Methylphenidate HCl is a central nervous system (CNS) stimulant. The mode of therapeutic action in Attention Deficit Hyperactivity Disorder (ADHD) is not known. Methylphenidate is thought to block the reuptake of norepinephrine and dopamine into the presynaptic neuron and increase the release of these monoamines into the extraneuronal space. Methylphenidate is a racemic mixture comprised of the d- and l-threo enantiomers. The d-threo enantiomer is more pharmacologically active than the l-threo enantiomer.
The pharmacokinetics of the METADATE CD methylphenidate hydrochloride formulation have been studied in healthy adult volunteers and in children with Attention Deficit Hyperactivity Disorder (ADHD).
Absorption And Distribution
Methylphenidate is readily absorbed. METADATE CD has a plasma/time concentration profile showing two phases of drug release with a sharp, initial slope similar to a methylphenidate immediate-release tablet, and a second rising portion approximately three hours later, followed by a gradual decline. (See Figure 1 below.)
Comparison Of Immediate Release (IR) And METADATE CD Formulations After Repeated Doses Of Methylphenidate HCl In Children With ADHD
METADATE CD was administered as repeated once-daily doses of 20 mg or 40 mg to children aged 7-12 years with ADHD for one week. After a dose of 20 mg, the mean (±SD) early Cmax was 8.6 (±2.2) ng/mL, the later Cmax was 10.9 (±3.9)* ng/mL and AUC0-9h was 63.0 (±16.8) ng•h/mL. The corresponding values after a 40 mg dose were 16.8 (±5.1) ng/mL, 15.1 (±5.8)* ng/mL and 120 (±39.6) ng•h/mL, respectively. The early peak concentrations (median) were reached about 1.5 hours after dose intake, and the second peak concentrations (median) were reached about 4.5 hours after dose intake. The means for Cmax and AUC following a dose of 20 mg were slightly lower than those seen with 10 mg of the immediate-release formulation, dosed at 0 and 4 hours.
*25-30% of the subjects had only one observed peak (Cmax) concentration of methylphenidate.
Following single oral doses of 10-60 mg methylphenidate free base as a solution given to ten healthy male volunteers, Cmax and AUC increased proportionally with increasing doses. After the 60 mg dose, tmax was reached 1.5 hours post-dose, with a mean Cmax of 31.8 ng/mL (range 24.7-40.9 ng/mL).
Following one week of repeated once-daily doses of 20 mg or 40 mg METADATE CD to children aged 7-12 years with ADHD, Cmax and AUC were proportional to the administered dose.
In a study in adult volunteers to investigate the effects of a high-fat meal on the bioavailability of a dose of 40 mg, the presence of food delayed the early peak by approximately 1 hour (range -2 to 5 hours delay). The plasma levels rose rapidly following the food-induced delay in absorption. Overall, a high-fat meal increased the Cmax of METADATE CD by about 30% and AUC by about 17%, on average (see DOSAGE and ADMINISTRATION).
After a single dose, the bioavailability (Cmax and AUC) of methylphenidate in 26 healthy adults was unaffected by sprinkling the capsule contents on applesauce as compared to the intact capsule. This finding demonstrates that a 20 mg METADATE CD Capsule, when opened and sprinkled on one tablespoon of applesauce, is bioequivalent to the intact capsule.
Metabolism And Excretion
In humans, methylphenidate is metabolized primarily via deesterification to alpha-phenyl-piperidine acetic acid (ritalinic acid). The metabolite has little or no pharmacologic activity.
In vitro studies showed that methylphenidate was not metabolized by cytochrome P450 isoenzymes, and did not inhibit cytochrome P450 isoenzymes at clinically observed plasma drug concentrations.
The mean terminal half-life (t½) of methylphenidate following administration of METADATE CD (t½=6.8h) is longer than the mean terminal (t½) following administration of methylphenidate hydrochloride immediate-release tablets (t½=2.9h) and methylphenidate hydrochloride sustained-release tablets (t½=3.4h) in healthy adult volunteers. This suggests that the elimination process observed for METADATE CD is controlled by the release rate of methylphenidate from the extended-release formulation, and that the drug absorption is the rate-limiting process.
The pharmacokinetics of methylphenidate after a single dose of METADATE CD were similar between adult men and women.
The influence of race on the pharmacokinetics of methylphenidate after METADATE CD administration has not been studied.
The pharmacokinetics of methylphenidate after METADATE CD administration have not been studied in children less than 6 years of age.
There is no experience with the use of METADATE CD in patients with renal insufficiency. After oral administration of radiolabeled methylphenidate in humans, methylphenidate was extensively metabolized and approximately 80% of the radioactivity was excreted in the urine in the form of ritalinic acid. Since renal clearance is not an important route of methylphenidate clearance, renal insufficiency is expected to have little effect on the pharmacokinetics of METADATE CD.
There is no experience with the use of METADATE CD in patients with hepatic insufficiency.