Temozolomide is an alkylating drug. The chemical name of temozolomide is 3,4-dihydro-3-methyl-4-oxoimidazo[5,1d]- as -tetrazine-8-carboxamide. The structural formula of temozolomide is:
The material is a white to light tan/light pink powder with a molecular formula of C 6 H 6 N 6 O 2 and a molecular weight of 194.15. The molecule is stable at acidic pH (<5) and labile at pH >7; hence temozolomide can be administered orally. The prodrug, temozolomide, is rapidly hydrolyzed to the active 5-(3-methyltriazen-1-yl) imidazole-4-carboxamide (MTIC) at neutral and alkaline pH values, with hydrolysis taking place even faster at alkaline pH.
Temozolomide capsules, USP
Temozolomide capsules, USP for oral use contains either 5 mg, 20 mg, 100 mg, 140 mg, 180 mg, or 250 mg of temozolomide.
The inactive ingredients are as follows:
Temozolomide capsules USP 5 mg: lactose anhydrous (168 mg), colloidal anhydrous silica (1 mg), sodium starch glycolate (16 mg), tartaric acid (7 mg), and stearic acid (3 mg).
Temozolomide capsules USP 20 mg: lactose anhydrous (14.6 mg), colloidal anhydrous silica (0.2 mg), sodium starch glycolate (3.2 mg), tartaric acid (1.4 mg), and stearic acid (0.6 mg).
Temozolomide capsules USP 100 mg: lactose anhydrous (73 mg), colloidal anhydrous silica (1 mg), sodium starch glycolate (16 mg), tartaric acid (7 mg), and stearic acid (3 mg).
Temozolomide capsules USP 140 mg: lactose anhydrous (102.2 mg), colloidal anhydrous silica (1.4 mg), sodium starch glycolate (22.4 mg), tartaric acid (9.8 mg), and stearic acid (4.2 mg).
Temozolomide capsules USP 180 mg: lactose anhydrous (131.4 mg), colloidal anhydrous silica (1.8 mg), sodium starch glycolate (28.8 mg), tartaric acid (12.6 mg), and stearic acid (5.4 mg).
Temozolomide capsules USP 250 mg: lactose anhydrous (182.5 mg), colloidal anhydrous silica (2.5 mg), sodium starch glycolate (40 mg), tartaric acid (17.5 mg), and stearic acid (7.5 mg).
The body of the capsules is made of gelatin, and is white. The body of 250 mg capsule contain additionally sodium lauryl sulfate. The cap is also made of gelatin, and the colors vary based on the dosage strength. The capsule body and cap are imprinted with pharmaceutical branding ink, which contains black iron oxide, potassium hydroxide and shellac.
Temozolomide capsules USP 5 mg: The green cap contains gelatin, titanium dioxide, iron oxide yellow and FD&C Blue 2.
Temozolomide capsules USP 20 mg: The yellow cap contains gelatin, titanium dioxide and iron oxide yellow.
Temozolomide capsules USP 100 mg: The pink cap contains gelatin, titanium dioxide and iron oxide red.
Temozolomide capsules USP 140 mg: The transparent blue cap contains gelatin and FD&C Blue 2.
Temozolomide capsules USP 180 mg: The maroon cap contains gelatin, iron oxide red, iron oxide yellow and titanium dioxide.
Temozolomide capsules USP 250 mg: The white cap contains gelatin, titanium dioxide and sodium lauryl sulfate.
Temozolomide is not directly active but undergoes rapid nonenzymatic conversion at physiologic pH to the reactive compound 5-(3-methyltriazen-1-yl)-imidazole-4-carboxamide (MTIC). The cytotoxicity of MTIC is thought to be primarily due to alkylation of DNA. Alkylation (methylation) occurs mainly at the O 6 and N 7 positions of guanine.
Following a single oral dose of 150 mg/m 2 , the mean C max value for temozolomide was 7.5 mcg/mL and for MTIC was 282 ng/mL. The mean AUC value for temozolomide was 23.4 mcg·hr/mL and for MTIC was 864 ng·hr/mL.
Following a single 90-minute intravenous infusion of 150 mg/m 2 , the mean C max value for temozolomide was 7.3 mcg/mL and for MTIC was 276 ng/mL. The mean AUC value for temozolomide was 24.6 mcg·hr/mL and for MTIC was 891 ng·hr/mL.
Temozolomide exhibits linear kinetics over the therapeutic dosing range of 75 mg/m 2 /day to 250 mg/m 2 /day.
The median T max is 1 hour.
Effect of Food
The mean C max and AUC decreased by 32% and 9%, respectively, and median Tmax increased by 2-fold (from 1 to 2.25 hours) when temozolomide capsules were administered after a modified high-fat breakfast (587 calories comprised of 1 fried egg, 2 strips of bacon, 2 slices of toast, 2 pats of butter, and 8 oz whole milk).
Temozolomide has a mean apparent volume of distribution of 0.4 L/kg (%CV=13%). The mean percent bound of drug-related total radioactivity is 15%.
Clearance of temozolomide is about 5.5 L/hr/m 2 and the mean elimination half-life is 1.8 hours.
Temozolomide is spontaneously hydrolyzed at physiologic pH to the active species, MTIC and to temozolomide acid metabolite. MTIC is further hydrolyzed to 5-amino-imidazole-4-carboxamide (AIC), which is known to be an intermediate in purine and nucleic acid biosynthesis, and to methylhydrazine, which is believed to be the active alkylating species. Cytochrome P450 enzymes play only a minor role in the metabolism of temozolomide and MTIC. Relative to the AUC of temozolomide, the exposure to MTIC and AIC is 2.4% and 23%, respectively.
About 38% of the administered temozolomide total radioactive dose is recovered over 7 days: 38% in urine and 0.8% in feces. The majority of the recovery of radioactivity in urine is unchanged temozolomide (6%), AIC (12%), temozolomide acid metabolite (2.3%), and unidentified polar metabolite(s) (17%).
No clinically meaningful differences in the pharmacokinetics of temozolomide were observed based on age (range: 19 to 78 years), gender, smoking status (smoker vs. non-smoker), creatinine clearance (CLcr) of 36 to 130 mL/min/m 2 , or mild to moderate hepatic impairment (Child Pugh class A and B). The pharmacokinetics of temozolomide has not been studies in patients with CLcr < 36 mL/min/m 2 , end-stage renal disease on dialysis, or severe hepatic impairment (Child Pugh class C).
Drug Interaction Studies
Effect of Other Drugs on Temozolomide Pharmacokinetics
In a multiple-dose study, administration of Temozolomide capsules with ranitidine did not change the C max or AUC values for temozolomide or MTIC.
A population analysis indicated that administration of valproic acid decreases the clearance of temozolomide by about 5%.
A population analysis did not demonstrate any influence of coadministered dexamethasone, prochlorperazine, phenytoin, carbamazepine, ondansetron, histamine-2-receptor antagonists, or phenobarbital on the clearance of orally administered temozolomide.
Temozolomide is carcinogenic in rats at doses less than the maximum recommended human dose. Temozolomide induced mammary carcinomas in both males and females at doses 0.13 to 0.63 times the maximum human dose (25 to 125 mg/m 2) when administered orally on 5 consecutive days every 28 days for 6 cycles. Temozolomide also induced fibrosarcomas of the heart, eye, seminal vesicles, salivary glands, abdominal cavity, uterus, and prostate, carcinomas of the seminal vesicles, schwannomas of the heart, optic nerve, and harderian gland, and adenomas of the skin, lung, pituitary, and thyroid at doses 0.5 times the maximum daily dose. Mammary tumors were also induced following 3 cycles of temozolomide at the maximum recommended daily dose.
Temozolomide is a mutagen and a clastogen. In a reverse bacterial mutagenesis assay (Ames assay), temozolomide increased revertant frequency in the absence and presence of metabolic activation. Temozolomide was clastogenic in human lymphocytes in the presence and absence of metabolic activation.
Temozolomide impairs male fertility. Temozolomide caused syncytial cells/immature sperm formation at doses 50 and 125 mg/m 2 (0.25 and 0.63 times the human dose of 200 mg/m 2) in rats and dogs, respectively, and testicular atrophy in dogs at 125 mg/m 2.
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