2.1 Dosage

Therapy with Betaine Anhydrous for Oral Solution should be directed by physicians knowledgeable in the management of patients with homocystinuria.

Adults and Pediatric Patients 3 Years of Age and Older
The recommended dosage is 6 grams per day, administered orally in divided doses of 3 grams twice daily.

Pediatric Patients Less than 3 Years of Age
The recommended starting dosage is 100 mg/kg/day divided in twice daily doses, and then increased weekly by 50 mg/kg increments.

Monitoring
Monitor patient response to Betaine Anhydrous for Oral Solution by homocysteine plasma concentration. Increase the dosage in all patients gradually until the plasma total homocysteine concentration is undetectable or present only in small amounts. An initial response in homocysteine plasma concentrations usually occurs within several days and steady state plasma concentrations occur within a month.

Monitor plasma methionine concentrations in patients with CBS deficiency [See Warnings and Precautions (5.1)].

Maximum Dosage
Dosages of up to 20 grams/day have been necessary to control homocysteine concentrations in some patients. However, one pharmacokinetic and pharmacodynamic in vitro simulation study indicated minimal benefit from exceeding a twice-daily dosing schedule and a 150 mg/kg/day dosage for Betaine Anhydrous for Oral Solution.

2.2 Preparation and Administration Instructions

• Shake bottle lightly before removing cap.
• Measure the number of scoops for the patient's dose with the scoop provided. One level scoop (1.9cc) is equivalent to 1 gram of betaine anhydrous powder.
• Mix powder with 4 to 6 ounces (120 to 180 mL) of water, juice, milk, or formula until completely dissolved, or mix with food, then ingest mixture immediately.
  
• Always replace the cap tightly after using and protect the bottle from moisture.
  

5.1 Hypermethioninemia in Patients with CBS Deficiency

Patients with homocystinuria due to cystathionine beta-synthase (CBS) deficiency may also have   elevated plasma methionine concentrations. Treatment with Betaine Anhydrous for Oral Solution may further increase methionine concentrations due to the remethylation of homocysteine to methionine. Cerebral edema has been reported in patients with hypermethioninemia, including patients treated with Betaine Anhydrous for Oral Solution [see Adverse Reactions (6.2)]. Monitor plasma methionine concentrations in patients with CBS deficiency. Plasma methionine concentrations should be kept below 1,000 micromol/L through dietary modification and, if necessary, a reduction of Betaine Anhydrous for Oral Solution dosage.

6.1 Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in 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 assessment of clinical adverse reactions is based on a survey study of 41 physicians, who treated a total of 111 homocystinuria patients with Betaine Anhydrous for Oral Solution. Adverse reactions were retrospectively recalled and were not collected systematically in this open-label, uncontrolled, physician survey. Thus, this list may not encompass all types of potential adverse reactions, reliably estimate their frequency, or establish a causal relationship to drug exposure. The following adverse reactions were reported (Table 1):

6.2 Post-marketing Experience

The following adverse reactions have been identified during post approval use of Betaine Anhydrous for Oral Solution. 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.

Severe cerebral edema and hypermethioninemia have been reported within 2 weeks to 6 months of starting Betaine Anhydrous for Oral Solution therapy, with complete recovery after discontinuation of Betaine Anhydrous for Oral Solution. All patients who developed cerebral edema had homocystinuria due to CBS deficiency and had severe elevation in plasma methionine concentrations (range 1,000 to 3,000 microM). As cerebral edema has also been reported in patients with hypermethioninemia, secondary hypermethioninemia due to betaine therapy has been postulated as a possible mechanism of action [see Warnings and Precautions (5.1)].

Other adverse reactions include: anorexia, agitation, depression, irritability, personality disorder, sleep disturbed, dental disorders, diarrhea, glossitis, nausea, stomach discomfort, vomiting, hair loss, hives, skin odor abnormalities, and urinary incontinence.

8.1 Pregnancy

Risk Summary
Available data from a limited number of published case reports and post marketing experience with Betaine Anhydrous for Oral Solution use in pregnancy have not identified any drug associated risks for major birth defects, miscarriage, or adverse maternal or fetal outcomes. Animal reproduction studies have not been conducted with betaine.

The estimated 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 U.S. 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.

8.2 Lactation

Risk Summary There are no data on the presence of betaine in human or animal milk, the effects on the breastfed child, or the effects on milk production. The developmental and health benefits of breastfeeding should be considered along with the mother’s clinical need for Betaine Anhydrous for Oral Solution and any potential adverse effects on the breastfed child from Betaine Anhydrous for Oral Solution or from the underlying maternal condition.

8.4 Pediatric Use

The safety and effectiveness of Betaine Anhydrous for Oral Solution have been established in pediatric patients. The majority of case studies of homocystinuria patients treated with Betaine Anhydrous for Oral Solution have been pediatric patients, including patients ranging in age from 24 days to 17 years [see Clinical Studies (14)]. Children younger than 3 years of age may benefit from dose titration [see Dosage and Administration (2.1)].

12.1 Mechanism of Action

Betaine Anhydrous for Oral Solution acts as a methyl group donor in the remethylation of homocysteine to methionine in patients with homocystinuria. Betaine occurs naturally in the body. It is a metabolite of choline and is present in small amounts in foods such as beets, spinach, cereals, and seafood.

12.2 Pharmacodynamics

Betaine Anhydrous for Oral Solution was observed to lower plasma homocysteine concentrations in three types of homocystinuria, including CBS deficiency; MTHFR deficiency; and cbl defect. Patients have taken Betaine Anhydrous for Oral Solution for many years without evidence of tolerance. There has been no demonstrated correlation between Betaine concentrations and homocysteine concentrations.

In CBS-deficient patients, large increases in methionine concentrations over baseline have been observed. Betaine Anhydrous for Oral Solution has also been demonstrated to increase low plasma methionine and S- adenosylmethionine (SAM) concentrations in patients with MTHFR deficiency and cbl defect.

12.3 Pharmacokinetics

Pharmacokinetic studies of Betaine Anhydrous for Oral Solution are not available. Plasma betaine concentrations following administration of Betaine Anhydrous for Oral Solution have not been measured in patients and have not been correlated to homocysteine concentrations.

13.1 Carcinogenesis, Mutagenesis, Impairment of Fertility

Long-term carcinogenicity and fertility studies have not been conducted with Betaine Anhydrous for Oral Solution. No evidence of genotoxicity was demonstrated in the following tests: metaphase analysis of human lymphocytes; bacterial reverse mutation assay; and mouse micronucleus test.