Minocin (Minocycline Hydrochloride) - Description and Clinical Pharmacology

To reduce the development of drug-resistant bacteria and maintain the effectiveness of MINOCIN^® (minocycline hydrochloride) Pellet-Filled Capsules and other antibacterial drugs, MINOCIN^® (minocycline hydrochloride) Pellet-Filled Capsules should be used only to treat or prevent infections that are proven or strongly suspected to be caused by bacteria.

DESCRIPTION

MINOCIN^® minocycline hydrochloride, is a semisynthetic derivative of tetracycline, 4,7-Bis(dimethylamino)-1,4,4a,5,5a,6,11,12a-octahydro-3,10,12,12a-tetrahydroxy-1,11-dioxo-2-naphthacenecarboxamide monohydrochloride.

Its structural formula is:

MINOCIN^® Pellet-Filled Capsules for oral administration contain pellets of minocycline HCl equivalent to 50 mg or 100 mg of minocycline in microcrystalline cellulose.

The capsule shells contain the following inactive ingredients: Blue 1, Gelatin, Titanium Dioxide and Yellow 10. The 50 mg capsule shells also contain Black and Yellow Iron Oxides.

CLINICAL PHARMACOLOGY

Following a single dose of two MINOCIN^® 100 mg pellet-filled capsules administered to 18 normal fasting adult volunteers, maximum serum concentrations were attained in 1 to 4 hours (average 2.1 hours) and ranged from 2.1 to 5.1 µg/mL (average 3.5 µg/mL). The serum half-life in the normal volunteers ranged from 11.1 to 22.1 hours (average 15.5 hours).

When MINOCIN^® Pellet-Filled Capsules were given concomitantly with a high-fat meal, which included dairy products, the extent of absorption of MINOCIN^® Pellet-Filled Capsules was unchanged compared to dosing under fasting conditions.  The mean T_max was delayed by one hour when administered with food, compared to dosing under fasting conditions. MINOCIN^®   Pellet-Filled Capsules may be administered with or without food.

In previous studies with other minocycline dosage forms, the minocycline serum half-life ranged from 11 to 16 hours in 7 patients with hepatic dysfunction, and from 18 to 69 hours in 5 patients with renal dysfunction. The urinary and fecal recovery of minocycline when administered to 12 normal volunteers was one-half to one-third that of other tetracyclines.

Microbiology

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

Minocycline 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 gram-positive microorganisms have been shown to be resistant to tetracyclines, culture and susceptibility testing are especially recommended. Tetracycline antibiotics should not be used for streptococcal diseases unless the organism has been demonstrated to be susceptible. Tetracyclines are not the drug of choice in the treatment of any type of staphylococcal infection.

Bacillus anthracis ¹

Listeria monocytogenes ¹

Staphylococcus aureus

Streptococcus pneumoniae

AEROBIC GRAM-NEGATIVE MICROORGANISMS

Bartonella bacilliformis

Brucella species

Calymmatobacterium granulomatis

Campylobacter fetus

Francisella tularensis

Haemophilus ducreyi

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 tests are especially recommended.

Acinetobacter species

Enterobacter aerogenes

Escherichia coli

Haemophilus influenzae

Klebsiella species

Neisseria gonorrhoeae ¹

Neisseria meningitidis ¹

Shigella species

“OTHER” MICROORGANISMS

Actinomyces species¹

Borrelia recurrentis

Chlamydia psittaci

Chlamydia trachomatis

Clostridium species¹

Entamoeba species

Fusobacterium nucleatum subspecies fusiforme ¹

Mycobacterium marinum

Mycoplasma pneumoniae

Propionibacterium acnes

Rickettsiae

Treponema pallidum subspecies pallidum ¹

Treponema pallidum subspecies pertenue ¹

Ureaplasma urealyticum

¹When penicillin is contraindicated, tetracyclines are alternative drugs in the treatment of infections caused by the cited microorganisms.

Susceptibility Tests

Susceptibility testing should be performed with tetracycline since it predicts susceptibility to minocycline. However, certain organisms (eg, some staphyloccocci, and Acinetobacter species) may be more susceptible to minocycline and doxycycline than to tetracycline.

Dilution techniques:

Quantitative methods are used to determine antimicrobial minimal inhibitory concentrations (MICs). These MICs provide estimates of the susceptibility of bacteria to antimicrobial compounds. The MICs should be determined using a standardized procedure. Standardized procedures are based on a dilution method ^{Ref1, Ref3} (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 testing aerobic gram-negative microorganisms (Enterobacteriaceae), Acinetobacter species and Staphylococcus aureus:

MIC (µg/mL)	Interpretation
≤4.0	Susceptible (S)
8.0	Intermediate (I)
≥16.0	Resistant (R)

For testing Haemophilus influenzae² and Streptococcus pneumonia³ :

MIC (µg/mL)	Interpretation
≤2.0	Susceptible (S)
4.0	Intermediate (I)
≥8.0	Resistant (R)

² These interpretative standards are applicable only to broth microdilution susceptibility testing with Haemophilus influenzae using Haemophilus Test Medium.^Ref1 

³ These interpretative standards are applicable only to broth microdilution susceptibility testing using cation-adjusted Muller-Hinton broth with 2-5% lysed horse blood.¹

For testing Neisseria gonorrhoeae⁴ :

MIC (µg/mL)	Interpretation
≤0.25	Susceptible (S)
0.5-1.0	Intermediate (I)
≥2.0	Resistant (R)

⁴ These interpretative standards are applicable only to agar dilution susceptibility testing using GC agar base and 1% defined growth supplements.^Ref1

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 which 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 therapy 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 Range (µg/mL)
Escherichia coli ATCC 25922	0.5-2.0
Enterococcus faecalis ATCC 29212	8.0-32.0
Staphylococcus aureus ATCC 25923	0.25-1.0
Haemophilus influenzae ATCC 49247	4.0-32.0
Streptococcus pneumoniae ATCC 49619	0.12-0.5
Neisseria gonorrhoeae ATCC 49226	0.25-1.0

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 ^{Ref2, Ref3} requires the use of standardized inoculum concentrations. This procedure uses paper disks impregnated with 30 µg tetracycline (class disk) or 30 µg minocycline to test the susceptibility of microorganisms to minocycline.

Reports from the laboratory providing results of the standard single-disk susceptibility test with a 30-µg tetracycline or minocycline disk should be interpreted according to the following criteria:

For testing aerobic gram-negative microorganisms (Enterobacteriaceae), Acinetobacter species and Staphylococcus aureus:

Zone Diameter (mm)	Interpretation
≥19	Susceptible (S)
15-18	Intermediate (I)
≤14	Resistant (R)

For testing Haemophilus influenzae ⁵:

Zone Diameter (mm)	Interpretation
≥29	Susceptible (S)
26-28	Intermediate (I)
≤25	Resistant (R)

⁵ These zone diameter standards are applicable only to susceptibility testing with Haemophilus influenzae using Haemophilus Test Medium and a 30-µg tetracycline disk. ^Ref2

For testing Neisseria gonorrhoeae ⁶:

Zone Diameter (mm)	Interpretation
≥38	Susceptible (S)
31-37	Intermediate (I)
≤30	Resistant (R)

⁶ These interpretative standards are applicable only to disk diffusion testing using GC agar and 1% growth supplements, and a 30-µg tetracycline disk. ^Ref2 For testing Streptococcus pneumoniae ⁷:

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

⁷ These interpretative standards are applicable only to disk diffusion testing using Muller-Hinton agar adjusted with 5% sheep blood and a 30-µg tetracycline disk. ^Ref2

For testing Vibrio cholerae ⁸:

Zone Diameter (mm)	Interpretation
≥19	Susceptible (S)
15-18	Intermediate (I)
≤14	Resistant (R)

⁸ These interpretative standards are applicable only to disk diffusion testing performed with a 30-µg tetracycline disk.^Ref2 

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.

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-µg tetracycline or minocycline disk should provide the following zone diameters in these laboratory test quality control strains:

Microorganism	Zone Diameter Range (mm)
	Tetracycline	Minocycline
Escherichia coli ATCC 25922	18-25	19-25
Staphylococcus aureus ATCC 25923	24-30	25-30
Haemophilus influenzae ATCC 49247	14-22	–
Neisseria gonorrhoeae ATCC 49226	30-42	–
Streptococcus pneumoniae ATCC 49619	27-31	–

ANIMAL PHARMACOLOGY AND TOXICOLOGY

MINOCIN^® minocycline HCl has been observed to cause a dark discoloration of the thyroid in experimental animals (rats, minipigs, dogs, and monkeys). In the rat, chronic treatment with minocycline hydrochloride has resulted in goiter accompanied by elevated radioactive iodine uptake and evidence of thyroid tumor production. Minocycline hydrochloride has also been found to produce thyroid hyperplasia in rats and dogs.