Clinical Pharmacology for Ztalmy
Mechanism Of Action
The precise mechanism by which ganaxolone exerts its therapeutic effects in the treatment of seizures associated with CDD is unknown, but its anticonvulsant effects are thought to result from positive allosteric modulation of the gamma-aminobutyric acid type A (GABAA) receptor in the CNS.
Pharmacodynamics
Cardiac Electrophysiology
At therapeutic exposures, ZTALMY does not prolong the QTc interval. QT effects of ZTALMY at high clinical exposure scenarios have not been evaluated.
Pharmacokinetics
Absorption
Following oral administration of ZTALMY, ganaxolone is absorbed with a time to maximum plasma concentration (Tmax) of 2 to 3 hours.
Effect of Food
When ZTALMY was administered with a high-fat meal, the Cmax and AUC increased by 3- and 2-fold, respectively, when compared to administration under fasted conditions. ZTALMY was administered with food in the clinical efficacy study, Study 1 [see Dosage and Administration (2.1)]. The efficacy of ZTALMY when administered in the fasted state is unknown.
Distribution
Ganaxolone is approximately 99% protein-bound in serum.
Elimination
The terminal half-life for ganaxolone is 34 hours.
Metabolism
Ganaxolone is metabolized by CYP3A4/5, CYP2B6, CYP2C19, CYP2D6, UGT1A3, UGT1A6, UGT1A9, UGT2B7, and UGT2B15.
Excretion
Following a single oral dose of 300 mg [14C]-ganaxolone to healthy male subjects, 55% of the total radioactivity was recovered in feces (2% as unchanged ganaxolone) and 18% of the total radioactivity dose was recovered in urine (undetected as unchanged ganaxolone).
Specific Populations
Age, sex, and race are not expected to have a clinically-relevant effect on ganaxolone pharmacokinetics, after accounting for body weight.
Pediatric Patients
After accounting for body weight, the observed pharmacokinetic exposures in patients in Study 1 [see Clinical Studies (14)] were comparable across the age groups 2 to less than 6 years of age (n=45), 6 to less than 12 years of age (n=28), and 12 to less than 18 years of age (n=16).
Patients with Renal Impairment
Following oral administration of a single 300 mg dose of ZTALMY in subjects with severe renal impairment (creatine clearance between 15 and 30 mL/min as estimated by Cockcroft-Gault formula), the AUC0-INF of ganaxolone decreased 8% and Cmax decreased 11% as compared to that in subjects with normal renal function (creatinine clearance ≥ 90 mL/min as estimated by Cockcroft-Gault formula). The changes in ganaxolone exposures when administered in patients with impaired renal function (creatinine clearance <90 mL/min) are not expected to be clinically significant.
Patients with Hepatic Impairment
The influence of hepatic impairment on the pharmacokinetics of ganaxolone was studied following a single oral dose of ZTALMY 300 mg. In subjects with mild hepatic impairment (Child-Pugh class A), Cmax and AUClast increased by 38% and 8%, respectively, compared to subjects with normal hepatic function. In subjects with moderate hepatic impairment (Child-Pugh class B), Cmax and AUClast increased by 45% and 50%, respectively, compared to subjects with normal hepatic function. In subjects with severe hepatic impairment (Child-Pugh class C), Cmax and AUClast increased by 148% and 269%, respectively, compared to subjects with normal hepatic function [see Dosage and Administration (2.3) and Use in Specific Populations (8.6)].
Drug Interaction Studies
Clinical Studies CYP3A4 Inducers
Coadministration of ZTALMY with rifampin, a strong inducer of CYP2C19 and CYP3A4, and a
moderate inducer of CYP2B6, decreased Cmax and AUC of ganaxolone by 57% and 68%, respectively, in healthy subjects [see Drug Interactions (7.2)]. No dedicated drug-interaction studies were conducted with moderate or weak CYP3A4 inducers.
CYP3A4 Inhibitors
Coadministration of ZTALMY with itraconazole, a strong CYP3A4 inhibitor, increased the AUC of ganaxolone by 17% in healthy subjects (Cmax was unchanged). Changes in ganaxolone exposures when coadministered with strong, moderate, or weak CYP3A4 inhibitors are not expected to be clinically significant.
CYP3A4 Substrates
Coadministration of ganaxolone at steady state (400 mg twice daily; 0.44 times the maximum recommended dosage) with midazolam, a sensitive CYP3A4 substrate, did not result in clinically relevant changes in exposures of the substrate in healthy subjects.
In Vitro Studies CYP450 Enzymes
Ganaxolone does not inhibit CYP1A2, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, or CYP3A4/5 at clinically relevant concentrations. Ganaxolone does not induce CYP1A2, CYP2B6, or CYP3A4 at clinically relevant concentrations.
UGT Enzymes
Ganaxolone is a substrate for UGT1A3, UGT1A6, UGT1A9, UGT2B7, and UGT2B15. Ganaxolone does not inhibit UGT1A1, UGT1A3, UGT1A4, UGT1A6, UGT1A9, or UGT2B7.
Transporter Systems
Ganaxolone is not a substrate of BCRP, P-gp, OCT1, OCT2, OATP1B1, or OATP1B3 at clinically relevant concentrations. Ganaxolone does not inhibit BCRP, P-gp, MATE1, MATE2-K, OAT1, OAT3, OCT1, OCT2, OATP1B1, OATP1B3, or BSEP at clinically relevant concentrations.