Update on Lyme disease
by Bill at 6/08/2004 01:24:00 PM
Just browsing the Sanford Guide to antimicrobial treatment between appointments yesterday and came across some tick bite regiments of interest. A sigle dose of 200mg of Doxyclycline (taken with food) can be used after a tick bite; particularly a nymphal partially engorged deer tick bite, in an endemic area (read, rural Pennsylvania) can be used as post exposure prophylaxis to prevent the develope of Lyme disease. In one study (NEJM 345:79 & 133, 2001.) erythema migrans, a sign of Lyme, occured in 3% of the control group after documented tick bite and 0.4% of Doxycycline group.
Thanks for the info. So should I ask my doctor for a doxycycline prescription? Maybe I could order some online.
Online, it's $40 for 30 100mg capsules (with a free online doctor "consultation"). If I buy veterinary grade doxycycline (is there any difference?) it's only $12.
Oh well. They say that it's the tick you don't find that gets you, anyway.
I have no idea if veterinary grade doxy is equivalent, my gut instincts tell me it probably is, all check online today for more info. I would ask your doctor (or PA) what they know about post exposure prophylaxis, as they work in an endemic area.
found this on Up To Date, can't do a link as it is a pay site, still looking into veterinary grade doxycycline.
Immediate antibiotic prophylaxis — One randomized, double-blind trial of 482 patients residing in an endemic area from whom Ixodes scapularis ticks had been removed within 72 hours found that doxycycline (200 mg PO as a single dose) was effective in preventing Lyme disease (0.4 versus 3.2 percent for placebo) [1]. Doxycycline produced more adverse effects, especially nausea and vomiting than placebo.
However, most studies of immediate antibiotic treatment after tick bite have not shown significant benefits with this approach. A meta-analysis evaluated three prospective, randomized, double-blind trials in which antibiotic prophylaxis (eg, ampicillin) or placebo was administered to more than 600 individuals following an Ixodes tick bite in areas endemic for Lyme disease [2]. The average rate of infection in those receiving placebo was 1.4 percent compared to no cases of Lyme disease in those receiving antibiotic prophylaxis; this difference was not statistically significant. It was estimated that only one case of Lyme disease would be prevented for every 83 individuals given amoxicillin prophylaxis. However, for every single case of Lyme disease prevented by amoxicillin, a drug-induced rash would be expected in eight, and a life-threatening reaction in one of the 83 people receiving the antibiotic.
The meta-analysis considered all comers with Ixodes scapularis bites [2]. If a high-risk group could be identified in whom the odds of developing Lyme disease were higher, the benefits of prophylaxis may be shifted in a more positive direction. The duration of tick attachment is one factor which may identify a high-risk group. Entomologists identified the ticks in the prophylaxis study cited above and found that nymphal ticks were more likely than adult female ticks to transmit Lyme disease (5.6 versus 0 percent); partially engorged nymphal ticks appeared to be the most likely to transmit (9.9 versus 0 percent for flat nymphal ticks) [1].
A flat (ie, unengorged with blood) tick has not yet taken its blood meal. It is only well after the start of the blood meal, perhaps 24 or more hours after initial attachment, that B. burgdorferi is spread from the tick. While the tick's gut is empty, B. burgdorferi is found on the inner aspect of the mid-gut. When the tick feeds, blood enters the mid-gut and the B. burgdorferi changes its coating proteins, escapes the mid-gut and ultimately gets to the salivary glands. As the tick fills up with blood, it seeks to rid itself of the excess water (blood is composed of approximately 50 percent water) by salivation back into the wound from which the blood was extracted. Along with the water goes the organism and this is how B. burgdorferi enters the host. The process takes many hours to complete. Thus, a flat/unengorged tick will in all likelihood not have spread the infection.
There is reason to believe that the likelihood of acquiring Lyme disease is higher if the tick removed is engorged (ie, the tick was attached longer, had taken a blood meal and the B. burgdorferi had entered the host). In one study, the risk of getting Lyme disease from a firmly attached but unengorged tick was only about 1 percent in an area in which 15 percent the ticks were infected [3]. In another series, the incidence of Lyme disease was significantly higher when the duration of attachment was at least 72 hours: 3 of 15 such cases (20 percent) developed Lyme disease compared to 1 of 94 (1.1 percent) in whom the tick was attached for less than 72 hours [4].
In a cost-benefit analysis of antibiotic prophylaxis for Lyme disease for tick bites, it was found that prophylaxis would be warranted if the incidence of Lyme disease following tick bite were to be 3.6 percent [5]. Thus, removal of an engorged Ixodes tick suggests that prophylaxis may be indicated.
1) Well, I would say not to worry about the vet grade doxy, unless you are just curious. I was mostly kidding, and I think I would still need to get my vet to give my dog a prescription before I could buy it.
2) That part about Lyme disease bacteria being spread because the tick basically spits back into your blood stream makes me hate ticks even more. Drinking my blood and spitting up in me - the nerve!
3) I think it is common wisdom around here that if you find an engorged tick on you, you go see the doctor after removing it. I think that most physicans in this area will prescribe antibiotics even if there are no symptoms of Lyme (e.g. the bullseye rash, fever).
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