In-vitro Activity of Three Brands of Ceftriaxone against different

Methods: This comparative study was carried in Kathmandu Medical College Teaching Hospital (KMCTH), Basic Science Complex, Duwakot, Bhaktapur in 2009. Thirteen clinical isolates isolated from the specimens processed in the Microbiology Laboratory at KMCTH were used. Minimum inhibitory concentration (MIC) of three brands of ceftriaxone (A, B, and C) was determined by agar dilution and antibiotic resistance patterns were deduced by disc diffusion test.


INTRODUCTION
3][4][5] It is also commonly used in intensive care units of Nepal. 5[7] Ceftriaxone is imported in Nepal and the success of the treatment relies on correct identifi cation of the pathogen, appropriate antibiotic and dose, duration, and most importantly potency.Different brands of ceftriaxone are available in the market and prescription of one brand primarily depends upon the favor of the physician involved in the treatment process giving little attention to the potency.Hence, we have determined the in-vitro antimicrobial activity of three brands of ceftriaxone against the clinical isolates and studied their antibiotic resistance patter.
Three brands of ceftriaxone powder for injection was purchased from a commercial source and were blinded as A, B, and C. MIC (mg/L) to three brands of ceftriaxone was determined by agar dilution as recommended by CLSI. 8Briefl y, the stock concentrations of each brand of ceftriaxone were prepared as previously described. 9eftriaxone solution was added to the molten Muller Hinton agar (Himedia, India) to provide two fold serial dilutions ranging from 0.25 to 256 mg/L.Few pinpoint colonies of overnight grown bacteria were suspended in peptone water to reach the turbidity of 0.5 McFarland standard (BaSO 4 turbidity standard). 9The 0.001 ml inoculating loop was used to deliver 10 4 colony forming unit (cfu)/spot of bacteria into the agar plate containing the ceftriaxone.The plates were incubated at 35ºC for 16 to 20 hours.The growth of a single colony or a haze was not considered.The lowest concentration of antibiotic that showed no bacterial growth was considered as MIC.E. coli ATCC 25922 and S. aureus ATCC 25923 were used as a quality control strains.
E. coli ATCC 25922 and S. aureus ATCC 25923 were used as quality control strains.

RESULTS
The in-vitro activity of three brands of commonly used ceftriaxone was studied by determining MIC by agar dilution.The result showed that two brands (A and C) had consistent in-vitro activity against all the isolates.MIC for these two brands ranged from <0.25 to >256 mg/L while brand B was relatively less active and the MIC was higher by at least 2 fold for some of the isolates (Table 1).MIC obtained for the control strains were within the acceptable limits and all brands had MIC less than 0.25 mg/L.The zone of inhibition obtained by disc diffusion test correlated well with the MIC obtained by agar dilution.1).Ceftriaxone resistant isolates (n=6) showed in-vitro resistance to numerous antibiotics (7 to 15) while most of them were susceptible to imipenem and amino glycosides.

DISCUSSION
Ceftriaxone, an extended spectrum cephalosporin is active against Gram positive and negative bacterial isolates and mostly for pathogens causing meningitis due to its high level in CSF. 1 On light of emergence of multidrug resistant pathogens to penicillins, quinolones, tetracyclines, and narrow spectrum cephalosporins the role of extended spectrum cephalosporins is even more crucial.The effective treatment relies on several factors and most importantly the correct antibiotic and potency of the active drug.
We determined the in-vitro activity of three different brands of commercially available cefriaxone.The brand B had lower in-vitro activity than its competitor brands A and C. The MIC obtained for this brand was at least two fold higher than other brands for some isolates while for others all brands had MIC either <0.25 mg/L or >256 mg/L.The ceftriaxone concentration tested ranged from 0.25 mg/L to 256 ml/L and since isolates had MIC <0.25 mg/L and >256 mg/L, the invitro activity on two extremes couldn't be known.The activity of brand B could have been known if ceftriaxone concentration <0.25 or >256 mg/L were tested.For an isolate EC1032, MIC was 64 mg/L for all brands and this couldn't be explained.Study comparing different brands of ceftriaxone is scare in literature and we could not compare our study with others.
Among 13 multidrug resistant clinical isolates studied 6 were resistant to ceftriaxone.Ceftriaxone resistant isolates were further resistant to numerous antibiotics leaving the choice for imipenem and aminoglycosides.Ceftriaxone resistant clinical strains are emerging worldwide.Although, ceftriaxone resistant E. coli and Klebsiella spp.are scarce in literaturers, ceftriaxone resistant Salmonella spp.has been rising in Nepal. 7,10The resistance to this antibiotic is also a global concern. 6ftriaxone resistance is conferred by the plasmid borne CTX-M, CMY-2, TEM and SHV extended spectrum -lactamase enzyme (ESBL) and plasmid and chromosomal borne AmpC ESBL and resistance can spread rapidly to the susceptible isolates through horizontal gene transfer. 6,11,12Molecular epidemiology of resistance genes conferring resistance to this antibiotic is mandatory to formulate treatment guidelines and to know the extent of resistance gene spread caused by indiscriminate use of less potent antibiotic.

CONCLUSIONS
Ceftriaxone is an antibiotic widely used in clinical practice and is imported in Nepal.Hence, concerned authority has to consider the cost implications to the patient, family and the country before endorsing less potent ceftriaxone brands in the country.Prudent and potent antibiotic use will help prevent emergence and spread of antibiotic resistant strains, which in turn will benefi t the patient and Nation as a whole.
Thapa et al.In-vitro Activity of Three Brands of Ceftriaxone Against Different Clinical Isolates