CLINICAL PHARMACOLOGY
Tetracyclines are readily
absorbed and are bound to plasma proteins in varying degree. They are
concentrated by the liver in the bile, and excreted in the urine and feces at
high concentrations and in a biologically active form.
Following a single 100 mg dose
administered in a concentration of 0.4 mg/mL in a one-hour infusion, normal
adult volunteers average a peak of 2.5 mcg/mL, while 200 mg of a concentration
of 0.4 mg/mL administered over two hours averaged a peak of 3.6 mcg/mL.
Excretion of doxycycline by the kidney is about 40 percent/72 hours in
individuals with normal function (creatinine clearance about 75 mL/min.). This
percentage excretion may fall as low as 1-5 percent/72 hours in individuals
with severe renal insufficiency (creatinine clearance below 10 mL/min.).
Studies have shown no significant difference in serum half-life of doxycycline
(range 18-22 hours) in individuals with normal and severely impaired renal
function.
Hemodialysis does not alter
this serum half-life of doxycycline.
Microbiology
Mechanism Of Action
Doxycycline inhibits bacterial protein synthesis by
binding to the 30S ribosomal subunit. Doxycycline has bacteriostatic activity
against a broad range of Gram-positive and Gram-negative bacteria.
Resistance
Cross resistance with other tetracyclines is common.
Antimicrobial Activity
Doxycycline has been shown to be active against most
isolates of the following microorganisms, both in vitro and in clinical
infections as described in the INDICATIONS AND USAGE section of the package
insert for VIBRAMYCIN.
Gram-Negative Bacteria
Acinetobacter species
Bartonella bacilliformis
Brucella species
Klebsiella species
Klebsiella granulomatis
Campylobacter fetus
Enterobacter aerogenes
Escherichia coli
Francisella tularensis
Haemophilus ducreyi
Haemophilus influenza
Neisseria gonorrhoeae
Shigella species
Vibrio cholera
Yersinia pestis
Gram-Positive Bacteria
Bacillus anthracis
Listeria monocytogenes
Streptococcus pneumoniae
Anaerobic Bacteria
Clostridium species
Fusobacterium fusiforme
Propionibacterium acnes
Other Bacteria
Nocardiae and other aerobic Actinomyces species
Borrelia recurrentis
Chlamydophila psittaci
Chlamydia trachomatis
Mycoplasma pneumoniae
Rickettsiae
Treponema pallidum
Treponema pallidum subspecies 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 Testing Methods
When available, the clinical microbiology laboratory
should provide cumulative reports of 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 test method1,2,4 (broth or agar).
The MIC values should be interpreted according to criteria provided in Table 1.
Diffusion Techniques
Quantitative methods that require measurement of zone
diameters can also provide reproducible estimates of the susceptibility of bacteria
to antimicrobial compounds. 1,3,4 Â The zone size should be
determined using a standardized test method.This procedure uses paper disks
impregnated with 30-μg doxycycline to test the susceptibility of
microorganisms to doxycycline. The disk diffusion interpretive criteria are
provided in Table 1.
Anaerobic Techniques
For anaerobic bacteria, the susceptibility to doxycycline
can be determined by a standardized test method5. The MIC values
obtained should be interpreted according to the criteria provided in Table 1.
Table 1: Susceptibility Test Interpretive Criteria for
Doxycycline and Tetracycline
Bacteriaa |
Minimal Inhibitory Concentration (mcg/mL) |
Zone Diameter (mm) |
Agar Dilution (mcg/mL) |
S |
I |
R |
S |
I |
R |
S |
I |
R |
Acinetobacter spp. |
Doxycycline |
≤4 |
8 |
≥16 |
≥13 |
10-12 |
≤9 |
- |
- |
- |
Tetracycline |
≤4 |
8 |
≥16 |
≥15 |
12-14 |
≤11 |
- |
- |
- |
Anaerobes |
Tetracycline |
- |
- |
- |
- |
- |
- |
≤4 |
8 |
≥16 |
Bacillus anthracisb |
Doxycycline |
≤1 |
- |
- |
- |
- |
- |
- |
- |
- |
Tetracycline |
≤1 |
- |
- |
- |
- |
- |
- |
- |
- |
Brucella speciesb |
Doxycycline |
≤1 |
- |
- |
- |
- |
- |
- |
- |
- |
Tetracycline |
≤1 |
- |
- |
- |
- |
- |
- |
- |
- |
Enterobacteriaceae |
Doxycycline |
≤4 |
8 |
≥16 |
≥14 |
11-13 |
≤10 |
- |
- |
- |
Tetracycline |
≤4 |
8 |
≥16 |
≥15 |
12-14 |
≤11 |
- |
- |
- |
Franciscella tularensisb |
Doxycycline |
≤4 |
- |
- |
- |
- |
- |
- |
- |
- |
Tetracycline |
≤4 |
- |
- |
- |
- |
- |
- |
- |
- |
Haemophilus influenzae |
Tetracycline |
≤2 |
4 |
≥8 |
≥29 |
26-28 |
≤25 |
- |
- |
- |
Mycoplasma pneumoniaeb |
Tetracycline |
- |
- |
- |
- |
- |
- |
≤2 |
- |
- |
Nocardiae and other aerobic Actinomyces speciesb |
Doxycycline |
≤1 |
2-4 |
≥8 |
- |
- |
- |
- |
- |
- |
Neisseria gonorrhoeaec |
Tetracycline |
- |
- |
- |
≥38 |
31-37 |
≤30 |
≤0.25 |
0.5- 1 |
≥2 |
Streptococcus pneumoniae |
Doxycycline |
≤0.25 |
0.5 |
≥1 |
≥28 |
25-27 |
≤24 |
- |
- |
- |
Tetracycline |
≤1 |
2 |
≥4 |
≥28 |
25-27 |
≤24 |
- |
- |
- |
Vibrio cholerae |
Doxycycline |
≤4 |
8 |
≥16 |
- |
- |
- |
- |
- |
- |
Tetracycline |
≤4 |
8 |
≥16 |
- |
- |
- |
- |
- |
- |
Yersinia pestis |
Doxycycline |
≤4 |
8 |
≥16 |
- |
- |
- |
- |
- |
- |
Tetracycline |
≤4 |
8 |
≥16 |
- |
- |
- |
- |
- |
- |
Ureaplasma urealyticum |
Tetracycline |
- |
- |
- |
- |
- |
- |
≤1 |
- |
≥2 |
a Organisms susceptible to tetracycline are
also considered susceptible to doxycycline. However, some organisms that are
intermediate or resistant to tetracycline may be susceptible to doxycycline.
b The current absence of resistance isolates precludes defining any
results other than “Susceptible”. If isolates yielding MIC results other than
susceptible, they should be submitted to a reference laboratory for further
testing.
c Gonococci with 30 mcg tetracycline disk zone diameters of <19
mm usually indicate a plasmid-mediated tetracycline resistant Neisseria
gonorrhoeae isolate. Resistance in these strains should be confirmed by a dilution
test (MIC ≥ 16 mcg/mL). |
A report of Susceptible
(S) indicates that the antimicrobial drug is likely to inhibit growth of the
microorganism if the antimicrobial drug reaches the concentration usually
achievable at the site of infection. A report of Intermediate (I)
indicates that the result should be considered equivocal, and, if the
microorganism is not fully susceptible to alternative, clinically feasible
drugs, the test should be repeated. This category implies possible clinical
applicability in body sites where the drug product is physiologically
concentrated or in situations where high dosage of drug can be used. This
category also provides a buffer zone that prevents small uncontrolled technical
factors from causing major discrepancies in interpretation. A report of Resistant
(R) indicates that the antimicrobial drug is not likely to inhibit growth of
the microorganism if the antimicrobial drug reaches the concentrations usually
achievable at the infection site; other therapy should be selected.
Quality Control
Standardized susceptibility test procedures require the
use of laboratory controls to monitor and ensure the accuracy and precision of
the supplies and reagents used in the assay, and the techniques of the
individuals performing the test.1,2,3,4,5,6,7 Standard doxycycline
and tetracycline powders should provide the following range of MIC values noted
in Table 2. For the diffusion technique using the 30 mcg doxycycline disk the
criteria noted in Table 2 should be achieved.
Table 2: Acceptable Quality Control Ranges for
Susceptibility Testing for Doxycycline and Tetracycline
QC Strain |
Minimal Inhibitory Concentration (mcg/mL) |
Zone Diameter (mm) |
Agar Dilution (mcg/mL) |
Enterococcusfaecalis ATCC 29212 |
Doxycycline |
2-8 |
- |
- |
Tetracycline |
8-32 |
- |
- |
Escherichia coli ATCC 25922 |
Doxycycline |
0.5-2 |
18-24 |
- |
Tetracycline |
0.5-2 |
18-25 |
- |
Eggerthella lenta ATCC 43055 |
Doxycycline |
2-16 |
- |
- |
Haemophilus influenzae ATCC 49247 |
Tetracycline |
4-32 |
14-22 |
- |
Neisseriagonorrhoeae ATCC 49226 |
Tetracycline |
- |
30-42 |
0.25-1 |
Staphylococcus aureus ATCC 25923 |
Doxycycline |
- |
23-29 |
- |
Tetracycline |
- |
24-30 |
- |
Staphylococcus aureus ATCC 29213 |
Doxycycline |
0.12-0.5 |
- |
- |
Tetracycline |
0.12-1 |
- |
- |
Streptococcus pneumoniae ATCC 49619 |
Doxycycline |
0.015-0.12 |
25-34 |
- |
Tetracycline |
0.06-0.5 |
27-31 |
- |
Bacteroidesfragilis ATCC 25285 |
Tetracycline |
- |
- |
0.12-0.5 |
Bacteroides thetaiotaomicron ATCC 29741 |
Doxycycline |
2-8 |
- |
- |
Tetracycline |
- |
- |
8-32 |
Mycoplasma pneumoniae ATCC 29342 |
Tetracycline |
0.06-0.5 |
- |
0.06-0.5 |
Ureaplasma urealyticum ATCC 33175 |
Tetracycline |
- |
- |
≥8 |
REFERENCES
1. Clinical and Laboratory Standards Institute (CLSI). Performance
Standards for Antimicrobial Susceptibility Testing; Twenty-Sixth Informational
Supplement, CLSI document M100-S26 [2016]. Clinical and Laboratory Standards
Institute, 950 West Valley Road, Suite 2500, Wayne, Pennsylvania 19087, USA.
2. Clinical and Laboratory Standards Institute (CLSI). Methods
for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow
Aerobically; Approved Standard -Tenth Edition. CLSI document M07-A10 [2015],
Clinical and Laboratory Standards Institute, 950 West Valley Road, Suite 2500,
Wayne, Pennsylvania 19087, USA.
3. Clinical and Laboratory Standards Institute (CLSI). Performance
Standards for Antimicrobial Disk Diffusion Susceptibility Tests; Approved
Standard – Twelfth Edition CLSI document M02-A12 [2015], Clinical and
Laboratory Standards Institute, 950 West Valley Road, Suite 2500, Wayne,
Pennsylvania 19087, USA.
4. Clinical and Laboratory Standards Institute (CLSI). Methods
for Antimicrobial Dilution and Disk Susceptibility Testing of Infrequently
Isolated or Fastidious Bacteria; Approved Guideline – Third Edition CLSI
document M45-A3 [2015], Clinical and Laboratory Standards Institute, 950 West
Valley Road, Suite 2500, Wayne, Pennsylvania 19087, USA.
5. Clinical and Laboratory Standards Institute (CLSI). Methods
for Antimicrobial Susceptibility Testing of Anaerobic Bacteria; Approved
Standard -Eighth Edition. CLSI document M11-A8 [2012]. Clinical and Laboratory
Standards Institute, 950 West Valley Road, Suite 2500, Wayne, PA 19087 USA.
6. Clinical and Laboratory Standards Institute. Susceptibility
Testing of Mycobacteria, Nocardiae, and Other Aerobic Actinomycetes; Approved
Standard—Second Edition. CLSI document M24-A2[2011]. Clinical and Laboratory
Standards Institute, 950 West Valley Road, Suite 2500, Wayne, PA 19087 USA.
7. Clinical and Laboratory Standards Institute. Methods
for Antimicrobial Susceptibility Testing for Human Mycoplasmas; Approved
Guideline. CLSI document M43-A [2011]. Clinical and Laboratory Standards
Institute, 950 West Valley Road, Suite 2500, Wayne, PA 19087 USA.