPROTOZOAL TOXICITIES

• Neurotoxicity - May occur when drugs affect nervous tissue, causing tremors, ataxia, seizures, or weakness.

• Bone Marrow Suppression - Reduced production of blood cells may lead to anemia, leukopenia, or thrombocytopenia.

• Hepatotoxicity - Liver injury may develop because many antiprotozoals undergo hepatic metabolism.

• Nephrotoxicity - Some drugs may damage renal tissue, especially at high doses.

• Species-Specific Toxicity - Certain species are more sensitive to particular drugs, making proper drug selection important.

ANTIPROTOZOAL RESISTANCE

• Misuse Leading to Resistance - Repeated exposure to the same drug allows resistant protozoa to survive and multiply.

• Rotation Programs in Poultry - Alternating anticoccidial classes helps delay resistance development.

• Combination Therapy - Using multiple drugs with different mechanisms may improve efficacy and reduce resistance.

• Drug Residue Concerns - Improper withdrawal periods may leave residues in animal products intended for human consumption.

Polyenes

Targets fungal cell membranes and are used for serious systemic fungal infections or localized fungal disease. They are among the oldest antifungal classes.

Azoles

Are widely used antifungals that inhibit fungal growth by disrupting cell membrane formation. They may be used topically or systemically depending on the infection.

Allylamines

Are especially effective against dermatophytes (skin fungi) and are commonly used for infections involving skin, hair, and nails.

Echinocandins

Targets the fungal cell wall rather than the cell membrane. Veterinary use is relatively limited but may be considered for severe infections.

Antimetabolites

These drugs interfere with fungal nucleic acid production, preventing growth and replication. They are often used together with other antifungal drugs.

ANTIFUNGAL MECHANISMS OF ACTION

• Ergosterol Targeting - Many antifungals target ergosterol, the fungal equivalent of cholesterol, because it is essential for membrane stability.

• Cell Membrane Disruption - Damage to the fungal membrane causes leakage of cellular contents and cell death.

• Cell Wall Synthesis Inhibition - Prevents the formation of the fungal cell wall, making the organism fragile and unable to survive.

• Nucleic Acid Synthesis Inhibition - Blocks DNA and RNA production, preventing fungal replication.

• Mitotic Spindle Function Inhibition - Interferes with fungal cell division by disrupting chromosome separation.

MAJOR CLINICAL PRINCIPLES OF ANTIFUNGAL THERAPY

• Long Treatment Duration - Fungal infections often require weeks to months of therapy because fungi grow slowly.

• Difficulty of Fungal Eradication - Fungi may be deeply embedded in tissues, making complete elimination difficult.

• Importance of Culture and Diagnosis - Correct identification of the fungal species helps select the most effective treatment.

• Monitoring Liver Enzymes - Many antifungals can affect the liver, making monitoring important during treatment.

• Relapse Prevention - Treatment should continue long enough to eliminate residual organisms and prevent recurrence.

• Drug Penetration into CNS and Skin - Successful treatment depends on whether the drug reaches the infected tissue at therapeutic concentrations.

COMMON ANTIFUNGAL TOXICITIES

• Hepatotoxicity - Liver injury is one of the most important adverse effects.

• Nephrotoxicity - Some antifungals can damage renal tissue.

• Gastrointestinal Upset - Vomiting, diarrhea, and reduced appetite may occur.

• Bone Marrow Suppression - Some drugs decrease blood cell production.

• Teratogenic Effects - Certain antifungals may harm the developing fetus.

ANTIFUNGAL RESISTANCE MECHANISMS

• Altered Ergosterol Pathways - Fungi modify membrane synthesis pathways, reducing drug effectiveness.

• Biofilm Formation - Biofilms create a protective environment that limits drug penetration.

• Efflux Pumps - Fungal cells actively pump drugs out before toxic concentrations can accumulate.

• Incomplete Treatment Leading to Resistance - Stopping therapy too early allows surviving fungi to persist and adapt.

Benzimidazoles

Broad-spectrum anthelmintics effective against many nematodes and some cestodes and trematodes. They are among the most commonly used dewormers in veterinary medicine.

Macrocyclic Lactones

Broad-spectrum antiparasitic drugs active against many internal and external parasites. They are especially important for heartworm prevention.

Imidazothiazoles

Anthelmintics that primarily target nematodes by causing parasite paralysis.

Tetrahydropyrimidines

Drugs commonly used against gastrointestinal nematodes. They cause paralysis, allowing parasites to be expelled.

Piperazine

A narrow-spectrum dewormer mainly used against roundworms.

Praziquantel

One of the most important drugs for treatment of tapeworm infections.

Flukicides

Specialized anthelmintics used against trematodes (flukes), especially liver flukes that cause major economic losses in livestock.

ANTHELMINTIC MECHANISMS OF ACTION

• Microtubule Inhibition - Prevents nutrient uptake and cell division within the parasite.

• Glutamate-Gated Chloride Channel Activation - Causes paralysis through increased chloride influx and nervous system depression.

• Nicotinic Receptor Agonism - Produces persistent muscle contraction followed by paralysis.

• GABA-Mediated Paralysis - Suppresses neuromuscular activity leading to flaccid paralysis.

• Increased Calcium Permeability - Causes severe muscle contraction and damage to parasite integument.

ANTHELMINTIC RESISTANCE CONCEPTS

• Causes of Resistance - Genetic selection of parasites that survive treatment.

• Underdosing - Subtherapeutic doses allow partially resistant parasites to survive.

• Frequent Treatment - Excessive treatment increases selection pressure.

• Refugia Preservation - Maintaining a population of untreated susceptible parasites helps dilute resistant genes.

• Combination Deworming - Multiple mechanisms reduce survival of resistant parasites.

• Rotation Strategies - Alternating classes may help slow resistance development.

ANTHELMINTIC TOXICITIES

• Neurotoxicity - Most commonly associated with drugs affecting parasite nervous systems.

• Bone Marrow Suppression - Can occur with some agents, especially at excessive doses.

• Teratogenicity - Certain drugs may cause fetal abnormalities.

• Colic and GI Signs - May occur following treatment, particularly with heavy parasite burdens.

• Species Sensitivity - Some breeds or species are more susceptible to toxicity.

Pyrethrins and Pyrethroids

Common insecticides used against fleas, ticks, and flies. Many also provide repellent effects.

Organophosphates

Potent insecticides that act on the nervous system of parasites but have significant toxicity concerns.

Carbamates

Similar to organophosphates but generally produce reversible enzyme inhibition.

Formamidines

Used primarily against ticks and mites and possess additional neurologic effects.

Phenylpyrazoles

Broad-spectrum ectoparasiticides commonly used in topical flea and tick products.

Isoxazolines

Modern systemic flea and tick medications with prolonged activity and excellent efficacy.

Insect Growth Regulators (IGRs)

Prevent immature parasites from developing into adults, helping break the life cycle.

Neonicotinoids

Selective insecticides commonly applied topically for flea control.

ECTOPARASITIC MECHANISMS OF ACTION

• Sodium Channel Effects - Cause repetitive nerve firing leading to paralysis and death.

• Acetylcholinesterase Inhibition - Allows excessive acetylcholine accumulation resulting in continuous nerve stimulation.

• Alpha-2 Receptor Effects - Disrupt nervous system activity in parasites while also producing effects in the host.

• GABA Inhibition - Removes inhibitory nervous system control, causing hyperexcitation and death.

• GABA and Glutamate Channel Inhibition - Produces uncontrolled neural activity in parasites.

• Interruption of Life Cycle - Prevents egg hatching or larval maturation.

• Nicotinic Receptor Action - Overstimulates insect nervous systems causing paralysis and death.

INTEGRATED PARASITE CONTROL

Environmental Control - Reducing parasite habitats decreases reinfection.

Vector Control - Controlling insects and ticks reduces disease transmission.

Sanitation - Removal of contaminated feces and organic material lowers parasite exposure.

Pasture Management - Proper grazing practices reduce parasite burden in livestock.

Resistance Prevention - Responsible drug use slows development of resistance.

Client Education - Owner compliance is essential for successful parasite control.

ECTOPARASITE TOXICOLOGY

• Species Sensitivity - Different species metabolize drugs differently and may show varying toxic responses.

• Cat Toxicity with Permethrin - Cats lack adequate metabolic pathways for permethrin detoxification, making exposure potentially life-threatening.

• Organophosphate Poisoning - Results from excessive cholinergic stimulation causing salivation, lacrimation, urination, diarrhea, tremors, and respiratory distress.

• Human Exposure Risks - Improper handling may result in accidental poisoning.

• Environmental Contamination - Drug residues may affect wildlife, aquatic organisms, and ecosystems.