Ceftazidime 1g q6h or 2g q12h?

[xiongliang0]

Ceftazidime is a third-generation cephalosporin with a broad gram-negative spectrum including Enterobacteriaceae, P. aeruginosa, and Hemophilus species. Gram-positive and anaerobic activity is weaker than most other cephalosporins and penicillins. Organisms with an MIC ≤ 8 µg/ml are considered sensitive, while organisms with an MIC ≥ 32 µg/ml are considered resistant. Emergence of resistant strains of P.aeruginosa, Escherichia coli, Enterobacter sp., Klebsiella sp., and Citrobacter sp. during ceftazidime therapy is a growing concern. The antipseudomonal activity of ceftazidime
is similar to piperacillin. Piperacillin/tazobactam combined with an aminoglycoside is the antipseudomonal antibiotic regimen of choice in this institution.

The elimination half-life of ceftazidime is 1.5 to 2 hours in patients with normal renal function. The drug is dosed every 8 to 12 hours in these patients. Peak serum levels of 69-90 µg/ml are achieved following a 1 gm dose of ceftazidime.

[xiongliang0]

I try to expect the blood level of this drug by using the following formulas:

IV Cmax in the steady condition=
IVGTT Cmax in the steady condition=
Cmin in the steady condition=

As above it is said that peak serum levels of 69-90 ug/ml are achieved followinga 1gm dose of ceftazidime(IV). Organisms with an MIC<=8 ug/ml are considered sensitive.

So accroding to the formluas I can expect the Cmax and the Cmin in different regimens.The resault is as follow:

All regimens T=0.5h Half-life of Ceftazidime is 2h.

Dose Fequency Cmax(ug/ml) Cmin(ug/ml)
1 gm IVGTT Q6H 72.4 - 94.4 10.8 - 14.0
2 gm IVGTT Q12H 64.4 - 83.9 1.2 - 1.6

So I think for Serve infection the regimen of 1 gm Q6H can make sure the serum level of Ceftazidime all upper the MIC while 2 gm Q12H can not.

Any ideas? Am I right?