Nitrosoureas

Nitrosoureas

Nitrosoureas are alkylating agents that work by halting cancer cell reproduction. They include:

• carmustine

• lomustine

• streptozocin.

Pharmacokinetics

When administered topically to treat mycosis fungoides (a rare skin malignancy), carmustine is 5% to 28% systemically absorbed.After oral administration, lomustine is absorbed adequately,though incompletely.

I.V. is the way

Streptozocin and carmustine are administered I.V. because they’re poorly absorbed orally.

Metabolism and excretion

Nitrosoureas are lipophilic (attracted to fat), distributing to fattytissues and cerebrospinal fluid. They’re metabolized extensivelybefore urine excretion.

Pharmacodynamics

During a process called bifunctional alkylation, nitrosoureas in-terfere with amino acids, purines, and DNA needed for cancer cells to divide, thus halting their reproduction.

Pharmacotherapeutics

The nitrosoureas are highly lipid (fat) soluble, which allows them or their metabolites to easily cross the blood-brain barrier. Be-cause of this ability, nitrosoureas are used to treat brain tumors and meningeal leukemias.

Drug interactions

Each of the nitrosoureas has its own interactions with other drugs. Cimetidine may increase carmustine’s bone marrow toxici-ty. Streptozocin prolongs the elimination half-life of doxorubicin, prolonging the leukopenia and thrombocytopenia. (See Adversereactions to nitrosoureas.)