Immunoassay-based determination of phenobarbital using size-exclusion chromatography

[Determination of phenobarbital in human urine and serum using flow injection chemiluminescence]

A sensitive chemiluminescence method, based on the enhancive effect of phenobarbital on the chemiluminescence reaction between luminol and dissolved oxygen in a flow injection system, was proposed for the determination of phenobarbital. The chemiluminescence intensity responded to the concentration of phenobarbital linearly ranging from 0.05 to 10 ng x ml(-1) with the detection limit of 0.02 ng x ml(-1) (3 sigma). At a flow rate of 2.0 ml x min(-1), a complete determination of phenobarbital, including sampling and washing, could be accomplished in 0.5 min, offering the sampling efficiency of 120 h(-1) accordingly. The method was applied successfully in an assay of PB for pharmaceutical preparations, human urine and serum without any pretreatment with recovery from 95.7 to 106.7% and RSDs of less than 3.0%.

Recombinant protein detection in crude extracts by flow-injection immunoassay

An immunofluorescence method that allows detection and quantification of recombinant proteins in complex mixtures (e.g. crude cell extracts and fermentation media) is described. The method is based on a non-denaturing chromatographic analysis which is performed after the addition of a fluorescently labelled antibody specific for the target protein. HPLC analysis through a size-exclusion column allows to separate and quantify the immunocomplex and the excess antibody, which are the only fluorescent species in the mixture. The method was applied to the analysis of recombinant human Fabs expressed in bacteria. Preliminary validation data are reported.

Susceptibility of bacteria from feline and canine urinary tract infections to doxycycline and tetracycline concentrations attained in urine four hours after oral dosage

OBJECTIVES

To measure urinary concentrations of doxycycline in cats and dogs and tetracycline in dogs 4 h after conventional oral dosing and determine whether these antibiotics were present in sufficient concentrations to be effective against common feline and canine urinary tract pathogens as assessed in vitro by Epsilometer and disc diffusion antimicrobial susceptibility methods.

DESIGN

A prospective study involving oral administration to clinically normal cats and dogs of doxycycline or tetracycline (dogs only) and culture of bacteria from dogs and cats with urinary tract infections to determine their susceptibility to both doxycycline and tetracycline in vitro.

PROCEDURE

In the first study, nine cats and eight dogs were administered doxycycline monohydrate (5 mg/kg every 12 h) and a further eight dogs were administered tetracycline hydrochloride (20 mg/kg every 8 h) for 72 h. Blood was collected at 2 and 4 h, and urine at 4 h, after the last dose. The concentration of each agent in serum and urine was determined by modified agar diffusion. In the second study, 45 urine samples from cats and dogs with urinary tract infections were cultured. Every bacterial isolate was tested in vitro using both Epsilometer (doxycycline and tetracycline) and disc diffusion (doxycycline, tetracycline or amoxycillin-clavulanate) tests.

RESULTS

Serum doxycycline concentrations in sera of cats and dogs at 2 h were 4.2 +/- 1.0 mg/mL and 3.4 +/- 1.1 mg/mL, respectively. The corresponding concentrations at 4 h were 3.5 +/- 0.7 mg/mL and 2.8 +/- 0.6 mg/mL. Urinary doxycycline concentrations at 4 h (53.8 +/- 24.4 mg/mL for cats and 52.4 +/- 24.1 mg/mL for dogs) were substantially higher than corresponding serum values. Serum tetracycline concentrations in dogs at 2 and 4 h, and in urine at 4 h, were 6.8 +/- 2.8, 5.4 +/- 0.8, 144.8 +/- 39.4 mg/mL, respectively. Most of the urinary tract pathogens (35/45) were susceptible to urinary concentrations of doxycycline and 38/45 were susceptible to tetracycline. In contrast 41/45 of all isolates were susceptible to amoxycillin-clavulanate.

CONCLUSION

This is the first report of urinary concentrations of doxycycline after conventional oral administration. Concentrations attained in the urine of normal cats and dogs were sufficient to inhibit the growth of a significant number of urinary tract pathogens and thus doxycycline may be a useful antimicrobial agent for some urinary tract infections.