DOC 100

Indications

• Bacterial infections
• Respiratory tract infections
• Urinary tract infections
• Acne
• Malaria prophylaxis
• Periodontal disease

Dosage

Children: For children aged 8 years and older, the usual dose for most infections is 2 mg/kg body weight as a loading dose on the first day, followed by 1 mg/kg daily. For children under 8 years, doxycycline is generally not recommended.

Adults: The usual adult dose for most infections is 100 mg to 200 mg daily, administered in one or two divided doses.

Mechanism of action

Doxycycline inhibits bacterial protein synthesis by binding to the 30S ribosomal subunit. This binding prevents the attachment of aminoacyl-tRNA to the acceptor site on the mRNA-ribosome complex, thereby inhibiting the elongation of the peptide chain and ultimately leading to bacteriostatic effects.

Pharmacodynamics

Doxycycline exhibits a time-dependent killing effect, with its efficacy being related to the duration of exposure above the minimum inhibitory concentration (MIC). It has a longer half-life compared to other tetracyclines, allowing for once or twice daily dosing. It also possesses anti-inflammatory properties, which can contribute to its effectiveness in treating acne and other inflammatory conditions.

Pharmacokinetics

Doxycycline is well absorbed from the gastrointestinal tract, with an oral bioavailability of approximately 90%. It is widely distributed throughout body tissues and fluids, including the central nervous system. The drug is primarily excreted in the bile and undergoes enterohepatic recirculation, with minimal renal excretion. Its half-life is approximately 18-22 hours, allowing for convenient dosing schedules.

Contra-indications

• Hypersensitivity to doxycycline or any of the tetracycline antibiotics.
• Severe renal impairment (creatinine clearance < 50 mL/min).
• Pregnancy, particularly during the second and third trimesters.

Adverse effects

• Gastrointestinal disturbances (nausea, vomiting, diarrhea).
• Photosensitivity reactions.
• Esophageal irritation or ulceration.
• Skin rashes.
• Alterations in liver function tests.
• Intracranial hypertension.

Interactions

• Antacids containing aluminum, calcium, or magnesium can reduce the absorption of doxycycline.
• Iron preparations may also interfere with absorption.
• Oral contraceptives may be less effective when used concurrently with doxycycline.
• Warfarin and other anticoagulants may have increased effects.

Precautions

• Use with caution in patients with a history of esophageal disorders.
• Monitor liver function in patients with pre-existing liver disease.
• Caution in renal impairment, as dosage adjustments may be necessary.
• Avoid use in children under 12 years of age due to potential effects on bone growth and teeth.

Pregnancy

Doxycycline is contraindicated in pregnancy, especially during the second and third trimesters due to the risk of harm to the developing fetus, including effects on bone and teeth.

Breast-feeding

Doxycycline is excreted in breast milk. Caution is advised when administering to nursing mothers, as it may affect the infant's teeth and bone development.

Storage

Store in a cool, dry place away from direct sunlight. Keep out of reach of children.

Formulations

• Capsules
• Tablets
• Oral suspension
• Injectable solution