APA (7e ed.) Bronvermelding

Katigbak, A. F. (2003). Almost 80 percent of Pfizer's sildenafil users prefer not to take other ED medications. Philippine Star.

Chicago (17e ed.) Bronvermelding

Katigbak, Antonio F. "Almost 80 Percent of Pfizer's Sildenafil Users Prefer Not to Take Other ED Medications." Philippine Star 2003.

MLA (9e ed.) Bronvermelding

Katigbak, Antonio F. "Almost 80 Percent of Pfizer's Sildenafil Users Prefer Not to Take Other ED Medications." Philippine Star, 2003.