Allopregnanolone is available only through a restricted program called the Zulresso REMS Program that requires the drug to be administered by a healthcare provider in a certified healthcare facility. The REMS requires that patients be enrolled in the program prior to administration of the drug. Dose
It is given continuously by intravenous infusion over a period of 60 hours (2.5 days). The dosage of brexanolone is progressively adjusted over a range of 30 to 90 μg/kg/hour during this period.Several warnings and precautions are addressed in a boxed warning in the drugs prescribing information. Because of the risk of serious harm due to the sudden loss of consciousness, patients must be monitored for excessive sedation and sudden loss of consciousness and have continuous pulse oximetry monitoring (monitors oxygen levels in the blood). While receiving the infusion, women must be accompanied during interactions with children. Women should be counseled on the risks of allopregnanolone treatment and instructed that they must be monitored for these effects at a healthcare facility for the entire 60 hours of infusion. Women who have received the treatment should not drive, operate machinery, or do other dangerous activities until feelings of sleepiness from the treatment have completely gone away. Available forms
Brexanolone is an aqueous mixture of synthetic allopregnanolone and sulfobutyl ether β-cyclodextrin (betadex sulfobutyl ether sodium), a solubilizing agent. It is provided at an allopregnanolone concentration of 100 mg/20 mL (5 mg/mL) in single-dose vials for use by intravenous infusion.
However, it is only able to do so at micromolar concentrations, which, similarly to the case of the L-VGCCs, are far greater than the low nanomolar concentrations of allopregnanolone estimated to be present in the brain. Biphasic actions at the GABAA receptor
Increased levels of allopregnanolone can produce paradoxical effects, including negative mood, anxiety, irritability, and aggression. This appears to be because allopregnanolone possesses biphasic, U-shaped actions at the GABAA receptor – moderate level increases (in the range of 1.5–2 nmol/L total allopregnanolone, which are approximately equivalent to luteal phase levels) inhibit the activity of the receptor, while lower and higher concentration increases stimulate it. This seems to be a common effect of many GABAA receptor positive allosteric modulators. In accordance, acute administration of low doses of micronized progesterone (which reliably elevates allopregnanolone levels) has been found to have negative effects on mood, while higher doses have a neutral effect. Antidepressant effects
The mechanism by which neurosteroid GABAA receptor PAMs like brexanolone have antidepressant effects is unknown. Other GABAA receptor PAMs, such as benzodiazepines, are not thought of as antidepressants and have no proven efficacy, despite clinicians prescribing Alprazolam for depression in the past. Neurosteroid GABAA receptor PAMs are known to interact with GABAA receptors and sub-populations differently than benzodiazepines. As examples, GABAA receptor-potentiating neurosteroids may preferentially target δ subunit-containing GABAA receptors, and enhance both tonic and phasic inhibition mediated by GABAA receptors.