Absorption
Extended-Release Oral Suspension
Following a single 18.8 mg dose of DYANAVEL XR extended-release oral suspension in 29 healthy adult subjects under fasting conditions in a crossover study, the median (range) time to peak plasma concentrations (Tmax) for both d- and l- isomers of amphetamine were 4 (2 to 7) hours after dosing. Peak concentrations (Cmax) of d- and l-amphetamine were 102% and 106%, respectively, of the Cmax of immediate-release (IR) mixed amphetamine salts (MAS) tablets. The relative bioavailability of DYANAVEL XR compared with an equal dose of IR MAS tablets is 106% for d- and 111% for l-amphetamine.
Following a single 18.8 mg dose of DYANAVEL XR extended-release oral suspension in 28 healthy adult subjects in a crossover study under fasting conditions, the median (range) time to peak plasma concentrations (Tmax) were about 4 (2 to 7) hours and 5 (3 to 7) hours for d- and l-amphetamine, respectively. Peak concentration (Cmax) was 93% and 94%, respectively, of the Cmax of extended release (ER) MAS capsules. The relative bioavailability of DYANAVEL XR compared with an equal dose of ER MAS capsules is 94% for both d- and l-amphetamine.
Figure 1. Mean d- and l-Amphetamine Plasma Concentration-Time Profile Following Administration of a Single Dose (18.8 mg amphetamine base) of DYANAVEL XR Extended-Release Oral Suspension and MAS ER Under Fasting Conditions
Figure1 (Dyanavel Xr Oral Suspension And Tablets 2)
Extended-Release Tablet
Following a single 20 mg dose of DYANAVEL XR extended-release tablets (swallowed whole) to 36 healthy adults under fasted conditions in a crossover study, the median (range) time to peak plasma concentration (Tmax) for both d- and l-amphetamine, were 5.0 (2 to 9) hours after dosing. Peak concentrations (Cmax) for both d- and l-amphetamine, were 101% of the Cmax of DYANAVEL XR oral suspension. The relative bioavailability of DYANAVEL XR tablets compared with an equal dose of DYANAVEL XR oral suspension, for d- and l-amphetamine, were 105% and 106%, respectively.
Dyanavel XR extended-release tablets chewed or swallowed whole under fasted conditions did not significantly affect exposure and Tmax.
Figure 2. Mean Plasma d-and l-Amphetamine Concentration-Time Profiles for DYANAVEL XR Extended-Release Tablet and DYANAVEL XR Extended-Release Oral Suspension
Figure2 (Dyanavel Xr Oral Suspension And Tablets 3)
Effect of Food
Extended-Release Oral Suspension
Ingestion of 18.8 mg of DYANAVEL XR extended-release oral suspension with a high-fat meal increased the average Cmax of both isomers of DYANAVEL XR by about 2%, decreased the AUC of d- and l-amphetamine by 5.7% and 7.4%, respectively. A delay of Tmax by approximately 1 hour was observed for both isomers.
Extended-Release Tablet
Ingestion of 20 mg DYANAVEL XR extended-release tablets with a high-fat meal decreased the average Cmax of both isomers of amphetamine by about 3%, decreased AUC of d- and l-amphetamine by about 4.0% and 7.3%, respectively. Median Tmax was not delayed for either isomer.
Elimination
The mean plasma terminal elimination half-lives of d- and l-amphetamine were 12.4 hours and 15.1 hours, respectively, following a single 18.8 mg dose of DYANAVEL XR extended-release oral suspension.
The mean plasma terminal elimination half-lives of d- and l-amphetamine were 13.5 hours and 17.3 hours, respectively, following a single 20 mg dose of DYANAVEL XR extended-release tablets.
Metabolism
Amphetamine is reported to be oxidized at the 4 position of the benzene ring to form 4‑hydroxyamphetamine, or on the side chain A or B carbons to form alpha-hydroxy-amphetamine or norephedrine, respectively. Norephedrine and 4-hydroxy-amphetamine are both active and each is subsequently oxidized to form 4-hydroxy-norephedrine. Alpha-hydroxy-amphetamine undergoes deamination to form phenylacetone, which ultimately forms benzoic acid and its glucuronide and the glycine conjugate hippuric acid. Although the enzymes involved in amphetamine metabolism have not been clearly defined, CYP2D6 is known to be involved with formation of 4-hydroxy-amphetamine. Because CYP2D6 is genetically polymorphic, population variations in amphetamine metabolism are a possibility.
Excretion
With normal urine pH, approximately half of an administered dose of amphetamine is recoverable in urine as derivatives of alpha-hydroxy-amphetamine and approximately another 30%-40% of the dose is recoverable in urine as amphetamine itself.
Specific Populations
Pediatric Patients
Following a single 10 mg dose of DYANAVEL XR extended-release oral suspension in pediatric subjects with ADHD (aged 6 to 12 years) under fasting conditions, peak plasma concentrations of d-and l-amphetamine occurred at a median time of 3.9 and 4.5 hours after dosing, respectively. The mean plasma terminal elimination half-lives of d- and l-amphetamine were 10.4 hours and 12.1 hours, respectively.
Patients with Hepatic or Renal Impairment
No specific studies have been conducted to evaluate the effect of renal impairment or hepatic impairment on the PK after DYANAVEL XR administration. However, urinary recovery of amphetamine has been reported to range from 1% to 75%, depending on urinary pH, with the remaining fraction of the dose hepatically metabolized. Consequently, both hepatic and renal dysfunctions have the potential to inhibit the elimination of amphetamine and result in prolonged exposures.
Drug Interaction Studies
CYP Enzymes
In vitro experiments with human microsomes indicate minor inhibition of CYP2D6 by amphetamine and minor inhibition of CYP1A2, 2D6, and 3A4 by one or more metabolites. However, because of the probability of auto-inhibition and the lack of information on the concentration of these metabolites relative to in vivo concentrations, no predications regarding the potential for amphetamine or its metabolites to inhibit the metabolism of other drugs by CYP isozymes in vivo can be made.
Urine pH Modulators
Because amphetamine has a pKa of 9.9, urinary recovery of amphetamine is highly dependent on pH and urine flow rates. Alkaline urine pH results in less ionization and reduced renal elimination; acidic pH and high flow rates result in increased renal elimination with clearances greater than glomerular filtration rates, indicating the involvement of active secretion. In addition, any decrease in amphetamine’s metabolism that might occur due to drug interactions or genetic polymorphisms is more likely to be clinically significant when renal elimination is decreased [see Drug Interactions (7.1)].
Alcohol Effect
There is no in vivo study conducted for the effect of alcohol on drug exposure. An in vitro dissolution study on DYANAVEL XR extended-release oral suspension showed alcohol-induced dose dumping potential in the presence of 40% alcohol. A similar study on the DYANAVEL XR extended-release tablets showed no alcohol-induced dose dumping in the presence of 40% alcohol. Dose dumping was not observed in the presence of 5%, 10%, or 20% alcohol concentrations for either product.