The in-vitro activity of doxycycline and minocycline against anaerobic bacteria

New developments in chemotherapeutic options for Clostridium difficile colitis

PURPOSE OF REVIEW

Clostridium difficile infections (CDIs) are of increasing concern in healthcare due to increasing incidence as well as suboptimal response to standard therapies. This review focuses on current updates in chemotherapeutic treatment options for primary CDI as well as for relapse.

RECENT FINDINGS

Metronidazole and vancomycin remain the standard therapy for mild and severe CDI, respectively. Fidaxomicin was approved for use in CDI by the US Food and Drug Administration in 2011 and new studies have shown a decreased rate of recurrence as compared with vancomycin as well as potential promise for use as a chaser. Rifaximin may be useful in salvage therapy for recurrent CDI as well as for a chaser. Tigecycline, teicoplanin, doxycycline, linezolid, nitazoxanide, amixicile, LFF571, and CB-183 315 have in-vitro activity and are under different stages of study. Monoclonal antitoxin antibodies for prevention of relapse of CDI are currently under evaluation in a phase 3 clinical trial.

SUMMARY

A variety of promising new treatment options for Clostridium difficile are under development, although further studies are necessary to determine the efficacy of these newer treatments for cure and preventing disease relapse.

Minocycline: old and new therapeutic uses

Since the introduction of minocycline HCl in the late 1960's, it has been used for disease states that have ranged from typical community-acquired infectious diseases to others that are non-infectious, such as resistant rheumatoid arthritis. Owing to its high penetration characteristics throughout the body, minocycline can be used in the treatment of a wide variety of extracellular and intracellular pathogens. This review examines the known and potential therapeutic uses of minocycline in a clinical setting.

Does doxycycline protect against development of Clostridium difficile infection?

BACKGROUND

Receipt of antibiotics is a major risk factor for Clostridium difficile infection (CDI). Doxycycline has been associated with a lower risk for CDI than other antibiotics. We investigated whether doxycycline protected against development of CDI in hospitalized patients receiving ceftriaxone, a high-risk antibiotic for CDI.

METHODS

We studied adults admitted to an academic county hospital between 1 June 2005 and 31 December 2010 who received ceftriaxone to determine whether the additional receipt of doxycycline decreased the risk of CDI. Patients were followed from first administration of ceftriaxone to occurrence of CDI or administrative closure 30 days later.

RESULTS

Two thousand three hundred five unique patients comprising 2734 hospitalizations were studied. Overall, 43 patients developed CDI within 30 days of ceftriaxone receipt, an incidence of 5.60 cases per 10 000 patient-days. The incidence of CDI was 1.67 cases per 10 000 patient-days in those receiving doxycycline, compared to 8.11 per 10 000 patient-days in those who did not receive doxycycline. In a multivariable model adjusted for age, gender, race, comorbidities, hospital duration, pneumonia diagnosis, surgical admission, and duration of ceftriaxone and other antibiotics, for each day of doxycycline receipt the rate of CDI was 27% lower than a patient who did not receive doxycycline (hazard ratio, 0.73; 95% confidence interval, .56-.96).

CONCLUSIONS

In this cohort of patients receiving ceftriaxone, doxycycline was associated with lower risk of CDI. Guidelines recommend this combination as a second-line regimen for some patients with community-acquired pneumonia (CAP). Further clinical studies would help define whether doxycycline-containing regimens should be a preferred therapy for CAP.

The glycylcyclines: a comparative review with the tetracyclines

The tetracycline class of antimicrobials exhibit a broad-spectrum of activity against numerous pathogens, including Gram-positive and Gram-negative bacteria, as well as atypical organisms. These compounds are bacteriostatic, and act by binding to the bacterial 30S ribosomal subunit and inhibiting protein synthesis. The tetracyclines have been used successfully for the treatment of a variety of infectious diseases including community-acquired respiratory tract infections and sexually transmitted diseases, as well in the management of acne. The use of tetracyclines for treating bacterial infections has been limited in recent years because of the emergence of resistant organisms with efflux and ribosomal protection mechanisms of resistance. Research to find tetracycline analogues that circumvented these resistance mechanisms has lead to the development of the glycylcyclines. The most developed glycylcycline is the 9-tert-butyl-glycylamido derivative of minocycline, otherwise known as tigecycline (GAR-936). The glycylcyclines exhibit antibacterial activities typical of earlier tetracyclines, but with more potent activity against tetracycline-resistant organisms with efflux and ribosomal protection mechanisms of resistance. The glycylcyclines are active against other resistant pathogens including methicillin-resistant staphylococci, penicillin-resistant Streptococcus pneumoniae, and vancomycin-resistant enterococci. Tigecycline is only available in an injectable formulation for clinical use unlike currently marketed tetracyclines that are available in oral dosage forms. Tigecycline has a significantly larger volume of distribution (> 10 L/kg) than the other tetracyclines (range of 0.14 to 1.6 L/kg). Protein binding is approximately 68%. Presently no human data are available describing the tissue penetration of tigecycline, although studies in rats using radiolabelled tigecycline demonstrated good penetration into tissues. Tigecycline has a half-life of 36 hours in humans, less than 15% of tigecycline is excreted unchanged in the urine. On the basis of available data, it does not appear that the pharmacokinetics of tigecycline are markedly influenced by patient gender or age. The pharmacodynamic parameter that best correlates with bacteriological eradication is time above minimum inhibitory concentration. Several animal studies have been published describing the efficacy of tigecycline. Human phase 1 and 2 clinical trials have been completed for tigecycline. Phase 2 studies have been conducted in patients with complicated skin and skin structure infections, and in patients with complicated intra-abdominal infections have been published as abstracts. Both studies concluded that tigecycline was efficacious and well tolerated. Few human data are available regarding the adverse effects or drug interactions resulting from tigecycline therapy; however, preliminary data report that tigecycline can be safely used, is well tolerated and that the adverse effects experienced were typical of the tetracyclines (i.e. nausea, vomiting and headache). Tigecycline appears to be a promising new antibacterial based on in vitro and pharmacokinetic/pharmacodynamic activity; however more clinical data are needed to fully evaluate its potential.

In vitro release of doxycycline from bioabsorbable materials and acrylic strips

Treatment of marginal periodontitis may include use of local antibiotics. In the present in vitro study the bioabsorbable materials Surgicel, Tissell, and CollaCote and acrylic strips were examined for release of doxycycline into liquids and residual antibacterial activity of the materials. Pieces of material were incubated in 1 ml of water or human serum which was exchanged every day for 9 days. The concentration of doxycycline in the liquids was measured spectrophotometrically while the residual antibacterial activity of the materials was determined microbiologically. Surgicel constantly showed very high concentrations and level of residual activity. The acrylic strip and CollaCote decreased to low levels of both concentration and residual activity in a few days. Tissell was intermediate with a continuous decrease in concentration but rather high level of residual activity throughout the study. In serum the acrylic strip was partly dissolved and Surgicel was totally dissolved after 2 days. Left undisturbed in serum Surgicel was not dissolved for 2 weeks. These results indicate that Surgicel and Tissel may be capable of prolonged release of doxycycline in vivo.