• Safety of the Standard Titration Schedule in PD Population as Measured by the Number of Patients That Are Able to Increase the Dose to 20 mg Daily [ Time Frame: 1 year ] [ Designated as safety issue: Yes ]
• Number of Participants That Tolerated Each Dose of Isradipine [ Time Frame: 1 year ] [ Designated as safety issue: Yes ]
  Tolerability= maximum tolerated dose
• Number of Participants That Tolerated Each Dose Level of Isradipine Between PD Patients Treated With Antihypertensive Agent and Not on Antihypertensive Agent [ Time Frame: 1 year ] [ Designated as safety issue: Yes ]

  At the time of enrollment, some patients were currently being treated with antihypertensive agents including Propanolol, Toprol, Lisinopril, Diovan, Norvasc.

  HTN+: Participants on an antihypertensive agent HTN-: Participants not on an antihypertensive agent

• Number of Participants That Completed the Study at Each Dose Level of Isradipine [ Time Frame: 1 year ] [ Designated as safety issue: Yes ]
• Change in Motor UPDRS Scores: Baseline vs. Final Visit [ Time Frame: 12 weeks ] [ Designated as safety issue: No ]

  Baseline visit = Week 0 Final visit = Week 12

  Unified Parkinson's Disease Rating Scale (UPDRS)is made up of the following sections:

  Part I: evaluation of Mentation, behavior, and mood Part II: self evaluation of the activities of daily life Part III: clinician-scored motor evaluation Part IV: Hoehn and Yahr stating of severity of Parkinson disease. Part V: Schwab and England ADL scale Only part three was used for this assessment.

  The higher the UPDRS score, the greater the disability from PD.

  The range for scores for Section III is 0 to 108.

• Pharmacokinetic Data - Mean Serum Concentration and Dosage Exposure Across the Dose Range of Isradipine [ Time Frame: 1 year ] [ Designated as safety issue: No ]
  Mean Plasma Concentration (+/- SD ng/mL)

• Safety of the standard titration schedule in PD population as measured by the proportion of patients that are able to increase the dose to 20 mg daily. [ Time Frame: 1 year ] [ Designated as safety issue: Yes ]
• Comparison of tolerability of isradipine across the titration dose range between PD patients treated with dopaminergic therapy and not treated with dopaminergic therapy. [ Time Frame: 1 year ] [ Designated as safety issue: Yes ]
• Comparison of tolerability of isradipine across the titration dose range between PD patients treated with antihypertensive agent and not on antihypertensive agent. [ Time Frame: 1 year ] [ Designated as safety issue: Yes ]
• Analysis of the dose best tolerated in PD population- the median number of patients that were treated with each dose of isradipine. [ Time Frame: 1 year ] [ Designated as safety issue: Yes ]
• Impact of isradipine on PD motor disability as measured by UPDRS scale [ Time Frame: 1 year ] [ Designated as safety issue: No ]
• Pharmacokinetic data - correlation of the serum concentration and dosage exposure across the dose range of isradipine. [ Time Frame: 1 year ] [ Designated as safety issue: No ]

The objective of this study is to establish the safety and tolerability of isradipine, sustained release preparation in patients with PD. This study is a logical continuation of the project that is being completed now and is conducted in preparation to NIH submission of the pivotal study on the efficacy of this agent for neuroprotection in PD. This study is conducted in parallel with Dr. Surmeier's work on further development of the preclinical data. The focus of his work now is to establishing the correlation between the dose that demonstrated neuroprotective effect in animal model and the dose used for clinical practice.

Hypothesis 1: Patients with PD will be able to tolerate isradipine across the FDA recommended dose range. We expect 10% attrition due to hypotensive effect of the agent.

Hypothesis 2: Patients with PD and concomitant stable hypertension will be able to tolerate isradipine provided that the dose of the concomitant antihypertensive agent is adjusted based on the blood pressure reading.

Inclusion Criteria:

1. Patients with idiopathic Parkinson's disease age 30-75
2. Hoehn and Yahr stage <2.5
3. PD duration less than 5 years
4. For the subjects treated with PD medications, the regimen has to be stable for >1 month prior to enrollment

Exclusion Criteria:

1. Atypical Parkinsonian syndrome
2. Patients with history of stable hypertension treated with other antihypertensive agents will be allowed provided that the doses of concomitant anti HTN therapy can be reduced/adjusted during the study based on the BP readings. The number of concomitant antihypertensive agents should not exceed two. The dose of concomitant antihypertensive agents has to be stable for > 1 month
3. Presence of orthostatic hypotension at the screening visit defined as > 20 mmHg change in systolic BP and 10mm change in diastolic BP after 2 min of standing, or baseline BP <90/60.
4. Presence of other medical conditions that in the opinion of the investigator will preclude safe use of the drug.
5. Presence of cognitive dysfunction as determined by MMSE score <24
6. Failure to sign the informed consent
7. Inability to cooperate with the study procedures
8. Presence of motor fluctuations
9. History of bradycardia defined as heart rate < 55
10. Women of childbearing potential who are not surgically sterilized have to use a reliable measure of contraception and have a negative urine pregnancy test at screening
11. Participation in other investigational drug trials within 30 days prior to screening
12. History of brain surgery for Parkinson's Disease.