From the timeline...
“Late summer” (mid-to-late-August?) 2001—ATTA and AL-SHEHHI go to Huber Drugs in Delray Beach, FL, where the owner Greg Chatterton later identified them as frequent customers. ATTA seeks treatment for “palms that appeared to be reddened from a chemical burn or raw from construction work.” Link Chatterton asks if he had been working with solvents or dipping his hands into chemicals such as ammonia or chlorine, which ATTA denied. When asked what he did for a living, ATTA replies that he was in computer work. ATTA is given a tube of Acid Mantle, a cream which restores acidity to skin that’s been exposed to too much base, such as ammonia. ATTA pays $5.49 for it. AL-SHEHHI complains of chest congestion and a cough and is given Robitussin and urged to seek medical treatment at Urgi-Med, a nearby walk-in clinic. Within a day or two, AL-SHEHHI returns with a prescription for an antibiotic, which Chatterton said he filled. Chatterton could not recall which drug was prescribed, only that it was not for Ciproflaxin, later famous as the anti-anthrax drug of choice. The FBI perused the store’s records, which are not computerized, and concluded that AL-SHEHHI must have used an alias. “That’s why they came here,” said Chatterton later. “Think about it—you go to a small-town pharmacy, not part of a computer bank” which would archive prescription records. Urgi-Med at first confirmed to a reporter that “at least one hijacking suspect” had been treated at the clinic, but a manager for the clinic later called the reporter back and said that clinic officials would have no comment on the matter.
Another of the terrorists was treated for a sore which, upon reflection, the doctor concluded was probably cutaneous anthrax. I'll see if I can find the timeframe on that next.