Doxycycline | Tetracycline Antibiotic | CAS 564-25-0

Product Name: Doxycycline
CAS No.: 564-25-0 (base)
Chemical Name: (4S,4aR,5S,5aR,6R,12aS)-4-(dimethylamino)-1,4,4a,5,5a,6,11,12a-octahydro-3,5,10,12,12a-pentahydroxy-6-methyl-1,11-dioxonaphthacene-2-carboxamide
Molecular Formula: C₂₂H₂₄N₂O₈
Appearance: Yellow crystalline powder
Solubility: Monohydrate – sparingly soluble in water; hyclate – freely soluble in water and methanol
Stability: Relatively stable but sensitive to light and moisture

1. Introduction

Doxycycline is a semi-synthetic broad-spectrum tetracycline antibiotic. It has a bacteriostatic effect by disrupting protein synthesis in the microbial cell. It is effective for respiratory tract, urogenital, skin, and soft tissue infections.

Doxycycline is a derivative of oxytetracycline and belongs to the tetracycline antibiotic group. It is characterized by higher lipophilicity compared to other tetracyclines, which provides better tissue penetration and a longer half-life. This allows for once or twice daily dosing.

2. Chemical Structure & Synthesis

Doxycycline is a 6-deoxy-5-hydroxytetracycline. Often used as salts (hyclate or monohydrate) to improve stability and solubility.

Synthesis: Doxycycline is obtained by chemical modification of oxytetracycline or methacycline. One method involves catalytic hydrogenation of methacycline.

3. Mechanism of Action

Doxycycline reversibly binds to the 30S subunit of the bacterial ribosome, blocking the attachment of aminoacyl-tRNA to the mRNA-ribosome complex. This leads to inhibition of protein synthesis in the microbial cell, exerting a bacteriostatic effect.

4. Antimicrobial Spectrum

Broad spectrum including:

• Gram-positive bacteria (Staphylococcus spp., Streptococcus spp.)

• Gram-negative bacteria (Haemophilus influenzae, Escherichia coli, Neisseria gonorrhoeae)

• Atypical microorganisms (Mycoplasma pneumoniae, Chlamydia spp., Rickettsia spp.)

• Spirochetes (Borrelia burgdorferi, Treponema pallidum)

• Some protozoa (Plasmodium falciparum)

5. Pharmacokinetics

Well and almost completely absorbed from the gastrointestinal tract, regardless of food intake. Has a high degree of plasma protein binding. Penetrates well into most tissues and body fluids, including bile, synovial fluid, and pleural effusion. Minimally metabolized. Excreted in urine and feces.

6. Applications

• Respiratory tract infections: Bronchitis, pneumonia (including Mycoplasma and Chlamydia)

• Urogenital infections: Urethritis, cervicitis (chlamydial and mycoplasmal), syphilis (penicillin allergy), gonorrhea

• Skin and soft tissue infections: Acne vulgaris, rosacea, infected wounds

• Intestinal infections: Cholera, traveler's diarrhea

• Vector-borne infections: Lyme disease, rickettsioses (typhus, Q fever), brucellosis, tularemia

• Malaria: Prophylaxis and treatment (in combination or as monotherapy for prophylaxis)

• Anthrax: Treatment and prophylaxis

7. Conclusion

Doxycycline is a valuable broad-spectrum antibiotic with a convenient dosing regimen. Its effectiveness in treating infections caused by atypical pathogens and good tolerability make it the drug of choice in many clinical situations. However, as with other antibiotics, the growing problem of microbial resistance remains relevant.