TETRACYCLINES

Synonyms: Oxytetracycline, chlortetracycline, tetracycline, and doxycycline are several types of this antibiotic.

Mechanism of Action:

 The tetracyclines exert their antimicrobial action by inhibiting the 30s ribosomal unit of bacteria resulting in reduced protein synthesis.

The mechanism for the cardiovascular effects is due to a propylene glycol vehicle. It is thought that the propylene glycol induces histamine release leading to cardiovascular collapse.

 Another proposed mechanism for cardiovascular collapse relates to the ability of tetracycline to chelate calcium in serum acute renal failure.

 Hepatotoxicity may be noted with tetracycline administration that is due to triglyceride accumulation in the mitochondria and hepatic cells

Clinical Signs:

 Clinical signs associated with tetracycline induced renal disease include vomiting, diarrhea, dehydration, and oliguria.

Signs associated with cardiovascular toxicosis include severe hypotension, decreased heart rate, collapse, and acute death.

Clinical Pathology:

 Urinalysis may reveal proteinuria, increase in tubular casts, and the inability to concentrate urine.

Serum chemistries may show elevated urea, creatinine, and hyperphosphatemia.

 Hemoglobinuria may be associated with tetracycline administration. Elevated serum concentrations of hepatic enzymes may be associated with administration of tetracyclines.

 Lesions:Renal nephrosis is associated with tetracyclineinduced nephrotoxicosis.

Treatment:

Animals that exhibit cardiovascular collapse may be treated symptomatically with fluids and calcium gluconate.

 Concurrent intravenous administration of fluids and diuretics (mannitol and furosemide) may prevent renal toxicosis by maintaining normal urine production.

 Hemodialysis may be necessary if the renal function is severely compromised.

 Prognosis:. The prognosis is guarded with cardiovascular collapse.