Actinomyces species
Bartonella bacilliformis
Borrelia recurrentis
Chlamydia psittaci
Chlamydia trachomatis
Mycoplasma pneumoniae
Rickettsiae
Treponema pallidum
Treponema pertenue
Ureaplasma urealyticum

Parasites

Balantidium coli
Entamoeba species
Plasmodium falciparum

Doxycycline has been found to be active against the asexual erythrocytic forms of Plasmodium falciparum but not against the gametocytes of P. falciparum. The precise mechanism of action of the drug is not known.

Susceptibility Test Methods

When available, the clinical microbiology laboratory should provide cumulative results of the in vitro susceptibility test results for antimicrobial drugs used in local hospitals and practice areas to the physician as periodic reports that describe the susceptibility profile of nosocomial and community-acquired pathogens. These reports should aid the physician in selecting the most effective antimicrobial.

Dilution Techniques

Quantitative methods are used to determine antimicrobial minimum inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using a standardized procedure based on dilution methods (broth, agar, or microdilution),^5,7 or equivalent using standardized inoculum and concentrations of doxycycline. The MIC values should be interpreted according to the criteria provided in Table 1.

Diffusion Techniques

Quantitative methods that require measurement of zone diameters also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. The standard procedure^6,7 requires the use of standardized inoculum concentrations. This procedure uses paper disks impregnated with 30 mcg doxycycline to test the susceptibility of microorganisms to doxycycline. Interpretation involves the correlation of the diameter obtained in the disk test with the MIC for doxycycline. Reports from the laboratory providing results of the standard single-disk susceptibility test with a 30 mcg doxycycline disk should be interpreted according to the criteria in Table 1:

Table 1: Susceptibility Test Interpretive Criteria for Doxycycline

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