A simplified tetracycline assay

Uptake of tetracycline by aortic aneurysm wall and its effect on inflammation and proteolysis

BACKGROUND

Proteolytic degradation of the aortic wall by matrix metalloproteinases (MMPs) is considered important in the pathogenesis of abdominal aortic aneurysms (AAAs). Many of these MMPs are inhibited by tetracycline derivatives, which may have the potential to retard aneurysm growth.

METHODS

Patients undergoing elective repair of an AAA (n = 5) received an intravenous bolus of tetracycline (500 mg) on induction of anaesthesia and levels of tetracycline in serum, aneurysm wall and mural thrombus were assessed by microbiological assay. In a separate series of patients (n = 7) aneurysm biopsies were placed into explant culture (with and without tetracyline) and the accumulation of protein, hydroxyproline, MMP-9, interleukin (IL) 6 and monocyte chemoattractant protein (MCP) 1 in the medium was assessed by colorimetric assay or immunoassay.

RESULTS

At aortic cross-clamping the median concentration of tetracycline was 8.3 microg/ml in serum, 2.9 microg per g tissue in aortic wall and zero in mural thrombus. Tetracycline inhibited, in a concentration-dependent manner, both MMP-9 and MCP-1 secretion (P = 0.022 and P = 0.018 respectively), but did not alter hydroxyproline or IL-6 secretion. At the highest concentration of tetracycline (100 microg/ml) median MMP-9 secretion was reduced from 27 to 5 ng/ml (P = 0.007) and median MCP-1 secretion was reduced from 50 to 10 ng/ml (P = 0.008).

CONCLUSION

Tetracycline rapidly penetrates the aortic wall, but the concentration achieved may be insufficient to alter collagen turnover through limitation of MMP production or activity.

Mathematical description of the concentration of oxytetracycline and penicillin-G in tissue cages in calves as related to the serum concentration

A mathematical model based on Fick's laws of diffusion describing the concentration of drug in tissue cage models was elaborated. The model takes into account differences in protein binding, tissue cage geometry and serum pharmacokinetics. The validity of the model was tested against experimental data obtained from a tissue cage model in calves by simultaneous fitting to serum and tissue cage fluid (TCF) data in a non-linear least-squares regression computer program. Concentrations of penicillin-G (pen-G) in serum and TCF following intravenous (i.v.) administration of potassium pen-G were adequately described by the mathematical model. Concentrations in TCF after intramuscular (i.m.) administration of the same drug and of procaine pen-G could be predicted by the mathematical model. Concentrations of oxytetracycline (OTC) in serum and TCF following i.v. administration and continuous i.v. infusions were also adequately described by the model, and TCF concentrations after i.m. administration of the same drug could be roughly predicted. The results indicate that pen-G and OTC have the same permeability coefficient for transport from serum to TCF.

Distribution of oxytetracycline to tissue cages and granuloma pouches in calves and effect of acute inflammation on distribution to tissue cages

The effect of acute inflammation on oxytetracycline (OTC) distribution was studied in a tissue cage model in calves. An acute inflammatory reaction was induced in tissue cages by injecting lipopolysaccharide (LPS) from Salmonella typhimurium. The distribution of OTC to tissue cage fluid (TCF) was also compared with distribution to fluid from granuloma pouches (GPF). Tissue from LPS-injected cages showed histological changes indicating an acute inflammatory reaction. Concentrations of OTC were higher in LPS cages than in controls; at 1, 2, 4 and 10 h the difference was statistically significant (P less than 0.05). Numerically the overall elimination rate constant (kel) was larger, elimination half-life (t1/2) shorter, peak concentration (Cmax) higher, and time of peak concentration (Tmax) shorter in LPS cages than in controls. The area under the curve (AUC) of OTC was greater and the ratio AUCTCF/AUCserum was higher in LPS cages than in controls. Although statistically significant differences were not found for all the pharmacokinetic parameters, it was concluded that distribution to and elimination from LPS cages were both faster than in controls. Concentration-time profiles of OTC were similar in TCF and GPF in that concentrations were lower and elimination was more prolonged than in serum. Levels were higher in GPF than in TCF up to 3 h after injection; thereafter the relationship was reversed. Distribution to and elimination processes from GPF appeared to be faster than from TCF as numerically kel was higher, t1/2 shorter and Tmax shorter in GPF than in TCF. It was concluded that the granuloma pouch model and the tissue cage model have similarities in distribution and elimination patterns and that differences are most probably due to differences in the ratio of the surface area to the volume.

Studies on the bioavailability of tetracycline chloride after oral administration to calves and pigs

The serum concentrations of tetracycline (TC) were studied in calves after administration in the milk replacer and in pigs after administration in feed and drinking water. Serum concentrations of potential therapeutic value (greater than 1 microgram/ml) were obtained in the calves when TC was fed in the milk replacer at a dose of 25 mg/kg body weight twice daily. Significantly higher serum concentrations were achieved after a single oral dose (50 mg/kg) given in the milk replacer than afer the same dose given as a water drench four hours after the first daily milk feeding. The difference was explained by the fact that the calves probably consumed their daily amount of concentrate and an unknown amount of hay previous to the drench. Earlier studies showed that concentrates reduce the bioavailability of tetracyclines more than a conventional milk replacer. Serum concentrations of potential therapeutic value could not be achieved in the pigs in spite of recommended doses. The TC concentrations in the water were 400 mg/l and 800 mg/l. Tetracycline did not appear to influence the water consumption. Serum concentrations were highest in the evening and fell during the night. The highest levels after 400 mg/l water were 0.30-0.47 microgram/ml. The corresponding levels after 800 mg/l were 0.65-1.15 micrograms/ml. It was concluded that feed seriously reduced the bioavailability of TC. The influence of feeding was demonstrated in a single dose study. Fasted animals showed much higher serum levels than non-fasted ones. Very low and constant serum levels (about 0.2mg/ml occurred when TC mixed in the feed at a concentration of 1,00 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Concentrations of sulphadimidine, oxytetracycline and penicillin G in serum, synovial fluid and tissue cage fluid after parenteral administration to calves

Drug concentrations in serum, synovial fluid and tissue cage fluid (TCF) in calves were measured after single i.m. doses of oxytetracycline hydrochloride (OTC), procaine penicillin G (PPG) and potassium penicillin G (KPG) and single i.v. doses of sulphadimidine (SDM) and OTC. For all drugs, concentration-time curves in serum and synovial fluid were not identical but they had similar profiles, with peak levels occurring at about the same time. Concurrent concentrations were lower in synovial fluid than in serum. For each drug, elimination half-lives from synovial fluid and from serum were similar, except for penicillin G after KPG administration which had a significantly longer half-life from synovial fluid than from serum (P less than 0.05). Of the two penicillin G preparations, PPG gave a significantly higher synovial fluid:serum area under curve (AUC) ratio than did KPG; 0.76 +/- 0.10 and 0.54 +/- 0.12, respectively (P less than 0.05). For OTC, the synovial fluid:serum AUC-ratio was 0.33 +/- 0.12 after i.m. and 0.34 +/- 0.08 after i.v. administration. Drug concentration-time curves of TCF had different profiles compared with serum, with relatively low and delayed peak levels and slow elimination from TCF. TCF:serum AUC-ratios did not differ significantly for i.m. and i.v. administration of OTC; 0.10 +/- 0.10 and 0.19 +/- 0.03 respectively (P greater than 0.05). Potassium penicillin G (KPG), however, gave a significantly higher TCF:serum AUC-ratio than PPG; 0.55 +/- 0.21 and 0.19 +/- 0.07, respectively (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)

Phototoxicity of tetracyclines as related to singlet oxygen production and uptake by polymorphonuclear leukocytes

The photo-induced singlet oxygen production of six tetracyclines was measured as tryptophan degradation. Demethylchlortetracycline was the most efficient singlet oxygen producer followed by doxycycline. The least efficient producer was minocycline. Doxycycline, however, was the most potent inducer of photodamage to polymorphonuclear leukocytes (PMNLs) followed by demethylchlortetracycline. Accordingly, the singlet oxygen production during irradiation did not correlate with the induction of photodamage to the PMNLs. However, the uptake of doxycycline by the cells was 3 times higher than that of demethylchlortetracycline, and the tetracycline-induced photodamage to the PMNLs correlated with the product of singlet oxygen production during irradiation and the drug uptake by the cells.

Penetration of oxytetracycline into tissue-cages in calves

Concentrations of oxytetracycline (OTC) in serum and tissue-cage fluid (TCF) from subcutaneous tissue-cages were determined after single and repeated intravenous and intramuscular doses of 10 mg/kg to calves. Intravenous administration resulted in higher levels, and greater area under curve (AUC) in TCF, than did intramuscular administration. However, the penetration measured as the ratio of AUC in TCF to AUC in serum was equal, and therefore independent of the route of administration. A linear relationship between AUC in serum and AUC in TCF could be demonstrated. Half-lives of OTC in serum were 4.9 +/- 3.1 h after intravenous, and 6.1 +/- 2.0 h after intramuscular administration. In TCF the half-lives were 21.5 +/- 4.4 h and 24.5 +/- 11.5 h after intravenous and intramuscular administration, respectively. Repeated dosing resulted in accumulation of OTC in TCF. Lesser accumulation in older cages indicated altered characteristics of the cages with the passage of time. In serum, no substantial accumulation was seen after repeated i.v. dosing until the dosing interval was shortened to 6 h.

Doxycycline determination in human serum and urine by high-performance liquid chromatography

A reversed-phase high-performance liquid chromatographic method for quantitative doxycycline determination in human serum and urine is described. The drug was extracted from buffered (pH 6.1) serum or urine into ethyl acetate. A structural analog, demeclocycline, was added as the internal standard. A 10-cm X 2-mm i.d., 5-micrometers Lichrosorb RP8 column with acetonitrile-0.1 M citric acid as the eluent was used. The effluent was monitored at 350 nm. The extraction recovery from spiked serum was 87-8 +/- 4.3% (mean +/- SD, n = 11); for urine, a value of 92.2 +/-2.0% (mean +/- SD, n = 10) was found. Within-run and within-day relative standard deviations averaged (x = 2.5 micrograms/ml, n = 10) and 4.75% (x = 2.6 micrograms/ml, n = 9), respectively. The detection limit was estimated at 50 ng/ml of serum. No significant extra peaks were observed in chromatograms obtained on serum or urine extracts, suggesting the probable absence of metabolic processes in vivo.

Mechanism of fluorometric analysis of tetracycline involving metal complexation

Tetracycline complexation with calcium and organic ligands was studied using fluorescence, circular dichroism, and solvent extraction methods. The results were used to interpret the mechanism of the commonly used fluorometric methods for the analysis of tetracycline in biological fluids. Tetracycline formed ternary calcium complexes with barbital sodium and L-tryptophan in alkaline solutions. The circular dichroism studies indicate that the calcium ion in these complexes is bound to the C-4 dimethylamino and the C-12a hydroxyl groups of tetracycline. These ternary complexes are strongly fluorescent and can be extracted easily into 1-butanol or ethyl acetate. Based on the characteristics of the ternary complexes and of the tetracycline degradation products, it is concluded that only the active form of tetracycline can be complexed and extracted for fluorescence analysis.

Bioavailability of tetracycline and doxycycline in fasted and nonfasted subjects

The influence of various test meals and fluid volumes on the relative bioavailability of commercial formulations of doxycycline hyclate and tetracycline hydrochloride was studied in healthy human volunteers. Serum levels of tetracycline were uniformly reduced by approximately 50% by all test meals, whereas serum levels of doxycycline were reduced by 20%. The reduction of tetracycline serum levels will likely be of clinical significance. The bioavailability of each drug was almost identical from an oral solution and from capsules in fasted subjects. The rate of doxycycline absorption was reduced when capsules were administered with a small volume of water, but the overall efficiency of absorption of both drugs was essentially independent of co-administered fluid volume. The use of 8-h serum data provides a reliable estimate of drug bioavailability for tetracycline and, to a lesser extent, for doxycycline.

Sustained action tetracycline preparation--tetrabid-organon blood level study

A comparison of the plasma levels of tetracycline obtained whilst taking standard therapeutic doses of Tetrabid-Organon was made in twelve healthy volunteers. Two standard production batches were used in the study which was conducted under double-blind conditions. Sampling 12 hours and 8 hours after dosing showed no significant differences in plasma levels, with each batch. Even at these lowest levels satisfactory concentrations were rapidly obtained following initial administration, and were maintained when the drug was given at 12-hourly intervals. No side-effects of the drug were noted.

Separation and detection of tetracyclines by high-speed liquid chromatography

The high-speed liquid chromatographic behavior of 15 tetracyclines on anion- and cation-exchange columns is described and illustrated by typical separations of a number of tetracycline derivatives on several systems, as well as by the resolution of tetracycline from its degradation products epi-, epianhydro-, and anhydrotetracycline. These serve as a basis for a rapid, convenient, and precise method for the direct detection of the tetracycline antibiotics and their degradation products.