Clinical Drug Experience Knowledgebase

Phase IIa Prospective Study to Evaluate the Safety and Measure Efficacy of Anti-chlamydophila Antibiotic Combination (ACAC) Therapy Comprising 100mg Doxycycline, 500mg Azithromycin and 300mg Rifabutin in the Treatment of Patients With Coronary Heart Disease (CHD)

Chlamydophila pneumoniae has been evaluated as one potential underlying cause of CHD. The strongest evidence supporting this hypothesis comes from multiple investigators who enrolled over 19,217 subjects in 'Anti-Chlamydia trials'. However, these studies can be questioned on the basis of the type and duration of therapy. The recent change of the genus no longer permits treatment of C. pneumoniae as if it were Chlamydia trachomatis - which can generally be cured with a short course of macrolides [azithromycin, roxithromycin or clarithromycin] used in the majority of subjects analysed in this meta-analysis. C. pneumoniae is largely intra-cellular and its preferred locations (arterial muscle cells and macrophages) may contribute to its persistence in the body. C. pneumoniae can be refractory to antibiotic treatment in spite of in vitro susceptibility to various macrolides and ansamycins likely due to the use of sub-optimal dosages, which has been shown to encourage or induce persistence of C. pneumoniae in vitro. Rupp et al (2009) reported C. pneumoniae to infiltrated poptotic neutrophils that are subsequently taken up by monocyte-derived macrophages, thereby preventing clearance by the body's immune system and preventing susceptibility in the presence of antibiotics.

The previously reported trials have used short-term or recurrent treatment. The rationale for combined antibiotic long-term therapy stems from experience with other intracellular bacteria e.g. Mycobacterium tuberculosis, characterized by its dormant forms and affinity for developing resistance. The presence of infection in arterial cells with associated fibrosis and calcification for a considerable time may warrant prolonged treatment to enable antibiotic penetration into infected spaces. The occurrence of dormant forms also requires long-term treatment to anticipate the 'awakening' of dormant bacterial cells so that antibiotics can be effective during their division phase. The use of a combination therapy rather than a single agent to address dormant forms is concurrent with experience with other chronic and multiple resistant strain infections such as H. pylori, M. tuberculosis, and Mycobacterium avium paratuberculosis which are treated with combination antibiotics to minimise the development of resistant strains. Indeed, in the C. pneumoniae/CHD trials, the only trial that showed marked improvement in primary end points was the trial that used multiple antibiotics albeit for 7 days22. Hence, it would be reasonable to trial an appropriate multiple-antibiotic regimen in CHD

In this trial, antibiotics against C. pneumoniae known to be active within cells will be used. The three drugs will be administered simultaneously to minimise resistance development, and these will be used for a minimum of 3 months. At this stage ideal duration of treatment is not known.

In preliminary clinical experience of 5 subjects, with 3-6 month treatment using clarithromycin, rifabutin and doxycycline, subjects noted reduced shortness of breath, angina episodes, and marked improvement in claudication. The dosage schedule for this trial will be initiated as half doses in the first week followed by full dosages from week two onwards. This is designed as to minimize the onset of potential adverse effects in subjects. The dose-escalating schedule allows introduction of the medications into the body and maximizing bioavailability yet minimizing the potential adverse events.

The experience with long term use of a combination of three antibiotics in Mycobacterium avium paratuberculosis and Crohn's disease has been largely in younger subjects who did not receive anti-platelet agents as concomitant therapies, and thus, macrolide anti-platelet agent interactions have not been observed. In the proposed group of subjects with CHD disease, clarithromycin has a known interaction with anti-platelet agents and therefore in this group, clarithromycin will be substituted by azithromycin, a similar macrolide that demonstrates the same intracellular activity against C. pneumoniae but does not exhibit such interaction with anti-platelet agents. The azithromycin dose will be reduced due to its longer half-life, resulting in longer bioavailability duration in the body. Due to reported occasional QT-prolongation at high doses of azithromycin, ECG monitoring of the QT-interval will be carried out.