Doxycycline

Drug Interactions Because tetracyclines have been shown to depress plasma prothrombin activity, patients who are on anticoagulant therapy may require downward adjustment of their anticoagulant dosage. Since bacteriostatic drugs may interfere with the bactericidal action of penicillin, it is advisable to avoid giving tetracycline in conjunction with penicillin. Barbiturates, carbamazepine, and phenytoin decrease the half-life of doxycycline. The concurrent use of tetracycline and Penthrane ® (methoxyflurane) has been reported to result in fatal renal toxicity. Concurrent use of tetracycline may render oral contraceptives less effective.

Doxycycline treats bacterial infections including rickettsial infections, respiratory tract infections caused by Mycoplasma pneumoniae, sexually transmitted infections (chlamydia, gonorrhea, syphilis), and gram-negative bacterial infections. It's also used for malaria prophylaxis in travelers and post-exposure anthrax prevention. The label emphasizes: "doxycycline hyclate should be used only to treat or prevent infections that are proven or strongly suspected to be caused by susceptible bacteria."

DOSAGE AND ADMINISTRATION: NOTE: Rapid administration is to be avoided. Parenteral therapy is indicated only when oral therapy is not indicated. Oral therapy should be instituted as soon as possible. If intravenous therapy is given over prolonged periods of time, thrombophlebitis may result. The usual dosage and frequency of administration of Doxycycline for Injection (100 to 200 mg/day) differs from that of the other tetracyclines (1 to 2 g/day). Exceeding the recommended dosage may result in an increased incidence of side effects. Studies to date have indicated that doxycycline hyclate at the usual recommended doses does not lead to excessive accumulation of the antibiotic in patients with renal impairment. Adults The usual dosage of doxycycline for injection is 200 mg on the first day of treatment administered in one or two infusions. Subsequent daily dosage is 100 to 200 mg depending upon the severity of infection, with 200 mg administered in one or two infusions. In the treatment of primary and secondary syphilis, the recommended dosage is 300 mg daily for at least 10 days. In the treatment of inhalational anthrax (post-exposure) the recommended dose is 100 mg of doxycycline, twice a day. Parenteral therapy is only indicated when oral therapy is not indicated and should not be continued over a prolonged period of time. Oral therapy should be instituted as soon as possible. Therapy must continue for a total of 60 days. Pediatric Patients For all pediatric patients weighing less than 45 kg with severe or life-threatening infections (e.g., anthrax, Rocky Mountain spotted fever), the recommended dosage is 2.2 mg/kg of body weight administered every 12 hours. Children weighing 45 kg or more should receive the adult dose (see WARNINGS and PRECAUTIONS ). For pediatric patients with less severe disease (greater than 8 years of age and weighing less than 45 kg), the recommended dosage schedule is 4.4 mg/kg of body weight divided into two doses on the first day of treatment, followed by a maintenance dose of 2.2 mg/kg of body weight (given as a single daily dose or divided into twice daily doses). For pediatric patients weighing over 45 kg, the usual adult dose should be used. In the treatment of inhalational anthrax (post-exposure) the recommended dose is 2.2 mg/kg of body weight, twice a day in children weighing less than 45 kg. Parenteral therapy is only indicated when oral therapy is not indicated and should not be continued over a prolonged period of time. Oral therapy should be instituted as soon as possible. Therapy must continue for a total of 60 days. General The duration of infusion may vary with the dose (100 to 200 mg/day), but is usually one to four hours. A recommended minimum infusion time for 100 mg of a 0.5 mg/mL solution is one hour. Therapy should be continued for at least 24 to 48 hours after symptoms and fever have subsided. The therapeutic antibacterial serum activity will usually persist for 24 hours following recommended dosage. Intravenous solutions should not be injected intramuscularly or subcutaneously. Caution should be taken to avoid the inadvertent introduction of the intravenous solution into the adjacent soft tissue.

Gastrointestinal effects predominate: nausea, vomiting, diarrhea, anorexia. Skin reactions include rashes, photosensitivity, and rarely Stevens-Johnson syndrome. Other reported effects: tooth discoloration, esophageal ulceration, intracranial hypertension, and hypersensitivity reactions.