D-Amphetamine Content in Vyvanse 50mg
A 50mg dose of Vyvanse (lisdexamfetamine dimesylate) contains approximately 14.8-15mg of d-amphetamine after complete conversion in the body.
Pharmacological Conversion
Lisdexamfetamine is a prodrug consisting of d-amphetamine covalently bonded to L-lysine, which is therapeutically inactive until metabolized in the body to release active d-amphetamine 1, 2. The molecular weight ratio determines the actual amphetamine content:
- Lisdexamfetamine dimesylate has a molecular weight of 455.6 g/mol
- D-amphetamine has a molecular weight of 135.2 g/mol
- The conversion ratio is approximately 0.2948 (29.48%)
Therefore, 50mg of lisdexamfetamine dimesylate yields approximately 14.8mg of d-amphetamine after complete hydrolysis 3, 1.
Clinical Pharmacokinetics
The conversion process occurs through rate-limited hydrolysis in the body, with L-lysine being cleaved to gradually release pharmacologically active d-amphetamine 2. This mechanism provides:
- Median time to maximum d-amphetamine concentration (Tmax) of 3.0 hours after oral administration 3
- Steady-state d-amphetamine concentrations achieved by day 5 of daily dosing 3
- Linear pharmacokinetics at therapeutic doses (30-70mg) 1
Important Clinical Context
When considering total amphetamine exposure, this 14.8mg of pure d-amphetamine from Vyvanse 50mg is not equivalent to 15mg of mixed amphetamine salts (Adderall), because Adderall contains a 3:1 ratio of d-amphetamine to l-amphetamine salts, resulting in different pharmacological effects 4.
The maximum recommended daily amphetamine dose for adults with ADHD is 40-50mg total daily dose, and Vyvanse can be titrated up to a maximum approved dose of 70mg daily 5, 6.