Unraveling the energetics and mode of the recognition of antibiotics tetracycline and rolitetracycline by bovine serum albumin.

An understanding of the detailed energetics and mechanism of the binding of drugs with target proteins is essential for devising guidelines to synthesize new drugs. Binding of the antibiotic drugs tetracycline and rolitetracycline with serum albumin has been studied by a combination of isothermal titration calorimetry, differential scanning calorimetry, steady-state and time-resolved fluorescence, and circular dichroism spectroscopies. Both tetracycline and rolitetracycline bind to bovine serum albumin in a sequential manner with first binding being the major binding event with an association constant of the order of 10(4) for tetracycline and 10(3) for rolitetracycline, respectively. Ionic strength dependence and binding in the presence of tetrabutylammonium bromide and sucrose indicate involvement of a mix of hydrophobic, ionic, and hydrogen bonding interactions. The isothermal titration calorimetry results for the binding of these drugs to bovine serum albumin in the presence of warfarin and in the presence of each other indicate that both these drugs share binding site 2 on bovine serum albumin. The differential scanning calorimetry results provide quantitative information on the effect of drugs on the stability of bovine serum albumin. A comparison of isothermal titration calorimetry and fluorescence results demonstrates that the former technique has been able to explain the sequential binding events that can be missed by the fluorescence measurements.

[Tetracycline in the evaluation of bone turnover]. / La tetraciclina nella valutazione del turnover osseo.

A new and easy technique for the fluorimetric evaluation of rolitetracycline calcium complex was studied. The study was carried out in 3 different groups of rats; an increase in power of fluorescence in the rats on a low calcium diet (LC) and on a low calcium diet plus vitamin D (LC + D) versus the group of rats on a normal calcium diet (NC) was found. Moreover, the amount of spongy bone showed a significant decrease in bone mass in the first two groups (LC and LC + D) versus control. These data indicated that the bone tie of tetracycline was only related to the high turnover of bone and there was no relationship with bone mass. This new technique, in comparison with the others, (double marking and evaluation of space between the two fluorescent bands) enables to evaluate the kind and the evolution of bone rarefaction by biopsy.

Age dependency of rolitetracycline-induced hepatic steatosis.

A comparative study on the effect of rolitetracycline (50 micrograms/g i.v.) on the hepatic content of triglycerides and the release of esterified fatty acids from the liver into the blood was performed in young and adult NMRI mice of both sexes. Rolitetracycline caused an accumulation of triglycerides only in the livers of adult animals, the effect being much more pronounced in females than in males. In agreement with this a very strong inhibition of lipid release from the liver and a significant decrease of the esterified fatty acids of the serum was produced only in adult females. The results suggest that the livers of young animals of both sexes are relatively resistant to the steatotic effect of rolitetracycline.

Effect of unilateral nephrectomy on the pharmacokinetics of rolitetracycline in rabbits.

An analysis of the single-dose pharmacokinetics of rolitetracycline in rabbits after unilateral nephrectomy is presented. Rolitetracycline was injected i.v. 3.5 mg/kg before operation and after 2 weeks, 3 months and 6 months from unilateral nephroctomy. The concentration of the antibiotic in plasma was estimated by the fluorimetric method of Kohn. The two-compartment open model was applied to calculate rolitetracycline concentration changes. The calculations of pharmacokinetic parameters were performed using the Hewlett-Packard 9830B computer and fitting the concentrations of the antibiotic in blood to the general biexponential equation. AUC of rolitetracycline was increased in operated animals by 130% after 6 months. The mean kel at this time decreased, while t0.5 beta was prolonged from 1.0 h to 3.0 h. It is assumed that the dosage regimen of rolitetracycline should be changed in subjects possessing one kidney.

Distribution of pyrrolidinomethyl-tetracycline (rolitetracycline) and tetracycline in blood and various organs of mice measured by high pressure liquid chromatography.

By means of a newly developed high-pressure liquid chromatographic method the organ distribution of tetracycline (TC) and pyrrolidinomethyl-tetracycline (PMT) has been studied. When mice were treated with 50 mg/kg i.v. TC or PMT these antibiotics could be detected in all organs investigated (liver, kidney, heart, lung, muscle, spleen). Especially high concentrations were found in liver and kidneys, where TC and PMT could be detected up to 6 h. In animals treated with PMT part of the PMT applied decomposed slowly yielding TC, which was found together with PMT in blood and all organs.

[Tetracycline levels in the sputum in chronic obstructive bronchitis (author's transl)]. / Tetracyclin-Spiegel im Sputum bei chronisch-obstruktiver Bronchitis.

After 3 control days, the tetracycline concentration in the sputum of 34 patients was measured daily on 7 days during treatment with the antibiotic. 14 patients took tetracycline (Hostacyclin) in normal doses (2X500 mg or 2X1000 mg) by mouth. 20 patients received rolitetracycline (Reverin) 2X275 mg i.v. daily. With considerable individual fluctuations, sputum concentrations were attained in all series ranging from 1.5 to 2.0 microgram/ml after intravenous administration and from 1.1 to 1.6 microgram/ml after oral dosage. The higher dosage administered orally had no greater influence on the sputum concentration. In each case, sputum levels were attained which lie above the necessary minimum concentrations (0.5 microgram/ml).

[Concentration of antibiotics in the human lung. Clinical studies of Reverin distribution in various pulmonary lobes]. / Antibiotika-Konzentration in der menschlichen lunge. Klinische Untersuchung der Reverin-Verteilung in verschiedenen Lungenlappen

On 12 patients with bronchial carcinoma serum and lung-tissue concentration levels of tetracyclin were measured. The concentration levels of the antibiotic were twice as high in the lung tissue as in the serum. In the lower lobe of the lung significantly higher values were measured than in the upper lobe. The demonstrated tissue levels of Pyrrolidino-methyltetracyclin (Reverin) in human lung are high enough to be effective in pulmonary bacterial infection.

[Studies on the absorption and excretion of doxycycline for intravenous use (author's transl)].

The absorption and excretion of a new doxycycline solution for intravenous use (DOTC iv) were studied with the following results. 1. Serum levels following one shot intravenous injection of DOTC iv in glucose solution showed a good dose-response comparable with that of the same dose injection of pyrrolidinomethyltetracycline (PRM-TC). The urinary excretion was also examined. In 200 mg injection, nausea, general warm feeling, odor in mouth and tongue numbness were complained. 2. When DOTC iv was injected intramuscularly, the serum level did not reach the peak value and low level continued for a long time. Moderate local pain was complained at the site of injection. 3. The serum level following drip infection of DOTC dry fill showed a dose-response as well. The local vein tolerated well. 4. No abnormalities were found in clinical and laboratory examinations in all volunteers.