Back to Antimicrobial Agents

Hyclate/Hydrochloride (used in the injectable form, tablets and capsules)
Monohydrate (used in oral powder for reconstitution)
Calcium(used in oral syrup form)

Brands

Vibramycin; Vibra Tabs
Vibaravenos Tetracycline (long acting injectable form of Doxycycline).

Availability

Capsules: 50 mg & 100 mg
Suspension as 5 mg/mL in 60mL bottles
Powder for injection in 100 mg & 200 mg vials.

Pharmacology

Doxycycline is a semi-synthetic tetracycline derived from oxytetracycline. It is seen as a hydrochloride in injectable or oral form, and monohydrate as an oral powder that is reconstituted.

Being a part of the class of tetracyclines it generally acts as bacteriostatic, inhibiting protein synthesis of susceptible organisms. Doxycycline is slowly and much better absorbed in the GI tract when taken orally than are other tetracyclines, and blood levels are sustained longer.

Doxycycline is more lipid soluble and penetrates body tissues and fluids better than other tetracyclines. The drug has a longer half life, and better central nervous system penetration than other tetracyclines, making it a preferred drug choice of the tetracyclines in small animals.
*Note: animal studies indicate that the tetracyclines cross the placenta and penetrate fetal tissue, as well as being excreted in breast milk. It is recommended that it not be given in pregnancy or during lactation.

Doxycycline is uniquely eliminated through the GI tract and excreted primarily in the feces in an inactive form, and therefore does not adversely affect intestinal flora making it less likely to cause diarrhea. It is also excreted through the kidneys to a lesser extent than other tetracyclines, making it a drug of choice where there is a history of renal insufficiency.

Indications

Indicated for susceptiple upper and lower respiratory infection, soft tissue infection, and urinary tract infection resulting from Gram-negative bacteria.

Principally used in the treatment of infections caused by mycoplasma, spirochetes, chlamydia and rickettsia. Doxycycline can be used against some of the Gram-positive strains of staphylococcus and streptococci. It can be used simultaneously with enrofloxacin (Baytril), or azithromycin (Zithromax), or in addition with nebulized treatments of gentamicin and or albuterol.

Drug Interactions or Contraindications

Doxycycline has a decreased effect when given with antiacids that contain aluminum, calcium, zinc, or magnesium, or with iron containing preparations (example: multivitamins).

Bacteriostatic tetracycline drugs may interfere with the bactericidal effect of the penicillins, cephalosporins, and the aminoglycosides. However, there continues to be discussion regarding whether this interaction is clinically significant. (Veterinary Drug Handbook, Third Edition)

Increases levels/toxicity of oral digoxin.

Can retard fetal skeletal development. Do not use in very young or pregnant animals.

Adverse Reactions

Blood:   neutropenia, eosinophilia

CNS:   increased intracranial pressure

GI:  diarrhea

Skin:   phlebitis, itching, abscess from injectable

Other:   hepatotoxicity

Dosage Recommendations

2.5 mg/kg , PO , q12hrs, 14 to 30 days  ^{2  1}
5 mg/kg , PO , q12hrs, 14 to 30 days when used in pneumonia ¹

or

2.5 mg/lb , PO , BID (as recommended on RMCA Drug Chart) ⁴

or

100 mg capsule in 4mL water/fresh daily = .10mL/lb for 14 to 30 days (as recommended on RMCA Drug Chart) ⁴

or

2.5mg/lb to 5mg/lb BID  ³

or

Long acting injectable Vibaravenos: 70 mg/kg , SQ or IM ; once every 7 days  (as derived from ⁶; and as recommended by Animal Medical Center Manhattan).

or

Long acting injectable Vibaravenos: 70 mg/kg to 100 mg/kg, SQ or IM ; once every 7 days  ²⁶

Doxycycline in Treatment Regimen

The following dosage guideline for use of doxycycline in rats with early or mild URI suspected to have Mycoplasma as the pathogen, is recommended by Dr. Michael Hutchinson, DVM; Animal General, Cranberry Township, PA. ¹⁸, and is based on his experience treating rats and current literature:

Doxycycline 5 mg/kg ,PO (oral), BID for 10-30 days.

If not responding in reasonable time frame: Give along with enrofloxacin.

For serious and advanced lung infection continue doxycycline along with enrofloxacin and add nebulized treatments with gentocin and albuterol. In addition include dexamethasone in the treatment regimen.

For treatment regimen recommended by Dr. Hutchinson, see articles Mycoplasma or Pneumonia in the Health section of the Rat Guide. Also see individual monographs for more information on the above drugs in the Medication section of the Rat Guide.

*Note: In rats with respiratory illness, where the suspected pathogen is believed to be mycoplasma, the use of doxycycline in combination with enrofloxacin has been found to be effective at controlling clinical signs of illness. ¹⁸

Considerations

• Doxycycline may be given with food. Reports indicate that the drug appears to be only 20% hindered by the intake of food or dairy and is not deemed clinically significant. ⁶

  However, absorption of doxycycline is impaired by calcium, magnesium, and iron containing preparations. It is recommended they be given two hours before or after giving doxycyline.

• Although the manufacturer states that it does not affect the GI flora it is recommended that a probiotic containing lactobacillus be given, such as Bene-Bac, if the drug is used in conjunction with other antibiotics that adversely affect normal GI flora.
• Reconstituted monohydrate oral suspension in water can be stored at room temperature for 14 days.
• If mixing capsules in water, stabilty ranges from 12 to 48 hours. It is advisable to mix fresh daily, although new 2002 literature indicates that it remains stable for 14 days if refrigerated.
• Powder if stored in tightly closed container is stable for up to one year.
• Reconstituted Doxycycline Hyclate/Hydrochloride, and long acting Vibaravenos should be refrigerated and kept for 72 hours following reconstitution.

Reference

• Doxycycline. (n.d.). Retrieved December 12, 2008, from www.ashp.org/s_ashp/docs/files/practice_and_policy/doxycycline.pdf.
• Vibramycin (doxycycline calcium, doxycycline hyclate, doxycycline monohydrate) U.S. Physician Prescribing Information. (n.d.). Retrieved December 12, 2008, from http://media.pfizer.com/files/products/uspi_vibramycin_vibra-tabs.pdf.

Posted on June 23, 2003, 14:40, Last updated on April 11, 2010, 16:30 | Antimicrobial Agents