Acyclovir (Aciclovir) | Antiviral | CAS 59277-89-3

Product Name: Acyclovir (Aciclovir)
CAS No.: 59277-89-3
Chemical Name: 9-(2-hydroxyethoxymethyl)guanine
Molecular Formula: C₈H₁₁N₅O₃
Appearance: White or almost white crystalline powder
Solubility: Sparingly soluble in water; soluble in dilute acids and alkalis
Stability: Relatively stable when stored in a dry place

1. Introduction

Acyclovir is an antiviral agent, a synthetic analog of the purine nucleoside guanosine. It is selectively active against herpes viruses (Herpes simplex types 1 and 2) and Varicella zoster virus. It is phosphorylated to its active form, inhibiting viral DNA polymerase.

Viral infections caused by the Herpesviridae family represent a significant medical problem. Acyclovir, developed in the 1970s, was a breakthrough in the treatment of these infections. Its mechanism of action is based on specific activation by viral enzymes, providing high selectivity and low toxicity to host cells.

2. Chemical Structure & Synthesis

Acyclovir is an acyclic analog of deoxyguanosine, lacking the cyclic sugar moiety.

Synthesis: Acyclovir is synthesized from guanine or its derivatives by attaching an acyclic side chain. One common method involves the reaction of 2-amino-6-chloropurine with 2-(2-chlorophenyl)oxyethanol, followed by hydrolysis and replacement of chlorine with a hydroxyl group.

3. Mechanism of Action

Acyclovir is a prodrug. In virus-infected cells, it is phosphorylated by viral thymidine kinase to acyclovir monophosphate. Cellular enzymes then sequentially phosphorylate it to acyclovir diphosphate and acyclovir triphosphate. Acyclovir triphosphate competitively inhibits viral DNA polymerase and, being incorporated into viral DNA, terminates its chain because it lacks the 3'-hydroxyl group required for elongation.

Selectivity: High selectivity of action is due to the fact that the first phosphorylation step is catalyzed predominantly by viral thymidine kinase, whose activity is significantly lower or absent in uninfected cells.

4. Pharmacokinetics

After oral administration, bioavailability is 15–30%. Widely distributed in tissues and body fluids, including cerebrospinal fluid. Excreted primarily unchanged by the kidneys.

5. Applications

• Treatment of HSV-1 and HSV-2 infections:

  • Herpes of the skin and mucous membranes (including primary and recurrent genital herpes)

  • Herpetic encephalitis

  • Herpetic keratitis (as an ophthalmic ointment)

• Treatment of Varicella zoster virus (VZV) infections:

  • Chickenpox (especially in immunocompromised patients or severe cases)

  • Shingles (Herpes zoster)

• Prophylaxis of herpetic infections in immunocompromised patients (e.g., after organ transplantation, HIV infection)

6. Conclusion

Acyclovir is a highly effective and relatively safe antiviral drug that revolutionized the treatment of herpesvirus infections. Its selective mechanism of action minimizes toxicity to the host, making it the drug of choice in many clinical situations. Despite the emergence of new antiviral agents, acyclovir retains its importance in clinical practice.