• C-max: Concentration of the Peak in the Plasma Concentration Curve [ Time Frame: In Visit 3 (day 7) and Visit 4 (day 14): Repeated Assessment 1:00 h before and 0:30 h, 1:15 h, 2:15 h, 3:15 h, 4:15 h, 4:50 h, 5:30 h, 6:15 h, 8:00 h after medication intake ] [ Designated as safety issue: Yes ]
  
• AUC-(0-inf): Area under the plasma concentration versus time curve extrapolated to infinity time [ Time Frame: In Visit 3 (day 7) and Visit 4 (day 14): Repeated Assessment 1:00 h before and 0:30 h, 1:15 h, 2:15 h, 3:15 h, 4:15 h, 4:50 h, 5:30 h, 6:15 h, 8:00 h after medication intake ] [ Designated as safety issue: Yes ]
  

• Efficacy measure: SKAMP Combined rating, SKAMP-Attention subscale, SKAMP-Deportment subscale in a laboratory classroom setting. [ Time Frame: In Visit 3 (day 7) and Visit 4 (day 14): Repeated Assessment at 0:25 h before and 0:50 h, 1:50 h, 2:50 h, 3:50 h, 5:50 h, 7:20 h after medication intake ] [ Designated as safety issue: No ]
  
• Efficacy measure: Nisonger Child Behavior Rating Form - typical IQ Version (NCBRF-TIQ)from the primary caregiver. [ Time Frame: Visite 2 ( Baseline, day 0), Visit 3 (day 7), Visit 4 (day 14) ] [ Designated as safety issue: No ]
  
• Clinical Global Impressions - Severity of Illness scale (CGI-S) and Clinical Global Impressions - Improvement scale (CGI-I) by a child & adolescent psychiatrist [ Time Frame: Visite 2 ( Baseline, day 0), Visit 3 (day 7), Visit 4 (day 14) ] [ Designated as safety issue: No ]
  
• Assessment of Adverse Events [ Time Frame: Visite 2 (Baseline, day 0), Visit 3 (day 7) and Visit 4 (day 14) ] [ Designated as safety issue: Yes ]
  

Study Design

This is a single center, Phase I, prospective, randomized, single blind, two-treatment cross-over study. 24 patients will be enrolled. Study duration for each patient is approximately 4 weeks (from screening/inclusion). Based on the assumption of 5 months recruitment, the total study duration will be approximately 6 month.

Target Population

A number of 24 prepubertal boys aged 8 - 14 years with Diagnosis of ADHD according to DSM IV will be enrolled in this study to ensure that 18 subjects will complete all assessments. The prepuberal status will be determined by Tanner stages ≤ 2. Diagnosis will be confirmed by the K-SADS-PL.

Patients will only be allowed to enter the trial if subject and subject´s parents/legal guardians provide informed consent about participation (following full explanation of the trial) and a written informed consent document is signed. In addition, it has to be verified by a physician that the patient meets all of the Inclusion Criteria and none of the Exclusion Criteria.

Study Treatment

Study medications will be either Ritalin LA 20 mg or Medikinet ret. 20 mg. Patients with a pre-treatment of psychotropic drugs other than Methylphenidate will have an individual washout period before inclusion to the study. This individual washout period will last 5 elimination half-life of the taken drug.

After randomization the patients will enter a 2 week treatment phase with a crossover at day 8. Patients randomized to Sequence 1 will be treated with Ritalin LA for the first week (day 1 to day 7) and with Medikiniet ret. for the second week (day 8 to day 14); patients randomized to Sequence 2 will be treated with Medikinet ret. for the first week (day 1 to day 7) and with Ritalin LA for the second week (day 8 to day 14). The study population will be randomized equally to the Sequence 1 or Sequence 2 group at Visit 2. The study ends 5 weeks after enrollment of the last patient (total study end).