When administering antibiotics to an animal, it is important to know the details of each antibiotic; the use of all antibiotic medications poses a number of risks to the patient. Antibiotics must be administered as prescribed and specific instructions must be strictly adhered to.
Penicillin (Benzylpenicillin and procaine penicillin)
Anaphylaxis/anaphylactic reactions occur after previous exposure/allergy to penicillin. Mild symptoms include skin wheals or edema, and in severe cases this can cause the animal to collapse suddenly and experience difficulty breathing. This is usually fatal. If the animal survives the allergic reaction, penicillin should not be injected again as the next injection may be fatal.
Procaine is the agent used to stabilize penicillin for intramuscular injection. If procaine is inadvertently injected into a vein, it can cause extreme stimulation of the central nervous system, including frantic and uncontrollable behavior. This is not an allergic reaction. Most horses survive this reaction, but they can be fatally and seriously injured. Keeping procaine penicillin refrigerated and ensuring careful injection techniques can reduce this risk.
Tetracyclines (oxytetracycline, doxycycline)
Nephrotoxicity/renal injury (see aminoglycosides). Risk increases with dehydration, use of other nephrotoxic drugs, and with kidney disease. The risk is reduced if the animal is well hydrated and normal renal function is ensured as far as possible.
These drugs can cause syncope and death if given rapidly intravenously. Diluting the drugs with sterile saline and giving them slowly intravenously reduces this risk. Tendon relaxation may occur. This will reverse over time after completion of antibiotic therapy. Teeth may become discolored, especially in young animals, and this may be permanent.
Aminoglycosides (gentamicin and amikacin)
Nephrotoxicity/Renal Injury. Increased risk of nephrotoxicity is associated with duration of treatment (more than 7-10 days), dehydration, treatment with other medications affecting renal function, existing kidney disease, and high doses. Initial symptoms may be vague and include failure to thrive, weight loss, or abnormal blood results. Mild cases may return to normal after a period of time and a small amount of treatment. Severe cases may lead to kidney failure and possibly even death of the animal. To reduce these risks, it is important to ensure that the correct dose is given to the animal only once a day, that hydration is monitored, and that blood tests are performed to monitor drug levels and kidney function.