ANTIPARASITICS

Overview

Antiparasitics, drugs which kill or inhibit the growth of parasitic organisms, may be subdivided into the following therapeutic categories:

• antinematodal
• anticestodal and antitrematodal
• antiprotozoal
• insecticide

Ideal Parasite Control

• Ideal parasite control -- good husbandry practices
• Vaccination -- second best
• Drugs Important
  • Still necessary
  • Of major importance

Characteristics of the ideal antiparasitic

• Effective at removing parasites -- They have a broad spectrum of action. They are active against all developmental stages of the parasite as well as against both tissue and luminal forms.
  
• Safe to use -- They have a large Therapeutic index, do not discolor body fluids or those who administer them. There are no tissue residues and/or a short withdrawal time. They do not interact with other drugs or environmental toxins. They are not toxic to young or old animals.
  
• Convenient to use They are effective with one dose treatment to minimize the cost and stress of handling the animals. They have convenient dose forms that are easy to administer. In some cases, this means an oral dose form. In others, e.g., where individual treatment of large numbers of cattle is required, injectable forms are superior to oral forms. Because fasting is both a nuisance and requires sometimes difficult pre-treatment work, no-fasting is required. No-purgation is ideal because it decreases the number of drugs, number of handlings, and the resultant mess. Short withdrawal times allow more rapid marketing and lessened need to keep treated animals specifically identified.
  
• Low cost -- The drug itself as formulated must be inexpensive. Moreover, particularly in mass therapy situations, it must be inexpensive to administer. This includes labor cost and stress (which is a cost) to the animal(s) being treated.

Routes of administration

• Many routes; depends on --
  • Animals --
    • Number
    • Kind
  • Drug
    • Pharmacokinetics
    • Stability
• Oral -- most common
  • Capsules, tablets, and boluses
    can be given by hand or with a balling gun.
  • Small amounts of a liquid
    can be given with a dose syringe
  • Irritating solution and large amounts of liquid
    require installation of a stomach tube
  • tube or paste gun
  • Long term therapy and/or treatment of large numbers
    
    • feed additives as powders or drug impregnated resin beads are used. The beads may be less likely to provide long term contamination of feed handling and mixing equipment.
    • mineral or salt supplements, blocks, or mixes
    • drinking water
  
  
• Parenteralgenerally discouraged
  • Risks
    • syringes and needles
    • introduction of infectious agents
    • animals must be handled
  • Advantageous
    • animals going through chutes anyway
    • deliver "Known" dose easily IM or SC
    • Rarely: IV or intratracheally
  
  
• Topical many advantages
  • Easy to spray large numbers of animals
  • Dips
  • Pour-ons and spot-ons are convenient and easy
  • CONCERN: highly concentrated dose forms hazardous

REFERENCES

• Barragry, TB, Clinical Pharmacology of Endoparasiticides, Chapter 4, pp 80-118, in Veterinary Drug Therapy, Lea & Febiger, Philadelphia, 1994
• Ching Chang Wang. Basic Principles of Antiparasitic Chemotherapy, Ch. 55 in Basic and Clinical Pharmacology, 2nd ed., Ed by B.G Katzung. Lange Medical Publications, Los Altos, CA, 1984. pp. 611-621.
• Mansour, Tag E. 1979. Chemotherapy of Parasitic Worms: New Biochemical Strategies. Science 205(3):462-469. EXCELLENT REVIEW.
• Am J Vet Res 44(11):2186-2187, 1983. Avermectins
• J Neurochem 34:351-358, 1980. Avermectins
• Armour, J., "Modern anthelmintics for farm animals", Chapter 10 in Pharmacological Basis of Large Animal Medicine, eds. J.A. Bogan, P. Lees, and A.T. Yoxall, Blackwell Scientific Publications, Boston, 1983. 565 pp.
• Karns, P.A. and D.G. Luther. (1984). A survey of adverse effects associated with ivermectin use in Louisiana horses. JAVMA 185(7): 782-783.
• IVERMECTIN USE. Letter from Edward Boraski, Director, Technical Services, MSD AGVET, Rahway, NJ. DVM NEWS MAGAZINE November 1984.
• IVERMECTIN USE. Letter from Duane N. Schulze, Practitioner, Pigeon, MI. DVM NEW MAGAZINE, Fall 1984.
• Lynn'95: Lynn, Randy, [Title??? ] in Georgi's Parasitology for Veterinarians, Ed. Dwight D. Bowman, W.B. Saunders, Philadelphia, 1995. 636.089696 G296p 1995
• Marshboom, Toxicology Applied Pharmacology 24:371, 1973.(MEBENDAZOLE)
• Roudebush, Phil. An Updated Guide to the Chemotherapy of Small Animal Intestinal Parasites. Mississippi State University College of Veterinary Medicine News Publication. Fall 1984
• Webster, L.T., Jr., Drugs Used in The Chemotherapy of Helminthiasis, Chapter 40 in GG8th90.
• USPDI'94: United States Pharmacopeia Drug Information, 1994 edition
• Courtney & Roberson'95: Courtney, CH, and EL Robinson. Antinematodal Drugs, Ch. 45, in Veterinary Pharmacology and Therapeutics, 7th edition, Ed. HR Adams, Iowa State University Press, Ames. 1995.

New Refs not used in preparing these notes, yet.

• Medleau, Linda. 1994. Ivermectin ... , Vet. Med. August, p 770 - .
• Jetter, Swingle, Greek, Moriello. 1991. Treatment of Common Parasiticidal Toxicities in Small Animals. Feline Practice 19(4):11 - .(July/Aug).

Random Notes that need to be included in appropriate place in antiparasitic notes.

• From Lynn'95;
  * p247 on Selectivity -- Ascarids are very sensitive to piperazines, hookworms are refractory
  * Most breeds of cattle & dogs tolerate phosphorus insecticides -- Brahman cattle, Greyhound & Whippet dogs are likely to be fatally intoxicated by such treatment.
  
• Lynn'95
  * P248 -- Fenoxycarb -- marketed as BASUS to vets for flea control;
  LOGIC as fire ant control
  TORUS for cockroach control
• Lynn'95
  *ON Insecticides
  Federal Environmental Pesticide Control Act of 1972 (FEPCA).
  FEPCA is administered by the EPA
  Controls distribution, sales, and use of pesticides in the U.S. State governments may establish stricter controls.
• .National Poison Control Center -- 800-548-2423.
• Reinemeyer, C.R., Faulkner, C.T., Assadi-Rad, A.M., Burr, J.H., and Patton, S. 1995. Comparison of efficacies of three hearworm preventatives against experimentally induced infections with Ancylostoma caninum and Toxocara canis in pups. JAVMA 206(11): 1710-1715.
  Not cited in these notes yet. Just added reference 5/31/95. added also to antifilaricides