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Mesna (Mesna) - Description and Clinical Pharmacology

 
 



DESCRIPTION

Mesna Injection is a detoxifying agent to inhibit the hemorrhagic cystitis induced by ifosfamide. The active ingredient, mesna, is a synthetic sulfhydryl compound designated as sodium-2-mercaptoethane sulfonate with a molecular formula of C2H5NaO3S2 and a molecular weight of 164.18. Its structural formula is as follows:

Mesna Injection is a sterile, nonpyrogenic, aqueous solution of colorless to light pink appearance in clear glass multidose vials for intravenous administration. Mesna Injection contains 100 mg/mL mesna, 0.25 mg/mL edetate disodium and sodium hydroxide for pH adjustment and qs with Water for Injection. Mesna Injection multidose vials also contain 10.4 mg/mL of benzyl alcohol as a preservative. The solution has a pH range of 6.5 to 7.4.

CLINICAL PHARMACOLOGY

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

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.

NONCLINICAL TOXICOLOGY

Carcinogenesis, Mutagenesis, Impairment of Fertility

No long-term studies in animals have been performed to evaluate the carcinogenic potential of mesna.

Mesna was not genotoxic in the in vitro Ames bacterial mutagenicity assay, the in vitro mammalian lymphocyte chromosomal aberration assay or the in vivo mouse micronucleus assay.

No studies on male or female fertility were conducted. No signs of male or female reproductive organ toxicity were seen in 6-month oral rat studies (≤2000 mg/kg/day) or 29-week oral dog studies (520 mg/kg/day) at doses approximately 10-fold higher than the maximum recommended human dose on a body surface area basis.

CLINICAL STUDIES

Intravenous Mesna

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 mesna was administered together with these doses of ifosfamide, the incidence of hematuria was less than 7%.

Table 4. Percent of Mesna Patients Developing Hematuria (≥50 RBC/hpf or macrohematuria)

*Ifosfamide dose 1.2 g/m2 d x 5

†Ifosfamide dose 2 g/m2 to 4 g/m2 d x 3 to 5

Study Conventional Uroprophylaxis
(number of patients)
Standard Mesna Intravenous
Regimen (number of patients)
Uncontrolled Studies*
Study 1 16% (7/44) -
Study 2 26% (11/43) -
Study 3 18% (7/38) 0% (0/21)
Study 4 - 0% (0/32)
Controlled Studies †
Study 5 31% (14/46) 6% (3/46)
Study 6 100% (7/7) 0% (0/8)

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