Uptake of minocycline by Escherichia coli

Uptake of tetracyclines into Escherichia coli was assessed with a strain carrying a tetA-lacZ translational fusion, in which expression of the enzyme is controlled by the pSC101 tetR repressor gene, by examining beta-galactosidase induction. The ability of tetracycline analogues to induce beta-galactosidase synthesis was correlated with their hydrophobicity, such that hydrophobic analogues were poor enzyme inducers. Treatment of E. coli with polymyxin B nonapeptide (PMBN) rendered cells more permeable to minocycline, but not to tetracycline.

Plasma levels of oxytetracycline, doxycycline, and minocycline in pigs after oral administration in feed

Steady-state plasma levels were determined for oxytetracycline (OTC), doxycycline (DC), and minocycline (MC) after medication with different in-feed concentrations. Each concentration of the three tetracyclines was examined in six pigs. The animals were housed in individual pens and fed twice daily with an interval of 12 h. All pigs consumed their feed within 1 h after it was provided. Concentrations of 400, 800, 1,600, and 2,400 mg of OTC per kilogram of feed induced steady-state plasma levels ranging from .13 to .22, .19 to .50, .39 to 1.43, and 1.41 to 2.14 micrograms/ml, respectively. On a feed intake basis, pigs received 13, 26, 54 to 81, and 108 mg of OTC per kilogram of BW per day, respectively. Steady-state plasma levels after medication with 200, 400, and 800 mg of DC or MC per kilogram of feed ranged from .37 to .89, .71 to 1.14, and 1.62 to 3.18 micrograms/ml for DC and from .21 to .60, .43 to 1.05, and 1.19 to 2.62 micrograms/ml for MC. Pigs consumed 7, 13, and 26 mg of DC and 9, 18, and 36 mg of MC per kilogram of BW per day, respectively. For all three tetracyclines there was an increase in steady-state plasma levels when concentrations in feed or per kilogram of BW increased. Plasma levels were determined with both a HPLC method and a microbiological method. A good correlation existed between the results obtained by both methods. It was concluded that based on plasma levels and known in vitro activity DC and MC could be good alternatives for OTC to treat respiratory tract infections in pigs.

Penetration of minocycline into lung tissues

The penetration of minocycline into different lung tissues and bronchial mucus was studied in 17 patients undergoing pulmonary surgery for cancer. The patients received oral minocycline 100 mg at night for 3 days preceding surgery. Minocycline concentrations were measured in plasma samples collected before the operation and in tissues and mucus taken from in and around the part of the lung that was surgically removed. Mean tissue or mucus concentration to plasma concentration ratios were 3.78 +/- 1.10 for lung parenchyma, 4.04 +/- 1.31 for bronchial walls, 3.37 +/- 1.00 for pulmonary arterial walls, 1.99 +/- 1.80 for intraluminal mucus collected from bronchi located in healthy tissue proximal to the tumour, 5.16 +/- 3.26 for intraluminal mucus collected in a bronchus distal to the tumour, and 3.06 +/- 1.99 for catheter-collected mucus from the trachea and principal bronchi. These results indicate that minocycline is found in high concentration in all types of lung tissue and mucus in man.

Effect of low-level and intermittent minocycline therapy on the growth of Mycobacterium leprae in mice

We evaluated the minimal concentrations of minocycline in the diet and in serum required to inhibit the growth of seven Mycobacterium leprae isolates in mice. Minocycline concentrations of 0.01 and 0.04% in the diet, which resulted in levels in serum of less than or equal to 0.17 and 0.51 microgram/ml, respectively, were consistently and completely inhibitory. Even 0.004% dietary minocycline (levels in serum, less than or equal to 0.08 microgram/ml) partially inhibited five of these strains, while 0.001% minocycline was consistently inactive. For five of these isolates, minocycline at a concentration of 0.04% in the diet given 3 days (Monday, Wednesday, Friday) and 1 day weekly completely inhibited the growth of M. leprae, and minocycline given even 1 day monthly was partially inhibitory for three of these five M. leprae isolates.

[Diffusion of minocycline in pulmonary tissue]

The penetration of minocycline into lung tissue was evaluated in 14 patients about to undergo excision of the lung for cancer. The patients received minocycline orally in doses of 100 mg twice a day for 3 days, the 100 mg in the morning of the operation day. Minocycline concentrations were measured in plasma samples taken before surgery and in the lung tissue resected. The mean tissue/plasma concentration ration was 3.17 +/- 0.41 (range: 1.5 to 7.48). The same ratios were obtained in peritumoral and tumoral tissues. These results indicate that minocycline penetrates well into tissues.

Absence of minocycline in sebum?

The authors studied the bioavailability of minocycline in sebum and serum. Blood and sebum samples were collected weekly for 6 weeks from ten healthy volunteers taking 200 mg of minocycline every day for 4 weeks. Sebum was collected by direct extraction with petroleum ether from the forehead. After evaporation, sebum was weighed on a scale accurate to 10 micrograms. Determination of minocycline in serum and sebum was performed using a high performance liquid chromatography technique (HPLC), with a better detection limit at 352 nm than at 400 nm (20 ng/ml and 0.324 microgram/ml respectively). Our results contrast with other studies since no minocycline was detected in the sebum samples of treated subjects and microbiological assays of minocycline in sebum were also negative. In our opinion, the current hypothesis claiming that the effectiveness of minocycline in the treatment of acne vulgaris is based on sebaceous secretion should be reconsidered.

Therapeutic focus. Minocycline in the treatment of acne

Minocycline has an established place in the oral therapy of acne. Prolonged courses of therapy have an acceptable safety profile. Where therapy with oxytetracycline has failed, minocycline is still likely to prove effective. The twice-daily dosage and ease of absorption from the gastrointestinal tract offer significant advantages over other tetracyclines. The simpler minocycline regime and early onset of clinical improvement are likely to result in better patient compliance, and hence optimise therapeutic response. There is therefore justification for the use of minocycline as first-line oral therapy, but, whether as a first- or second-line therapy, minocycline is a valuable drug in the treatment of this very distressing disorder. The earlier effective therapy is used in a patient with acne, the less physical and psychological scarring will remain thereafter.

Doxycycline and minocycline in the treatment of respiratory infections: a double-blind comparative clinical, microbiological and pharmacokinetic study

A group of 41 patients, all admitted to hospital because of acute purulent exacerbations of chronic respiratory disease, were treated with either doxycycline or minocycline in a double-blind randomized study. Drug dosage was one 100 mg capsule twice daily for seven days. Bacteriological and clinical assessment before and immediately after treatment showed no significant differences between the doxycycline and the minocycline groups, nor did further evaluation after seven days follow-up. Pharmacokinetic studies showed that the Cmax and 0-11 h AUC values in blood were higher for doxycycline, whereas the sputum Cmax was, on average, higher for minocycline because of the greater penetration of the latter. The MIC values for the two antibiotics differed slightly, usually, but not always, in favour of minocycline. Problems were experienced with both agents in the eradication of Haemophilus influenzae. The net clinical results with the two drugs were identical.

Clinical pharmacokinetics of doxycycline and minocycline

Doxycycline and minocycline are second-generation tetracyclines. They are readily absorbed, distributed throughout the organism as a function of their lipophilicity and eliminated in both the urine and the faeces. The influence of age, renal disease, malnutrition and hyperlipidaemia is reviewed, together with the main pharmacokinetic interactions.

[Minocycline diffusion into prostatic tissue]

We evaluated the concentration of minocycline in human prostatic tissue. Twenty-six patients undergoing transurethral resection of prostate, two patients undergoing open prostatectomy for benign prostatic hyperplasia and two patients undergoing radical cystoprostatectomy for bladder cancer were studied. Prostatic tissue and blood were sampled at 1, 2 or 3 hours after the intravenous administration of 200 mg of minocycline. The concentration of minocycline was 2.95 +/- 1.39 micrograms/ml (mean +/- SD) in serum and 1.97 +/- 0.79 cg/g (mean +/- SD) in the prostatic tissue. The ratio of the prostatic concentration/serum concentration was 0.76 +/- 0.33 (mean +/- SD).

Antimicrobial activity of 1,2,5-selenadiazoles

Ten patients with soft-tissue infections due to Staphylococcus aureus were treated with minocycline, a semisynthetic tetracycline with potent in vitro antistaphylococcal effects. Serum concentrations averaged three to five times the concentration of minocycline required to inhibit growth of S. aureus in vitro. Clearing of the infecting organism was slow (less than 50% of lesions were sterile on day 10 of therapy), but clinical improvement was noted in 8 of 10 patients.