Zovirax 800mg 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 purine nucleoside analog
Pregnancy Category
Category B
FDA Approved
Jan 1982
DEA Schedule
Not Controlled
Overview
What is this medicine?
Acyclovir is an antiviral medicine used to treat infections caused by certain types of viruses, including herpes simplex (which causes cold sores and genital herpes) and varicella zoster (which causes chickenpox and shingles). It works by stopping the growth and spread of the virus in the body.
How to Use This Medicine
Taking Your Medication Correctly
To get the most benefit from your medication, follow your doctor's instructions carefully. Read all the information provided with your prescription and follow the instructions precisely. You can take this medication with or without food, but if it causes stomach upset, take it with food to help minimize this side effect.
If you are taking this medication to treat cold sores, chickenpox, shingles, or genital herpes, it's essential to start taking it as soon as your 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 exactly as directed by your doctor or healthcare provider, even if you start feeling better. This will help ensure that the infection is fully treated and reduce the risk of complications.
Storing and Disposing of Your Medication
To maintain the quality and safety of your medication, store it at room temperature, away from direct light and moisture. Keep it in a dry place, such as a closet or drawer, and avoid storing it in the bathroom. Make sure to keep all medications out of the reach of children and pets to prevent accidental ingestion.
When disposing of unused or expired medication, do not flush it down the toilet or pour it down the drain unless specifically instructed to do so. Instead, check with your pharmacist for guidance on the best way to dispose of your medication. You may also want to explore local drug take-back programs 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, follow your doctor's instructions carefully. Read all the information provided with your prescription and follow the instructions precisely. You can take this medication with or without food, but if it causes stomach upset, take it with food to help minimize this side effect.
If you are taking this medication to treat cold sores, chickenpox, shingles, or genital herpes, it's essential to start taking it as soon as your 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 exactly as directed by your doctor or healthcare provider, even if you start feeling better. This will help ensure that the infection is fully treated and reduce the risk of complications.
Storing and Disposing of Your Medication
To maintain the quality and safety of your medication, store it at room temperature, away from direct light and moisture. Keep it in a dry place, such as a closet or drawer, and avoid storing it in the bathroom. Make sure to keep all medications out of the reach of children and pets to prevent accidental ingestion.
When disposing of unused or expired medication, do not flush it down the toilet or pour it down the drain unless specifically instructed to do so. Instead, check with your pharmacist for guidance on the best way to dispose of your medication. You may also want to explore local drug take-back programs 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
- Take the medicine exactly as prescribed by your doctor, even if you start to feel better. Do not skip doses.
- Drink plenty of fluids while taking acyclovir to help prevent kidney problems.
- Acyclovir is not a cure for herpes infections and does not prevent the spread of herpes to others. Avoid sexual contact during outbreaks.
- For cold sores, start treatment at the first sign of an outbreak (tingling, itching, or burning).
Available Forms & Alternatives
Available Strengths:
Generic Alternatives:
Dosing & Administration
Adult Dosing
Standard Dose:
Varies by indication. For Herpes Zoster: 800 mg orally 5 times daily for 7 to 10 days. For Genital Herpes (initial episode): 200 mg orally 5 times daily for 10 days. For Genital Herpes (chronic suppressive therapy): 400 mg orally twice daily.
Dose Range:
200 - 800 mg
Condition-Specific Dosing:
Herpes Zoster:
800 mg orally 5 times daily for 7 to 10 days
Genital Herpes (initial episode):
200 mg orally 5 times daily for 10 days
Genital Herpes (recurrent episodes):
200 mg orally 5 times daily for 5 days OR 400 mg orally 3 times daily for 5 days OR 800 mg orally twice daily for 2 days
Genital Herpes (chronic suppressive therapy):
400 mg orally twice daily
Varicella (Chickenpox):
800 mg orally 4 times daily for 5 days
Pediatric Dosing
Neonatal:
Not established for oral formulation; IV dosing used for neonatal herpes simplex.
Infant:
Not established for oral formulation; IV dosing used for severe infections.
Child:
Varicella (2 years and older): 20 mg/kg orally (up to 800 mg) 4 times daily for 5 days. Herpes Simplex (immunocompromised): 20 mg/kg orally (up to 800 mg) 3-5 times daily.
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 or reduce dose. For Zoster: 800 mg 3 times daily. For Genital Herpes: 200 mg 3 times daily.
Moderate:
CrCl 10-25 mL/min: Adjust dosing interval or reduce dose. For Zoster: 800 mg twice daily. For Genital Herpes: 200 mg twice daily.
Severe:
CrCl <10 mL/min: Adjust dosing interval or reduce dose. For Zoster: 800 mg once daily. For Genital Herpes: 200 mg once daily.
Dialysis:
Hemodialysis: Administer dose after dialysis. For Zoster: 800 mg once daily, with an additional dose after each dialysis. For Genital Herpes: 200 mg once daily, with an additional dose after each dialysis. Peritoneal Dialysis: No significant removal, follow severe impairment 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). It is selectively phosphorylated by the viral enzyme thymidine kinase (TK) to acyclovir monophosphate, which is then converted to acyclovir triphosphate by cellular kinases. Acyclovir triphosphate inhibits viral DNA replication by three mechanisms: 1) competitive inhibition of viral DNA polymerase, 2) incorporation into viral DNA resulting in chain termination, and 3) inactivation of the viral DNA polymerase.
Pharmacokinetics
Absorption:
Bioavailability:
15-30% (oral, dose-dependent)
Tmax:
1.5-2.5 hours
FoodEffect:
Food does not significantly affect the extent of absorption.
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 (normal renal function); significantly prolonged in renal impairment.
Clearance:
Primarily renal clearance (glomerular filtration and tubular secretion).
ExcretionRoute:
Renal (urine)
Unchanged:
62-91% (excreted unchanged in urine)
Pharmacodynamics
OnsetOfAction:
Variable, depends on viral replication cycle and host immune response. Clinical improvement typically seen within 24-72 hours.
PeakEffect:
Peak plasma concentrations reached within 1.5-2.5 hours.
DurationOfAction:
Plasma concentrations decline rapidly due to short half-life, necessitating frequent dosing.
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 sensations, such as burning, numbness, or tingling
Changes in speech
Kidney Problems
Severe and potentially life-threatening kidney problems have been reported with this medication. If you experience any of the following symptoms, contact your doctor right away:
Inability to pass urine
Blood in the urine
Changes in the amount of urine passed
Unexpected weight gain
Blood Problems
Rare but serious blood problems, such as thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS), have been reported with this medication. If you experience any of the following symptoms, contact your doctor right away:
Feeling very tired or weak
Bruising or bleeding
Dark urine or yellow skin or 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 Side Effects
Like all medications, this drug can cause side effects. Many people experience no side effects or only mild ones. If you notice any of the following side effects, or if they bother you or do not go away, contact your doctor:
Upset stomach or vomiting
Feeling tired or weak
Reporting Side Effects
If you have questions about side effects or want to report any, 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 sensations, such as burning, numbness, or tingling
Changes in speech
Kidney Problems
Severe and potentially life-threatening kidney problems have been reported with this medication. If you experience any of the following symptoms, contact your doctor right away:
Inability to pass urine
Blood in the urine
Changes in the amount of urine passed
Unexpected weight gain
Blood Problems
Rare but serious blood problems, such as thrombotic thrombocytopenic purpura/hemolytic uremic syndrome (TTP/HUS), have been reported with this medication. If you experience any of the following symptoms, contact your doctor right away:
Feeling very tired or weak
Bruising or bleeding
Dark urine or yellow skin or 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 Side Effects
Like all medications, this drug can cause side effects. Many people experience no side effects or only mild ones. If you notice any of the following side effects, or if they bother you or do not go away, contact your doctor:
Upset stomach or vomiting
Feeling tired or weak
Reporting Side Effects
If you have questions about side effects or want to report any, 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., little or no urination, painful or difficult urination, swelling in your feet or ankles, feeling tired or short of breath)
- Signs of nervous system problems (e.g., agitation, confusion, hallucinations, unusual thoughts or behavior, tremors, seizures)
- Easy bruising or bleeding, unusual weakness
- Severe skin rash, blistering, peeling skin
- Signs of an allergic reaction (e.g., hives, difficulty breathing, swelling of your face, lips, tongue, or throat)
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 allergic reaction you experienced, including any symptoms that occurred.
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. Never start, stop, or change the dose 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 allergic reaction you experienced, including any symptoms that occurred.
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. Never start, stop, or change the dose 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 other symptoms of genital herpes. Additionally, genital herpes can still be transmitted even if 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 other symptoms of genital herpes. Additionally, genital herpes can still be transmitted even if 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:
- Nausea
- Vomiting
- Diarrhea
- Headache
- Confusion
- Hallucinations
- Seizures
- Kidney failure (e.g., decreased urine output)
What to Do:
Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. Treatment is supportive and may include hemodialysis to remove acyclovir from the blood.
Drug Interactions
Major Interactions
- Foscarnet (increased risk of renal toxicity)
- Mycophenolate Mofetil (MMF) - Acyclovir can increase MMF concentrations, potentially leading to toxicity. Monitor MMF levels.
Moderate Interactions
- Probenecid (decreases renal clearance of acyclovir, increasing plasma concentrations and half-life)
- Cimetidine (may slightly increase acyclovir AUC, but generally not clinically significant)
- Nephrotoxic drugs (e.g., aminoglycosides, NSAIDs, cyclosporine, tacrolimus) - concurrent use may increase risk of renal dysfunction. Monitor renal function closely.
Monitoring
Baseline Monitoring
Renal function (serum creatinine, BUN, eGFR)
Rationale: Acyclovir is primarily renally eliminated; baseline assessment is crucial for dose adjustment, especially in elderly or those with pre-existing renal impairment.
Timing: Prior to initiation of therapy.
Hydration status
Rationale: Adequate hydration is important to prevent renal tubular crystalluria.
Timing: Prior to and during therapy.
Routine Monitoring
Renal function (serum creatinine, BUN)
Frequency: Periodically, especially in patients with renal impairment, elderly, or those receiving concomitant nephrotoxic drugs.
Target: Within patient's baseline or normal limits.
Action Threshold: Significant increase above baseline or normal range; consider dose adjustment or discontinuation.
Urine output
Frequency: Daily, especially in hospitalized patients or those at risk of dehydration.
Target: Adequate for hydration status.
Action Threshold: Decreased urine output; assess for dehydration or renal dysfunction.
Neurological status (for high doses or impaired renal function)
Frequency: Daily observation for signs of neurotoxicity.
Target: Normal mental status.
Action Threshold: Confusion, hallucinations, tremors, seizures; discontinue drug and provide supportive care.
Symptom Monitoring
- Nausea
- Vomiting
- Diarrhea
- Headache
- Rash
- Malaise
- Dizziness
- Confusion
- Hallucinations
- Seizures
- Signs of kidney problems (e.g., decreased urination, swelling in ankles/feet)
- Signs of allergic reaction (e.g., rash, itching/swelling, severe dizziness, trouble breathing)
Special Patient Groups
Pregnancy
Acyclovir is Pregnancy Category B. Extensive data from pregnancy registries and observational studies have not shown an increased risk of birth defects or adverse pregnancy outcomes with acyclovir use. It is often used to treat or suppress herpes infections during pregnancy, especially near term to prevent neonatal herpes.
Trimester-Specific Risks:
First Trimester:
No increased risk of major birth defects observed.
Second Trimester:
No increased risk of adverse outcomes observed.
Third Trimester:
Often used for suppression of recurrent genital herpes to prevent transmission to neonate during delivery.
Lactation
Acyclovir is excreted into breast milk. The amount ingested by the infant is generally considered low and unlikely to cause adverse effects. The American Academy of Pediatrics considers acyclovir compatible with breastfeeding. Monitor breastfed infants for diarrhea or rash.
Infant Risk:
L2 (likely compatible)
Pediatric Use
Dosing is weight-based for children, especially for varicella. Oral acyclovir is generally not recommended for children under 2 years for varicella unless immunocompromised. IV acyclovir is used for severe infections in neonates and infants. Renal function should be monitored, especially in younger children.
Geriatric Use
Elderly patients are more likely to have decreased renal function, which can lead to higher acyclovir concentrations and increased risk of adverse effects, particularly neurological. Dose adjustments based on creatinine clearance are essential. Ensure adequate hydration.
Clinical Information
Clinical Pearls
- Acyclovir is most effective when initiated at the earliest sign or symptom of a viral outbreak (e.g., within 24 hours of rash onset for shingles or chickenpox).
- Adequate hydration is critical during acyclovir therapy, especially with higher doses or IV administration, to prevent renal crystalluria.
- Acyclovir does not eradicate the latent virus and is not a cure for herpes infections; it only helps manage acute outbreaks and suppress recurrences.
- Resistance to acyclovir can occur, particularly in immunocompromised patients, and is usually due to mutations in viral thymidine kinase or DNA polymerase.
- Neurological adverse effects (e.g., confusion, hallucinations, seizures) are rare but more common in elderly patients, those with renal impairment, or at high doses. Discontinuation usually resolves these symptoms.
Alternative Therapies
- Valacyclovir (prodrug of acyclovir, better oral bioavailability, less frequent dosing)
- Famciclovir (prodrug of penciclovir, similar efficacy to acyclovir/valacyclovir, less frequent dosing)
- Penciclovir (topical cream for herpes labialis)
Cost & Coverage
Average Cost:
$30 - $150 per 30 tablets (800mg)
Generic Available:
Yes
Insurance Coverage:
Tier 1 or Tier 2 (generic), Tier 3 (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.