Zovirax 400mg Tablets
It is used to treat shingles or certain other herpes infections.It is used to treat chickenpox.It may be given to you for other reasons. Talk with the doctor.
Drug Class
Antiviral
Pharmacologic Class
Synthetic nucleoside analog
Pregnancy Category
Category B
FDA Approved
Jan 1985
DEA Schedule
Not Controlled
Overview
What is this medicine?
Acyclovir is an antiviral medicine used to treat infections caused by herpes viruses, such as cold sores, genital herpes, chickenpox, and shingles. It works by stopping the virus from growing and spreading in your body. It does not cure these infections but helps to reduce the severity and duration of outbreaks.
How to Use This Medicine
Taking Your Medication Correctly
To get the most benefit from your medication, take it exactly as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. You can take this medication with or without food. If it causes stomach upset, taking it with food may help.
If you're using this medication to treat cold sores, chickenpox, shingles, or genital herpes, start taking it as soon as symptoms appear. The sooner you begin treatment, the more effective it will be. Don't delay, as taking it too late may reduce its effectiveness.
Continue taking your medication as prescribed by your doctor or healthcare provider, even if you start feeling better. It's essential to complete the full treatment course as directed.
Storing and Disposing of Your Medication
To maintain the quality and safety of your medication, store it at room temperature, away from light and moisture. Keep it in a dry place, and avoid storing it in a bathroom. Ensure that all medications are kept out of reach of children and pets.
When disposing of unused or expired medication, do not flush it down the toilet or pour it down the drain unless instructed to do so. Instead, consult with your pharmacist for guidance on the best disposal method. You may also want to check if there are any drug take-back programs available in your area.
What to Do If You Miss a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next scheduled dose, skip the missed dose and continue with your regular dosing schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
To get the most benefit from your medication, take it exactly as directed by your doctor. Carefully read all the information provided with your prescription, and follow the instructions closely. You can take this medication with or without food. If it causes stomach upset, taking it with food may help.
If you're using this medication to treat cold sores, chickenpox, shingles, or genital herpes, start taking it as soon as symptoms appear. The sooner you begin treatment, the more effective it will be. Don't delay, as taking it too late may reduce its effectiveness.
Continue taking your medication as prescribed by your doctor or healthcare provider, even if you start feeling better. It's essential to complete the full treatment course as directed.
Storing and Disposing of Your Medication
To maintain the quality and safety of your medication, store it at room temperature, away from light and moisture. Keep it in a dry place, and avoid storing it in a bathroom. Ensure that all medications are kept out of reach of children and pets.
When disposing of unused or expired medication, do not flush it down the toilet or pour it down the drain unless instructed to do so. Instead, consult with your pharmacist for guidance on the best disposal method. You may also want to check if there are any drug take-back programs available in your area.
What to Do If You Miss a Dose
If you miss a dose, take it as soon as you remember. However, if it's close to the time for your next scheduled dose, skip the missed dose and continue with your regular dosing schedule. Do not take two doses at the same time or take extra doses to make up for the missed one.
Lifestyle & Tips
- Drink plenty of fluids while taking this medication to help prevent kidney problems.
- Even with treatment, herpes infections can still be spread to others. Avoid sexual contact during outbreaks of genital herpes.
- Complete the full course of medication as prescribed, even if your symptoms improve, to ensure the infection is fully treated and to prevent resistance.
- For recurrent genital herpes, discuss suppressive therapy with your doctor if outbreaks are frequent or severe.
Available Forms & Alternatives
Available Strengths:
Generic Alternatives:
Dosing & Administration
Adult Dosing
Standard Dose:
Varies by indication. For chronic suppression of recurrent genital herpes: 400mg twice daily.
Dose Range:
200 - 800 mg
Condition-Specific Dosing:
Initial Genital Herpes:
400mg 3 times daily for 7-10 days OR 200mg 5 times daily for 10 days
Chronic Suppressive Therapy for Recurrent Genital Herpes:
400mg twice daily
Intermittent Therapy for Recurrent Genital Herpes:
400mg 3 times daily for 5 days (initiate at first sign/symptom)
Herpes Zoster (Shingles):
800mg 5 times daily for 7-10 days (initiate at first sign/symptom)
Varicella (Chickenpox):
800mg 5 times daily for 7 days (initiate at first sign/symptom)
Pediatric Dosing
Neonatal:
Not established for oral formulation; IV acyclovir used for neonatal HSV.
Infant:
Not established for oral formulation; IV acyclovir used for severe infections.
Child:
Varicella (âĨ2 years): 20 mg/kg (max 800 mg) 4 times daily for 5 days. Other indications vary by weight/age.
Adolescent:
Dosing generally follows adult recommendations for specific indications (e.g., genital herpes, zoster).
Dose Adjustments
Renal Impairment:
Mild:
CrCl 25-50 mL/min: Adjust dosing interval (e.g., for 400mg BID, consider 400mg once daily or 200mg BID depending on indication).
Moderate:
CrCl 10-25 mL/min: Adjust dosing interval (e.g., for 400mg BID, consider 200mg once daily or 400mg every 24 hours depending on indication).
Severe:
CrCl <10 mL/min: Adjust dosing interval (e.g., for 400mg BID, consider 200mg every 24-48 hours depending on indication).
Dialysis:
Hemodialysis: Administer dose after dialysis session. Peritoneal Dialysis: No significant removal, follow CrCl <10 mL/min guidelines.
Hepatic Impairment:
Mild:
No adjustment needed.
Moderate:
No adjustment needed.
Severe:
No adjustment needed.
Pharmacology
Mechanism of Action
Acyclovir is a synthetic purine nucleoside analog with in vitro and in vivo inhibitory activity against herpes simplex virus types 1 (HSV-1), 2 (HSV-2), and varicella-zoster virus (VZV). Acyclovir is selectively phosphorylated by the viral enzyme thymidine kinase (TK) to acyclovir monophosphate, which is then converted to acyclovir diphosphate by cellular guanylate kinase and finally to acyclovir triphosphate by other cellular enzymes. Acyclovir triphosphate inhibits viral DNA replication by three mechanisms: 1) competitive inhibition of viral DNA polymerase, 2) incorporation into and termination of the growing viral DNA chain, and 3) inactivation of the viral DNA polymerase.
Pharmacokinetics
Absorption:
Bioavailability:
15-30% (oral)
Tmax:
1.5-2 hours
FoodEffect:
Food does not significantly affect the absorption of acyclovir.
Distribution:
Vd:
0.8 L/kg
ProteinBinding:
9-33%
CnssPenetration:
Limited (CSF concentrations are approximately 50% of plasma concentrations)
Elimination:
HalfLife:
2.5-3.3 hours (in patients with normal renal function)
Clearance:
Not available (highly variable)
ExcretionRoute:
Renal (glomerular filtration and tubular secretion)
Unchanged:
60-80%
Pharmacodynamics
OnsetOfAction:
Not precisely defined for clinical effect; antiviral activity begins upon cellular uptake and phosphorylation.
PeakEffect:
Not precisely defined for clinical effect; correlates with peak plasma concentrations (Tmax).
DurationOfAction:
Related to dosing interval and viral replication cycle; requires frequent dosing due to short half-life.
Safety & Warnings
Side Effects
Urgent Side Effects: Seek Medical Help Right Away
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical attention immediately:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Behavioral problems
Mood changes
Feeling confused
Hallucinations (seeing or hearing things that are not there)
Seizures
Shakiness
Feeling dizzy or sleepy
Abnormal burning, numbness, or tingling sensations
Changes in speech
Severe kidney problems, which may be indicated by:
+ Inability to pass urine
+ Blood in the urine
+ Changes in the amount of urine passed
+ Unexpected weight gain
Life-threatening blood disorders, such as thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS), which may be indicated by:
+ Feeling extremely tired or weak
+ Bruising or bleeding
+ Dark urine or yellow skin and eyes
+ Pale skin
+ Changes in the amount of urine passed
+ Changes in eyesight
+ Weakness or numbness on one side of the body
+ Trouble speaking or thinking
+ Changes in balance
+ Fever
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other unusual symptoms, contact your doctor or seek medical attention:
Upset stomach or vomiting
Feeling tired or weak
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects not mentioned here. If you have questions or concerns about side effects, contact your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Although rare, some people may experience severe and potentially life-threatening side effects while taking this medication. If you notice any of the following symptoms, contact your doctor or seek medical attention immediately:
Signs of an allergic reaction, such as:
+ Rash
+ Hives
+ Itching
+ Red, swollen, blistered, or peeling skin with or without fever
+ Wheezing
+ Tightness in the chest or throat
+ Trouble breathing, swallowing, or talking
+ Unusual hoarseness
+ Swelling of the mouth, face, lips, tongue, or throat
Behavioral problems
Mood changes
Feeling confused
Hallucinations (seeing or hearing things that are not there)
Seizures
Shakiness
Feeling dizzy or sleepy
Abnormal burning, numbness, or tingling sensations
Changes in speech
Severe kidney problems, which may be indicated by:
+ Inability to pass urine
+ Blood in the urine
+ Changes in the amount of urine passed
+ Unexpected weight gain
Life-threatening blood disorders, such as thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS), which may be indicated by:
+ Feeling extremely tired or weak
+ Bruising or bleeding
+ Dark urine or yellow skin and eyes
+ Pale skin
+ Changes in the amount of urine passed
+ Changes in eyesight
+ Weakness or numbness on one side of the body
+ Trouble speaking or thinking
+ Changes in balance
+ Fever
Other Possible Side Effects
Like all medications, this drug can cause side effects. While many people may not experience any side effects or only minor ones, it's essential to discuss any concerns with your doctor. If you experience any of the following side effects or any other unusual symptoms, contact your doctor or seek medical attention:
Upset stomach or vomiting
Feeling tired or weak
Reporting Side Effects
This list is not exhaustive, and you may experience other side effects not mentioned here. If you have questions or concerns about side effects, contact your doctor. You can also report side effects to the FDA at 1-800-332-1088 or online at https://www.fda.gov/medwatch.
Seek Immediate Medical Attention If You Experience:
- Signs of kidney problems (e.g., decreased urination, swelling in feet or ankles, unusual tiredness)
- Signs of allergic reaction (e.g., rash, itching/swelling, severe dizziness, trouble breathing)
- Neurological changes (e.g., confusion, hallucinations, unusual behavior, seizures, tremors)
- Severe stomach pain, nausea, vomiting, or diarrhea
- Unusual bruising or bleeding
Before Using This Medicine
Before Taking This Medication: Important Information to Share with Your Doctor
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the symptoms you experienced as a result of the allergy.
All medications you are currently taking, including prescription and over-the-counter (OTC) drugs, natural products, and vitamins. This information will help your doctor and pharmacist identify potential interactions between this medication and other substances you are taking.
* Any existing health problems, as this medication may interact with certain conditions.
To ensure your safety, it is crucial to verify that it is safe to take this medication with all your current medications and health conditions. Do not initiate, stop, or adjust the dosage of any medication without first consulting your doctor.
It is essential to inform your doctor about the following:
Any allergies you have, including allergies to this medication, its components, or other substances, such as foods or drugs. Be sure to describe the symptoms you experienced as a result of the allergy.
All medications you are currently taking, including prescription and over-the-counter (OTC) drugs, natural products, and vitamins. This information will help your doctor and pharmacist identify potential interactions between this medication and other substances you are taking.
* Any existing health problems, as this medication may interact with certain conditions.
To ensure your safety, it is crucial to verify that it is safe to take this medication with all your current medications and health conditions. Do not initiate, stop, or adjust the dosage of any medication without first consulting your doctor.
Precautions & Cautions
Important Warnings and Cautions
When taking this medication, it is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are using this drug.
To stay hydrated, drink plenty of non-caffeinated liquids every day, unless your doctor advises you to limit your fluid intake.
If you are 65 years or older, use this medication with caution, as you may be more susceptible to side effects.
If you are pregnant, planning to become pregnant, or breastfeeding, consult your doctor to discuss the potential benefits and risks to you and your baby.
Herpes Infection Considerations
This medication is not a cure for herpes infections. Consult your doctor to understand the treatment goals and expectations.
If you have genital herpes, note that this medication will not prevent the spread of the infection. Avoid any sexual activity when you have active sores or symptoms of genital herpes. Additionally, genital herpes can still be transmitted even when you do not have visible symptoms. To reduce the risk of transmission, use a latex or polyurethane condom during sexual activity and consult your doctor for further guidance.
When taking this medication, it is essential to inform all your healthcare providers, including doctors, nurses, pharmacists, and dentists, that you are using this drug.
To stay hydrated, drink plenty of non-caffeinated liquids every day, unless your doctor advises you to limit your fluid intake.
If you are 65 years or older, use this medication with caution, as you may be more susceptible to side effects.
If you are pregnant, planning to become pregnant, or breastfeeding, consult your doctor to discuss the potential benefits and risks to you and your baby.
Herpes Infection Considerations
This medication is not a cure for herpes infections. Consult your doctor to understand the treatment goals and expectations.
If you have genital herpes, note that this medication will not prevent the spread of the infection. Avoid any sexual activity when you have active sores or symptoms of genital herpes. Additionally, genital herpes can still be transmitted even when you do not have visible symptoms. To reduce the risk of transmission, use a latex or polyurethane condom during sexual activity and consult your doctor for further guidance.
Overdose Information
Overdose Symptoms:
- Increased BUN and serum creatinine (indicating renal dysfunction)
- Lethargy
- Confusion
- Hallucinations
- Seizures
- Coma
What to Do:
Seek immediate medical attention. Hemodialysis can significantly remove acyclovir from the blood. Call 1-800-222-1222 (Poison Control).
Drug Interactions
Major Interactions
- Foscarnet (increased risk of renal toxicity)
- Mycophenolate mofetil (increased concentrations of both drugs)
Moderate Interactions
- Probenecid (decreases renal clearance of acyclovir, increasing plasma levels and half-life)
- Cimetidine (may increase acyclovir AUC, but clinical significance is minor)
- Nephrotoxic drugs (e.g., aminoglycosides, NSAIDs, cyclosporine, tacrolimus) - potential for additive renal toxicity, especially in patients with pre-existing renal impairment.
Monitoring
Baseline Monitoring
Renal function (BUN, serum creatinine)
Rationale: Acyclovir is primarily renally eliminated; baseline assessment is crucial for dose adjustment, especially in elderly or renally impaired patients.
Timing: Prior to initiation of therapy.
Hydration status
Rationale: Adequate hydration is important to prevent renal tubular crystallization, especially with IV acyclovir, but also relevant for high oral doses.
Timing: Prior to and during therapy.
Routine Monitoring
Renal function (BUN, serum creatinine)
Frequency: Periodically during prolonged therapy or in patients with risk factors for renal impairment (e.g., elderly, concomitant nephrotoxic drugs).
Target: Within normal limits or stable for patient's baseline.
Action Threshold: Significant increase in BUN/creatinine; consider dose adjustment or discontinuation.
Hydration status
Frequency: Daily, especially during acute high-dose therapy.
Target: Adequate fluid intake.
Action Threshold: Signs of dehydration; encourage fluid intake.
Clinical response to therapy
Frequency: Daily/as needed
Target: Resolution or improvement of viral symptoms.
Action Threshold: Lack of improvement or worsening symptoms; consider resistance or alternative diagnosis.
Symptom Monitoring
- Signs of renal dysfunction (decreased urine output, swelling)
- Neurological symptoms (confusion, hallucinations, seizures, tremors, especially in renally impaired or elderly patients)
- Gastrointestinal upset (nausea, vomiting, diarrhea)
- Headache
- Rash
Special Patient Groups
Pregnancy
Acyclovir is generally considered safe for use during pregnancy when clinically indicated. The Acyclovir in Pregnancy Registry (1984-1999) did not show an increased risk of birth defects compared to the general population. Use should be based on a risk-benefit assessment.
Trimester-Specific Risks:
First Trimester:
No increased risk of major birth defects observed in human studies.
Second Trimester:
No specific risks identified.
Third Trimester:
No specific risks identified; may be used for suppressive therapy near term to prevent neonatal herpes transmission.
Lactation
Acyclovir is excreted into breast milk. However, infant exposure is low, and adverse effects in breastfed infants are not expected. Considered compatible with breastfeeding by most experts (Lactation Risk Category L2).
Infant Risk:
Low risk; monitor infant for diarrhea or rash, though these are rare.
Pediatric Use
Dosing is weight-based for many indications in children. Oral acyclovir is generally not recommended for neonates or infants due to poor bioavailability and the need for higher systemic levels for severe infections (IV acyclovir is preferred). Close monitoring for renal function and neurological side effects is important.
Geriatric Use
Elderly patients are more likely to have decreased renal function, which can lead to increased acyclovir concentrations and a higher risk of adverse effects, particularly neurological ones (e.g., confusion, hallucinations). Dose adjustment based on creatinine clearance is crucial. Adequate hydration is also important.
Clinical Information
Clinical Pearls
- For optimal efficacy in acute infections (e.g., herpes zoster, varicella), initiate acyclovir therapy as early as possible, ideally within 24-72 hours of rash onset.
- Acyclovir is not a cure for herpes infections; it only helps manage symptoms and reduce the frequency/severity of outbreaks.
- Resistance to acyclovir can occur, especially in immunocompromised patients with prolonged or repeated exposure. Suspect resistance if lesions fail to respond to appropriate dosing.
- Ensure adequate hydration, especially with high doses or in patients with impaired renal function, to prevent renal tubular crystallization.
- Valacyclovir and famciclovir are prodrugs of acyclovir and penciclovir, respectively, offering improved oral bioavailability and less frequent dosing compared to acyclovir.
Alternative Therapies
- Valacyclovir (Valtrex) - prodrug of acyclovir with better bioavailability, allowing less frequent dosing.
- Famciclovir (Famvir) - prodrug of penciclovir, also with better bioavailability and less frequent dosing.
- Penciclovir (Denavir) - topical cream for herpes labialis.
Cost & Coverage
Average Cost:
$10 - $50 per 30 tablets (generic 400mg)
Generic Available:
Yes
Insurance Coverage:
Tier 1 (Generic) or Tier 2 (Brand)
General Drug Facts
If your symptoms or health issues persist or worsen, it's essential to contact your doctor for further guidance. To ensure your safety, never share your medication with others or take someone else's medication. Some medications may come with an additional patient information leaflet, so be sure to check with your pharmacist for more information. If you have any questions or concerns about your medication, don't hesitate to reach out to your doctor, nurse, pharmacist, or other healthcare provider. In the event of a suspected overdose, immediately call your local poison control center or seek medical attention. When seeking help, be prepared to provide details about the medication taken, the amount, and the time it happened.