Amoxicillin in the treatment of infections of the lower respiratory tract

Survey of systemic antimicrobial prescribing for dogs by Victorian veterinarians

OBJECTIVE

Investigate the current antimicrobial prescribing patterns of veterinarians in Victoria for dogs and compare these results to patterns described 20 years ago.

METHODS

A questionnaire was sent to 1380 veterinarians in Victoria. The first section collected demographic information of respondents. The second and third sections evaluated respondents' approach to use of antimicrobial drugs for scenarios in dogs in which 'clinical evidence suggests bacterial infection is the likely cause' and where 'it is unknown whether bacterial infection plays a role'. The final section evaluated respondents' approach to use of antimicrobial drugs during dental extraction in a dog.

RESULTS

Of the 1380 veterinarians who were contacted, 259 responses were received (response rate 19%). Of these respondents, 95% (246/259) completed their veterinary degree at the University of Melbourne. The ratio of female to male respondents was 2.1 : 1 (171 : 82) and of urban to rural respondents was 1.9 : 1 (159 : 85). Drug selection for some scenarios was open to criticism. For example, to treat chronic prostatitis 16% (42/259) of respondents selected amoxicillin-clavulanate even though it has poor penetration of prostatic tissues. Some prescribing choices have changed since 1997; for example, for acute tracheobronchitis, 36% (73/204) of respondents indicated they would use antimicrobials, compared with 87% of respondents in 1997. For the treatment of idiopathic vestibular disease, only 5% (10/197) of respondents in the current study versus 45% (294/654) in the 1997 survey opted to use antimicrobials.

CONCLUSION

Antimicrobial drug selection for treatment of dogs by registered veterinarians in Victoria was generally consistent with recent recommendations, although some details were widely variable.

Prolonged antibiotics for non-cystic fibrosis bronchiectasis in children and adults

BACKGROUND

The vicious cycle hypothesis for bronchiectasis predicts that bacterial colonisation of the respiratory tract perpetuates inflammatory change. This damages the mucociliary escalator, preventing bacterial clearance and allowing persistence of pro-inflammatory mediators. Conventional treatment with physiotherapy and intermittent antibiotics is believed to improve the condition of people with bronchiectasis, although no conclusive data show that these interventions influence the natural history of the condition. Various strategies have been tried to interrupt this cycle of infection and inflammation, including prolonging antibiotic treatment with the goal of allowing the airway mucosa to heal.

OBJECTIVES

To determine the benefits of prolonged antibiotic therapy in the treatment of patients with bronchiectasis.

SEARCH METHODS

We searched the Cochrane Airways Group Trials Register and reference lists of identified articles. Searches were current as of February 2014.

SELECTION CRITERIA

Randomised trials examining the use of prolonged antibiotic therapy (for four or more weeks) in the treatment of bronchiectasis compared with placebo or usual care.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed trial quality and extracted data. We contacted study authors to ask for missing information.

MAIN RESULTS

Eighteen trials met the inclusion criteria, randomly assigning a total of 1157 participants. Antibiotics were given for between four weeks and 83 weeks. Limited meta-analysis was possible because of the diversity of outcomes reported in these trials. Based on the number of participants with at least one exacerbation, the meta-analysis showed significant effects in favour of the intervention (odds ratio (OR) 0.31, 95% confidence interval (CI) 0.19 to 0.52; P value < 0.00001), with events occurring in 271 per 1000 people in the intervention arm (95% CI 126 to 385) and in 546 per 1000 in the control population, based on evidence of moderate quality. A non-statistically significant reduction in hospitalisation favoured the use of prolonged antibiotics with a moderate quality grade of supporting evidence (37 per 1000 in the intervention arm (95% CI 13 to 96) and 87 per 1000 in control (OR 0.40, 95% CI 0.14 to 1.11; P value = 0.08). Drug resistance developed in 36 of 220 participants taking antibiotics compared with 10 of 211 participants given placebo or standard therapy (OR 3.48, 95% CI 1.20 to 10.07; P value = 0.02), translating to natural frequencies of 155 per 1000 in the intervention arm (95% CI 59 to 346) and 50 per 1000 in the control arm. The intervention was well tolerated with no overall significant difference in withdrawal between treatment and placebo groups (OR 0.91, 95% CI 0.56 to 1.49). Diarrhoea was commonly reported as an adverse event, particularly with an oral intervention.

AUTHORS' CONCLUSIONS

Available evidence shows benefit associated with use of prolonged antibiotics in the treatment of patients with bronchiectasis, at least halving the odds of exacerbation (with 275 fewer exacerbations per every 1000 people treated in the antibiotic arm compared with the control arm) and hospitalisation (50 fewer hospitalisations per 1000 people in the antibiotic arm compared with the control arm). However, the risk of emerging drug resistance is increased more than threefold. This review is limited by diversity of trials and by evidence of moderate to low quality. Further randomised controlled trials with adequate power and standardised end points are required.

A comparative study of amoxycillin and pivampicillin in persistent Haemophilus influenzae infection of the lower respiratory tract in children with chronic lung disease

A double-blind cross-over study was undertaken to compare the efficacy of amoxycillin and pivampicillin on Haemophilus influenzae infection of the lower respiratory tract in children. 20 patients with cystic fibrosis (CF) or chronic obstructive pulmonary disease (COPD) due to other causes were included in the study. All patients had a history of regularly harbouring H. influenzae in sputum and repeated treatment failures with pivampicillin. 18 completed two 14-day courses in random order with equimolar doses of pivampicillin (80 mg/kg/day) and amoxycillin (62 mg/kg/day). Both drugs were well tolerated with no serious side effects, but pivampicillin was associated with more pronounced nausea. In steady state the mean serum concentrations of antibiotics 2 and 4 h after medication were 9.7 and 3.7 micrograms/ml for pivampicillin and 19.1 and 7.9 micrograms/ml for amoxycillin (p less than 0.01). Eradication of H. influenzae and clinical improvement was seen in one-third of the courses with both drugs. Betalactamase producing ampicillin-resistant strains emerged during 58% of the amoxycillin courses, but only in 16% of the pivampicillin courses (p less than 0.001). The high number of treatment failures and the development of resistant strains indicate that betalactamase inhibitors may possibly improve the efficacy of these drugs, especially of amoxycillin, in these patients.

Amoxicillin and potassium clavulanate: an antibiotic combination. Mechanism of action, pharmacokinetics, antimicrobial spectrum, clinical efficacy and adverse effects

The combination of amoxicillin and potassium clavulanate will soon be marketed in 2:1 and 4:1 fixed ratio dosage forms. In vitro and in vivo evidence suggests that clavulanic acid, a potent inhibitor of many bacterial beta-lactamase enzymes, will increase the spectrum of amoxicillin to include, at achievable serum concentrations, Haemophilus influenzae, H. ducreyi, Neisseria gonorrhoeae, Staphylococcus aureus and Branhamella catarralis and, at achievable urine levels, many beta-lactamase-producing strains of E. coli, Klebsiella, Proteus and Citrobacter. Both amoxicillin and clavulanic are well absorbed after oral administration, reach peak serum levels in 40-120 min and have similar half-lives of 45 to 90 min. This combination will be suitable for the treatment of complicated urinary tract infections, otitis media, sinusitis and respiratory tract infections. However, precise recommendations for its use will need to await further clinical trials that compare amoxicillin/clavulanate to alternative therapies.

A review of the therapeutic efficacy of aerosolized and endotracheally instilled antibiotics

Achievement of sufficient concentrations of aerosolized antibiotic at the site of infection is limited by technical problems in antibiotic delivery and by drug inactivation. Antibiotic delivery by aerosolization is generally associated with minimal systemic absorption, whereas systemic absorption may be significant after endotracheal instillation. Methodologic problems make correlations between clinical response and sputum antibiotic concentrations difficult. Studies suggest that aerosolized antibiotics are of little value in the treatment of chronic bronchopulmonary infections. Endotracheal instillation appears to be associated with favorable clinical responses, possibly due to enhanced antibiotic delivery to the site of infection. Prophylactic aerosolized antibiotics are effective in altering sputum flora; reduction in mortality from acquired pneumonia has not been demonstrated. The development of resistant organisms may occur as a result of prophylactic treatment.

Bacterial kill rates of amoxycillin and ampicillin at exponentially diminishing concentrations simulating in vivo conditions

The responses of bacteria exposed to amoxycillin and ampicillin were studied at continuously decreasing levels with half-life values similar to those which could occur in vivo. For Escherichia coli, the kill-rates were higher with amoxycillin than with ampicillin. The bactericidal response was exponential. With an antibiotic half-life of one hour, the amoxycillin first order inactivation rate was 3.544 h-1 and the viable cell half-life was 0.196 h; the respective values for ampicillin were 2.341 h-1 and 0.296 h. With an antibiotic half-life of five hours, the inactivation rate was 0.704 h-1 corresponding to a viable cell half-life of 0.985 h for amoxycillin compared to 0.358 h-1 and 1.937 h respectively for ampicillin. Comparison of viable counts and photometric monitoring showed that the former is the preferable method for recording the bacterial response to these beta-lactam antibiotics. During the phase of exponential kill, a plateau occurred in the optical density values. This was due in part to an increased biomass per cell. During the recovery phase, the number of viable cells started to increase several hours sooner than did the rise in optical density. For Staphylococcus aureus,the rates of kill were similar with both agents. Amoxycillin had a long bacteriostatic phase which was not seen with ampicillin. This led to a longer lasting antibacterial effect and reduction to a lower total count with amoxycillin. With staphylococci, the viable counts and the photometric responses were parallel.

Amoxycillin for parenteral use: a pharmacological and clinical evaluation

Pharmacological studies with intramuscular amoxycillin and intramuscular ampicillin were carried out in ten patients. Serum, urine levels, urinary recovery and renal clearance of intramuscular amoxycillin were similar to intramuscular ampicillin and to oral amoxycillin. The time to peak serum concentration was later for amoxycillin. Sputum levels were higher for amoxycillin. Amoxycillin intramuscularly was more painful than ampicillin in eleven out of thirty patients. The clinical response, evaluated in twenty-five patients was good and similar to ampicillin in our experience.

The aminopenicillins: development and comparative properties

In this review we have compared and contrasted the antibacterial and pharmacological properties of the aminopenicillins currently available. It is apparent that there is little hard evidence (except in the case of thphoid fever) that either amoxycillin or the pro-drug esters of ampicillin are significantly more effective than ampicillin itself, despite their better absorption and higher serum levels. However, amoxycillin and the ampicillin pro-drug esters do cause fewer bowel side-effects than ampicillin, which may justify their use despite the extra cost involved. The problem of susceptibility to penicillinases is unlikely to be solved by modification of the aminopenicillin molecule. A more likely solution is administration of these substances with beta-lactamase inhibitors such as clavulanic acid. Trials with such combinations are already under way.

Studies on aminopenicillin developments. Proceedings of a symposium. Concluding remarks

This symposium has focused on the bacteriological, pharmacokinetic, therapeutic, and adverse effects of the aminopenicillins. The compounds which are currently being assessed are primarily amoxycillin, ampicillin, bacampicillin, pivampicillin, and talampicillin. The three last mentioned are prodrugs which upon gastrointestinal absorption are rapidly split to yield circulating ampicillin. Pharmacokinetics and side-effects are reasons why one may narrow the selection of most suitable compounds within this group down to three. Ampicillin and amoxycillin are primary choices for parenteral dosage, and amoxycillin and bacampicillin the most suitable for oral therapy.

Cefuroxime in the treatment of lower respiratory tract infection

Cefuroxime is a new parenteral antibiotic with a wider spectrum of activity than earlier cephalosporins and is particularly active against Haemophilus influenzae, including strains resistant to ampicillin due to beta-lactamase production. From 18 centres, 274 patients suffering with 275 infections were treated with cefuroxime sodium using the standard regimen of 750 mg 8-hourly by intramuscular injection. The clinical results showed a 90% success rate in the patients with bronchopneumonia (105), 91% in patients with post-operative pneumonia (74), and 89% in the patients with acute exacerbations of chronic bronchitis (96). Renal function was closely monitored during therapy, and no adverse changes attributable to cefuroxime therapy were seen in any patient, including those who also received frusemide. Two patients (0.7%) developed a rash, although 8 penicillin-allergic patients were treated without incident. From these studies, it can be concluded that 750 mg cefuroxime 8-hourly is effective in the treatment of lower respiratory tract infections. It is suggested that the attributes of this antibiotic may offer several advantages over existing therapies.

Penetration of amoxicillin into cerebrospinal fluid

The penetration of amoxicillin into cerebrospinal fluid (CFS) in the presence of meningeal inflammation was evaluated in patients with tuberculous meningitis. Serum and CSF concentrations of amoxicillin were measured at 2 h in nine patients who received a 1-g oral dose and at 1.5 and 4 h in ten patients who received a 2-g intravenous injection of sodium amoxicillin. After the oral dose, CSF concentrations ranged from 0.1 to 1.5 mug/ml. After the intravenous injection, CSF concentrations ranged from 2.9 to 40.0 mug/ml at 1.5 h and from 2.6 to 27.0 mug/ml at 4 h. These data on penetration suggest that parenterally administered sodium amoxicillin may be of value in the therapy of acute bacterial meningitis.

Effect of erythromycin and amoxycillin on Bordetella pertussis in the nasopharynx

The effectiveness of oral erythromycin and amoxycillin in eradicating Bordetella pertussis from the nasopharynx was compared. Erythromycin in a dosage of 40--50 mg/kg/day was significantly more effective than amoxycillin in a dosage of 25--30 mg/kg/day. The organism did not disappear in three cases receiving a lower dosage of erythromycin. As antibiotic treatment does not affect the clinical course of fully-developed whooping cough, erythromycin is indicated primarily when particularly susceptible individuals are threatened by exposure. In such cases erythromycin should be given as soon as whooping cough is suspected.

Sputum and serum levels of amoxycillin in chronic bronchial infections

A study of 11 patients suffering from acute exacerbations of chronic bronchial infection, all with purulent (Mp+++) sputum, showed that good penetration of amoxycillin into such sputum occurs. The levels of amoxycillin in sputum doubled proportionally with the oral dose, at least up to dosages of 2 g. High dosages or oral amoxycillin may therefore, be advantageous in the treatment of chronic bronchial infection. In a study of 30 chronic bronchitic patients, whose sputum varied in purulence from mucoid to purulent (Mp+++) the concentration of amoxycillin in sputum containing approximately 50% pus (Mp++) was significantly higher than that in any other degree of purulence. These results indicate that amoxycillin penetrates best into sputum at an intermediate degree of purulence.

Amoxycillin: A review of its antibacterial and pharmacokinietic properties and therapeutic use

Amoxycillin2 is an acid stable semisynthetic penicillin closely related to ampicillin. Unlike pivampicillin and hetacillin, amoxycillin is not converted to ampicillin in the body. The antibacterial spectrum and level of activity of amoxycillin is essentially the same as for ampicillin, and there is complete cross-resistance between the two drugs. After oral administration, amoxycillin is better absorbed than ampicillin. Mean peak serum levels of amoxycillin are generally twice those of ampicillin after an equal dose. The better absorption and penetration into certain body tissues and fluids of amoxycillin and its greater activity against experimental infections in mice, suggest that it might be preferred to ampicillin in the treatment of some infections, but any clear superiority over ampicillin in clinical practice has yet to be demonstrated. However, these properties have enabled amoxycillin to be given at half the dose of ampicillin without loss of therapeutic efficacy, and the princpal side-effects of skin rashes and diarrhoea have tended to be less frequent with amoxycillin than with ampicillin. Other side-effects are essentially similar in nature to those reported with ampicillin.