Both doxycycline and amoxicillin are antibiotics. They belong to different classes and have different mechanisms of action. While they both have broad spectrum activity against various gram-positive and gram-negative bacteria, some resistance has developed to both drugs. The choice of which antibiotic to use will be made by the treating doctor according to the illness, organism causing it, and susceptibility of the organism.
While both antibiotics fight bacterial infections, the way in which they do that differs. Doxycycline belongs to the class of drugs called tetracyclines, which work by interfering with protein synthesis of the bacteria, thus not allowing the organism to replicate. It is referred to as a bacteriostatic agent, which means that it stops the bacteria from multiplying. The body's immune system kills off the bacteria already there.
Doxycycline is used to treat a range of susceptible conditions including genital infections, lung infections and ricketsial diseases. Due to the development of bacterial resistance its role in bacterial infections has decreased slightly. It may also be used longer term, to treat severe acne. Doxycycline is also used for malaria prophylaxis and, in combination with other drugs, malaria treatment.
Amoxicillin is a beta-lactamase sensitive penicillin with extended spectrum. It works by interfering with bacterial cell walls. Again, resistance has developed in some organisms, so it is often combined with another drug, clavulanic acid, which has restored its effectiveness. Amoxicillin is generally used to treat infections such as otitis media, sinusitis and lower respiratory tract infections.
As with any medication, both doxycycline and amoxicillin may interact with other medications, the oral contraceptive pill being one of them. All drugs, including over-the-counter, homeopathic and complementary medications should be discussed with the doctor. Pregnancy, desired pregnancy and lactation should also be discussed. Pregnant women should not take doxycycline, though amoxicillin is considered relatively safe during pregnancy.
Completing the course of an antibiotic is essential and this applies to both doxycycline and amoxicillin. Stopping a course before completion increases the risk of developing resistance, making treatment of future infections far more difficult. The prescribed dose and duration should be followed exactly.
Both drugs may cause adverse effects, some gastrointestinal, such as nausea, vomiting and diarrhea. Should these be severe, the doctor should be consulted. Taking doxycycline and amoxicillin with food may help to reduce the gastrointestinal side effects. Doxycycline may cause irritation of the esophagus, or throat, so it is recommended that it is taken with a large glass of water, while in an upright position, and to avoid lying down for some time after.