Antibiotiques (dosage plasmatique)

Antibiotics (plasma assay)


The examination adjusts the optimal dose of antibiotics in case of under-dosing (treatment failure) but also of an overdose, then with its risk of toxicity.


This is to test the bactericidal activity of a patient serum with antibiotics against the bacterium considered responsible for the infection.

Antibiotics (plasma assay)

Two blood sampling 10 mL each:

– One before taking or injection of antibiotics;

– The other about 1 hour after IM injection, or 30 minutes following IV, or 5 minutes after IV infusion.

The tubes are sent to the laboratory, references being made of the sampling time and the type of treatment made between the two.

The serum can be stored at – 20 ° C for several days.

Are also possible biological fluids samples: cerebrospinal fluid, urine, but also tissue specimens such as bone and lung.

The dosage is usually radioimmunoassay or enzyme immunoassay as microbiology.


According antibiotics (amino acids, due to their low safety margin, are often dosed), serum levels are:

– Gentamicin, sisomicin, dibekacin, tobramycin or nétimicine: residual rate (TR) must be less than 2 mg / L for serum (TS) in peak between 4 and 10 mg / L;

– Amikacin: TR: <8 mg / L; TS peak in 20 to 30 mg / L;

– Vancomycin: TR: 5 to 10 mg / L; TS peak: 20 to 40 mg / L.

If TR is too high, there is a risk of oto or nephrotoxicity. It is then necessary between doses or injections.

If TR is too low, the efficiency may be insufficient. Catches must then be reconciled.

Too high serum peak, coupled with normal TR means excessive dosage.

TR and TS must be considered simultaneously.



Practical advice:

If the dosage of antibiotics allows monitoring and evaluation of treatment, it can also test the effectiveness of new treatments.


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