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**22** 

**Pharmacokinetic – Pharmacodynamic** 

Nora Mestorino and Jorge O. Errecalde *Department of Pharmacology and Toxicology,* 

> *Faculty of Veterinary Science, Universidad Nacional de La Plata,*

> > *Buenos Aires, Argentina*

**Considerations for Bovine Mastitis Treatment** 

Bovine mastitis is a disease that affects dairy herd production, characterized by considerable economical loss due to diminished milk secretion, potential productive cow damage, increase in production costs and milk contamination. Intramammary infection (IMMI) is the most common reason for the use of antimicrobials in dairy cows. Antimicrobials (ATMs) have been used to treat mastitis for more than fifty years, but consensus about the most

*Staphylococcus aureus* is considered one of the main bacteria causing bovine mastitis, which is widely distributed in different countries. *S. aureus* is Gram-positive cocci, catalase-positive and facultative anaerobe. The *Staphylococcus* genus comprises more than thirty species which are able to colonize many environments and are part of the cutaneous or mucousal flora of various animals and humans. The intracellular survival of *S. aureus* is believed to contribute to the recurrence of some infections such as mastitis. Some publications reported the ability of this pathogen to colonize multiple cell types. However the precise fate of

The general lack of therapeutic success against subclinical mastitis caused by *S. aureus* has prompted a reevaluation of treatment strategies. Despite the availability of several antibiotics with good in vitro activity, cure rates are poor, suggesting that inadequate concentrations of active antibiotic are coming into contact with the infecting bacteria for

Over the last few years, much concern has been raised regarding the optimization of antibiotic use, owing to the worrying increase of bacterial resistance. In this context, progress in the field of anti-infective pharmacology has led to the emergence of a new discipline, referred to as pharmacokinetics/pharmacodynamics (PK/PD) of antibiotics, the discipline that strives to understand the relationships between drug concentrations and effects, both desirable (bacterial killing) and undesirable (bacterial resistance). Over the past 15 years, three key PK/PD parameters have been elaborated, which determine how

efficient, safe, and economical treatment is still lacking.

intracellular *S. aureus* is still poorly understood.

sufficient time and /or adequate concentrations to be effective.

**1. Introduction** 

