Chenodiol

CTEXLI is indicated for the treatment of cerebrotendinous xanthomatosis (CTX) in adults. CTEXLI is a bile acid indicated for treatment of cerebrotendinous xanthomatosis (CTX) in adults. ( 1 )

Tablets: 250 mg of chenodiol as white film-coated tablets imprinted with “MP” on one side and "250" on the other side. CTEXLI tablets: 250 mg. ( 3 )

None. None. ( 4 )

Hepatotoxicity : Obtain baseline liver transaminase and total bilirubin levels in all patients and monitor yearly and as clinically indicated. Interrupt treatment until the levels have returned to baseline values. For persistent or recurrent liver test abnormalities, consider discontinuing CTEXLI. ( 5.1 )

5.1 Hepatotoxicity Chenodiol, including CTEXLI, has been associated with hepatotoxicity [see Adverse Reactions ( 6 )] . In Trial 1, one CTEXLI-treated patient (7%) had increased ALT levels > 3 times ULN, which led to treatment interruption. Patients with pre-existing liver disease or bile duct abnormalities may be at higher risk for hepatotoxicity during treatment with CTEXLI. Published reports suggest patients who are poor sulfators of lithocholic acid are more likely to develop chenodiol-induced serum aminotransferase elevations [see Clinical Pharmacology ( 12.3 )] . Obtain baseline liver transaminase (ALT, AST) and total bilirubin levels in all patients prior to treatment initiation with CTEXLI. If liver transaminase levels are elevated > 3 times ULN or total bilirubin level is >2 times ULN, interrupt treatment with CTEXLI until the levels have returned to baseline values. Monitor liver transaminase and total bilirubin levels yearly and as clinically indicated. For persistent or recurrent liver test abnormalities, consider discontinuing CTEXLI. Inform the patient of the symptoms of hepatotoxicity (e.g., abdominal pain, bruising, dark-colored urine, fatigue, bleeding, jaundice, nausea, and pruritus). If clinical signs and symptoms consistent with hepatotoxicity occur, have the patient discontinue CTEXLI immediately.

The following clinically significant adverse reaction is described elsewhere in the labeling:

• Hepatotoxicity [see Warnings and Precautions ( 5.1 )] The most common adverse reactions (incidence > 14%) are diarrhea, headache, abdominal pain, constipation, hypertension, muscular weakness, and upper respiratory tract infection. ( 6.1 ) To report SUSPECTED ADVERSE REACTIONS, contact Mirum Pharmaceuticals at 1-855-MRM-4YOU or FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

6.1 Clinical Trials Experience Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice. The safety of CTEXLI was evaluated in a randomized, double blind, placebo-controlled, 2-period, 2-treatment crossover trial in 14 patients (16 to 55 years of age) with CTX (Trial 1). CTEXLI is not approved for use in pediatric patients. The dosage of CTEXLI was 250 mg orally three times a day [see Clinical Studies ( 14 )]. The mean (SD) chenodiol exposure during Trial 1 was 139.1 (26.7) days. The most common adverse reactions which occurred in two or more patients ( > 14%) during CTEXLI treatment (including the two 8-week open-label treatment periods) were diarrhea (36%), headache (21%), and abdominal pain (including abdominal pain upper) (14%), constipation (14%), hypertension (14%), muscular weakness (14%), and upper respiratory tract infection (14%). In Trial 1, one CTEXLI-treated patient (7%) had increased ALT levels > 3x ULN, which led to treatment interruption.

6.2 Postmarketing Experience The following adverse reactions have been identified during post approval use of chenodiol. Because these reactions are reported voluntarily from a population of uncertain size, it is not always possible to reliably estimate their frequency or establish a causal relationship to drug exposure.

• Hepatobiliary Disorders: Hepatotoxicity [see Warnings and Precautions ( 5.1 )]
• Immune System Disorders: Hypersensitivity reactions such as facial swelling, pruritus, rash, urticaria.

• Bile acid sequestering agents and aluminum-based antacids: Avoid concomitant use with CTEXLI. ( 7.1 )
• Coumarin and its derivatives: Monitor prothrombin time and adjust dosage accordingly. ( 7.2 )

7.1 Effect of Other Drugs on CTEXLI Co-administration of bile acid sequestering agents, such as cholestyramine and colestipol, or aluminum-based antacids may decrease absorption of CTEXLI in the intestine and may result in decreased efficacy of CTEXLI. Avoid concomitant use of bile acid sequestering agents or aluminum-based antacids with CTEXLI.

7.2 Effect of CTEXLI on Other Drugs Due to potential hepatotoxicity, CTEXLI may affect the pharmacodynamics of coumarin and its derivatives, causing unexpected prolongation of the prothrombin time and hemorrhage. If concomitant use of CTEXLI with coumarin or its derivatives is unavoidable, monitor prothrombin time. Adjust the dosage of coumarin or its derivatives in accordance with its approved product labeling.

8.1 Pregnancy Risk Summary Available data from published case reports over decades of use with chenodiol during pregnancy have not identified an increased risk of major birth defects, miscarriage, or other adverse maternal or fetal outcomes. Serious hepatic, renal and adrenal lesions occurred in fetuses of female Rhesus monkeys treated at doses 1 to 2 times the recommended human dose based on body surface area (mg/m 2 ). Hepatic lesions also occurred at doses comparable to the human dose based on body surface area in neonatal baboons born to mothers administered chenodiol during pregnancy ( see Data ). The animal study findings have not been demonstrated with human use. The background risk of major birth defects and miscarriage for the indicated population is unknown. All pregnancies have a background risk of birth defect, loss, or other adverse outcomes. In the US general population, the estimated background risk of major birth defects and miscarriage in clinically recognized pregnancies is 2 to 4% and 15 to 20%, respectively. Data Animal Data Hepatic lesions were reported in neonatal baboons whose mothers had received 18 to 38 mg/kg of chenodiol throughout pregnancy (0.6 to 1.4 times the recommended human dose based on body surface area). Serious hepatic, renal and adrenal lesions were also reported in fetuses of female Rhesus monkeys given 60 to 90 mg/kg/day from GD 21-45 of pregnancy (1 to 2 times the recommended human dose based on body surface area). Non-human primates form sulfate conjugates of the known hepatotoxic bacterial metabolite of chenodiol, lithocholic acid, to a lesser extent than reported in humans, which may exaggerate the toxicity of orally dosed chenodiol compared to humans. However, there is also evidence that the hepatobiliary toxicity is partly due to the parent drug, chenodiol.

8.2 Lactation Risk Summary There are no data on the presence of chenodiol in either human or animal milk, the effects on the breastfed infant, or the effects on milk production. The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for CTEXLI and any potential adverse effects on the breastfed infant from CTEXLI or the underlying maternal condition.

8.4 Pediatric Use The safety and effectiveness of CTEXLI for the treatment of CTX have not been established in pediatric patients.

8.5 Geriatric Use Trial 1 of CTEXLI in patients with CTX did not include patients aged 65 years and older.

Endogenous chenodiol (chenodeoxycholic acid) is a primary bile acid, synthesized from cholesterol in the liver. In CTX, the major bile acid synthesis pathways are disrupted due to partial or total deficiency in sterol 27-hydroxylase encoded by the CYP27A1 gene. CTEXLI may act to replace deficient levels of the endogenous bile acid chenodeoxycholic acid in patients with CTX. Increased chenodiol levels in the enterohepatic bile acid pool restore the activation of farnesoid X receptor (FXR) and downregulate CYP7A1 leading to suppression and reduction of atypical bile acids and bile alcohols including cholestanol and 23S-pentol.