Creamy oblong tablet with small brown spots marked with a score line. The tablets can be divided into halves.
Tablets for oral administration containing cephalexin (as cephalexin monohydrate PhEur) in three strengths:
Rilexine 75 containing 75mg cephalexin
Rilexine 300 containing 300mg cephalexin
Rilexine 600 containing 600mg cephalexin
Pharmacodynamic properties
The active ingredient of product is Cefalexin monohydrate.
Cefalexin is a bactericidal antibiotic of the cephalosporin family which acts by inhibiting the nucleopeptide synthesis of the bacterial wall. It is obtained by hemi-synthesis from the 7- amino cephalosporanic nucleus. Cephalosporins interfere with transpepditation by acylating the enzyme making it unable to cross-link muramic acid-containing peptidoglycan strands. The inhibition of the biosynthesis of the material required to build the cell wall results in a defective cell wall which is consequently osmotically unstable. The combined action results in cell lysis and filament formation.
Cefalexin is active against a wide range of gram-positive and gram-negative aerobic bacteria: Staphylococcus spp. (including penicillin-resistant strains), Streptococcus spp., Escherichia coli, Klebsiella spp., Salmonella spp. and Pasteurella multocida. Cefalexin is not inactivated by β-lactamases produced by gram-positive bacteria and which usually affect penicillins.
Cefalexin had a time-dependent bactericidal activity on both tested bacteria species, Staphylococcus felis (gram-positive) and Pasteurella multocida (gram-negative). In vitro activity of Cefalexin towards European strains isolated in 2003-2006 in cats exhibiting cutaneous or subcutaneous infections showed that the MIC90 was 2 µg/ml for Staphylococcus spp. and Pasteurella spp. and 0.5 µg/ml for Streptococcus spp. These susceptible genera were also the bacteria the most-frequently isolated from wounds and abscesses in cats.
Resistance to Cefalexin may be due to one of the following mechanisms of resistance. Firstly, the production of various beta-lactamases (cephalosporinase), that inactivate the antibiotic, is the most prevalent mechanism among gram-negative bacteria. Secondly, a decreased affinity of the PBPs (penicillin-binding proteins) for β-lactam drugs is frequently involved for β-lactam resistant gram-positive bacteria. Lastly, efflux pumps, extruding the antibiotic from the bacterial cell, and structural changes in porins, reducing passive diffusion of the drug through the cell wall, may contribute to improve the resistant phenotype of a bacterium.
Well-known cross-resistance (involving the same resistance mechanism) exists between antibiotics belonging to the β-lactam group due to structural similarities. It occurs with βlactamases enzymes, structural changes in porins or variations in efflux pumps. Coresistance (different resistance mechanisms involved) has been described in Escherichia coli due to a plasmid harbouring various resistance genes.
Pharmacokinetic particulars
Dogs
After single oral administration of the recommended dosage of 15 mg of cefalexin per kg of bodyweight to Beagle dogs, plasma concentrations were observed within 30 minutes. The plasma peak was observed at 1.3 hour with a plasma concentration of 18.2 µg/ml. The bioavailability of the active was over 90 %. Cefalexin was detected until 24 hours after the administration. The first urine specimen was collected within 2 to 12 hours with peak concentrations of cefalexin measured at 430 to 2758 µg/ml within 12 hours.
After repeated oral administration of the same dosage, twice a day for 7 days, plasma peaks occurred 2 hours later with a concentration of 20 µg/ml. Over the treatment period, concentrations were maintained above 1 µg/ml. The mean elimination half-life is 2 hours. Skin levels were around 5.8 to 6.6 µg/g, 2 hours after treatment.
Cats
A single oral administration of 15 mg of Cefalexin per kg of bodyweight in cats led to a bioavailability of 56 %. The plasma peak was observed at 1.55 hour following administration with a plasma concentration above 15.1 µg/ml. The mean plasma half-life was about 1 to 2 hours. The first urine specimen was collected between 4 and 24 hours with the highest concentrations ranging between 63.7 and 393 µg/ml, occurring within 24 hours.
With the same dosage administered over 7 days, twice a day, the highest urine concentration of Cefalexin reached between 518 and 1256 µg/ml.