Mesnex Injection

MESNEX is indicated as a prophylactic agent in reducing the incidence of ifosfamide-induced hemorrhagic cystitis.

Limitation of Use:
MESNEX is not indicated to reduce the risk of hematuria due to other pathological conditions such as thrombocytopenia.

Hypersensitivity Reactions

MESNEX may cause systemic hypersensitivity reactions, including anaphylaxis. These reactions may include fever, cardiovascular symptoms (hypotension, tachycardia), acute renal impairment, hypoxia, respiratory distress, urticaria, angioedema, laboratory signs of disseminated intravascular coagulation, hematological abnormalities, increased liver enzymes, nausea, vomiting, arthralgia, and myalgia. These reactions may occur with the first exposure or after several months of exposure. Monitor for signs or symptoms. Discontinue MESNEX and provide supportive care.

Dermatologic Toxicity

Drug rash with eosinophilia and systemic symptoms and bullous and ulcerative skin and mucosal reactions, consistent with Stevens-Johnson syndrome or toxic epidermal necrolysis have occurred. MESNEX may cause skin and mucosal reactions characterized by urticaria, rash, erythema, pruritus, burning sensation, angioedema, periorbital edema, flushing and stomatitis. These reactions may occur with the first exposure or after several months of exposure. Discontinue MESNEX and provide supportive care.

Benzyl Alcohol Toxicity

Benzyl alcohol, a preservative in MESNEX, has been associated with serious adverse reactions and death (including gasping syndrome) in neonates, premature, and low-birth weight infants. The minimum amount of benzyl alcohol at which toxicity may occur is not known. Consider the combined daily metabolic load of benzyl alcohol from all sources when prescribing MESNEX (10.4 mg benzyl alcohol per mL). Neonates, premature, and low-birth weight infants, as well as patients receiving high dosages, may be more likely to develop toxicity. Monitor patients for signs or symptoms of toxicity. Avoid use in neonates, premature, and low-birth weight infants. [See Use in Specific Populations (8.4)].

Laboratory Test Interferences

False-Positive Urine Tests for Ketone Bodies

A false positive test for urinary ketones may arise in patients treated with MESNEX when using nitroprusside sodium-based urine tests (including dipstick tests). The addition of glacial acetic acid can be used to differentiate between a false positive result (cherry-red color that fades) and a true positive result (red-violet color that intensifies).

False-Negative Tests for Enzymatic CPK Activity

MESNEX may interfere with enzymatic creatinine phosphokinase (CPK) activity tests that use a thiol compound (e.g., N-acetylcysteine) for CPK reactiviation. This may result in a falsely low CPK level.

False-Positive Tests for Ascorbic Acid

MESNEX may cause false-positive reactions in Tillman’s reagent-based urine screening tests for ascorbic acid.

Use in Patients with a History of Adverse Reactions to Thiol Compounds

MESNEX is a thiol compound, i.e., a sulfhydryl (SH) group-containing organic compound. Hypersensitivity reactions to MESNEX and to amifostine, another thiol compound, have been reported. It is not clear whether patients who experienced an adverse reaction to a thiol compound are at increased risk for a hypersensitivity reaction to MESNEX.

No clinical drug interaction studies have been conducted with MESNEX.

Mechanism of Action

Mesna reacts chemically with the urotoxic ifosfamide metabolites, acrolein and 4-hydroxy-ifosfamide, resulting in their detoxification. The first step in the detoxification process is the binding of mesna to 4-hydroxy-ifosfamide forming a non-urotoxic 4-sulfoethylthioifosfamide. Mesna also binds to the double bonds of acrolein and to other urotoxic metabolites and inhibits their effects on the bladder.

Pharmacokinetics

Absorption

Following oral administration, peak plasma concentrations were reached within 1.5 to 4 hours and 3 to 7 hours for free mesna and total mesna (mesna plus dimesna and mixed disulfides), respectively. Oral bioavailability averaged 58% (range 45 to 71%) for free mesna and 89% (range 74 to 104%) for total mesna based on plasma AUC data from 8 healthy volunteers who received 1200 mg oral or intravenous doses.

Food does not affect the urinary availability of orally administered MESNEX.

Distribution

Mean apparent volume of distribution (Vd) for mesna is 0.652 ± 0.242 L/kg after intravenous administration which suggests distribution to total body water (plasma, extracellular fluid, and intracellular water).

Metabolism

Analogous to the physiological cysteine-cystine system, mesna is rapidly oxidized to its major metabolite, mesna disulfide (dimesna). Plasma concentrations of mesna exceed those of dimesna after oral or intravenous administration.

Excretion

Following intravenous administration of a single 800 mg dose, approximately 32% and 33% of the administered dose was eliminated in the urine in 24 hours as mesna and dimesna, respectively. Mean plasma elimination half-lives of mesna and dimesna are 0.36 hours and 1.17 hours, respectively. Mesna has a plasma clearance of 1.23 L/h/kg.

Intravenous MESNEX

Hemorrhagic cystitis produced by ifosfamide is dose dependent (Table 4). At a dose of 1.2 g/m2 ifosfamide administered daily for 5 days, 16 to 26% of the patients who received conventional uroprophylaxis (high fluid intake, alkalinization of the urine, and the administration of diuretics) developed hematuria (>50 RBC per hpf or macrohematuria) (Studies 1, 2, and 3). In contrast, none of the patients who received mesna injection together with this dose of ifosfamide developed hematuria (Studies 3 and 4). In two randomized studies, (Studies 5 and 6), higher doses of ifosfamide, from 2 g/m2 to 4 g/m2 administered for 3 to 5 days, produced hematuria in 31 to 100% of the patients. When MESNEX was administered together with these doses of ifosfamide, the incidence of hematuria was less than 7%.

Oral MESNEX

Clinical studies comparing recommended intravenous and oral MESNEX dosing regimens demonstrated incidences of grade 3 to 4 hematuria of <5%. Study 7 was an open label, randomized, two-way crossover study comparing three intravenous doses with an initial intravenous dose followed by two oral doses of MESNEX in patients with cancer treated with ifosfamide at a dose of 1.2 g/m2 to 2.0 g/m2 for 3 to 5 days. Study 8 was a randomized, multicenter study in cancer patients receiving ifosfamide at 2.0 g/m2 for 5 days. In both studies, development of grade 3 or 4 hematuria was the primary efficacy endpoint. The percent of patients developing hematuria in each of these studies is presented in Table 5.