Minocin (Minocycline HCl)


Minocin is a tetracycline antibiotic used to treat various bacterial infections, such as urinary tract infections, severe acne, tick fever, chlamydia, gonorrhea, etc.

Action And Clinical Pharmacology

Minocycline is a tetracycline with antibacterial activity against some Gram-negative and Gram-positive organisms. The action is primarily bacteriostatic and it is thought to exert its antimicrobial effect by the inhibition of protein synthesis.

Indications And Clinical Uses

  • Infections due to susceptible strains of the designated organisms: gallbladder infections caused by E. coli;
  • Urinary tract infections: cystitis, gonorrhea, pyelonephritis caused by E. coli, Proteus species, Klebsiella species, E. aerogenes, N. gonorrhea. When penicillin is contraindicated, minocycline may be employed as an alternative drug in the treatment of anal and pharyngeal gonorrhea and syphilis;
  • Skin and soft tissue infections: abscess, cellulitis, furunculosis, impetigo and pyoderma caused by: S. epidermidis, S. aureus, S. pyogenes, Proteus species, E. coli. Although tetracyclines are not the drugs of choice in any staphylococcal or streptococcal infection, minocycline could be useful in circumstances where these organisms are shown to be resistant to other agents but sensitive to minocycline. Bacterial evaluation of clinical cases involving proteus suggests a relatively lower success rate may be expected where these organisms are concerned;
  • Respiratory tract infections: Bronchitis, pharyngitis, pneumonia, bronchopneumonia, sinusitis and tonsillitis caused by: H. influenzae, Klebsiella species, Enterobacter species. Tetracyclines should not be prescribed for acute throat infections.


  • Pseudotumor cerebri;
  • Diarrhea from an infection with Clostridium difficile bacteria,;
  • High fluid pressure in the brain;
  • Decreased kidney function;
  • Liver problems;
  • Problems with food passing through the esophagus;
  • Abnormally high levels of nitrogen-containing compounds in your blood;
  • Allergies to tigecycline or tetracyclines;
  • Pregnancy.

Manufacturers’ Warnings In Clinical States

Newborns, Infants and Children: The use of tetracyclines, including minocycline, during tooth development (last half of pregnancy, infancy and childhood under the age of 13 years) has been shown to cause permanent tooth discoloration (yellow-grey-brown). This is more common during long-term use, but has been observed following short-term courses. Enamel hypoplasia has also been reported. All tetracyclines including minocycline 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 6 hours. This appeared to be reversible when the drug was discontinued. Minocycline should not be used in such patients unless other drugs are ineffective or are contraindicated.

It is advisable to avoid giving minocycline in conjunction with penicillin since some bacteriostatic drugs may interfere with the bactericidal action of penicillin.

Minocycline should not be used for the treatment of streptococcal diseases unless the organism is demonstrated to be sensitive, since most streptococci have been found to be resistant to tetracycline drugs. If it is deemed necessary that infection due to Group A beta-hemolytic streptococci be treated with minocycline, then such treatment should be continued for at least 10 days.

In the presence of significant renal impairment, usual oral doses may lead to excessive systemic accumulations of minocycline and possible liver toxicity. Under such conditions, lower than usual doses may be indicated. After initial therapy, and if therapy is prolonged, serum level determinations of the drug are advisable.

The anti-anabolic action of tetracyclines can also produce dose-related increases in BUN; consequently, in patients with significant renal impairment, elevated serum minocycline levels can lead to azotemia, hypophosphatemia and acidosis.

Renal failure, including interstitial nephritis has been reported rarely.

Minocycline is capable of aggravating the symptoms associated with lupus erythematosus. Therefore, caution should be taken when administering the drug to patients with this disease.

Minocycline has been shown to depress plasma prothrombin activity. Therefore, patients who are on anticoagulant therapy should be monitored regularly and may require downward adjustment of their anticoagulant dosage. Interference with vitamin K synthesis by microorganisms in the gut has been reported.

Cross-sensitization among the various tetracyclines is extremely common.

Pigmentation of skin, thyroid, bone and teeth have been reported occasionally in persons receiving minocycline usually for extended periods of time. The pigmentation may be irreversible.

Reduced efficacy and increased incidence of breakthrough bleeding has been suggested with concomitant use of tetracycline and oral contraceptive preparations.


The administration of minocycline to children under 13 years of age is not recommended.

Bulging fontanels have been reported in young infants following full therapeutic dosage of tetracyclines including minocycline. Pseudotumor cerebri has very rarely been reported in adults (see Adverse Effects).

Patients should be warned to avoid exposure to direct sunlight and/or ultraviolet light while under treatment with minocycline or other tetracycline drugs, and treatment should be discontinued at the first evidence of skin erythema or discomfort. Photosensitivity manifested by an exaggerated sunburn reaction has been observed in some individuals taking tetracyclines. Studies to date indicate that photosensitivity is rarely reported with minocycline.

Occupational Hazards: Patients treated with minocycline may suffer from headaches, light-headedness, dizziness or vertigo. Decreased hearing has been rarely reported in patients on minocycline. Administration in excess of the recommended dosage can increase the frequency and severity of these CNS symptoms. Patients should be cautioned about driving vehicles or using hazardous machinery while on drug therapy. These symptoms may disappear during therapy and usually disappear rapidly when the drug is discontinued.

As with other antibiotics, therapy may result in overgrowth of non-susceptible organisms (including fungi). If superinfection occurs, minocycline should be discontinued and appropriate therapy instituted.

The development of cross-resistance to many antibiotics can develop rapidly in several species of microorganisms. The clinician should bear this in mind if minocycline is not achieving expected results.

The frequency of resistance to minocycline in hemolytic streptococci is highest in strains from infections of the ear, wounds and skin. Culture and sensitivity studies should be performed whenever feasible and routinely in suspected streptoccal infections.

Since sensitivity reactions are more likely to occur in persons with a history of allergy, asthma, hay fever, or urticaria, minocycline should be used with caution in such individuals.

Before treating patients with gonorrhea, a darkfield examination should be made from any lesion suggestive of concurrent syphilis. Serological tests for syphilis should be repeated monthly for at least 4 months.

Minocycline should be used with caution in patients with hepatic dysfunction and in conjunction with alcohol or other hepatotoxic drugs.

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

Minocycline has been shown to depress plasma prothrombin activity. Therefore, patients who are on anticoagulant therapy should be monitored regularly and may require downward adjustment of their anticoagulant dosage. Interference with vitamin K synthesis by microorganisms in the gut has been reported.

Antacids containing aluminum, calcium or magnesium and oral iron preparations impair absorption and should not be given to patients taking oral minocycline.

Food and/or milk reduce the absorption of tetracycline. Minocycline is not affected to the same extent.

In a study by Leyden, the absorption of a single 100 mg dose of minocycline was inhibited by the ingestion of solid food by 13% (as measured by a reduction in mean serum concentration), and the absorption of a single 250 mg dose of tetracycline was inhibited by 46% when that antibiotic was administered with solid food. When administered with milk, the mean serum concentration of minocycline was reduced by 27% and that tetracycline, by 67%. The clinical significance of such declines in serum levels is not known.

Adverse Reactions

The following adverse reactions have been reported with the tetracycline analogues including minocycline:

  • CNS: increased intracranial pressure, light-headedness, dizziness or vertigo and, rarely, fainting spells have been reported with a variable but overall incidence of approximately 7% in patients treated. These symptoms usually disappear rapidly when the drug is discontinued. Headache, alone, has also been reported;
  • Gastrointestinal: anorexia, nausea, vomiting, diarrhea, stomatitis, glossitis, enterocolitis, pancreatitis, pruritus ani, constipation, dysphagia, inflammatory lesions (with monilial overgrowth) in the anogenital region, increases in liver enzymes, and rarely hepatitis and acute liver failure have been reported. Rare instances of esophagitis and esophageal ulcerations have been reported in patients taking the tetracycline-class antibiotics in capsule and tablet form. Most of these patients took the medication immediately before going to bed;
  • Teeth and bone: Dental staining (yellow-gray-brown) has been reported in children of mothers given tetracyclines, including minocycline, during the latter half of pregnancy, and in children given the drug during the neonatal period, infancy and childhood to age of 13 years. Enamel hypoplasia has also been reported. Discoloration of bones and teeth has been documented to occur rarely in adolescents and adults upon extended treatment. The effects may be irreversible. At present the mechanism of staining, although not completely elucidated, appears to be mediated by the formation of a stable iron complex;
  • Renal: Rise in BUN has been reported and is apparently dose-related. Increased excretion of nitrogen and sodium has also been reported. Renal failure, including interstitial nephritis has been reported rarely;
  • Skin: maculopapular and erythematous rashes. Rarely reported-exfoliative dermatitis, onycholysis, discoloration of the nails, pigmentation of the skin and mucous membrane, erythema multiforme, Stevens-Johnson syndrome. Lesions occurring on the glans penis have caused balanitis;
  • Hypersensitivity: urticaria, angioneurotic edema, polyarthralgia, anaphylaxis, anaphylactoid purpura, pericarditis and exacerbation of systemic lupus erythematosus;
  • Pseudotumor cerebri (benign intracranial hypertension) in adults has been associated with the use of tetracyclines. The usual clinical manifestations are headache and blurred vision. Bulging fontanels have been associated with the use of tetracyclines in infants. While both of these conditions and related symptoms usually resolve soon after discontinuation of the tetracycline, the possibility for permanent sequelae exists;
  • Other: elevated AST or ALT values, hepatic cholestasis, hemolytic anemia, neutropenia, thrombocytopenia and eosinophilia. When given over prolonged periods, minocycline, like other tetracyclines, has been reported to produce brown-black microscopic discoloration of the thyroid gland. Abnormalities of thyroid function have not been shown to date. If adverse reactions or idiosyncrasy occur, the administration should be discontinued and appropriate alternate therapy instituted.

Symptoms And Treatment Of Overdose

Symptoms: dizziness, nausea, vomiting, abdominal pain, intestinal hemorrhage, hypotension, lethargy, coma, acidosis, azotemia without a concomitant rise in creatinine.

Treatment: Specific antidote: None. General antidotes: Antacids (e.g., calcium carbonate or lactate, milk of magnesia, aluminum hydroxide) which form relatively insoluble complexes with minocycline. (Calcium Solution 5%: 50 g calcium carbonate or lactate dissolved in 1 000 mL water, yields a 5% solution). Gastric lavage, if necessary.

If you have any severe overdose symptoms, seek emergency medical attention or call the Poison Help line at 1-800-222-1222.

Dosage And Administration

Follow all directions given in the instructions. Use the medicine exactly as directed by your health care provider.

Take this medicine with a full glass of water, with or without food.

Do not break, crush, or chew a capsule/tablet. Swallow it whole.

You need to complete the prescribed treatment period, even if you feel better. If you interrupt the treatment course,  this can increase your risk of infection that is resistant to antibiotic.

Children (13 years and over): The usual dosage is 4 mg/kg initially followed by 2 mg/kg every 12 hours. Tetracyclines are not recommended in children under 13 years of age;

Adults: The usual oral dosage is 100 or 200 mg initially, followed by 100 mg every 12 hours. Alternatively, if more frequent doses are preferred, 2 or 4 doses of 50 mg may be given initially, followed by one 50 mg dose every 6 hours. Therapy should be continued for 1 or 2 days beyond the time when characteristic symptoms or fever have subsided.

For treatment of syphilis, therapy should be administered over a period of 10 or 15 days. Close follow-up, including laboratory tests, is recommended.

Concomitant Therapy: Antacids containing aluminum, calcium or magnesium and/or iron preparations impair absorption and should not be given to patients taking minocycline.

How long does it take for Minocin to clear acne?

The medicine can take about 6 to 8 weeks to start working, so your symptoms won’t improve right away. Even if you do not feel any better, you must keep taking this antibiotic as directed by your health care provider.

Your health care provider will likely prescribe this medicine for at least 3 months. If your acne improves quickly, they might reduce your dose or prescribe an alternative – a topical antibiotic.

Missed Dose

If you miss a dose of minocycline, take it as soon as you realize your mistake. If it is almost the time to take the next dose, skip the missed dose. Take your next dose at your usual time. Do not double the dose to make up for the missed dose.

Pregnancy and Lactation

Tetracyclines, including minocycline, are not recommended during pregnancy and lactation because of possible adverse effects on developing bones and teeth of the fetus and neonate. 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 embryotoxicity has also been noted in animals treated early in pregnancy. The safety for use during pregnancy has not been established.

Tetracyclines, including minocycline, are excreted in the milk of lactating women.

Can Minocin interact with other drugs?

Tell your health care provider about all your other drugs, vitamins and herbs, especially:

  • penicillin antibiotics such as amoxicillin, ampicillin, dicloxacillin, penicillin, ticarcillin, oxacillin, and others;
  • ergot medicines such as dihydroergotamine, ergonovine, methylergonovine, ergotamine;
  • isotretinoin;
  • blood thinners such as warfarin, Coumadin, Jantoven.

This list is not complete.


Store at room temperature away from sunlight, heat and moisture. Do not store in the bathroom. Keep away from children and pets. Properly discard this antibiotic when it is expired or no longer needed. Consult your pharmacist or a waste disposal company.


IMPORTANT: This is a summary and does NOT have all possible information about this medicine. This information does not assure that this medicine is safe or appropriate for you. This information cannot be used as a substitute for medical advice. Consult your health care provider if you have any health condition. Always ask your health care provider for complete information about this medicine and your individual health needs.

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