Acyclovir

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Generic Name of Acyclovir - Learn More

Acyclovir

Acyclovir Precaution - What You Need to Know

Acyclovir is generally well-tolerated, but certain precautions should be observed, particularly in specific populations or in patients with underlying health conditions.
- Pregnancy: Acyclovir is classified as a Category C drug during pregnancy. Although animal studies have shown some adverse effects, human data is limited. It should be used during pregnancy only when the benefits outweigh the potential risks, especially for life-threatening infections like herpes simplex or varicella-zoster.
- Breastfeeding: Acyclovir is excreted in breast milk, but at low concentrations. It is considered safe for use during breastfeeding, but close monitoring of the infant is recommended, particularly if the infant is premature or has renal problems.
- Renal Impairment: Acyclovir is primarily excreted through the kidneys, so patients with renal impairment (particularly those with severe kidney disease or dehydration) may require dose adjustments. Renal function should be monitored closely, as impaired renal function increases the risk of acyclovir toxicity, which can cause renal damage.
- Neurological Conditions: In patients with pre-existing neurological conditions, acyclovir should be used with caution, especially in higher doses, as it can lead to neurotoxic effects, including confusion, agitation, or seizures.
- Elderly: Older adults are at greater risk for renal and neurotoxic side effects, especially in those with impaired renal function. Lower doses or longer intervals between doses may be necessary in this population.
- Hydration: Dehydration can increase the risk of renal toxicity, so adequate hydration should be maintained during acyclovir therapy, particularly in patients receiving higher doses.

Acyclovir Indication - Uses and Benefits

Acyclovir is primarily indicated for the treatment of infections caused by herpesviruses. The main indications include:
- Herpes Simplex Virus (HSV) Infections: Acyclovir is effective in treating primary and recurrent infections caused by HSV, including oral herpes (cold sores), genital herpes, and herpes labialis. It can reduce the duration and severity of outbreaks, as well as suppress viral shedding.
- Varicella-Zoster Virus (VZV) Infections: Acyclovir is used for the treatment of shingles (herpes zoster) and chickenpox (varicella). Early treatment with acyclovir can reduce the severity and duration of symptoms, particularly in immunocompromised patients.
- Cytomegalovirus (CMV): Acyclovir is used off-label to treat CMV infections, especially in immunocompromised patients (e.g., organ transplant recipients).
- Off-Label Uses: Acyclovir has been used off-label for herpes encephalitis, prevention of neonatal herpes, and chronic suppression of recurrent herpes simplex infections. It is also sometimes used for prevention of herpes simplex in immunocompromised individuals, such as those undergoing chemotherapy or organ transplantation.

Acyclovir Contraindications - Important Warnings

Acyclovir should not be used in the following conditions:
- Hypersensitivity: Patients who are allergic to acyclovir or any of its components should not use this medication. Signs of hypersensitivity may include rash, itching, or swelling, and in severe cases, anaphylaxis could occur.
- Severe Renal Insufficiency: In patients with significant renal impairment (e.g., end-stage renal disease), acyclovir should be used cautiously or avoided unless necessary, as it can accumulate and increase the risk of toxicity.
- Dehydration: Acyclovir can cause renal toxicity, particularly in patients who are dehydrated. Hydration should be ensured, especially in those receiving intravenous acyclovir or high doses.
- Neurological Disorders: Patients with a history of seizures or severe neurological conditions should use acyclovir with caution due to the potential for neurotoxic side effects, including confusion, agitation, and seizures, especially at higher doses or in those with renal impairment.
- Pregnancy: Acyclovir should only be used during pregnancy if absolutely necessary and when the potential benefit outweighs the risks, especially in cases of severe herpesvirus infections.

Acyclovir Side Effects - What to Expect

Acyclovir is generally well-tolerated, but side effects may occur, particularly in patients with renal dysfunction or those receiving high doses.
- Common Side Effects:
- Nausea, vomiting, and diarrhea are mild and typically transient.
- Headache and dizziness can also occur but are usually mild.
- Serious Side Effects:
- Renal Toxicity: Acyclovir can cause renal impairment, especially in dehydrated or renally impaired patients. This can lead to acute renal failure if not properly managed.
- Neurotoxicity: High doses or renal dysfunction can result in confusion, hallucinations, agitation, and seizures, particularly in the elderly.
- Blood Disorders: Rarely, acyclovir can cause thrombocytopenia (low platelets), anemia, or leukopenia (low white blood cells), potentially increasing the risk of infections or bleeding.
- Hypersensitivity: Severe allergic reactions, such as rash, itching, and in rare cases, anaphylaxis, can occur, though these are uncommon.
- Long-Term Use: Prolonged use of acyclovir may increase the risk of renal and neurotoxic effects, particularly in patients with renal impairment.

Acyclovir Pregnancy Category ID - Safety Information

2

Acyclovir Mode of Action - How It Works

Acyclovir is a nucleoside analogue that works by inhibiting viral DNA synthesis. It is selectively activated within infected cells, where it is converted into its active form, acyclovir triphosphate.
- Inhibition of Viral DNA Polymerase: Acyclovir triphosphate competitively inhibits the viral DNA polymerase enzyme, preventing the incorporation of nucleotides into the growing viral DNA strand. This halts viral replication.
- Selective Activation: The conversion of acyclovir to its active form is catalyzed by the viral enzyme thymidine kinase, which is present in infected cells but absent in most normal cells. This selective activation helps minimize toxicity to healthy cells.
- Pharmacokinetics: Acyclovir is poorly absorbed from the gastrointestinal tract when taken orally (bioavailability of around 15-20%) but is well absorbed when administered intravenously. It is widely distributed throughout the body, including the cerebrospinal fluid, and is excreted unchanged in the urine. The half-life of acyclovir is about 2.5-3 hours in patients with normal renal function but is prolonged in those with renal impairment.

Acyclovir Drug Interactions - What to Avoid

Several significant drug interactions can affect the efficacy and safety of acyclovir.
- Probenecid: Probenecid, a drug used to treat gout, can reduce the renal clearance of acyclovir, increasing plasma levels and the risk of toxicity. If co-administered, careful monitoring of renal function and acyclovir levels is needed.
- Other Nephrotoxic Drugs: Acyclovir should be used with caution in combination with other nephrotoxic drugs, such as aminoglycoside antibiotics, NSAIDs, and cisplatin, as this can increase the risk of renal toxicity.
- Immunosuppressive Drugs: The use of acyclovir in combination with immunosuppressive drugs (such as corticosteroids or chemotherapy agents) can increase the risk of opportunistic infections, including herpesviruses. These interactions do not directly affect acyclovir but should be considered in immunocompromised patients.
- Zidovudine: There is a potential for enhanced neurotoxicity when acyclovir is used with zidovudine, a drug used to treat HIV. This combination requires careful monitoring, especially in patients with pre-existing neurological conditions.
- Food and Alcohol: There are no significant food interactions with acyclovir, though maintaining adequate hydration is important. Alcohol does not directly affect acyclovir but can exacerbate dehydration or liver stress, which could impair the body's ability to process the drug.

Acyclovir Adult Dose - Recommended Dosage

The typical adult dose of acyclovir depends on the condition being treated:
- For Herpes Simplex (HSV) Infections:
- Primary infection: 200 mg five times daily for 10 days.
- Recurrent infection: 400 mg three times daily for 5 days.
- For Shingles (Varicella-Zoster):
- 800 mg five times daily for 7-10 days.
- For Chickenpox (Varicella):
- 800 mg four times daily for 5 days.
- For Cytomegalovirus (CMV):
- 800 mg five times daily for prophylaxis in immunocompromised patients.
- Severe Infections: For more severe infections or in immunocompromised patients, intravenous acyclovir may be required, with a typical dose of 5-10 mg/kg every 8 hours, depending on the severity of the infection.

Acyclovir Child Dose - Dosage for Children

Acyclovir doses for children depend on the age and condition being treated:
- For Herpes Simplex Infections:
- Children 2 years and older: 200 mg five times daily for 10 days.
- For Shingles (Varicella-Zoster):
- 20 mg/kg (up to 800 mg) five times daily for 7 days.
- For Chickenpox:
- 20 mg/kg (up to 800 mg) four times daily for 5 days.
- For Neonates:
- 10 mg/kg every 8 hours for severe infections, with careful monitoring for renal and neurological side effects.

Acyclovir Renal Dose - Dosage for Kidney Conditions

For patients with renal impairment, acyclovir dosage must be adjusted:
- CrCl > 50 mL/min: No dose adjustment is necessary.
- CrCl 10-50 mL/min: The dose may be reduced by 25-50%, depending on the condition.
- CrCl < 10 mL/min: A significant reduction in dose and/or extension of dosing intervals may be necessary.
- Dialysis: Acyclovir should be given after dialysis since hemodialysis clears acyclovir from the blood.