Interference of iron with the absorption of tetracyclines in man

Ferrous sulphate administered together with tetracycline and three of its derivatives-oxytetracycline, methacycline, and doxycycline-was found seriously to impair the absorption of these antibiotics. Thus even small doses of iron taken simultaneously should be avoided during tetracycline treatment.

Detailed methodology and implementation of a semiautomated serial dilution microtechnique for antimicrobial susceptibility testing

The detailed methodology and implementation of a semiautomatic microtechnique for performing serial dilution antimicrobial susceptibility studies are described. Quantitative susceptibility studies to a battery of antimicrobials are performed routinely on all significant clinical isolates. Results are reported as the minimal inhibitory concentration in micrograms per milliliter of broth. Guidelines relating standard doses of antimicrobials with expected blood and urine levels are presented to facilitate the use of the quantitative data. This microtechnique is used to measure serum and other body fluid levels of antimicrobial agents to document the level attained with a specific course of therapy. This technique is highly reproducible and has a high correlation with, and is at least 10 times faster than, standard glass tube techniques.

Microbioassay of antimicrobial agents

A previously described agar-diffusion technique for microbioassay of antimicrobial agents has been modified to increase sensitivity of the technique and to extend the range of antimicrobial agents to which it is applicable. This microtechnique requires only 0.02 ml of an unknown test sample for assay, and is capable of measuring minute concentrations of antibiotics in buffer, serum, and urine. In some cases, up to a 20-fold increase in sensitivity is gained relative to other published standardized methods and the error of this method is less than +/-5%. Buffer standard curves have been established for this technique, concurrently with serum standard curves, yielding information on antimicrobial serum-binding and demonstrating linearity of the data points compared to the estimated regression line for the microconcentration ranges covered by this technique. This microassay technique is particularly well suited for pediatric research and for other investigations where sample volumes are small and quantitative accuracy is desired. Dilution of clinical samples to attain concentrations falling with the range of this assay makes the technique readily adaptable and suitable for general clinical pharmacological studies. The microassay technique has been standardized in buffer solutions and in normal human serum pools for the following antimicrobials: ampicillin, methicillin, penicillin G, oxacillin, cloxacillin, dicloxacillin, cephaloglycin, cephalexin, cephaloridine, cephalothin, erythromycin, rifamycin amino methyl piperazine, kanamycin, neomycin, streptomycin, colistin, polymyxin B, doxycycline, minocycline, oxytetracycline, tetracycline, and chloramphenicol.

Semisynthetic coumermycins: structure-activity relationships

The relative antimicrobial activity of a large series of semisynthetic coumermycins has been determined. Most of the derivatives, which were 3-substituted-4-hydroxy-8-methyl-7-[3-O-(5-methyl-2-pyrrolylcarbonyl) noviosyloxy] coumarins, had an in vitro antibacterial spectrum similar to that of the parent compound, coumermycin A(1), but were generally less potent in minimal inhibitory concentration (MIC) tests. Derivatives with an alkylcarboxamido, arylcarboxamido, or arylsulfonamido group in the 3 position had considerably greater in vitro activity than those possessing an amino-, aryl-, or alkyureido substituent. Efficacy in Staphylcoccous aureus Smith infections of mice was greater for those compounds with branched-chain alkylcarboxamido, unsubstituted, mono- or disubstituted aryl- and heteroaryl-carboxamido groups than for derivatives having an n-alkylcarboxamido, aralkyl-carboxamido, arylsulfonamido, or trisubstituted arylcarboxamido substituent. Significant in vitro activity against Klebsiella pneumoniae and other gram-negative species was restricted to those compounds having a 3-(3-n-alkyl-4-hydroxy-phenyl-carboxamido) group. Only the n-hexyl homologue demonstrated in vivo activity in a K. pneumoniae infection. Many derivatives were two- to threefold more active than coumermycin A(1) in orally treated mouse infections, despite the fact that their MIC values were considerably higher. This result was undoubtedly a reflection of the markedly greater oral absorbability possessed by many of the derivatives. Although peak oral mouse blood levels of some compounds were > 25 times higher than those of coumermycin A(1), their toxicity for the host was no greater. In addition, the semisynthetic coumermycins caused much less local irritation than coumermycin A(1) when administered parenterally.

Simple method for rapid determination of antibiotic blood levels

A simple method for the rapid determination of antibiotic blood levels is described. Results are readily obtainable within 4 to 6 hr. The reported procedure is based upon determination of the highest dilution of a patient's serum capable of inhibiting dextrose fermentation by a standardized inoculum of a staphylococcus strain or of an Escherichia coli strain, when colymycin or polymyxin are involved, as compared to previously determined endpoints in this regard of defined concentrations of the different antibiotics dissolved in normal human serum. Excellent correlation was observed with 36 serum specimens that contained different antimicrobial agents in varied concentrations when simultaneously assayed by the standard method and the subject procedure of this report.