Six Doxycycline Interactions that Affect Treatment

Six Doxycycline Interactions: Introduction

Tetracyclines are one of the oldest groups of antibiotics still in use today, although not all bacteria are sensitive to them. This twice-daily antibiotic can be an alternative to penicillin when contraindicated and is effective in rickettsial infections, sexually transmitted and respiratory tract infections, anthrax, or malaria prophylaxis. (1)

Doxycycline usage is affected by the interactions this antibiotic has with certain medications that result in an efficacy reduction. For example, antacids have a negative impact on doxycycline absorption. On the other hand, doxycycline reduces the clinical effect of oral contraceptives. This article explains the above and some other drug interactions. (1)

Keep reading to learn all reported doxycycline drug interactions to understand what measures should be taken in each case. In addition, find out the recommendations for its usage, contraindications, and side effects.

Doxycycline Interactions with Other Medications

Many medications interact with others when used together. Some of the interactions can change the efficacy or safety of the medicine.

Therefore, telling your doctor what medications you use before beginning a new treatment is essential. (2)

Below are listed interactions that doxycycline has with certain medications and the recommendations in each situation.

1. Penicillin

Doxycycline belongs to the tetracycline class of antibiotics. It has bacteriostatic activity and prevents the bacteria’s growth and spreading. Doxycycline works in a way that affects protein synthesis, which is important for bacterial spread and growth, the so-called bacteriostatic effect. (3)

Penicillin is an antibiotic representing another class of beta-lactam antibiotics. Penicillin, through its mechanism, makes bacteria unable to build cell walls. As a result, the bacteria’s wall becomes weak, the outside pressure pushes water into the cell, and the bacteria, in the end, die. This mechanism is called bactericidal. (4)

These two antibiotics have different mechanisms of action but interfere with each other. Doxycycline decreases the therapeutic efficacy of penicillin due to the antagonism that these two antibiotics have. Bacteriostatic antibiotics inhibit bacterial growth via nutrient limitation that often decreases the bactericidal effects of the other antibiotic. As a result, penicillin will not achieve the bacteria-killing effect. Even more, a study showed that 30% to 80% of bacterial cells treated with bactericidal-bacteriostatic drugs maintained cellular integrity and continued to divide after antibiotic exposure. Therefore, doxycycline and penicillin-based antibiotic (ampicillin, amoxicillin, or benzylpenicillin) are not recommended for concomitant use. (5-8)

2. Anticoagulant drugs

Anticoagulants, or blood thinners, are medications used to regulate blood clot formations. Blood clots are usually formed when there is an injury to stop bleeding. But, in some cases, blood clots are formed in other body parts like blood vessels or the heart and can cause heart attack, strokes, or blood flow blockage. In these cases, anticoagulants are used to stop clots from growing and prevent serious consequences. (9-10)

Prothrombin, a thrombin precursor, is a plasma protein produced in the liver. Prothrombin transforms into thrombin, which plays a crucial role in blood clot formation. The amount of thrombin formed by prothrombin is plasma prothrombin activity, which values range from 70% to 130%. Tetracyclines, including doxycycline, depress plasma prothrombin activity. (1, 11)

Before start using doxycycline, tell your doctor if you are using heparin, warfarin, dabigatran, rivaroxaban, or other anticoagulants. It may be necessary to adapt the dosage of your anticoagulant medication. (1)

3. Antacids

Antacids are medications that help with heartburn. They may contain aluminum, calcium, magnesium, bismuth subsalicylate, and iron-containing preparations that neutralize stomach acid. (12)

On the other hand, antacids decrease the absorption of doxycycline in the body. For this reason, the recommendation is to use antacids and supplements that contain aluminum, calcium, magnesium, bismuth subsalicylate, and iron two hours after you take doxycycline. (13)

4. Oral contraceptives

The notion that antibiotics make birth control pills less effective cannot be generalized to all antibiotics. However, in the case of doxycycline, it is accurate. It is another drug interaction of doxycycline you should take care of.

Doxycycline is an antibiotic that, while making pathogenic bacteria unable to spread and grow, at the same time affects other bacteria (microbiome) that live in the human body. The researchers suggest that doxycycline may affect estrobolome, a bacteria that lives in the gut. This bacteria produces the enzyme beta-glucuronidase, which transforms estrogens into active forms in healthy individuals. When the antibiotics disbalance microbiome and impact gut bacteria estrobolome, there is a lack of the enzyme, and estrogen will not become in an active form. (14)

Doxycycline impacts the contraceptives’ efficacy, so if taken together, the level of protection will not be as usual. If you take doxycycline for your bacterial infection, use other methods for pregnancy protection, and do not rely only on oral contraceptives that you take regularly. (1, 13)

5. Barbiturates

Barbiturates are medications used for the treatment of various diseases thanks to the sedative-hypnotic effect they have. They make patients feel relaxed or sleepy. Barbiturates can effectively treat seizure disorder, insomnia, preoperative anxiety, anesthesia, among other indications.

Barbiturates interact with many drugs, such as steroids, other antiepileptic drugs, and drugs for hepatitis C (15). Barbiturates but also phenytoin, and carbamazepine decrease the half-time of doxycycline. It means that doxycycline will be available in an effective amount in the body for a shorter time. As a consequence, the bacteriostatic effect will be reduced. (1)

6. Methoxyflurane

Methoxyflurane is an old medication used in anesthesia since 1960. Over the years, it has been shown that methoxyflurane possesses dose-dependent nephrotoxicity. Because of this, the manufacturer stopped its distribution in the U.S. However, in other countries, it is still available for use. (16-17)

For this reason, it is good to know that concurrent use of tetracycline, including doxycycline with methoxyflurane, can result in fatal renal toxicity.

What are Other Precautionary Measures When Using Doxycycline?

As with any other medication, if you are allergic to doxycycline, you should not use this antibiotic.

Doxycycline may cause Clostridium difficile-associated diarrhea (severe diarrhea with colonic inflammation and bleeding). So, if diarrhea happens, the doctor will evaluate it closely. (18)

The tetracycline class of antibiotics is known that may cause permanent discoloration of the teeth. As a result, teeth may become yellow-gray-brown. Due to this side effect, tetracycline, including doxycycline, is not recommended for children till 8 years of age, while in the period of tooth development. It is also not recommended for the last half of pregnancy and infancy. (1)

Some patients may experience an exaggerated sunburn reaction when taking tetracyclines. For this reason, limit your sun exposure while on tetracycline therapy. In addition, the overgrowth of organisms resistant to doxycycline, including fungi, may occur. In such a case, your doctor will re-evaluate the therapy.

Final Takeaways

Doxycycline is an antibiotic that can successfully treat infections caused by bacteria sensitive to doxycycline. However, its usage is limited due to hypersensitivity reactions and side effects.

Certain drug interactions require medication dose or timing adjustment, while concomitant use of doxycycline and penicillin is not recommended. Use alternative methods for pregnancy protection while using doxycycline rather than oral contraceptives.

The best way to avoid interactions is to tell your doctor the list of medications you take, including over-the-counter products and supplements.

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