The purpose of this clinical study is to compare the pharmacokinetic profiles of a topical cream formulation of 0.9% nitroglycerin, MQX 503, and Nitroglycerin Ointment 2%, USP.

Inclusion Criteria:

• 18 to 50 years of age
• Subjects who do not take any prescription medication or who can safely discontinue use prior to visit 1.
• Negative pregnancy test for fertile women and agree to use effective contaception throughout the study.

Exclusion Criteria:

• Subjects who can not safely discontinue current prescription medications.
• Subjects who have a known allergy to nitroglycerin or common topical formulation ingredients.
• Subjects with an unstable medical problem.
• Subjects who, within the past three months, have had either a myocardial infarction, uncontrolled congestive heart failure, unstable angina, uncontrolled hypotension, or uncontrolled hypertension.
• Subjects who participated in a study of any investigational drug or device within four weeks prior to Visit 1.
• Subjects who have screening laboratory values which are outside the normal range and which are considered to be clinically significant to the investigator.
• Subjects who have had major abdominal, thoracic, or vascular surgery within six months of Visit 1.
• Subjects with non-epithelialized skin lesions or interfering skin conditions at time of screening in the area where either study medication is to be applied.
• Pregnant or nursing women.
• Women of childbearing potential who are unable or unwilling to comply with the contraceptive requirements during the study period.