Doxycycline: Price, Dosage & Where to Buy

Doxycycline is a tetracycline antibiotic that inhibits bacterial protein synthesis. It is prescribed to treat a wide range of bacterial infections, including respiratory tract infections, sexually transmitted infections such as chlamydia, rickettsial diseases like Rocky Mountain spotted fever, and anthrax.

It is also used for malaria prophylaxis in short-term travellers. Doxycycline requires a prescription in the United Kingdom.

Doxycycline belongs to the tetracycline class of antibiotics. It works by inhibiting bacterial protein synthesis. Bacteria require protein synthesis to grow and reproduce.

Doxycycline binds to the 30S ribosomal subunit within bacterial cells, blocking the attachment of transfer RNA to the messenger RNA-ribosome complex. This prevents the addition of amino acids to the growing protein chain, effectively stopping bacteria from producing the proteins they need to survive.

Because doxycycline is bacteriostatic rather than bactericidal, it slows or stops bacterial growth rather than directly killing bacteria, allowing the body's immune system to clear the infection. This mechanism is effective against a broad range of gram-positive and gram-negative bacteria, as well as certain atypical pathogens and intracellular organisms.

Doxycycline treats infections caused by susceptible bacteria. It is indicated for rickettsial infections including Rocky Mountain spotted fever, typhus fever, Q fever, and tick fevers. It treats respiratory tract infections caused by Mycoplasma pneumoniae, Haemophilus influenzae, and Streptococcus pneumoniae.

Doxycycline is used for sexually transmitted infections including chlamydia (urethral, endocervical, and rectal infections), nongonococcal urethritis, lymphogranuloma venereum, and uncomplicated gonorrhoea when penicillin is contraindicated. It treats other infections such as syphilis, plague, tularaemia, cholera, brucellosis, anthrax (including inhalational anthrax post-exposure), and Lyme disease (relapsing fever due to Borrelia recurrentis).

Doxycycline may be useful adjunctive therapy in severe acne. It is also indicated for malaria prophylaxis due to Plasmodium falciparum in short-term travellers (less than 4 months) to areas with chloroquine-resistant or pyrimethamine-sulfadoxine-resistant strains.

The label lists capsules in strengths of 40 mg, 50 mg, 75 mg, 100 mg, and 150 mg, tablets in 20 mg, 50 mg, 75 mg, 100 mg, and 150 mg, delayed-release tablets in 50 mg, 60 mg, 75 mg, 100 mg, 150 mg, and 200 mg, and oral suspension at 25 mg/5 mL. The usual starting dose is 200 mg on the first day (administered as 100 mg every 12 hours), followed by a maintenance dose of 100 mg per day. For more severe infections, particularly chronic urinary tract infections, the label lists 100 mg every 12 hours.

For paediatric patients weighing less than 45 kg with severe or life-threatening infections, the recommended dosage is 2.2 mg/kg every 12 hours; children weighing 45 kg or more receive the adult dose. For malaria prophylaxis, the label lists 100 mg daily for adults and 2 mg/kg once daily (up to the adult dose) for children over 8 years. For inhalational anthrax post-exposure, the label lists 100 mg twice daily for 60 days in adults.

The label states that all doxycycline products are to be stored at 20° to 25°C (68° to 77°F), which corresponds to controlled room temperature. The label specifies that doxycycline should be dispensed in tight, light-resistant containers with a child-resistant closure.

Keeping the medicine in its original container, away from light and moisture, and out of reach of children will help to maintain quality. The medicine should not be stored in bathrooms or other damp areas.

If a dose is missed, it should generally be taken as soon as remembered unless it is nearly time for the next scheduled dose. Two doses should not be taken at once to make up for a missed dose. For infections, maintaining consistent blood levels of the antibiotic is important for effectiveness, so doses should be spaced as evenly as possible throughout the day.

For malaria prophylaxis, the label states that doxycycline should be continued daily during travel and for 4 weeks after leaving the malarious area, so maintaining the daily schedule is important. A pharmacist can provide guidance on what to do if a dose is missed.

There are no adequate and well-controlled studies on the use of doxycycline in pregnant women. An expert review concluded that therapeutic doses during pregnancy are unlikely to pose a substantial teratogenic risk, but the data are insufficient to state that there is no risk. A case-control study shows a weak but marginally statistically significant association with total malformations and use of doxycycline anytime during pregnancy, though this association was not seen during the period of organogenesis except for a marginal relationship with neural tube defect based on only two exposed cases.

Tetracyclines cross the placenta and can have toxic effects on the developing foetus. The label warns that tetracyclines may cause permanent tooth discolouration during the last half of pregnancy. Women who are pregnant or may become pregnant should discuss the risks and benefits of doxycycline with their doctor or pharmacist.