Is there a relationship between cytarabine pharmacokinetics and keratitis?--A case report.

While on therapy for acute myeloid leukemia, a 15-year-old girl developed extensive punctate keratitis of both eyes following high-dose cytarabine therapy (HD-Ara-C). Pharmacokinetic monitoring showed an increase of the Ara-C plasma levels up to twice the steady-state level within 10 minutes after discontinuation of the Ara-C infusion. Calculations of Ara-C plasma half-life, plasma clearance and volume of distribution were within the expected range. Owing to the short half-life of Ara-C in blood due to rapid deamination, varying infusion velocities will result in markedly varying plasma levels. Higher peak plasma levels lead to proportionally higher diffusion into compartments like tears, aqueous humor and cerebrospinal fluid. In compartments which lack noteworthy deaminase activity, dose intensity will be much more enhanced than in plasma. Peak plasma levels, therefore, may be associated with multifold local toxicity without concurrent increase of hematological toxicity. Especially when the drug is given in small volumes of infusion, these considerations should be taken into account. Precise control of infusion parameters and application of artificial tears for dilution of the Ara-C concentration on the corneal surface should be part of keratitis prophylaxis.