Plasma and sputum erythromycin concentrations in chronic bronchitis

Delivering Antibacterials to the Lungs

An important determinant of clinical outcome of a lower respiratory tract infection may be sterilization of the infected lung, which is also dependent on sustained antibacterial concentrations achieved in the lung. For this reason, recently there has been increased interest in measuring the concentration of antimicrobial agents at different potential sites of infection in the lung. Levels of antibacterials are now measured in bronchial mucosa, epithelial lining fluid (ELF) and alveolar macrophages, as well as in sputum. Penicillins and cephalosporins reach only marginal concentrations in bronchial secretions, whereas fluoroquinolones and macrolides have been shown to achieve high concentrations. The extent of penetration of different antibacterials into the bronchial mucosa is relatively high. This is also true for beta-lactams, although their tissue concentrations never reach blood concentrations. Antibacterials penetrate less into the ELF than into the bronchial mucosa, but fluoroquinolones appear to concentrate more into alveolar lavage than into bronchial mucosa. Pulmonary pharmacokinetics is a very useful tool for describing how drugs behave in the human lung, but it does not promote an understanding of the pharmacological effects of a drug. More important, instead, is the correlation between pulmonary disposition of the drug and its minimum inhibitory concentration (MIC) values for the infectious agent. The addition of bacteriological characteristics to in vivo pharmacokinetic studies has triggered a 'pharmacodynamic approach'. Pharmacodynamic parameters integrate the microbiological activity and pharmacokinetics of an anti-infective drug by focusing on its biological effects, particularly growth inhibition and killing of pathogens. Drugs that penetrate well and remain for long periods at the pulmonary site of infection often induce therapeutic responses greater than expected on the basis of in vitro data. However, although the determination of antibacterial concentrations at the site of infection in the lung has been suggested to be important in predicting the therapeutic efficacy of antimicrobial treatment during bacterial infections of the lower respiratory tract, some studies have demonstrated that pulmonary bacterial clearance is correlated more closely to concentrations in the serum than to those in the lung homogenates, probably because they better reflect antibacterial concentration in the interstitial fluid.

Pharmacokinetics of antimicrobial agents in the respiratory tract

The ability of antibiotics to penetrate into the respiratory tract has been investigated at several sites, namely, sputum and bronchial secretions, tissue homogenates, pleural fluid and, more recently, epithelial lining fluid and alveolar macrophages. The major reason for such investigations is that these data may be helpful to a more thorough understanding of drug distribution in the lung tissue and fluids and to a more accurate prediction of clinical outcome. However, the study of drug concentration at each of these sites presents problems in terms of methodology and data interpretation. The advantages and disadvantages of each of these methods are considered, and the data on penetration of betalactams, aminoglycosides, macrolides, fluoroquinolones and other antimicrobial agents (including antifungal and antiprotozoan drugs) are reviewed.

Effects of sub-MICs of erythromycin and other macrolide antibiotics on serum sensitivity of Pseudomonas aeruginosa

We examined the effects of sub-MICs of erythromycin (EM) and other macrolide antibiotics on the serum sensitivity of Pseudomonas aeruginosa. P. aeruginosa S-6 grown for 36 and 48 h on agar with 10 micrograms of EM per ml (1/10th the MIC) showed significantly increased sensitivity to human serum bactericidal activity compared with those of bacteria grown on agar without EM (P < 0.05). No changes in serum sensitivity were observed in bacteria grown for less than 24 h. This increased sensitivity was apparent even at a concentration of 1.5 micrograms of EM per ml (1/67th the MIC) in bacteria grown for 48 h (P < 0.01). Among the other macrolide antibiotics tested, clarithromycin also enhanced sensitivity to serum, but there were no changes in the sensitivities of bacteria grown on agar with kitasamycin, josamycin, rokitamycin, or oleandomycin even at a concentration of 12 micrograms/ml (1/16th, 1/16th, 1/8th, and 1/33rd the MICs, respectively). P. aeruginosa S-6 grown on agar with subinhibitory concentrations of EM showed decreased cell surface hydrophobicity in a dose-dependent manner, whereas oleandomycin and rokitamycin, even at a concentration of 12 micrograms/ml, induced a slight decrease in hydrophobicity which was approximately equivalent to that of 1.5 micrograms of EM per ml. Among six other strains of the nonmucoid phenotype, three strains became more sensitive to serum by exposure to 10 micrograms of EM per ml for 48 h. In contrast, no evident correlation between EM treatment and a change in serum sensitivity was observed in six strains of the mucoid phenotype, as judged by the results of experiments with both 2 and 0.4% serum. These results show that EM at subinhibitory concentrations enhances the serum sensitivity of some P. aeruginosa strains. Since induced serum sensitivity was accompanied by a decrease in bacterial cell surface hydrophobicity, EM may render P. aeruginosa more serum sensitive by changing the cell surface structure(s) of this organism.

Study of serum levels, venous irritation and gastrointestinal side-effects with intravenous erythromycin lactobionate in patients with bronchopulmonary infection

Sixteen patients with bronchopulmonary infection received 500 mg erythromycin lactobionate by intravenous infusion every 8 h for 2 days. The duration of infusion was either 30 (8 patients) or 60 min (8 patients). An inline filterset (0.22 micrometer) was included in the intravenous administration set in 4 patients of each infusion group. Serum erythromycin levels were obtained before and at various times for 8 h after the first and fourth doses and before and immediately after the other doses. The incidence and severity of venous irritation and gastrointestinal side-effects were assessed. Mean (S.D.) peak erythromycin levels for the 30 min infusion were 26.31 (6.89) micrograms/ml (first dose) and 26.85 (6.11) micrograms/ml (fourth dose) and for the 60 min infusions, 23.96 (7.91) micrograms/ml (first dose) and 23.65 (6.55) micrograms/ml (fourth dose). Venous irritation was experienced by 12 patients, ranging from localized discomfort to thrombophlebitis, but the severity was significantly reduced by inline filtration (P less than 0.005). Gastrointestinal side-effects were reported by 8 patients and 1 patient withdrew because of severe abdominal pain and nausea. These symptoms were usually relieved by spasmolytic agents and possibly could be explained by high concentrations reaching the gut wall either by biliary excretion or direct transport from blood and stimulating smooth muscle motility.

Penetration of piperacillin into bronchial mucosa and sputum

Bronchial mucosal biopsies were obtained during fibreoptic bronchoscopy in 12 patients receiving a new semisynthetic penicillin, piperacillin. The piperacillin levels estimated in bronchial mucosa exceeded those required to eradicate organisms associated with acute bronchitis, Haemophilus influenzae and Streptococcus pneumoniae, and compared favourably with those required for activity against a wide variety of anaerobic and Gram-negative organisms including Pseudomonas aeruginosa. Sputum and serum piperacillin levels were obtained from eight patients with bronchial disease receiving a five to seven day course (8 to 16 g/day). Sputum/serum level ratios were constant for the two dosages (10.7% for 8 g/day; 14.3% for 16 g/day) suggesting a diffusion transfer process, although the presence of pus in the sputum appeared to facilitate penetration. Seven patients achieved sputum levels exceeding those required for activity against Haemophilus influenzae and Streptococcus influenzae, and four for Pseudomonas aeruginosa. This study provides pharmacolinetic support of the use of piperacillin in bronchopulmonary infection.

Serum, saliva, and sputum levels of metronidazole in acute exacerbations of chronic bronchitis

We have evaluated the absorption and the penetration of metronidazole into the bronchial secretions and saliva in acute infective exacerbations of chronic bronchitis. Seventeen patients were given 400 mg orally three times daily for seven days and "steady state" levels were measured in serum, saliva, and sputum on the last day of treatment. Mean levels in the three biological fluids were not significantly different. Higher metronidazole levels in sputum tended to occur in patients with higher serum levels. In all but one patient, levels in serum and saliva were well within the therapeutic range. We conclude that this oral regimen results in therapeutic tissue levels in acute exacerbations of chronic bronchitis.

Activity of erythromycin against Haemophilus influenzae from respiratory tract infections

Ampicillin and amoxycillin are very frequently used for treating respiratory infections due to Haemophilis influenzae, but the emergence of beta-lactamase producing strains of this organism may limit their use. Erythromycin would be a suitable alternative but to date variable absorptions and reported minimal inhibitory concentrations (MICs) outside the range of achievable blood levels of erythromycin have prevented its use. The purpose of this study was to determine the MICs of erythromycin for strains of H. influenzae isolated from patients with lower respiratory tract infection and the frequency of beta-lactamase production in these strains. Eighty-five of 100 strains were sensitive to erythromycin (MIC much less than 2.00 mg/L). Eleven strains were resistant to ampicillin and 10 of these produced beta-lactamase. Nine beta-lactamase producing strains had MICs to erythromycin of 2.0 mg/L or less. With the blood levels of erythromycin obtainable with new formulations, this antibiotic should prove of use in the treatment of respiratory infections due to H. influenzae.