Pharmacoscintigraphic Study to Evaluate Two Sildenafil Products

Inclusion Criteria: * Male * Aged between 18 and 65 years inclusive * BMI between 18 and 30 kg/m2 inclusive * Body weight ≥50 kg * Understands and is willing, able and likely to comply with all study procedures and restrictions * Demonstrates understanding of the study and willingness to participate as evidenced by voluntary written informed consent (signed and dated) obtained before any trial related activities * Good general health with (in the opinion of the investigator) no clinically significant and relevant abnormalities of medical history or physical examination Exclusion Criteria: * Current or recurrent disease that, in the opinion of the physician responsible, could affect the study conduct or laboratory assessments (e.g. hepatic disorders, renal insufficiency, congestive heart failure). * Current or relevant previous history of serious, severe or unstable physical or psychiatric illness, any medical disorder that may require treatment or make the subject unlikely to fully complete the study, or any condition that presents undue risk from the study medication or procedures. * A history of current or relevant previous non self-limiting gastrointestinal disorders. * Currently suffering from disease known to impact gastric emptying, e.g. migraine, Type 1 or Type 2 diabetes mellitus. * Currently suffering from any oromucosal condition (e.g. salivary gland disorders, xerostomia, aphthous ulcers) or recent oral surgery that in the opinion of the physician responsible could interfere with the study objectives. * Currently or previously suffering from non-arteritic anterior ischaemic optic neuropathy (NAION). * Known hereditary degenerative retinal disorders such as retinitis pigmentosa. * Hypotension (blood pressure \<90/50 mmHg). * Recent history of stroke or myocardial infarction. * Laboratory screening results that suggest an abnormal liver and/or renal function. * Subject has a screening QTc value of greater than or equal to 450 msec or an ECG that is not suitable for QTc measurements (e.g. poorly defined termination of the T-wave). The ECG taken at screening must be considered not clinically significant by the Investigator/ study physician. * As a result of a physical examination or screening investigations, the physician responsible considers the volunteer unfit for the study. * Subject has taken prescribed medication within 14 days prior to the first assessment visit which, in the opinion of the physician responsible, will interfere with the study procedures or compromise safety. Subjects will be withdrawn from subsequent study days if they commence taking prescribed medication during the study period which, in the opinion of the physician responsible, will interfere with the study procedures or compromise safety. * Subject has taken over-the-counter (OTC) medication within 48 hours prior to the first assessment visit. This includes the use of vitamins and natural or herbal remedies. Subjects who have taken OTC medication may still be entered into the study if, in the opinion of the physician responsible, the medication will not interfere with the study procedures or compromise safety. * Concomitant use of other phosphodiesterase 5 (PDE5) inhibitors, or other pulmonary arterial hypertension (PAH) treatments containing sildenafil (REVATIO), or other treatments for erectile dysfunction. * Concomitant use of antihypertensive medications (e.g. diuretics, angiotensin converting enzyme (ACE) inhibitors etc). * Concomitant use of nitrate medications. * Recent history (within the last year) of alcohol or other substance abuse. * Subject has an average weekly alcohol intake of greater than 21 units. * Subject has positive urine drugs of abuse test at screening. * Subject has a positive breath alcohol test at screening. * Subject has recently discontinued smoking (less than 3 months). * Subject is currently a smoker or user of nicotine-containing products. * Subject has a positive urine cotinine test at screening. * Subject has a history of allergy to sildenafil, to any component of the dosage form, or any other allergy, which in the opinion of the physician responsible, contraindicates their participation. * Has an allergy to any of the contents of the standardised meals. * Subject is vegetarian. * Subject is lactose intolerant. * Participation in another clinical study (inclusive of final post-study examination) or receipt of an investigational drug within the 12 weeks before first screening visit. * Previous participation in this study. * Subject whose participation in this study will result in participation in more than four studies over a twelve month period. * An employee of the sponsor, client or study site or members of their immediate family. * Subjects for whom participation in this study will exceed the limits of total radiation exposure allowed in the previous twelve month period (5 mSv), or will exceed 10 mSv over the previous three year period. * Subjects who are intending to father a child in the 3 months following the study or are unwilling to abstain from sexual intercourse with pregnant or lactating women. * Subjects who are unwilling to use a condom/spermicide in addition to having their female partner use another form of contraception such as an intrauterine device (IUD), diaphragm with spermicide, oral contraceptives, injectable progesterone, subdermal implants or a tubal ligation if the woman could become pregnant from the time of the assessment visit until 3 months following the study. * Subject has donated blood or experienced significant blood loss within 3 months of screening and for the duration of the study. * Difficulty accessing forearm veins for cannulation or blood sampling. * Subject has any non-removable metal objects such as metal plates, screws etc in their chest or abdominal area, which in the opinion of the investigator, could affect the study conduct.