Doxycycline is a broad-spectrum antibiotic belonging to the tetracycline class. It is primarily used to treat infections caused by bacteria or parasites, such as respiratory, urinary tract, and skin infections, as well as specific infections like malaria and Lyme disease. This medication inhibits bacterial protein synthesis, thereby blocking their growth and reproduction.
Additionally, doxycycline is often used as a prophylactic agent, for example, to prevent malaria before travel, or to treat diseases caused by rickettsia, spirochetes, and other pathogens. Its advantages include good oral absorption, a long half-life, and once-daily dosing.
The scientific name of this drug is Doxycycline. Common brand names include:
Different countries or regions may have other brand names. Before use, ensure the active ingredient on the medication label is doxycycline.
Doxycycline is classified as an antibiotic of the tetracycline class, which includes drugs like tetracycline and minocycline. These drugs bind to the bacterial ribosome, inhibiting protein synthesis, and are effective against most Gram-positive and Gram-negative bacteria.
It is also categorized as a "broad-spectrum antibiotic," effective against various bacterial and parasitic infections. However, the principle of "narrow-spectrum priority" should be followed to prevent misuse and resistance development.
Main indications include: bacterial infections (such as pneumonia, cellulitis, sexually transmitted infections), parasitic infections (such as malaria, Lyme disease), and short-term treatment of certain autoimmune diseases (such as systemic lupus erythematosus). It can also be used for post-exposure prophylaxis, such as tetanus prevention after animal bites.
Special uses include: primary treatment for syphilis, treatment of rickettsial diseases, and adjunct therapy for tuberculosis. In some countries, it is also approved as a prophylactic option for travelers to prevent malaria.
Mild side effects include: gastrointestinal discomfort (nausea, diarrhea), esophageal irritation (may worsen if taken just before lying down), photosensitivity (increased skin redness or burning after sun exposure). About 10-20% of patients may experience these symptoms, which usually do not require discontinuation.
Serious side effects requiring immediate medical attention include: allergic reactions (difficulty breathing, hives), liver dysfunction (jaundice, dark urine), renal toxicity (decreased urine output, edema), and esophageal ulcers (more common with long-term fasting medication).
Contraindications: Contraindicated in individuals allergic to tetracyclines. Avoid use in children under 8 years old due to potential effects on teeth and bone development. Especially during pregnancy, particularly in the third trimester, as it may cause fetal teeth discoloration or bone growth issues.
Black Box Warning: This medication may induce severe allergic reactions. If experiencing difficulty breathing or systemic hives, discontinue immediately and seek medical attention. Long-term use may lead to superinfection (such as fungal infections), so monitor for oral ulcers or vaginal itching.
Concurrent use with antacids (containing aluminum, calcium, iron, magnesium) reduces absorption. It is recommended to separate administration by at least 2 hours. Combining with oral contraceptives may decrease contraceptive efficacy; additional barrier methods are advised.
Using with anticoagulants (warfarin) may enhance anticoagulant effects; INR monitoring is necessary. Taking with thyroid hormones can reduce efficacy; separate by 4 hours. Some anticonvulsants (e.g., carbamazepine) may lower doxycycline blood levels.
For adult infections, the typical initial dose is 200 mg, followed by 100 mg daily, for 7-14 days. Malaria prophylaxis involves 100 mg daily. In children, dosage is based on weight, usually 2 mg per kg per day, not exceeding 100 mg.
Take on an empty stomach (1 hour before or 2 hours after meals) to ensure optimal absorption. Drink with a full glass of water and remain upright for 20 minutes to prevent esophageal irritation. Capsules or tablets should not be chewed and should be swallowed whole.
If a dose is missed and more than 4 hours remain before the next dose, take it as soon as remembered. If less than 2 hours remain before the next dose, skip the missed dose and resume the regular schedule. Do not double doses to make up for missed ones.
Long-term missed doses may lead to treatment failure or resistance. Set reminders and store medication in a visible place to improve adherence.
Acute overdose may cause nausea, vomiting, abdominal pain. If overdose is suspected, seek immediate medical attention. Severe cases may require gastric lavage or activated charcoal to adsorb unabsorbed drug.
Chronic overdose can cause discoloration of teeth, liver and kidney dysfunction. Regular monitoring of liver enzymes (e.g., GPT, bilirubin) and renal function (creatinine clearance) is recommended. If unexplained fatigue or tea-colored urine occurs, discontinue and inform a healthcare provider.
Does doxycycline need to be taken with food?
It is recommended to take doxycycline on an empty stomach (1 hour before or 2 hours after meals) to ensure optimal absorption. If gastrointestinal discomfort occurs, it can be taken with a small amount of light food, but avoid foods or medications containing calcium, iron, or antacids (such as aluminum, magnesium) as they may affect absorption. Also, avoid these substances within 1-2 hours after taking the medication.
What should I do if I experience nausea or diarrhea while taking doxycycline?
For mild gastrointestinal discomfort, try taking the medication with food or with antacids that do not contain aluminum or magnesium to alleviate symptoms. If diarrhea is severe, persists over 48 hours, or is accompanied by blood in stool or dehydration, discontinue and consult a healthcare provider, as dosage adjustment may be necessary.
Which drugs or supplements may interact with doxycycline?
Doxycycline can interact with antacids, iron supplements, calcium or zinc-containing products, reducing absorption. Separate administration by at least 2-3 hours. It may enhance the effect of anticoagulants like warfarin, requiring regular INR monitoring. When used with oral contraceptives, efficacy may decrease, so additional contraceptive measures are recommended.
Should I take extra precautions against sun exposure while on doxycycline?
Yes. Doxycycline can cause photosensitivity, leading to skin redness or blistering after sun or UV exposure. During treatment, avoid prolonged sun exposure, use SPF 30 or higher sunscreen, wear long sleeves and hats. If skin burns or rashes occur, discontinue and seek medical attention.
What should I do if I miss a dose of doxycycline?
If a dose is missed and the time is short, take it as soon as remembered and adjust the next dose accordingly. If close to the next scheduled dose, skip the missed dose and continue with the regular schedule. Do not double doses to compensate for missed ones, as this may increase the risk of side effects or resistance.
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