NR 566 Week 5 Lyme Disease Pregnancy Case Analysis Example

Case Analysis: Erythema Migrans at 18 Weeks of Pregnancy, Why Doxycycline Steps Aside, Why Amoxicillin Takes Its Place and What Leaving Lyme Disease Untreated Would Cost

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College of Nursing, Chamberlain University

NR 566: Advanced Pharmacology for Care of the Family

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Month Day, Year

Case Analysis: Erythema Migrans at 18 Weeks of Pregnancy, Why Doxycycline Steps Aside, Why Amoxicillin Takes Its Place and What Leaving Lyme Disease Untreated Would Cost

Gestational Age Up Front

The patient is the same pregnant member of the household, now at 18 weeks and 2 days by the 12-week ultrasound. Exposure risk depends on timing, so it is stated first. Organ formation is complete; the second trimester is the period when drugs that affect bone and tooth development, or fetal kidney function, carry their particular concerns.

The Case

Ten days after a weekend camping trip in northern Wisconsin, the patient noticed an expanding red patch on the back of the left thigh. It is now 9 cm across, warm, painless and slightly clearer in the center. There is mild fatigue and a headache but no fever, joint swelling, facial weakness, palpitations or neck stiffness. The patient remembers removing a small tick two days into the trip. Examination shows a single erythema migrans lesion and no other findings; heart rate is regular at 84. The diagnosis of early localized Lyme disease is clinical in this setting, and serologic testing is not needed before treatment, because antibodies often have not yet developed at this stage (Lantos et al., 2021).

Why the Usual Agent Is Out

For a nonpregnant adult with erythema migrans, doxycycline 100 mg twice daily for 10 days is the standard first choice, because it also covers anaplasmosis, which the same tick can transmit (Lantos et al., 2021). In pregnancy, doxycycline is generally avoided. Tetracyclines bind calcium in developing bone and teeth, and older tetracycline formulations were linked to tooth discoloration and, rarely, to maternal liver toxicity in pregnancy. More recent observational data on short doxycycline courses are reassuring, but guidance for Lyme disease still prefers alternatives during pregnancy when an effective one exists (Lantos et al., 2021).

The paper does not reason from the old letter categories. Since the pregnancy and lactation labeling rule took effect in 2015, prescription drug labels describe risk in narrative sections on pregnancy, lactation and reproductive potential, summarizing human and animal data, rather than assigning a letter (U.S. Food and Drug Administration, 2014). The question here is therefore what is known about doxycycline in the second trimester, what the alternative is and how confident anyone can be. The honest answer is that the risk of a 10-day course is probably small, but an equally effective agent with a longer pregnancy record exists.

The Substitute, Defended

Amoxicillin 500 mg by mouth three times daily for 14 days. Dispense 42 capsules. No refills.

Amoxicillin is an accepted first-line treatment for erythema migrans and is the preferred choice in pregnancy (Lantos et al., 2021). Beta-lactams have extensive safety data across pregnancy. The patient's remote childhood rash with amoxicillin was assessed at the Week 3 visit as a low-risk, nonurticarial reaction, and cephalexin was then tolerated without problems, which supports giving amoxicillin now with a first dose observed in the clinic. If amoxicillin cannot be used, cefuroxime axetil 500 mg twice daily for 14 days is the next option; azithromycin is reserved for patients who cannot take either, because it is less effective for this infection.

The substitute brings its own costs. A three-times-daily schedule is harder than twice daily for a patient working warehouse shifts, so dose times are set to waking, mid-shift break and bedtime. Amoxicillin does not cover anaplasmosis; if fever, low white cell count or raised liver enzymes appear, that coinfection would need separate evaluation. Diarrhea is common.

The Cost of Treating Nothing

Leaving the infection untreated is not a neutral choice. Without treatment, Borrelia burgdorferi can disseminate within weeks, causing multiple skin lesions, facial nerve palsy, meningitis, carditis with heart block, and later arthritis (Lantos et al., 2021). Disseminated disease in pregnancy would require longer or intravenous therapy and carries its own risks to the patient. The evidence that untreated maternal Lyme disease harms the fetus is limited and inconsistent, but the clinical consequences for the pregnant patient alone justify treatment. Withholding antibiotics to avoid a small theoretical drug risk would expose the patient to a larger and better documented disease risk.

Lactation as Its Own Question

Lactation is a separate question, not a repeat of pregnancy. The patient plans to breastfeed. Amoxicillin passes into breast milk in small amounts and is considered compatible with breastfeeding, with occasional loose stools or diaper rash in the infant. If the patient were diagnosed after delivery while breastfeeding, a short doxycycline course would also be generally acceptable because absorption by the infant is limited, which is a different conclusion from the one reached in pregnancy. Stating this now helps the patient understand that a drug avoided in pregnancy is not automatically avoided later.

How Strong the Doxycycline Concern Really Is

The case for avoiding doxycycline in pregnancy rests largely on older tetracyclines, especially tetracycline itself given at high doses. A review of the available human data argued that doxycycline binds calcium less than older agents and that reports of tooth staining and maternal liver injury mostly involved those older drugs (Cross et al., 2016). That review is a reason not to panic if a patient has already taken a few doses of doxycycline before realizing they were pregnant. It is not a reason to choose doxycycline over amoxicillin when both are available, because amoxicillin is equally effective for erythema migrans and has the longer pregnancy record.

The Conversation

The patient asks whether the tick bite has harmed the baby. The answer given: early treatment of the rash is the most important step for both of them, the chosen antibiotic has a long safety record in pregnancy, and there is no recommendation to change prenatal care because of a treated early infection. The patient is told to take one capsule three times a day for 14 days, to finish the course and to call for fever, a new rash, facial drooping, palpitations, fainting or severe headache. The obstetric provider receives a note with the diagnosis, the drug and its start date.

Follow-Up

A telephone check at one week confirms that the rash is fading and that doses are being taken. The lesion should resolve within a few weeks; a persistent rash or new symptoms prompts a visit. The patient is counseled on tick prevention for the rest of the pregnancy: permethrin-treated clothing, repellent with an ingredient registered for use in pregnancy, and daily tick checks after time outdoors.

References

Cross, R., Ling, C., Day, N. P. J., McGready, R., & Paris, D. H. (2016). Revisiting doxycycline in pregnancy and early childhood: Time to rebuild its reputation? Expert Opinion on Drug Safety, 15(3), 367-382. https://doi.org/10.1517/14740338.2016.1133584

Lantos, P. M., Rumbaugh, J., Bockenstedt, L. K., Falck-Ytter, Y. T., Aguero-Rosenfeld, M. E., Auwaerter, P. G., Baldwin, K., Bannuru, R. R., Belani, K. K., Bowie, W. R., Branda, J. A., Clifford, D. B., DiMario, F. J., Halperin, J. J., Krause, P. J., Lavergne, V., Liang, M. H., Meissner, H. C., Nigrovic, L. E., . . . Zemel, L. S. (2021). Clinical practice guidelines by the Infectious Diseases Society of America (IDSA), American Academy of Neurology (AAN), and American College of Rheumatology (ACR): 2020 guidelines for the prevention, diagnosis and treatment of Lyme disease. Clinical Infectious Diseases, 72(1), e1-e48. https://doi.org/10.1093/cid/ciaa1215

U.S. Food and Drug Administration. (2014). Content and format of labeling for human prescription drug and biological products; requirements for pregnancy and lactation labeling (Final rule, 79 FR 72063). https://www.federalregister.gov/documents/2014/12/04/2014-28241/content-and-format-of-labeling-for-human-prescription-drug-and-biological-products-requirements-for