Demeclocycline is a tetracycline-class antibiotic developed in the 1960s and initially used for treating bacterial infections. Over time, its clinical use expanded to include the management of syndrome of inappropriate antidiuretic hormone secretion (SIADH) due to its ability to induce a mild nephrogenic diabetes insipidus and reduce water reabsorption in the kidneys. Unlike many other tetracyclines, demeclocycline’s use in SIADH is notable for targeting water balance rather than infection. Its development focused on creating a long-acting, orally administered tetracycline with reliable bioavailability, and it has been incorporated into therapy regimens for both infectious and endocrine-related disorders, with careful monitoring for potential nephrotoxicity and photosensitivity.
BRAND NAMES
Declomycin – the most widely recognized brand
Ledermycin – available in some regions.
MECHANISM OF ACTION
Demeclocycline is a tetracycline antibiotic that inhibits bacterial protein synthesis by binding reversibly to the 30S ribosomal subunit of susceptible bacteria. This binding prevents the attachment of aminoacyl-tRNA to the mRNA-ribosome complex, thereby blocking the addition of new amino acids to the growing peptide chain and inhibiting bacterial growth.
PHARMACOKINETICS
Absorption
Demeclocycline is well absorbed orally, with bioavailability ranging from approximately 50% to 60%. Peak plasma concentrations are usually achieved within 2 to 4 hours after ingestion. Absorption can be significantly reduced if the drug is taken with dairy products, antacids, or calcium-, magnesium-, or aluminum-containing supplements, as these can chelate the drug and prevent its uptake.
Distribution
Demeclocycline has a moderate volume of distribution, typically around 0.7–1 L/kg, indicating that it distributes well into body tissues but remains largely within the extracellular fluid.
Metabolism
Demeclocycline undergoes minimal hepatic metabolism. Most of the drug remains unchanged in the body and is excreted primarily via the urine and bile. Because it is not extensively metabolized, demeclocycline has a predictable pharmacokinetic profile, but this also means that impaired renal or hepatic function can significantly affect drug levels and increase the risk of toxicity.
Elimination
Demeclocycline is eliminated from the body primarily through renal excretion and, to a lesser extent, via biliary/fecal excretion. Approximately 40–60% of the drug is excreted unchanged in the urine, with the remainder eliminated in the feces. The elimination half-life ranges from 10 to 16 hours in healthy adults, allowing for typically twice-daily dosing.
PHARMACODYNAMICS
Demeclocycline exhibits two main pharmacodynamic actions. As a tetracycline antibiotic, it acts as a bacteriostatic agent by reversibly binding to the 30S ribosomal subunit of susceptible bacteria, inhibiting the attachment of aminoacyl-tRNA to the mRNA-ribosome complex and thereby preventing protein synthesis and bacterial growth.
ADMINISTRATION
Demeclocycline is administered orally, typically in the form of capsules or tablets. For antibacterial therapy, it is usually given every 6 to 12 hours, depending on the severity of the infection and the patient’s renal function.
DOSAGE AND STRENGTH
Demeclocycline is available in capsules or tablets of 150 mg strength. For the treatment of bacterial infections, the usual adult dosage is 200 mg every 6 to 12 hours, depending on the severity of the infection and renal function.
DRUG INTERACTIONS
Demeclocycline can interact with several medications due to its tetracycline properties and effects on renal function. Antacids and supplements containing calcium, magnesium, aluminum, or iron can chelate the drug, reducing its absorption and effectiveness.
FOOD INTERACTIONS
Demeclocycline absorption is significantly affected by certain foods and supplements. Dairy products such as milk, cheese, and yogurt, as well as foods or supplements containing calcium, magnesium, aluminum, or iron, can bind the drug in the gastrointestinal tract, reducing its absorption and therapeutic effectiveness.
CONTRAINDICATIONS
Demeclocycline is contraindicated in patients with hypersensitivity to tetracyclines or any component of the formulation. It should not be used in pregnant or breastfeeding women, as it can cause fetal harm and permanent tooth discoloration in infants.
SIDE EFFECTS
Nausea and vomiting
Diarrhea or abdominal discomfort
Loss of appetite
Photosensitivity (increased risk of sunburn)
Skin rash
Increased serum creatinine
Polyuria or nephrogenic diabetes insipidus
Rare acute kidney injury
OVER DOSAGE
Overdose of demeclocycline can lead to gastrointestinal, renal, and neurological toxicity. Common symptomsinclude nausea, vomiting, diarrhea, and abdominal pain. High doses may cause polyuria, dehydration, and electrolyte imbalances due to its effect on renal water handling.
TOXICITY
Demeclocycline toxicity primarily affects the renal, hepatic, and gastrointestinal systems, with additional risks for photosensitivity and neurological complications. Renal toxicity may manifest as nephrogenic diabetes insipidus, polyuria, increased serum creatinine, and, rarely, acute kidney injury. Hepatic effects include elevated liver enzymes and, in severe cases, hepatotoxicity.
