The effects of doxycycline, amoxicillin, cephalexin and enrofloxacin on primary and secondary hemostasis in dogs

Antimicrobials are widely used in veterinary medicine. Previous studies in humans and animals have indicated that certain antimicrobials cause a disturbance in hemostasis, including thrombocytopenia, platelet dysfunction and disorders of secondary hemostasis. The most commonly implicated antimicrobials include those in the beta-lactam family, however disturbances associated with sulfonamides, fluoroquinolones, tetracyclines, imipenem and metronidazole have also been identified. Many of the previous studies have used dosages of antimicrobials far in excess of published therapeutic dosage ranges, and very few in vivo studies assessing the effect of antimicrobials on hemostasis in veterinary medicine have been performed. The purpose of this study was to evaluate the effects of commonly used antimicrobials at therapeutic dosages on primary and secondary hemostasis in healthy dogs.; Ten healthy, purpose-bred beagles were administered oral doxycycline, amoxicillin, cephalexin and enrofloxacin in random order at standard therapeutic dosages for 7 days. A washout period of 7 days (minimum of 14 half-lives) was allowed between administration of each antimicrobial. In addition, four healthy, purpose-bred beagles were maintained as controls. Parameters measured included platelet count, hematocrit, prothrombin time, partial thromboplastin time, fibrinogen level and platelet function. Platelet function was assessed via buccal mucosal bleeding time, aggregometry and closure time in a platelet function analyzer (PFA-100(TM)).; Administration of all antimicrobials caused a slight decrease in platelet count. There was no significant difference in platelet function after administration of any antimicrobial. Administration of all antimicrobials caused a slight prolongation of PT and PTT, and a slight decrease in fibrinogen. The cause for these slight changes in hemostatic variables is unknown. Although not clinically relevant in healthy dogs, these alterations might result in hemorrhagic diatheses in dogs with underlying disease processes.; In conclusion, administration of selected commonly-used antimicrobials in healthy dogs resulted in slight hemostatic abnormalities, with no change in platelet function. Although these changes were clinically irrelevant in healthy dogs, further studies that evaluate the effects of antimicrobial administration on hemostasis in animals with underlying disease processes are warranted.