Classification of Antiviral Agents
Pharmacotherapy for chronic viral infection is based on synthetic compounds that suppress pathogen replication. Main drug groups:
- Nucleoside analogues: telbivudine and entecavir.
- Acyclic nucleotide analogues: adefovir (used as a prodrug).
Each substance possesses unique chemical structure characteristics and specific interactions with viral enzymes.
Mechanisms of Antiviral Action
The drugs aim to suppress hepatitis B virus DNA polymerase:
- Phosphorylation: Compounds are activated in the body by cellular enzymes.
- Competitive inhibition: Active metabolites compete with natural substrates for chain incorporation.
- Chain termination: Incorporation of the modified component halts further viral DNA synthesis.
Entecavir selectively blocks the viral polymerase, while telbivudine additionally causes structural termination of the growing chain.
Pharmacokinetics and Safety Profile
Pharmacological properties determine the rules for drug administration:
- Bioavailability: Pure adefovir has low values (around 12%), so it is administered as adefovir dipivoxil, which increases absorption up to 60%.
- Toxicity: Therapy with adefovir can be accompanied by dose-dependent renal tissue injury (nephrotoxic effect).
- Resistance: entecavir demonstrates an advantage over older agents, minimizing the likelihood of resistant strains emerging.
Application Limitations and Regulatory Status
The use of antiviral agents is strictly regulated:
- Telbivudine has an age restriction and is prescribed exclusively to patients over 18 years of age with a confirmed diagnosis of chronic infection.
- Adefovir exhibits high activity against strains resistant to lamivudine.