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  Discussion on Lyme disease multiplex question - and minocycline?
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Member:
arary

Posted on Friday, Sep 12, 2014 - 9:42 pm:

I'm actually writing to get some advice for a friend's horse that I help out with. About 2-3 months ago, the mare started acting resistant to work, didn't want to trot but would take off and buck in the canter. Tried to just ride through it (thinking maybe training problem at first) resulted in a horse who looked noticeable stiff and tight over the topline on the lunge and no better under saddle. Mare also became short in the LH at the trot when tracking left. A month off brought slight improvement.

A full lameness exam with a well respected sports medicine vet familiar with the horse revealed moderate soreness on palpation in the SI area, particularly on the left. She was sound on the straight but displayed shortened anterior phase of the stride when circling left. Flexions very mildly positive in all 4 legs, but to such a slight degree that most vets would not even catch it and consistent with results from previous exams when the horse was going sound and performing well.

Hocks injected 3 months ago for regular maintenance and no other symptoms found. Back has no soreness. Saddle fit ruled out. Vet performed ultrasound guided injection of the SI (injected 4 places) and thought the horse should be fine. Horse back in training for 1 month now and seems more comfortable but still not right. She's happier under saddle but still starts out short on LH at trot and just doesn't feel right.

Trainer suggested Lyme test so we had trainer's vet pull blood, but we're having trouble interpreting the results (multiplex performed at Cornell). OspA 2457 (positive), OspC 1464 (positive), and OspF 760 (equivocal). According to lab results this indicates Lyme disease, but trainer's vet feels that elevated OspA is due to receiving Lyme vaccine and other results are so mildly positive that she is ruling out Lyme. However, we are certain no Lyme vaccine was given in past 2 years. Don't know what the previous owner may have given before that.

How long does the vaccine last? If she was given a Lyme vaccine 3 years ago, could that still cause elevated OspA levels? Would you consider treating for Lyme at this point? If we want to treat, trainer's vet said she would not recommend oxytet at this point because of danger of adverse reactions or catheter infections (esp since she doesn't believe it's really Lyme) but would write script for doxy or minocycline, which is her top choice.

Have a phone call in to regular vet but wanted to do research first since it may be days before she calls back. What is your interpretation of these Lyme results? Feelings on monocycline? Should we get a 2nd opinion to rule out orthopedic problems first? Money is an issue since a fortune was already spent on the last lameness exam and SI injections, so we want to spend it wisely. Better to spend $ on Lyme treatment and see how she responds, or 2nd lameness exam with new vet?
Moderator:
DrO

Posted on Saturday, Sep 13, 2014 - 5:02 pm:

Hello Ang,
The use of minocycline in horses has not been well studied but early results seem promising:

Equine Vet J. 2012 Jul;44(4):453-8.

Pharmacokinetics and distribution of minocycline in mature horses after oral administration of multiple doses and comparison with minimum inhibitory concentrations.

Schnabel LV1, Papich MG, Divers TJ, Altier C, Aprea MS, McCarrel TM, Fortier LA.

Minocycline holds great potential for use in horses not only for its antimicrobial effects but also for its anti-inflammatory and neuroprotective properties. However, there are no pharmacokinetic or safety data available regarding the use of oral minocycline in horses.

OBJECTIVES:

To determine pharmacokinetics, safety and penetration into plasma, synovial fluid, aqueous humour (AH) and cerebral spinal fluid (CSF) of minocycline after oral administration of multiple doses in horses and to determine the minimum inhibitory concentrations (MIC) of minocycline for equine pathogenic bacteria.

METHODS:

Six horses received minocycline (4 mg/kg bwt q. 12 h for 5 doses). Thirty-three blood and 9 synovial fluid samples were collected over 96 h. Aqueous humour and CSF samples were collected 1 h after the final dose. Minocycline concentrations were measured using high pressure liquid chromatography. The MIC values of minocycline for equine bacterial isolates were determined.

RESULTS:

At steady state, the mean ± s.d. peak concentration of minocycline in the plasma was 0.67 ± 0.26 µg/ml and the mean half-life was 11.48 ± 3.23 h. The highest trough synovial fluid minocycline concentration was 0.33 ± 0.12 µg/ml. The AH concentration of minocycline was 0.09 ± 0.03 µg/ml in normal eyes and 0.11 ± 0.04 µg/ml in blood aqueous barrier-disrupted eyes. The mean CSF concentration of minocycline was 0.38 ± 0.09 µg/ml. The MIC values were determined for 301 isolates. Minocycline concentrations were above the MIC(50) and MIC(90) for many gram-positive equine pathogens.

POTENTIAL RELEVANCE:

This study supports the use of orally administered minocycline at a dose of 4 mg/kg bwt every 12 h for the treatment of nonocular infections caused by susceptible (MIC ≤ 0.25 µg/ml) organisms in horses. Further studies are required to determine the dose that would be effective for the treatment of ocular infections.

DrO
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