Adoxa

Description

Doxycycline (Adoxa) is a broad-spectrum antibiotic synthetically derived from oxytetracycline. Doxycycline 150 mg capsules contain doxycycline monohydrate equivalent to 150 mg of doxycycline for oral administration. Inactive ingredients include colloidal silicon dioxide, FD&C Red #40, FD&C Yellow #6, gelatin, magnesium stearate, microcrystalline cellulose, sodium starch glycolate, and titanium dioxide. Its molecular weight is 462.46. The chemical designation of the light-yellow crystalline powder is alpha-6-deoxy-5-oxytetracycline.

Structural formula:

C₂₂H₂₄N₂O₈•H₂O

Doxycycline has a high degree of lipid solubility and a low affinity for calcium binding. It is highly stable in normal human serum. Doxycycline will not degrade into an epianhydro form.

To reduce the development of drug-resistant bacteria and maintain the effectiveness of doxycycline capsules and other antibacterial drugs, doxycycline capsules should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria. When culture and susceptibility information are available, they should be considered in selecting or modifying antibacterial therapy. In the absence of such data, local epidemiology and susceptibility patterns may contribute to the empiric selection of therapy.

Doxycycline is indicated for the treatment of the following infections:

Rocky mountain spotted fever, typhus fever and the typhus group, Q fever, rickettsialpox, and tick fevers caused by Rickettsiae.
Respiratory tract infections caused by Mycoplasma pneumoniae.
Lymphogranuloma venereum caused by Chlamydia trachomatis.
Psittacosis (ornithosis) caused by Chlamydia psittaci.
Trachoma caused by Chlamydia trachomatis, although the infectious agent is not always eliminated as judged by immunofluorescence.
Inclusion conjunctivitis caused by Chlamydia trachomatis.
Uncomplicated urethral, endocervical or rectal infections in adults caused by Chlamydia trachomatis.
Nongonococcal urethritis caused by Ureaplasma urealyticum.
Relapsing fever due to Borrelia recurrentis.

Doxycycline is also indicated for the treatment of infections caused by the following gram-negative microorganisms:

Chancroid caused by Haemophilus ducreyi.
Plague due to Yersinia pestis (formerly Pasteurella pestis).
Tularemia due to Francisella tularensis (formerly Pasteurella tularensis).
Cholera caused by Vibrio cholerae (formerly Vibrio comma).
Campylobacter fetus infections caused by Campylobacter fetus (formerly Vibrio fetus).
Brucellosis due to Brucella species (in conjunction with streptomycin).
Bartonellosis due to Bartonella bacilliformis.
Granuloma inguinale caused by Calymmatobacterium granulomatis.

Because many strains of the following groups of microorganisms have been shown to be resistant to doxycycline, culture and susceptibility testing are recommended.

Doxycycline is indicated for treatment of infections caused by the following gram-negative microorganisms, when bacteriologic testing indicates appropriate susceptibility to the drug:

Escherichia coli
Enterobacter aerogenes (formerly Aerobacter aerogenes)
Shigella species
Acinetobacter species (formerly Mima species and Herellea species)
Respiratory tract infections caused by Haemophilus influenzae.
Respiratory tract and urinary infections caused by Klebsiella species.

Doxycycline is indicated for treatment of infections caused by the following gram-positive microorganisms, when bacteriologic testing indicates appropriate susceptibility to the drug: Upper respiratory infections caused by Streptococcus pneumoniae (formerly Diplococcus pneumoniae).

Upper respiratory infections caused by Streptococcus pneumoniae (formerly Diplococcus pneumoniae).
Skin and skin structure infections caused by Staphylococcus aureus.
Anthrax due to Bacillus anthracis, including inhalational anthrax (post-exposure); to reduce the incidence or progression of disease following exposure to aerosolized Bacillus anthracis.

Doxycycline is not the drug of choice in the treatment of any type of staphylococcal infections.

When penicillin is contraindicated, doxycycline is an alternative drug in the treatment of the following infections:

Uncomplicated gonorrhea caused by Neisseria gonorrhoeae.
Syphilis caused by Treponema pallidum.
Yaws caused by Treponema pertenue.
Listeriosis due to Listeria monocytogenes.
Vincent’s infection caused by Fusobacterium fusiforme.
Actinomycosis caused by Actinomyces israelii.
Infections caused by Clostridium species.

In acute intestinal amebiasis, doxycycline may be a useful adjunct to amebicides.

In severe acne, doxycycline may be useful adjunctive therapy.

Dosage And Administration

THE USUAL DOSAGE AND FREQUENCY OF ADMINISTRATION OF DOXYCYCLINE DIFFERS FROM THAT OF THE OTHER TETRACYCLINES. EXCEEDING THE RECOMMENDED DOSAGE MAY RESULT IN AN INCREASED INCIDENCE OF SIDE EFFECTS.

Adults

The usual dose of oral doxycycline is 200 mg on the first day of treatment (administered 100 mg every 12 hours or 50 mg every 6 hours) followed by a maintenance dose of 100 mg/day. The maintenance dose may be administered as a single dose or as 50 mg every 12 hours. In the management of more severe infections (particularly chronic infections of the urinary tract), 100 mg every 12 hours is recommended.

For Pediatric Patients Above Eight Years Of Age

The recommended dosage schedule for pediatric patients weighing 100 pounds or less is 2 mg/lb of body weight divided into two doses on the first day of treatment, followed by 1 mg/lb of body weight given as a single daily dose or divided into two doses, on subsequent days. For more severe infections up to 2 mg/lb of body weight may be used. For pediatric patients over 100 pounds the usual adult dose should be used.

Uncomplicated Gonococcal Infections In Adults (except anorectal infections in men)

100 mg, by mouth, twice a day for 7 days. As an alternate single visit dose, administer 300 mg stat followed in one hour by a second 300 mg dose.

Acute Epididymo-Orchitis Caused By N. gonorrhoeae

100 mg, by mouth, twice a day for at least 10 days.

Primary And Secondary Syphilis

300 mg a day in divided doses for at least 10 days.

Uncomplicated Urethral, Endocervical, Or Rectal Infection In Adults Caused By Chlamydia Trachomatis

100 mg, by mouth, twice a day for at least 7 days.

Nongonococcal Urethritis Caused By C. trachomatis and U. urealyticum

100 mg, by mouth, twice a day for at least 7 days.

Acute Epididymo-Orchitis Caused By C. trachomatis

100 mg, by mouth, twice a day for at least 10 days.

Inhalational Anthrax (post-exposure)

Adults: 100 mg of doxycycline, by mouth, twice a day for 60 days.

Children: weighing less than 100 pounds (45 kg): 1 mg/lb (2.2 mg/kg) of body weight, by mouth, twice a day for 60 days. Children weighing 100 pounds or more should receive the adult dose.

When used in streptococcal infections, therapy should be continued for 10 days.

Administration of adequate amounts of fluid along with capsule and tablet forms of drugs in the tetracycline class is recommended to wash down the drugs and reduce the risk of esophageal irritation and ulceration. (See ADVERSE REACTIONS.) If gastric irritation occurs, doxycycline may be given with food. Ingestion of a high fat meal has been shown to delay the time to peak plasma concentrations by an average of one hour and 20 minutes. However, in the same study, food enhanced the average peak concentration by 7.5% and the area under the curve by 5.7%.

How Supplied

Doxycycline Capsules 150 mg have a peach opaque cap printed “ADOXA®” in black ink/peach opaque body printed “150 mg” in black ink. Each capsule contains doxycycline monohydrate equivalent to 150 mg of doxycycline. They are supplied as follows:

Bottle of 60 NDC 10337-815-06

Store at 20° to 25°C (68° to 77°F). [See USP Controlled Room Temperature.]

DISPENSE IN A TIGHT LIGHT RESISTANT CONTAINER AS DEFINED IN THE USP/NF.

Manufactured by: PharmaDerm, A division of Fougera Pharmaceuticals Inc., Melville, NY 11747 USA. Manufactured by: PAR PHARMACEUTICAL COMPANIES, INC., Spring Valley, NY 10977 USA, IL221C. Revised: May 2013

Due to oral doxycycline’s virtually complete absorption, side effects to the lower bowel, particularly diarrhea, have been infrequent. The following adverse reactions have been observed in patients receiving tetracyclines:

Gastrointestinal

Anorexia, nausea, vomiting, diarrhea, glossitis, dysphagia, enterocolitis, and inflammatory lesions (with monilial overgrowth) in the anogenital region. Hepatotoxicity has been reported ^(b)(4).  These reactions have been caused by both the oral and parenteral administration of tetracyclines. Rare instances of esophagitis and esophageal ulcerations have been reported in patients receiving capsule and tablet forms of drugs in the tetracycline class. Most of these patients took medications immediately before going to bed. (See DOSAGE AND ADMINISTRATION.)

Skin

Maculopapular and erythematous rashes Stevens-Johnson syndrome, toxic epidermal necrolysis and erythema multiforme have been reported. Exfoliative dermatitis has been reported but is uncommon. Photosensitivity is discussed above. (See WARNINGS.)

Renaltoxicity

Rise in BUN has been reported and is apparently dose related. (See WARNINGS.)

Hypersensitivity Reactions

Urticaria, angioneurotic edema, anaphylaxis, anaphylactoid purpura, serum sickness, pericarditis, and exacerbation of systemic lupus erythematosus.

Blood

Hemolytic anemia, thrombocytopenia, neutropenia, and eosinophilia have been reported with tetracyclines.

Other

Bulging fontanels in infants and intracranial hypertension in adults. (See PRECAUTIONS –General.)

When given over prolonged periods, tetracyclines have been reported to produce brown-black microscopic discoloration of the thyroid gland. No abnormalities of thyroid function are known to occur.

Because tetracyclines have been shown to depress plasma prothrombin activity, patients who are on anticoagulant therapy may require downward adjustment of their anticoagulant dosage.

Since bacteriostatic drugs may interfere with the bactericidal action of penicillin, it is advisable to avoid giving tetracyclines in conjunction with penicillin.

Absorption of tetracyclines is impaired by antacids containing aluminum, calcium, or magnesium, and iron-containing preparations.

Barbiturates, carbamazepine, and phenytoin decrease the half-life of doxycycline.

The concurrent use of tetracycline and methoxyflurane has been reported to result in fatal renal toxicity.

Concurrent use of tetracycline may render oral contraceptives less effective.

Drug/Laboratory Test Interactions

False elevations of urinary catecholamine levels may occur due to interference with the fluorescence test.

THE USE OF DRUGS OF THE TETRACYCLINE CLASS DURING TOOTH DEVELOPMENT (LAST HALF OF PREGNANCY, INFANCY, AND CHILDHOOD TO THE AGE OF 8 YEARS) MAY CAUSE PERMANENT DISCOLORATION OF THE TEETH (YELLOW-GRAYBROWN). This adverse reaction is more common during long-term use of the drugs but has been observed following repeated short-term courses. Enamel hypoplasia has also been reported. TETRACYCLINE DRUGS, THEREFORE, SHOULD NOT BE USED IN THIS AGE GROUP, EXCEPT FOR ANTHRAX, INCLUDING INHALATIONAL ANTHRAX (POST-EXPOSURE), UNLESS OTHER DRUGS ARE NOT LIKELY TO BE EFFECTIVE OR ARE CONTRAINDICATED.

Clostridium difficile associated diarrhea (CDAD) has been reported with use of nearly all antibacterial agents, including doxycycline, and may range in severity from mild diarrhea to fatal colitis. Treatment with antibacterial agents alters the normal flora of the colon leading to overgrowth of C. difficile.

C. difficile produces toxins A and B which contribute to the development of CDAD. Hypertoxin producing strains of C. difficile cause increased morbidity and mortality, as these infections can be refractory to antimicrobial therapy and may require colectomy. CDAD must be considered in all patients who present with diarrhea following antibiotic use. Careful medical history is necessary since CDAD has been reported to occur over two months after the administration of antibacterial agents.

If CDAD is suspected or confirmed, ongoing antibiotic use not directed against C. difficile may need to be discontinued. Appropriate fluid and electrolyte management, protein supplementation, antibiotic treatment of C. difficile, and surgical evaluation should be instituted as clinically indicated.

All tetracyclines form a stable calcium complex in any bone-forming tissue. A decrease in the fibula growth rate has been observed in prematures given oral tetracycline in doses of 25 mg/kg every six hours. This reaction was shown to be reversible when the drug was discontinued.

Results of animal studies indicate that tetracyclines cross the placenta, are found in fetal tissues, and can have toxic effects on the developing fetus (often related to retardation of skeletal development). Evidence of embryo toxicity has been noted in animals treated early in pregnancy. If any tetracycline is used during pregnancy or if the patient becomes pregnant while taking these drugs, the patient should be apprised of the potential hazard to the fetus.

The antianabolic action of the tetracyclines may cause an increase in BUN. Studies to date indicate that this does not occur with the use of doxycycline in patients with impaired renal function.

Photosensitivity manifested by an exaggerated sunburn reaction has been observed in some individuals taking tetracyclines. Patients apt to be exposed to direct sunlight or ultraviolet light should be advised that this reaction can occur with tetracycline drugs, and treatment should be discontinued at the first evidence of skin erythema.

General

As with other antibiotic preparations, use of this drug may result in overgrowth of non-susceptible organisms, including fungi. If superinfection occurs, the antibiotic should be discontinued and appropriate therapy instituted.

Bulging fontanels in infants and benign intracranial hypertension in adults have been reported in individuals receiving tetracyclines. These conditions disappeared when the drug was discontinued.

Incision and drainage or other surgical procedures should be performed in conjunction with antibiotic therapy when indicated.

Prescribing doxycycline capsules in the absence of a proven or strongly suspected bacterial infection or a prophylactic indication is unlikely to provide benefit to the patient and increases the risk of the development of drug-resistant bacteria.

Laboratory Tests

In venereal disease when coexistent syphilis is suspected, a dark-field examination should be done before treatment is started and the blood serology repeated monthly for at least four months.

In long-term therapy, periodic laboratory evaluations of organ systems, including hematopoietic, renal, and hepatic studies should be performed.

Carcinogenesis And Mutagenesis And Impairment Of Fertility

Long-term studies in animals to evaluate the carcinogenic potential of doxycycline have not been conducted. However, there has been evidence of oncogenic activity in rats in studies with related antibiotics, oxytetracycline (adrenal and pituitary tumors) and minocycline (thyroid tumors). Likewise, although mutagenicity studies of doxycycline have not been conducted, positive results in in vitro mammalian cell assays have been reported for related antibiotics (tetracycline, oxytetracycline). Doxycycline administered orally at dosage levels as high as 250 mg/kg/day had no apparent effect on the fertility of female rats. Effect on male fertility has not been studied.

Pregnancy

Teratogenic Effects

Pregnancy Category D

There are no adequate and well-controlled studies on the use of doxycycline in pregnant short-term, first-trimester exposure. There are no human data available to assess the effects of long-term therapy of doxycycline in pregnant women such as that proposed for treatment of anthrax exposure. An expert review of published data on experiences with doxycycline use during pregnancy by TERIS – the Teratogen Information System – concluded that therapeutic doses during pregnancy are unlikely to pose a substantial teratogenic risk (the quantity and quality of data were assessed as limited to fair), but the data are insufficient to state that there is no risk.^a

A case-control study (18,515 mothers of infants with congenital anomalies and 32,804 mothers of infants with no congenital anomalies) shows a weak but marginally statistically significant association with total malformations and use of doxycycline anytime during pregnancy. (Sixty-three (0.19%) of the controls and 56 (0.30%) of the cases were treated with doxycycline.) This association was not seen when the analysis was confined to maternal treatment during the period of organogenesis (i.e., in the second and third months of gestation) with the exception of a marginal relationship with neural tube defect based on only two exposed cases.^b

A small prospective study of 81 pregnancies describes 43 pregnant women treated for 10 days with doxycycline during early first trimester. All mothers reported their exposed infants were normal at 1 year of age.^c

Labor And Delivery

The effect of tetracyclines on labor and delivery is unknown.

Nursing Mothers

Tetracyclines are excreted in human milk, however, the extent of absorption of tetracyclines, including doxycycline, by the breastfed infant is not known. Short-term use by lactating women is not necessarily contraindicated; however, the effects of prolonged exposure to doxycycline in breast milk are unknown.^d Because of the potential for adverse reactions in nursing infants from doxycycline, a decision should be made whether to discontinue nursing or to discontinue the drug, taking into account the importance of the drug to the mother. (See WARNINGS.)

Pediatric Use

See WARNINGS and DOSAGE AND ADMINISTRATION sections.

REFERENCES

a. Friedman JM and Polifka JE. Teratogenic Effects of Drugs. A Recredit for Clinicians (TERIS). Baltimore, MD: The Johns Hopkins University Press: 2000: 149-195.

b. Cziezel AE and Rockenbauer M. Teratogenic study of doxycycline. Obstet Gynecol 1997; 89: 524- 528.

c. Horne HW Jr. and Kundsin RB. The role of mycoplasma among 81 consecutive pregnancies: a prospective study. Int J Fertil 1980; 25: 315-317.

d. Hale T. Medications and Mothers Milk. 9th edition. Amarillo, TX: Pharmasoft Publishing 2000; 225- 226.

In case of overdosage, discontinue medication, treat symptomatically, and institute supportive measures. Dialysis does not alter serum half-life, and it would not be of benefit in treating cases of overdosage.

Contraindications

This drug is contraindicated in persons who have shown hypersensitivity to any of the tetracyclines.

Tetracyclines are readily absorbed and are bound to plasma proteins in varying degrees. They are concentrated by the liver in the bile and excreted in the urine and feces at high concentrations in a biologically active form. Doxycycline is virtually completely absorbed after oral administration.

Following a 200 mg dose of doxycycline monohydrate, 24 normal adult volunteers averaged the following serum concentration values:

Time (hr):	0.5	1.0	1.5	2.0	3.0	4.0	8.0	12.0	24.0	48.0	72.0
Conc: (mcg/mL)	1.02	2.26	2.67	3.01	3.16	3.03	2.03	1.62	0.95	0.37	0.15

Average Observed Values

Maximum Concentration	3.61 mcg/mL (± 0.9 sd)
Time of Maximum Concentration	2.60 hr (± 1.10 sd)
Elimination Rate Constant	0.049 per hr (± 0.030 sd)
Half-Life	16.33 hr (± 4.53 sd)

Excretion of doxycycline by the kidney is about 40%/72 hours in individuals with normal function (creatinine clearance about 75 mL/min). This percentage excretion may fall as low as 1 to 5%/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 to 22 hours) in individuals with normal and severely impaired renal function.

Hemodialysis does not alter serum half-life.

Microbiology

The tetracyclines are primarily bacteriostatic and are thought to exert their antimicrobial effect by the inhibition of protein synthesis. The tetracyclines, including doxycycline, have a similar antimicrobial spectrum of activity against a wide range of gram-positive and gramnegative microorganisms. Cross-resistance of these microorganisms to tetracyclines is common.

Doxycycline has been shown to be active against most strains of the following microorganisms, both in vitro and in clinical infections as described in the INDICATIONS AND USAGE section.

Aerobic Gram-Positive Microorganisms

Because many strains of the following groups of gram-positive microorganisms have been shown to be resistant to tetracyclines, culture and susceptibility testing are recommended:

Bacillus anthracis
Listeria monocytogenes
Staphylococcus aureus*

*Doxycycline is not the drug of choice in the treatment of any type of staphylococcal infection.

Up to 44 percent of strains of Streptococcus pyogenes and 74 percent of Streptococcus faecalis have been found to be resistant to tetracycline drugs. Therefore, tetracyclines should not be used to treat streptococcal infections unless the microorganism has been demonstrated to be susceptible.

Streptococcus pneumoniae

Aerobic Gram-Negative Microorganisms

Bartonella bacilliformis
Brucella species
Calymmatobacterium granulomatis
Campylobacter fetus
Francisella tularensis
Haemophilus ducreyi
Haemophilus influenzae
Neisseria gonorrhoeae
Vibrio cholerae
Yersinia pestis

Because many strains of the following groups of gram-negative microorganisms have been shown to be resistant to tetracyclines, culture and susceptibility testing are recommended:

Acinetobacter species
Enterobacter aerogenes
Escherichia coli
Klebsiella species
Shigella species

Anaerobic Microorganisms

Actinomyces israelii
Clostridium species
Fusobacterium fusiforme

Other Microorganisms

Borrelia recurrentis
Chlamydia psittaci
Chlamydia trachomatis
Mycoplasma pneumoniae
Rickettsiae
Treponema pallidum
Treponema pertenue

Susceptibility Tests

Dilution Techniques

Quantitative methods are used to determine antimicrobial minimum inhibitory concentrations (MIC’s). These MIC’s provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MIC’s should be determined using a standardized procedure. Standardized procedures are based on a dilution method^1,3 (broth or agar) or equivalent with standardized inoculum concentrations and standardized concentrations of tetracycline powder. The MIC values should be interpreted according to the following criteria for indicated aerobic microorganisms other than Haemophilus species, Neisseria gonorrhoeae, and Streptococcus pneumoniae:

MIC (mcg/mL)	Interpretation
≤ 4	Susceptible (S)
8	Intermediate (I)
> 16	Resistant (R)
When testing Haemophilus spp.a
MIC (mcg/mL)	Interpretation
≤ 2	Susceptible (S)
4	Intermediate (I)
> 8	Resistant (R)
When testing Neisseria gonorrhoeaeb
MIC (mcg/mL)	Interpretation
≤ 0.25	Susceptible (S)
0.5-1	Intermediate (I)
≥ 2	Resistant (R)
When testing Streptococcus pneumoniaec
MIC (mcg/mL)	Interpretation
≤ 2	Susceptible (S)
4	Intermediate (I)
≥ 8	Resistant (R)
a Interpretative criteria applicable only to tests performed by broth microdilution method using Haemophilus Test Medium (HTM).1,3 b Interpretative criteria applicable only to tests performed by agar dilution method using GC agar base with 1% defined growth supplement.1,3 c Interpretative criteria applicable only to tests performed by broth microdilution method using cationadjusted Mueller-Hinton broth with 2 to 5% lysed horse blood.1,3

A report of “Susceptible” indicates that the pathogen is likely to be inhibited if the antimicrobial compound in the blood reaches the concentrations usually achievable. 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 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” indicates that the pathogen is not likely to be inhibited if the antimicrobial compound in the blood reaches the concentrations usually achievable; other therapies should be selected.

Standardized susceptibility test procedures require the use of laboratory control microorganisms to control the technical aspects of the laboratory procedures. Standard tetracycline powder should provide the following MIC values:

Microorganism		MIC (mcg/mL)
Enterococcus faecalis	ATCC 29212	8-32
Escherichia coli	ATCC 25922	0.5-2
Haemophilus influenzaea	ATCC 49247	4-32
Neisseria gonorrhoeaeb	ATCC 49226	0.25-1
Pseudomonas aeruginosa	ATCC 27853	8-32
Staphylococcus aureus	ATCC 29213	0.12-1
Streptococcus pneumoniaec	ATCC 49619	0.12-0.5
a Range applicable only to tests performed by broth microdilution method using Haemophilus Test Medium(HTM).1,3 b Range applicable only to tests performed by agar dilution method using GC agar base with 1% defined growth supplement. 1,3 c Range applicable only to tests performed by broth microdilution method using cation-adjusted Mueller- Hinton broth with 2 to 5% lysed horse blood. 1,3

Diffusion Techniques

Quantitative methods that require measurement of zone diameters also provide reproducible estimates of the susceptibility of bacteria to antimicrobial compounds. One such standardized procedure requires the use of standardized inoculum concentrations. This procedure uses paper disks impregnated with 30 mcg of tetracycline or 30 mcg of doxycycline to test the susceptibility of microorganisms to doxycycline.

Reports from the laboratory providing results of the standard single-disk susceptibility test with 30 mcg tetracycline-class disk or the 30 mcg doxycycline disk should be interpreted according to the following criteria for indicated aerobic microorganisms other than Haemophilus species, Neisseria gonorrhoeae, and Streptococcus pneumoniae:

Zone Diameter (mm)		Interpretation
Tetracycline	Doxycycline
≥ 15	≥ 14	Susceptible (S)
12-14	11-13	Intermediate (I)
≤ 11	≤ 10	Resistant (R)
When testing Haemophilus spp.a
Zone Diameter (mm)		Interpretation
tetracycline
≥ 29		Susceptible (S)
26-28		Intermediate (I)
≤ 25		Resistant (R)
When testing Neisseria gonorrhoeaeb
Zone Diameter (mm)	Interpretation
tetracycline
≥ 38	Susceptible (S)
31-37	Intermediate (I)
≤ 30	Resistant (R)

Zone diameters ≤ 19 mm may indicate a plasmid-mediated tetracycline-resistant Neisseria gonorrhoeae (TRNG) isolate. These TRNG strains should be confirmed by the dilution test (MIC ≥ 16 mcg/mL).

When testing Streptococcus pneumonia^c

Zone Diameter (mm)	Interpretation
tetracycline
≥ 23	Susceptible (S)
19-22	Intermediate (I)
≤ 18	Resistant (R)

Interpretative criteria applicable only to tests performed by disk diffusion method using a 30 mcg tetracycline-class disk and using Haemophilus Test Medium (HTM).
^b Interpretative criteria applicable only to tests performed by disk diffusion method using a 30 mcg tetracycline-class disk and using GC agar base with 1% defined growth supplement.
^c Interpretative criteria applicable only to tests performed by disk diffusion method using a 30 mcg tetracycline-class disk and using Mueller-Hinton agar with 5% defibrinated sheep blood and incubated with 5% CO₂.^2,3

Interpretation should be as stated above for results using dilution techniques. Interpretation involves correlation of the diameter obtained in the disk test with the MIC for tetracycline or doxycycline, respectively.

As with standardized dilution techniques, diffusion methods require the use of laboratory control microorganisms that are used to control the technical aspects of the laboratory procedures. For the diffusion technique, the 30 mcg tetracycline-class disk or the 30 mcg doxycycline disk should provide the following zone diameters in these laboratory test quality control strains:

Microorganism		Zone Diameter (mm)
		tetracycline	doxycycline
Escherichia coli	ATCC 25922	18-25	18-24
Haemophilus influenzaea	ATCC 49247	14-22	—
Neisseria gonorrhoeaeb	ATCC 49226	30-42	—
Staphylococcus aureus	ATCC 25923	24-30	23-29
Streptococcus pneumoniaec	ATCC 49619	27-31	—
a Range applicable only to tests performed by disk diffusion method using a 30 mcg tetracycline-class disk and using Haemophilus Test Medium (HTM). 2,3 b Range applicable only to tests performed by disk diffusion method using a 30 mcg tetracycline-class disk and using GC agar base with 1% defined growth supplement. 2,3 c Range applicable only to tests performed by disk diffusion method using a 30 mcg tetracycline-class disk and using Mueller-Hinton agar with 5% defibrinated sheep blood and incubated with 5% CO2.2,3

Anaerobic Techniques

For anaerobic bacteria, the susceptibility to tetracycline as MIC’s can be determined by standardized test methods.⁴ The MIC values obtained should be interpreted according to the following criteria:

MIC (mcg/mL)	Interpretation
> 4	Susceptible (S)
8	Intermediate (I)
< 16	Resistant (R)

Interpretation is identical to that stated above for results using dilution techniques.

As with other susceptibility techniques, the use of laboratory control microorganisms is required to control the technical aspects of the laboratory standardized procedures. Standardized tetracycline powder should provide the following MIC values:

Microorganism		MIC (mcg/mL)
Bacteroides fragilisa	ATCC 25285	0.12-0.5
Bacteroides thetaiotaomicrona	ATCC 29741	8-32
a Range applicable only to tests performed by the reference agar dilution method.

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.

REFERENCES

1. M7-A7. Methods for dilution antimicrobial susceptibility tests for bacteria that grow aerobically; Approved standard – 7th edition. Clinical and Laboratory Standards Institute (Formerly NCCLS), Wayne, PA; 2006

2. M2-A9. Performance standards for antimicrobial disk susceptibility Tests; Approved standard – 9^th edition. Clinical and Laboratory Standards Institute (Formerly NCCLS), Wayne, PA; 2006.

3. M100-S17. Performance standards for antimicrobial susceptibility testing; 17th informational supplement. Clinical and Laboratory Standards Institute (Formerly NCCLS), Wayne, PA; 2007.

4. M11-A7. Methods for antimicrobial susceptibility testing of anaerobic bacteria; Approved standard – 7^th edition.Clinical and Laboratory Standards Institute (Formerly NCCLS), Wayne, PA; 2007.