Human Health Concerns When Working With Medications Around Horses

Factsheet - ISSN 1198-712X   -   Copyright Queen's Printer for Ontario
Agdex#: 460
Publication Date: 07/00
Order#: 00-063
Last Reviewed: 07/00
History: Original Factsheet
Written by: Dr. Bob Wright - Veterinary Scientist, Equine and Alternative Livestock/OMAFRA

Table of Contents

  1. Medications
  2. Routes of Human Exposure to Livestock Medicines
  3. Problems with Specific Chemicals
  4. Summary
  5. Protect yourself and others
  6. Who to Telephone for Help


There are a number of drugs which horse handlers must be careful with for their own health and protection. Carelessness can result in various degrees of risk from exposure to the product being used. Risk is the chance of being harmed or suffering loss. The person handling the drugs assumes risk each time an animal is given a treatment. Information about the potential human health hazards appears on the product label. For health and safety reasons, obey the details of these statements.

Routes of Human Exposure to Livestock Medicines

People expose themselves to potential injurious effects of drugs by five main routes: dermal (skin), eyes, injection into body tissue, inhalation (lungs), and ingestion.

  • Dermal exposure refers to contamination of the skin with the product. The amount of drug absorbed and the speed at which it is absorbed depends upon: the condition of the skin (intact or cuts), the body part contaminated and the drug itself (chemical properties). Injectable prostaglandins spilled onto the skin pose a unique risk to pregnant women.
  • Eye contamination is another form of dermal exposure. The common ways of eye contamination are from wiping your eyes with contaminated hands or from blow-backs. Blow-backs can occur because of choosing the wrong size of needle; the medication flows slowly or only with force through the needle. The needle becomes blocked either prior to placing the needle into the injection site or during the introduction of the needle through the skin, or the needle is improperly attached to the syringe. In all cases, when pressure is placed on the syringe, the medication sprays back into the face of the operator. Medications can be corrosive or irritating to the eyes. The eyes are a common entry route into the body.
  • Accidental injection usually occurs as a result of inappropriate restraint of the animal or carelessness. It can also occur because of improper disposal of sharps which include needles, syringes and blades. Sharps of all types should be placed in a puncture proof container after use. The container should be clearly marked "sharps". When the container becomes half full, contact your veterinarian or the local health unit for proper disposal.
  • Oral contamination can occur from inappropriate handling of the product. Removing or holding the plastic case, which normally protects the needle, in your teeth can lead to absorption orally. This is a bad habit to get into.
  • Inhalation exposure is usually as a result of inhaling powders or mists. This can occur when using fly sprays or disinfectants. Pay attention to the product details and the cautions. Protective clothing may be required. In some cases, the hiring of licensed professionals will be required.

Problems with Specific Chemicals

  • Antibiotics, such as penicillin, are commonly used as injectable products for horses. There is a proportion of the human population who are allergic to it.
  • Tranquilizers are commonly used to control horses during transportation, dental and hoof care procedures, as well as surgical procedures. These products are extremely useful but accidental exposure to a single drop of xylazine (e.g., Rompun®) can result in respiratory arrest in humans. The administration of tranquilizers has significant risk to both the animal and the person administering the product.
  • Hormones are synthetic and natural chemicals which can have major impacts on the reproductive cycles of animals and people and have widespread action on many body systems.
    • Prostaglandins have several pharmacological effects on the female reproductive system. They are used in horses to synchronize estrus cycles and as an aid in inducing heats in difficult breeders. Because of their effect on the reproductive cycle, pregnant women should not handle these drugs. In addition, asthmatics and those with bronchial diseases should handle these products with extreme caution. The prostaglandins are marketed in several products including Estrumate® and Lutalyse®. (Plumb 1999)
    • Regumate contains altrenogest which is a synthetic progestational agent used clinically to assist mares to establish the occurrence of estrus. Altrenogest can be absorbed from contact with skin. This oil-based product can penetrate porous gloves. Absorption can be increased from areas covered by occlusive materials, such as latex or rubber gloves. In case of accidental exposure, wash immediately with soap and water. If the eyes are exposed, flush immediately with water for 15 minutes and get medical help. The manufacturer warns against the following individuals handling the product: pregnant women, women with undiagnosed bleeding, people with thrombophlebitis disorders, those with estrogen dependant tumors, those with coronary disease, those with known or suspected carcinoma of the breast, people with benign or malignant tumors which developed during the use of oral contraceptives or estrogen containing products. (Plumb 1999)
  • Anti-inflammatory Medications.DMSO is well known to horse owners. The active ingredient is dimethyl sulphoxide which is a powerful solvent. It reduces swelling due to trauma because of its hygroscopic properties (takes up water). It can increase the penetration of low molecular weight allergens like penicillin G and can cause a marked local reaction if topically administered substances like liniments are present on the skin. Therefore, apply only to dry skin. Rubber gloves should be worn while applying DMSO. Human exposure will cause a garlic-like breath and might cause local skin reaction, headache and nausea. Use in well ventilated areas and avoid inhalation and contact with eyes. (Bayley 1999)
  • Anthelmintics. Dewormers such as the ivermectins (e.g., Eqvalan®) are powerful chemicals and are commonly used with horses. The manufacturer recommends not eating or smoking while using dewormers and to wash hands after use. Avoid contact with eyes. Dispose of unused products and containers by incineration or in a land fill because ivermectin may adversely affect fish or water borne organisms if disposed in water.


Medications should only be administered by or under the direction of a veterinarian. Veterinarians may only dispense medications to clients where there is a valid veterinarian/
client/patient relationship. Because the veterinarian is responsible for the proper use of medications dispensed by himself or herself, there will be variations in their comfort levels when considering whether to dispense medications to individual clients.

When using medications, ensure that you read the label and follow the warnings about human health dangers.

Protect yourself and others:

  • read and follow label warnings and precautions
  • avoid skin contact
  • restrain animals for treatment
  • wash hands or bathe after using medicines
  • change contaminated clothing
  • do not smoke or eat when handling medicines
  • lock storage rooms and cupboards

If indicated:

  • wear protective clothing
  • wear protective gloves
  • wear protective goggles

Who to Telephone for Help:

  • Your Physician
  • The Drug Manufacturer

Poison Information Centres:

Poison Control Centre for Ontario 1-416-813-5900, 1-800-268-9017

Ottawa Children's Hospital for Eastern Ontario
Emergency Department (Bilingual) 1-613-737-1100
Human or Animal 1-800-267-1373 (From 613 area code)


  1. N.G. Anderson, D. M. Alves, T. Blackwell, M.A. Godkin, G. Rietveld, D. Stark, and R. Tremblay. 1994. Livestock Medicines Manual, Second Edition. Livestock Technology, Ontario Ministry of Agriculture, Food and Rural Affairs.
  2. A. Bayley 1999. Compendium of Veterinary Products, 6th. edition.. North American Compendiums Ltd.
  3. D.C. Plump 1999. Veterinary Drug Handbook, Third Edition. Iowa State University Press

For more information:
Toll Free: 1-877-424-1300