Zovirax 200Mg Tab 25 s

Potential Overview:

• Generic Name: Acyclovir
• Brand Name: Zovirax
• Pack Size:25 tablets (200 mg each)

Mechanism of Action (MOA):

• Acyclovir is an antiviral medication that primarily works by interfering with the replication of certain herpes viruses.
• It is converted into its active form acyclovir triphosphate by the viral enzyme thymidine kinase in infected cells. Acyclovir triphosphate inhibits viral DNA polymerase, thereby preventing viral DNA synthesis. This prevents the virus from multiplying and spreading.
• Acyclovir is particularly effective against Herpes simplex virus (HSV), Varicella zoster virus (VZV), and Herpes zoster virus.

Indications:

Zovirax (Acyclovir) is used to treat:

• Herpes Simplex Virus (HSV) Infections:
  • Genital Herpes: Treatment of initial and recurrent genital herpes outbreaks.
  • Oral Herpes (Cold Sores): Treatment of oral herpes (HSV-1) infections.
  • Herpes Simplex Encephalitis: Treatment of viral brain infection.
• Varicella Zoster Virus (VZV) Infections:
  • Chickenpox: Treatment of varicella (chickenpox) in immunocompromised individuals and severe cases.
  • Shingles (Herpes Zoster): Treatment of shingles in adults and children over the age of 2.
• Prevention of HSV: In immunocompromised patients to prevent recurrent infections or outbreaks.

Dosage:

• Adults:
  • Herpes Simplex (Initial Infection): 200 mg every 4 hours (5 times a day) for 7–10 days.
  • Herpes Simplex (Recurrent Infection): 200 mg every 4 hours (5 times a day) for 5 days.
  • Herpes Zoster (Shingles): 800 mg every 4 hours (5 times a day) for 7 to 10 days.
  • Chickenpox: 800 mg 4 times daily for 5 days.
• Children:
  • The dosage for children varies based on the age and condition being treated. Generally, it is lower than adult doses, and exact dosing should be based on the doctor’s instructions.
• Renal Impairment: Dosage adjustments may be required for patients with kidney dysfunction (e.g., creatinine clearance <50 mL/min).

Always follow the healthcare provider’s prescribed dosage instructions.

Side Effects:

Common side effects of Zovirax (Acyclovir) include:

• Gastrointestinal: Nausea, vomiting, diarrhea, abdominal pain.
• Headache.
• Dizziness or lightheadedness.
• Fatigue.
• Skin reactions: Rash or itching.
• Elevated liver enzymes.

Serious side effects may include:

• Renal Impairment: Acyclovir can cause kidney damage, especially in high doses or in patients with preexisting kidney conditions.
• Neurological Effects: Confusion, agitation, or seizures (especially in elderly or those with kidney dysfunction).
• Blood Disorders: Rarely, anemia or thrombocytopenia (low platelet count).

Precautions:

• Kidney Function: Renal impairment can increase the risk of acyclovir toxicity, so dose adjustments are necessary for patients with kidney problems.
• Hydration: Ensure adequate fluid intake, especially in patients receiving high-dose acyclovir therapy, to reduce the risk of renal toxicity.
• Elderly Patients: The elderly may be more sensitive to the neurotoxic effects of acyclovir, particularly those with kidney impairment.
• Pregnancy and Lactation: Acyclovir is generally considered safe during pregnancy (Category B), but should be used only when necessary. It is excreted in breast milk, so caution is advised during breastfeeding.
• Immunocompromised Individuals: In patients with weakened immune systems (e.g., HIV/AIDS), the efficacy of acyclovir may be reduced, and prolonged treatment may be required.

Contraindications (CI):

• Hypersensitivity: Contraindicated in patients who are allergic to Acyclovir or any of its components.
• Severe Renal Disease: Acyclovir should be used with caution or avoided in patients with severe renal impairment unless dose adjustments are made.

Pharmacist Related Data

Chemical Name and Formula:

• Chemical Name: 9-(2-hydroxyethoxymethyl) guanine
• Molecular Formula: C8H11N5O3
• IUPAC Name: 2-amino-1,9-dihydro-9-[(2-hydroxyethoxy)methyl] purine

Half-Life:

• Half-Life: Approximately 2.5 to 3.3 hours in healthy individuals.
  • Prolonged Half-Life: In patients with renal impairment, the half-life can be significantly longer due to reduced renal clearance.

Metabolism:

• Acyclovir is partially metabolized in the liver, but it is not extensively metabolized like other drugs.
• It undergoes conversion to acyclovir triphosphate inside the infected cells, which is the active form that inhibits viral DNA synthesis.
• Inactive metabolites are formed, which are then excreted.

Drug Interactions with Food and Medicine:

Drug Interactions:

• Probenecid: Concomitant use can decrease renal clearance of acyclovir, increasing the risk of toxicity.
• Cimetidine: May increase acyclovir levels by inhibiting its renal clearance.
• Zidovudine: Co-administration with acyclovir may increase the risk of neurotoxicity in immunocompromised patients.
• Immunosuppressive drugs: Use with drugs like cyclosporine or tacrolimus may increase the risk of renal toxicity.
• Mycophenolate mofetil: Can increase the risk of renal impairment when used with acyclovir.

Food Interactions:

• There are no significant interactions with food. Acyclovir can be taken with or without food, though taking it with food may help reduce the potential for gastrointestinal upset.
• Hydration: It is important to maintain adequate hydration, especially during high-dose therapy, to reduce the risk of renal toxicity.

Pharmacodynamics:

• Mechanism of Action:
  Acyclovir is a nucleoside analogue that inhibits the replication of DNA in herpes viruses. It is converted into its active form, acyclovir triphosphate, by the viral enzyme thymidine kinase. Once active, acyclovir triphosphate inhibits viral DNA polymerase, blocking the viral DNA replication process.
• Effect:
  Acyclovir has a selective action against viruses that produce the enzyme thymidine kinase, making it particularly effective against Herpes Simplex Virus (HSV), Varicella Zoster Virus (VZV), and Cytomegalovirus (CMV).

Pharmacokinetics:

1. Absorption:
   • Acyclovir is well absorbed after oral administration, but it has low bioavailability of about 15–30% due to extensive first-pass metabolism in the liver.
   • Peak plasma concentrations are reached in about 1.5 to 2.5 hours after oral administration.
2. Distribution:
   • Acyclovir is widely distributed throughout the body and can cross the blood-brain barrier and penetrate cerebrospinal fluid.
   • It is also distributed in other body fluids, including saliva, semen, and breast milk.
   • Plasma protein binding is about 9-33%.
3. Metabolism:
   • Acyclovir is primarily metabolized in the liver, but it undergoes minimal metabolism compared to other drugs. It is converted into acyclovir monophosphate by the viral enzyme thymidine kinase in infected cells, and then further converted into acyclovir diphosphate and acyclovir triphosphate (the active form) by cellular enzymes.
4. Excretion:
   • Acyclovir is primarily excreted in the urine in its unchanged form (approximately 80% of the dose).
   • It is cleared from the body by renal excretion, so renal function must be monitored, especially in patients with preexisting kidney conditions.