Foscarnet Medication: Uses, Dosage, Side Effects & Guidelines

Summary of Key Points

Foscarnet is an antiviral medication used to treat serious viral infections, particularly in individuals with weakened immune systems. It works by inhibiting the replication of viruses such as cytomegalovirus (CMV) and herpes simplex virus (HSV). Foscarnet is typically administered intravenously (IV) and is generally reserved for cases where other treatments have not been effective. Always consult your healthcare provider before starting or adjusting your Foscarnet therapy.

Names of Medication

US Brand Name: Foscavir

Generic Name: Foscarnet

The generic name refers to the active ingredient in the medication, while the brand name is the name given by the manufacturer. In this article, the generic name (Foscarnet) will be used in parentheses for clarity.

Pharmacologic Category

Category: Antiviral Agent

Mechanism: Viral DNA Polymerase Inhibitor

Foscarnet Dosage Guidelines

Foscarnet is used to treat a variety of viral infections, and the dosage will depend on the specific condition being treated. It is essential to follow your healthcare provider’s instructions carefully and never adjust your dose without consulting them first. If you need to speak with a doctor, you can schedule a telemedicine appointment with one of our providers.

Foscarnet for CMV Retinitis

Induction Dose: 60 mg/kg every 8 hours or 90 mg/kg every 12 hours for 14 to 21 days.

Maintenance Dose: 90 to 120 mg/kg once daily.

Foscarnet for Herpes Simplex Virus (HSV) Infections

Induction Dose: 40 mg/kg every 8 hours for 2 to 3 weeks or until lesions heal.

Maintenance Dose: 90 to 120 mg/kg once daily.

Foscarnet for Varicella-Zoster Virus (VZV) Infections

Induction Dose: 40 mg/kg every 8 hours for 10 days.

Foscarnet for Acyclovir-Resistant Herpes Infections

Induction Dose: 40 mg/kg every 8 hours for 10 to 14 days.

Foscarnet for Human Immunodeficiency Virus (HIV) Infections

Induction Dose: 40 mg/kg every 8 hours for 14 to 21 days.

Foscarnet for Fungal Infections

Induction Dose: 40 mg/kg every 8 hours for 14 to 21 days.

Foscarnet for Epstein-Barr Virus (EBV) Infections

Induction Dose: 40 mg/kg every 8 hours for 14 to 21 days.

Foscarnet for Kaposi’s Sarcoma

Induction Dose: 40 mg/kg every 8 hours for 14 to 21 days.

Foscarnet for Pneumocystis Pneumonia

Induction Dose: 40 mg/kg every 8 hours for 14 to 21 days.

Foscarnet for Toxoplasmosis

Induction Dose: 40 mg/kg every 8 hours for 14 to 21 days.

Dosage Forms and Strengths

Foscarnet Injection: Solution, 24 mg/mL (available in 250 mL or 500 mL vials)

Foscarnet Administration Guidelines

Foscarnet is administered intravenously (IV), meaning it is delivered directly into a vein. The infusion typically takes 1 to 2 hours, depending on the dose. Staying well-hydrated during Foscarnet treatment is crucial to help prevent kidney complications. Your healthcare provider may recommend additional fluids before and after the infusion to support kidney function. Always follow the administration guidelines provided by your healthcare team.

Foscarnet Side Effects and Adverse Reactions

Like all medications, Foscarnet can cause side effects. Some are more common than others, and it’s important to report any unusual symptoms to your healthcare provider. If you experience severe side effects, seek medical attention immediately.

Common Foscarnet Side Effects

Nausea and Vomiting: Feeling nauseous or vomiting is common, especially during the initial doses.

Diarrhea: Loose stools may occur, but staying hydrated can help manage this symptom.

Headache: Some patients report mild to moderate headaches.

Serious Foscarnet Side Effects

Kidney Problems: Foscarnet can affect kidney function, so regular monitoring is essential.

Seizures: In rare cases, Foscarnet can cause seizures, particularly in patients with low calcium levels.

Electrolyte Imbalance: Foscarnet can lead to changes in blood levels of calcium, magnesium, and potassium, which may require monitoring and treatment.

Contraindications for Foscarnet

A contraindication is a specific situation where a medication should not be used because it may be harmful. Before starting any new medication, it’s important to know if you have any conditions that would make the drug unsafe. Below are the contraindications for taking Foscarnet:

Severe Kidney Disease: Foscarnet is primarily eliminated by the kidneys. If you have severe kidney disease, taking Foscarnet can lead to further kidney damage or toxic levels of the drug in your body.

Electrolyte Imbalance: Foscarnet can cause changes in electrolyte levels, such as calcium, magnesium, and potassium. If you already have an imbalance, this can worsen and lead to serious complications like seizures or heart problems.

Hypersensitivity or Allergy to Foscarnet: If you have had an allergic reaction to Foscarnet in the past, you should not take this medication, as it could cause severe allergic reactions, including anaphylaxis.

Foscarnet Drug Interactions

Foscarnet can interact with other medications, potentially leading to harmful side effects or reduced effectiveness. It’s important to inform your healthcare provider about all medications you are taking, including over-the-counter drugs and supplements. Below are some medications that may interact with Foscarnet:

Amphotericin B (Fungizone): This antifungal medication can increase the risk of kidney damage when taken with Foscarnet.

Gentamicin (Garamycin): This antibiotic may also increase the risk of kidney damage when combined with Foscarnet.

Cidofovir (Vistide): Another antiviral drug that, when taken with Foscarnet, can significantly increase the risk of kidney toxicity.

Other Nephrotoxic Drugs: Medications that can harm the kidneys, such as certain chemotherapy agents or nonsteroidal anti-inflammatory drugs (NSAIDs), should be used cautiously with Foscarnet.

Foscarnet in Pregnancy

Is it safe to take Foscarnet during pregnancy? The safety of Foscarnet medication in pregnant women has not been extensively studied. While animal studies suggest potential risks to the fetus, in cases of life-threatening infections, the benefits of using Foscarnet may outweigh the risks. If you are pregnant or planning to become pregnant, it is crucial to consult your healthcare provider before starting Foscarnet therapy. They can help you carefully weigh the risks and benefits and explore alternative treatments if necessary.

Foscarnet while Breastfeeding

Is it safe to take Foscarnet while breastfeeding? It is not clear whether Foscarnet sodium passes into breast milk. Due to the potential for serious side effects in a nursing infant, breastfeeding is generally not recommended while taking Foscarnet. If you are breastfeeding or plan to breastfeed, discuss your options with your healthcare provider. They may suggest alternative treatments or recommend temporarily stopping breastfeeding while using this antiviral drug.

Estimated Cost of Foscarnet Medication

The estimated cost of a 30-day supply of Foscarnet without insurance can vary. With a GoodRx coupon, the price typically ranges from $500 to $1,000. Prices may differ based on the pharmacy and location. It’s always a good idea to check with your pharmacy for the most accurate pricing.

Possible Alternatives to Foscarnet

If you are unable to take Foscarnet or are exploring alternative treatments, other options are available depending on the condition being treated. Always consult your healthcare provider before making any changes to your treatment plan. You can also schedule a telemedicine appointment with one of our providers to discuss your options.

1. Cytomegalovirus (CMV) Retinitis: Alternatives include Ganciclovir (Cytovene) or Valganciclovir (Valcyte). In some cases, intraocular antiviral injections may be considered.
2. Herpes Simplex Virus (HSV) Infections: Acyclovir (Zovirax) or Valacyclovir (Valtrex) are commonly used alternatives. These medications are generally well-tolerated and effective for treating HSV infections.
3. Varicella-Zoster Virus (VZV) Infections: Acyclovir (Zovirax) and Valacyclovir (Valtrex) are also effective for treating shingles and chickenpox caused by VZV.
4. Acyclovir-Resistant Herpes Infections: For Acyclovir-resistant herpes infections, Foscarnet is often the preferred treatment. However, Cidofovir (Vistide) may be considered as an alternative in some cases.
5. Human Immunodeficiency Virus (HIV) Infections: Antiretroviral therapy (ART) is the standard treatment for HIV. Common medications include Tenofovir (Viread), Emtricitabine (Emtriva), and Efavirenz (Sustiva). Lifestyle changes, such as maintaining a healthy diet and regular exercise, can also support immune health.
6. Fungal Infections: Antifungal medications like Fluconazole (Diflucan) or Itraconazole (Sporanox) are commonly used. Depending on the type of fungal infection, topical treatments or lifestyle changes, such as improving hygiene, may also be helpful.
7. Epstein-Barr Virus (EBV) Infections: There is no specific antiviral treatment for EBV. Supportive care, including rest, hydration, and over-the-counter pain relievers, is usually recommended.
8. Kaposi’s Sarcoma: This cancer is often treated with chemotherapy, radiation, or antiretroviral therapy if associated with HIV. Lifestyle changes, such as quitting smoking and maintaining a healthy diet, can also support treatment.
9. Pneumocystis Pneumonia (PCP): The first-line treatment for PCP is usually Trimethoprim-Sulfamethoxazole (Bactrim). Alternatives include Pentamidine (NebuPent) or Atovaquone (Mepron).
10. Toxoplasmosis: Pyrimethamine (Daraprim) combined with Sulfadiazine is the standard treatment. In some cases, Clindamycin (Cleocin) may be used as an alternative.

Recent Updates on Foscarnet Research

Recent research on Foscarnet has focused on its use in treating drug-resistant viral infections, particularly in immunocompromised patients. Studies show that Foscarnet remains effective for treating Acyclovir-resistant herpes infections and CMV retinitis in patients with HIV/AIDS. Ongoing research is exploring the potential of Foscarnet in combination with other antiviral agents to improve outcomes in patients with resistant viral infections. Additionally, researchers are investigating ways to reduce the nephrotoxic effects of Foscarnet, aiming to make the drug safer for long-term use.

Staying informed about new developments in your treatment options is essential. If you have any questions or concerns about Foscarnet or other medications, schedule a telemedicine appointment with one of our providers. We are here to guide you through your healthcare journey.

James Kingsley

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