To cite an article from the 1999 AAPS PharmSci Supplement:

Authors Title Journal Supplement. Year; Volume (Issue) Available from: URL.

For example:

A Al-Maaieh and D R Flanagan USE OF ELECTROLYTES TO IMPROVE LOADING OF WATER-SOLUBLE CATIONIC DRUGS IN BIODEGRADABLE MICROSPHERES PREPARED BY A SIMPLE O/W METHOD. AAPS PharmSci 1999 AAPS Annual Meeting Supplement. 1999; 1 (4) Available from: https://www.aapspharmaceutica.com/scientificjournals/pharmsci/am_abstracts/1999/2419.htm.

This follows the American Medical Association standard format for online journals.