In this information age you have several options if you want details regarding a drug. Your veterinarians are always a good source but may not have some of the details you want immediately at their fingertips. You could always do an internet search but the reliability of many sources could be questionable.
A good stop for brief general information on mechanisms of action, dosages and precautions is the monograph index from elephantcare.org:
Although their focus is elephants, the information on this site is heavily equine since there is more detail available on horses. To use this list you will need to know the generic/chemical name of the drug rather than the brand name. For example, ivermectin rather than Zimecterin.
An excellent source of information is the FDA’s NADA (new animal drug application) database. This contains material submitted to the FDA to fulfill the requirements for drug approval and will have information on things like effectiveness and safety. To find this, do a Google search for: [drug name] + species + NADA. The NADA reports look like this:
You can also search the FDA’s site to retrieve this information using the NADA number, drug chemical name or brand name:
The FDA additionally maintains a database of adverse drug experiences, listed by the drug’s chemical/generic name:
There are many limitations to these adverse event reports, including that they are only suspected, not actually proven, reactions to drugs. Also, for the FDA to list it, it has to be reported. There are likely many, many more adverse reactions than ever get reported.
If your horse has a bad drug reaction (which by definition also includes the drug not working), the FDA suggests you first contact the manufacturer so they can fill out a reporting form for the FDA. You can also request that your vet file a report. However, you can report the reaction yourself and I strongly suggest that you do so to make sure it gets done. Instructions are here:
The internet has made it possible to access drug information in more detail than ever possible before. Pay it forward by taking the time to report any suspected negative drug reactions.
Adverse reactions to vaccines, aka biologics, can also be reported. The USDA has jurisdiction over vaccines:
Eleanor Kellon, VMD