CLINICAL PHARMACOLOGY
Mechanism Of Action
Doxycycline is an antibacterial
drug [see Microbiology].
Pharmacokinetics
Doxycycline is virtually
completely absorbed after oral administration. Following single and
multiple-dose administration of Doxycycline Hyclate Delayed-Release Tablets,
200 mg to adult volunteers, average peak plasma doxycycline concentration (Cmax)
was 4.6 mcg/mL and 6.3 mcg/mL, respectively with median tmax of 3 hours; the
corresponding mean plasma concentration values 24 hours after single and
multiple doses were 1.5 mcg/mL and 2.3 mcg/mL, respectively. The mean Cmax and
AUC 0-∞ of doxycycline are 24% and 13% lower, respectively, following
single dose administration of Doxycycline Hyclate Delayed-Release Tablets, 100
mg with a high fat meal (including milk) compared to fasted conditions. The
mean Cmax of doxycycline is 19% lower and the AUC 0-∞ is unchanged
following single dose administration of Doxycycline Hyclate Delayed-Release
Tablets, 150 mg with a high fat meal (including milk) compared to fasted
conditions. The clinical significance of these decreases is unknown.
Doxycycline bioavailability from Doxycycline Hyclate Delayed-Release Tablets,
200 mg was not affected by food, but the incidence of nausea was higher in
fasted subjects. The 200 mg tablets may be administered without regard to meals.
When Doxycycline Hyclate
Delayed-Release Tablets are sprinkled over applesauce and taken with or without
water, the extent of doxycycline absorption is unchanged, but the rate of
absorption is increased slightly.
Tetracyclines are concentrated in bile by the liver and
excreted in the urine and feces at high concentrations and in a biologically
active form. Excretion of doxycycline by the kidney is about 40%/72 hours in
individuals with a creatinine clearance of about 75 mL/min. This percentage may
fall as low as 1-5%/72 hours in individuals with a creatinine clearance below
10 mL/min.
Studies have shown no significant difference in the serum
half-life of doxycycline (range 18 to 22 hours) in individuals with normal and
severely impaired renal function. Hemodialysis does not alter the serum
half-life.
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. Cross-resistance between
tetracyclines is common.
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 Doxycycline Hyclate Delayed-Release Tablets [see INDICATIONS AND
USAGE].
Gram-Negative Bacteria
Acinetobacter species Bartonella
bacilliformis Brucella species
Campylobacter fetus
Enterobacter aerogenes
Escherichia coli Francisella
tularensis Haemophilus ducreyi
Haemophilus influenzae
Klebsiella granulomatis
Klebsiella species
Neisseria gonorrhoeae Shigella species
Vibrio cholerae
Yersinia pestis
Gram-Positive Bacteria
Bacillus anthracis Streptococcus pneumoniae
Anerobic Bacteria
Clostridium species
Fusobacterium fusiforme
Propionibacterium acnes
Other Bacteria
Borrelia recurrentis
Chlamydophila psittaci
Chlamydia trachomatis
Mycoplasma pneumoniae
Norcardiae and other aerobic
Actinomyces species
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 Test Methods
When available, the clinical microbiology laboratory
should provide the results of in vitro susceptibility test results for
antimicrobial drugs used in resident hospitals 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 method (broth and/or agar)5,6,8.
The MIC values should be interpreted according to the criteria provided in
Table 2.
Diffusion Techniques
Quantitative methods that require measurement of zone
diameters can also provide reproducible estimates of the susceptibility of
bacteria to antimicrobial compounds. Zone size provides an estimate of the
susceptibility of bacteria to antimicrobial compounds. The zone size should be
determined using a standard test method5,7,8. This procedure uses
paper disks impregnated with 30 mcg doxycycline to test the susceptibility of
bacteria to doxycycline. The disk diffusion interpretive criteria are provided
in Table 2.
Anaerobic Techniques
For anaerobic bacteria, the susceptibility to doxycycline
can be determined by a standardized test method9. The MIC values
obtained should be interpreted according to the criteria provided in Table 2.
Table 2: 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 |
- |
- |
- |
Francisella tularensisb |
Doxycycline |
≤ 4 |
- |
- |
- |
- |
- |
- |
- |
- |
Tetracycline |
≤ 4 |
- |
- |
- |
- |
- |
- |
- |
- |
Haemophilus influenzae |
Tetracycline |
≤ 2 |
4 |
≥ 8 |
≥ 29 |
26-28 |
≤ 25 |
- |
- |
- |
Mycoplasma pneumoniaeb |
Tetracycline |
- |
- |
- |
- |
- |
- |
≤ 2 |
- |
- |
Nocardiae and other aerobic Actinomyces speciesab |
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 |
aOrganisms susceptible to tetracycline are
also considered susceptible to doxycycline. However, some organisms that are
intermediate or resistant to tetracycline may be susceptible to doxycycline.
bThe 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.
cGonococci with 30 mcg tetracycline disk zone diameters of less than
19 mm usually indicate a plasmidmediated tetracycline resistant Neisseria
gonorrhoeae isolate. Resistance in these strains should be confirmed by a
dilution test (MIC greater than or equal to 16 mcg/mL). |
A report of Susceptible (S) indicates that the
antimicrobial drug is likely to inhibit growth of the pathogen if the
antimicrobial drug reaches the concentrations usually achievable at the site of
infection. A report of Intermediate (I) indicates that the result should
be considered equivocal, and, if the bacteria 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
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 is not likely to inhibit growth of the pathogen 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 test5,6,7,8,9,10,11. Standard doxycycline
and tetracycline powders should provide the following range of MIC values noted
in Table 3. For the diffusion technique using the 30 mcg doxycycline disk the
criteria noted in Table 3 should be achieved.
Table 3: Acceptable Quality Control Ranges for
Susceptiblity Testing for Doxycycline and Tetracycline
QC Strain |
Minimal Inhibitory Concentration (mcg/mL) |
Zone Diameter (mm) |
Agar Dilution (mcg/mL) |
Enterococcus faecalis ATCC 29212 |
Doxycycline |
2 -8 |
- |
- |
Tetracycline |
8 -32 |
- |
- |
Escherichia coli ATCC 25922 |
Doxycycline |
0.5 - 2 |
18 -24 |
- |
Tetracycline |
0.5 -2 |
18 -25 |
- |
Eubacteria lentum ATCC 43055 |
Doxycycline |
2-16 |
|
|
Haemophilus influenzae ATCC 49247 |
Tetracycline |
4 -32 |
14 -22 |
- |
Neisseria gonorrhoeae 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 |
|
- |
Staphylococcus pneumoniae ATCC 49619 |
Doxycycline |
0.015 -0.12 |
25 -34 |
- |
Tetracycline |
0.06 -0.5 |
27 -31 |
- |
Bacteroides fragilis ATCC 25285 |
Tetracycline |
- |
- |
0.125 -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 |
Animal Toxicology And/Or Pharmacology
Hyperpigmentation of the thyroid has been produced by
members of the tetracycline-class in the following species: in rats by
oxytetracycline, doxycycline, tetracycline PO4, and methacycline; in minipigs
by doxycycline, minocycline, tetracycline PO4, and methacycline; in dogs by
doxycycline and minocycline; in monkeys by minocycline.
Minocycline, tetracycline PO4, methacycline, doxycycline,
tetracycline base, oxytetracycline HCl, and tetracycline HCl, were goitrogenic
in rats fed a low iodine diet. This goitrogenic effect was accompanied by high
radioactive iodine uptake. Administration of minocycline also produced a large
goiter with high radioiodine uptake in rats fed a relatively high iodine diet.
Treatment of various animal species with this class of
drugs has also resulted in the induction of thyroid hyperplasia in the
following: in rats and dogs (minocycline); in chickens (chlortetracycline); and
in rats and mice (oxytetracycline). Adrenal gland hyperplasia has been observed
in goats and rats treated with oxytetracycline.
Results of animal studies indicate that tetracyclines
cross the placenta and are found in fetal tissues.
Clinical Studies
This was a randomized, double-blind, active-controlled,
multicenter trial which enrolled 495 subjects, between 19 to 45 years of age
with a confirmed diagnosis of urogenital C. trachomatis infection less
than 14 days prior to enrollment, or partner(s) of a subject with a known
positive test for urogenital C. trachomatis infection.
The primary purpose of this study was to evaluate the
efficacy and safety of Doxycycline Hyclate Delayed-Release Tablets, 200 mg once
daily versus doxycycline hyclate capsules, 100 mg twice daily for seven days
for the treatment of uncomplicated urogenital C. trachomatis infection.
The primary efficacy objective was to demonstrate non-inferiority of the
Doxycycline Hyclate Delayed-Release Tablets 200 mg once daily treatment regimen
versus the doxycycline 100 mg twice daily treatment regimen for the indication
using a negative nucleic acid amplification test (NAAT) at the test of cure
visit (day 28) in the mITT population (subjects who were positive at baseline
and took at least one day of study drug).
Table 4: Primary Efficacy Outcome – Microbiological
Cure of C. trachomatis at Day 28
mITT Population |
Doxycycline Hyclate Delayed-Release Tablets, 200 mg once daily Cure Rate (%) |
Doxycycline hyclate capsules, 100 mg twice daily Cure Rate (%) |
Difference (%) |
N |
188 |
190 |
|
Microbiological Cure, n (%) |
163 (86.7) |
171 (90.0) |
-3.3% |
95% Confidence Interval for Cure Rate |
|
|
-10.3, 3.7 |
REFERENCES
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