From the Guidelines
Foscarnet is more likely to cause neutropenia than leukocytosis, with neutropenia being a significant concern due to its potential to increase the risk of infections. Foscarnet (sodium phosphonoformate) is an antiviral medication used to treat cytomegalovirus (CMV) retinitis and acyclovir-resistant herpes infections. According to the NCCN Guidelines panel 1, foscarnet is recommended for patients who cannot tolerate ganciclovir or for second-line pre-emptive therapy. The guidelines also mention that ganciclovir had a higher rate of early discontinuation because of neutropenia or thrombocytopenia, but there is limited data to recommend foscarnet as first-line treatment of CMV.
The mechanism behind foscarnet-induced neutropenia involves bone marrow suppression, which affects white blood cell production. Leukocytosis can also occur but is less frequent and may represent a reactive response to the medication or underlying infection. Clinicians should monitor complete blood counts regularly during foscarnet therapy, typically weekly for induction therapy and biweekly during maintenance. If severe neutropenia develops (absolute neutrophil count below 500 cells/mm³), dose reduction or temporary discontinuation may be necessary.
Some key points to consider when using foscarnet include:
- Foscarnet can cause nephrotoxicity and electrolyte abnormalities, but is generally tolerated 1
- The standard dosing for CMV retinitis is 60 mg/kg IV every 8 hours or 90 mg/kg IV every 12 hours for 2-3 weeks for induction, followed by maintenance therapy of 90-120 mg/kg IV once daily, with adjustments based on renal function
- Clinicians should weigh the benefits of foscarnet therapy against the potential toxicity associated with long-term antiviral use, particularly in patients with significant chronic GVHD.
From the FDA Drug Label
Marrow Suppression10% Anemia9% TABLE 12 CRRT: Selected Adverse Events
- Pts. = patients with event; †Rate = events/person/year; ‡ANC = absolute neutrophil count FoscavirN=88GanciclovirN=93CombinationN=93 No. EventsNo. Pts.*Rate†No. EventsNo. Pts.*Rate†No. EventsNo. Pts.*Rate† Anemia (Hgb <70g/L)1170.20970.1419150.33 Neutropenia‡ ANC <0.75 x 109 cells/L ANC <0.50 x 109 cells/L 8650 3225 1.530.91 9549 4128 1.510.80 10750 5128 1. 910.85
Foscarnet can cause neutropenia, as evidenced by the decrease in absolute neutrophil count (ANC) to <0.75 x 10^9 cells/L and <0.50 x 10^9 cells/L in some patients. However, there is no direct information in the provided drug labels that suggests foscarnet causes leukocytosis. 2 2
From the Research
Foscarnet and Its Effects on Leukocytosis or Neutropenia
- Foscarnet is an antiviral medication used to treat cytomegalovirus (CMV) infections, particularly in immunocompromised patients such as those with AIDS or undergoing hematopoietic stem cell transplantation 3, 4.
- The medication has been compared to ganciclovir in several studies, with results indicating that foscarnet is equally effective but may have a different side effect profile 5, 6, 7.
- Regarding its impact on leukocytosis or neutropenia, studies suggest that foscarnet may be associated with a lower risk of severe neutropenia compared to ganciclovir 5, 6.
- In a randomized multicenter trial, foscarnet was found to cause severe neutropenia in 4% of patients, compared to 11% of patients treated with ganciclovir 5.
- Another study found that foscarnet was well-tolerated and effective in preventing CMV disease in allogeneic marrow transplant recipients who were unable to receive ganciclovir due to neutropenia 6.
- However, foscarnet can still cause adverse events such as electrolyte abnormalities, neutropenia, and thrombocytopenia, although the incidence of these events may be lower compared to ganciclovir 7.
- Overall, the evidence suggests that foscarnet is less likely to cause neutropenia compared to ganciclovir, but its effects on leukocytosis are not well-established 3, 4, 5, 6, 7.