PHARMACOLOGY

Pharmacotherapeutic Group:Tetracycline Antibiotics

 Pharmacodynamic Properties:Doxycycline inhibits bacterial protein synthesis by binding to the 30s ribosomal subunit. It has bacteriostatic activity against a broad range of Gram positive and Gram negative bacteria.

 Pharmacokinetic Properties:

Absorption: Readily and almost completely absorbed from the gastrointestinal tract. Food and milk products may decrease absorption. Time to peak plasma concentration: 2 hr.

Distribution: Widely distributed in body tissues and fluids, with excellent penetration into the liver, kidneys and sinuses. Moderate penetration into CSF, crosses the placenta and enters the breast milk. Plasma protein binding: Approx. 80-95%

Metabolism: Partially inactivated in GI tract by chelation formation.

Excretion: Via urine (23%) and faeces (30%). Plasma half-life: 12-24 hr.

 INDICATIONS

Respiratory tract infections, skin infections, acne, bacterial keratitis, trachoma, genitourinary tract infections, syphilis, periodonitis

 DOSAGE & ADMINISTRATION

Adults: The usual dose of oral doxycycline is 200 mg on the first day of treatment (administered 100 mg every 12 hours or 50 mg every 6 hours) followed by a maintenance dose of 100 mg/day. The maintenance dose may be administered as a single dose or as 50 mg every 12 hours. In the management of more severe infections (particularly chronic infections of the urinary tract), 100 mg every 12 hours is recommended.

For pediatric patients above eight years of age: The recommended dosage schedule for pediatric patients weighing 100 pounds or less is 2 mg/lb of body weight divided into two doses on the first day of treatment, followed by 1 mg/lb of body weight given as a single daily dose or divided into two doses, on subsequent days. For more severe infections up to 2 mg/lb of body weight may be used. For pediatric patients over 100 pounds the usual adult dose should be used.

 ADVERSE DRUG REACTIONS

Permanent staining of teeth, rash, superinfection, nausea, GI upsets, glossitis, dysphagia, photosensitivity, hypersensitivity, haemolytic anaemia, thrombocytopenia, neutropenia and eosinophilia.
Potentially Fatal: Anaphylaxis.

 PRECAUTIONS

Patient with pre-existing Systemic Lupus Erythematosus (SLE), myasthenia gravis, hepatic and renal impairment, pregnancy. 

Patient Counselling: Avoid exposure to direct sunlight or UV light 

 DRUG INTERACTIONS:

Prolonged prothrombin time with anticoagulants (e.g. warfarin). May interfere with the bactericidal action of penicillin. Impaired absorption with antacids containing Aluminium, Calcium or Magnesium, oral Zinc, iron salts, and bismuth preparations. Barbiturates, carbamazepine and phenytoin decreases the half life of doxycycline.

 CONTRAINDICATIONS

Hypersensitivity to doxycycline and any of the tetracyclines. Concurrent use with methoxyflurane. Lactation.

PRESENTATION

T-DOX: Each box contains 10 Blisters of 10 Tablets per strip