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The absorption of demeclocycline is slower than that of tetracycline. The time to reach the peak concentration is about 4 hours. After a 150 mg oral dose of demeclocycline tablet, the mean concentrations at 1 hour and 3 hours are 0.46 and 1.22 μg/mL (n=6) respectively. The serum half-life ranges between 10 and 16 hours. When demeclocycline hydrochloride is given concomitantly with some dairy products, or antacids containing aluminum, calcium, or magnesium, the extent of absorption is reduced by more than 50%. Demeclocycline hydrochloride penetrates well into various body fluids and tissues. The percent of demeclocycline hydrochloride bound to plasma protein is about 40% using a dialysis equilibrium method and 90% using an ultra-filtration method. Demeclocycline hydrochloride, like other tetracyclines, is concentrated in the liver and excreted into the bile where it is found in much higher concentrations than in the blood. The rate of demeclocycline hydrochloride renal clearance (35 mL/min/1.73 m²) is less than half that of tetracycline. Following a single 150 mg dose of demeclocycline hydrochloride in normal volunteers, 44% (n=8) was excreted in urine and 13% and 46%, respectively, were excreted in feces in two patients within 96 hours as active drug.


Mechanism of Action

The tetracyclines are primarily bacteriostatic and are thought to exert their antimicrobial effect by the inhibition of protein synthesis. The tetracyclines, including demeclocycline have a similar antimicrobial spectrum of activity against a wide range of gram-negative and gram-positive organisms.

Mechanism(s) of Resistance

Resistance to tetracyclines may be mediated by efflux, alteration in the target site of tetracycline, enzymatic inactivation, and decreased bacterial permeability to the tetracycline or a combination of these mechanisms.

Cross Resistance

Cross-resistance between antibiotics of the tetracycline family occurs.

Demeclocycline has been shown to be active against most isolates of the following bacteria, in vitro and/or in clinical infections as described in the INDICATIONS AND USAGE section.

Gram-positive bacteria

Bacillus anthracis
Listeria monocytogenes

Staphylococcus aureus

Streptococcus pneumoniae

Gram-negative bacteria

Bartonella bacilliformis
Calymmatobacterium granulomatis

Campylobacter fetus

Francisella tularensis

Haemophilus ducreyi

Haemophilus influenzae

Neisseria gonorrhoeae

Vibrio cholerae

Yersinia pestis

Because isolates of the following groups of gram-negative bacteria have been shown to be resistant to tetracyclines, culture and susceptibility testing are especially recommended:

Acinetobacter species
Enterobacter aerogenes

Escherichia coli


Other microorganisms

Actinomyces israelii
Borrelia recurrentis

Chlamydia psittaci

Chlamydia trachomatis

Fusobacterium fusiforme

Mycoplasma pneumoniae

Propionibacterium acnes


Treponema pallidum
subspecies pallidum
Treponema pallidum
subspecies pertenue
Ureaplasma urealyticum

Susceptibility Test Methods

When available, the clinical microbiology laboratory should provide the results of in vitro susceptibility test results for antimicrobial drug products 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 an antibacterial drug product for treatment.

Dilution Techniques

Quantitaive 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)1,2,3. The MIC values should be interpreted according to the criteria 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. The zone size provides an estimate of the susceptibility of bacteria to antimicrobial compounds. The zone size should be determined using a standardized test method.2,4 This procedure uses paper disks impregnated with 30 mcg tetracycline to test the susceptibility of microorganisms to tetracycline. The disc diffusion interpretive criteria are provided in Table 1.

Table 1: Susceptibility Test Interpretive Criteria for Tetracycline

Pathogen Minimum Inhibitory Concentration (mcg/mL) Disk Diffusion (zone diameters in mm)
Enterobacteriaceae, Acinetobacter spp. ≤ 4 8 > 16 ≥ 15 12 -14 < 11
Haemophilus influenzae < 2 4 > 8 > 29 26-28 < 25
Neisseria gonorrhoeae < 0.25 0.5-1 > 2 > 38 31-37 < 30
Staphylococcus aureus ≤ 4 8 ≥ 16 ≥ 19 15-18 ≤ 14
S. pneumoniae (non-meningitis isolates) ≤ 1 2 ≥ 4 ≥ 28 25-27 ≤ 24
Bacillus anthracis < 1 -- -- -- -- --
Franciscella tularensis < 4 -- -- -- -- --

A report of Susceptible indicates that the antimicrobial is likely to inhibit growth of the pathogen if the antimicrobial compound reaches the concentrations at the infection site necessary to inhibit growth of the pathogen. A report of Intermediate 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 a high dosage of the drug product 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 indicates that the antimicrobial is not likely to inhibit growth of the pathogen if the antimicrobial compound 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 supplies and reagents used in the assay, and the techniques of the individuals performing the test.1,2,3,4 Standard tetracycline powder should provide the following range of MIC values noted in Table 2. For the diffusion technique using the 30 mcg tetracycline disk, the criteria in Table 2 should be achieved.

Table 2: Acceptable Quality Control Ranges for Tetracycline

QC Strain Minimum Inhibitory Concentrations (mcg/mL) Disk Diffusion (zone diameters in mm)
Escherichia coli ATCC* 25922 0.5 to 2 18 -25
Staphylococcus aureus ATCC 29213 0.12 to 1 ----
Staphylococcus aureus ATCC 25923 ---- 24-30
Haemophilus influenzae ATCC 49247 4 to 32 14 -22
Neisseria gonorrhoeae ATCC 49226 0.25 - 1 30 - 42
Streptococcus pneumoniae ATCC 49619 0.06 - 0.5 27 - 31
*ATCC = American Type Culture Collection

Animal Pharmacology And Animal Toxicology

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.


1. Clinical and Laboratory Standards Institute (CLSI.) Methods for Dilution Antimicrobial Susceptibility Tests for Bacteria that Grow Aerobically. Approved Standard – 9th Edition. CLSI document M7-A9, 950 West Valley Rd. Suite 2500,.Wayne, PA 19087, 2012.

2. CLSI. Performance Standards for Antimicrobial Susceptibility Testing. 22nd Informational Supplement. CLSI document M100-S22. Wayne, PA, 2012.

3. CLSI. Methods or Antimicrobial Dilution and Disk Susceptibility Testing of Infrequently Isolated or Fastidious Bacteria: Approved Guideline - 2nd Edition. CLSI document M45-A2. CLSI, Wayne, PA, 2011.

4. CLSI. Performance Standards for Antimicrobial Disk Susceptibility Tests. Approved Standard – 11th Edition. CLSI document M2-A11. Wayne, PA, 2012.

Last reviewed on RxList: 10/22/2012
This monograph has been modified to include the generic and brand name in many instances.

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