Why Two Capsules Of Doxycycline Are Needed At Once For Lyme Prevention

In our latest question and answer, our pharmacist discusses why taking 200mg of doxycycline is not the same as taking two 100mg doses separately.


So, it's late at night, and I can't call the doctor until tomorrow. I am a 24-year-old Caucasian male with no allergies. I recently took amoxicillin-clavulanate for strep throat and take Vyvanse and Ritalin daily. Today, I was prescribed doxycycline to treat Lyme disease after being bitten by a tick that may have been carrying it without my knowledge for several days. The doctor instructed me to take two pills at once for the treatment to be effective. However, there was an error in the prescription, and I only received one pill. I am now experiencing symptoms such as a rash around the bite mark and tingling. Should I take the one pill now and get the other one tomorrow, or should I wait until I can take both at once?

Asked by Christ On Jun 02, 2023

Answered by
Medical Content Reviewed By HelloPharmacist Staff

Published Jun 02, 2023
Last updated Jul 18, 2024

Key points

  • For effective Lyme disease prophylaxis, it is recommended to take a single dose of 200 mg of doxycycline. This higher dose ensures an adequate concentration of the medication in the bloodstream to effectively combat any potential infection from the tick bite.
  • Taking a lower dose, such as 100 mg followed by another 100 mg later, may not achieve the desired therapeutic concentration needed to prevent the development of Lyme disease.


It's unfortunate that there was a prescription error and you only received one pill of doxycycline instead of the intended two.

According to clinical guidelines and the CDC (Centers for Disease Control), for Lyme disease prophylaxis in high-risk situations, the recommended dose of doxycycline is 200 mg as a single dose. Taking the full 200 mg dose helps ensure an adequate concentration of the medication in your bloodstream to effectively combat any potential infection from the tick bite. Taking 100 mg now and waiting to take the second 100 mg pill later may not provide the desired therapeutic concentration in your blood.

It is important to emphasize that taking 200mg of doxycycline at once is crucial here. Taking 100mg now, then 100mg later, is not the same.

Doxycycline Dose Is Important

Here's an analogy to highlight the importance of concentration.

Imagine you have a chocolate drink mix that requires two scoops of powder to make a flavorful beverage.

If you were to mistakenly put only one scoop of powder into a single glass, the resulting drink would taste weak and diluted.

Let's consider another, similar, scenario. Instead of pouring both scoops into one glass, you divide the powder evenly and put one scoop into two separate glasses. Despite the fact that you now have a total of two scoops distributed between the two glasses, each drink will still taste weak because the concentration of the chocolate powder in each glass is insufficient.

In this analogy, the chocolate drink mix represents the doxycycline medication, and each scoop of powder represents the recommended dose of 100 mg. Taking only one pill and waiting to take the second pill later would be akin to dividing the two scoops of powder between two glasses. While the total dosage may be the same, the concentration of the medication in your bloodstream may not reach the desired level needed for effective treatment.

While this analogy is simple, it does accurately represent the problem with not taking 200mg as one dose.

Additional Thoughts

Doxycycline is commonly used for the treatment of Lyme disease when it is diagnosed, but it can also be used for prophylaxis (prevention) after a tick bite in certain situations.

If your doctor determines you are at 'high-risk' for infection, taking doxycycline within 72 hours of the tick bite can help prevent the development of Lyme disease.

I recommend contacting your doctor as soon as possible to discuss the prescription error and the symptoms you are experiencing. They will provide you with the best course of action based on your specific situation.

In the meantime, you can also consider taking precautions such as cleaning the bite area with soap and water, applying an antiseptic, and keeping an eye out for any changes in symptoms. Remember, it's essential to consult with your doctor to receive appropriate advice and ensure your specific situation is properly addressed.

Final Words

Thanks for reaching out and please feel free to do so again anytime!


  • Lyme Disease, CDC
  • Single-Dose Doxycycline for the Prevention of Lyme Disease, NEJM

About the Pharmacist

Dr. Brian Staiger, PharmD

Dr. Brian has been practicing pharmacy for over 13 years and has wide-ranging experiences in many different areas of the profession. From retail, clinical, program development, and administrative responsibilities, he's your knowledgeable and go-to source for all your pharmacy and medication-related questions! Dr. Brian Staiger also has herbalist training and educational certificates in the field of medical ethnobotany. Feel free to send him an email at [email protected]! You can also connect with Dr. Brian Staiger on LinkedIn.

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