Although the shortage of amoxicillin, especially its liquid and chewable forms, has proved frustrating for pharmacists, doctors and parents whose children have grown accustomed to the bubble-gum and strawberry-flavored varieties of the drug, experts say there is no reason to panic: Supplies of effective alternatives like cephalexin and clindamycin remain plentiful, according to the F.D.A.

But the process of tracking down a suitable alternative delays care and can be frustrating. “It’s already stressful to take care of a sick child, and now you’re having to find a prescription on top of it. But there are alternatives available that are appropriate for the age and the indication,” said Dr. Michael Ganio, senior director of pharmacy practice and quality at the American Society of Health-System Pharmacists

While hundreds of drugs including chemotherapy and anesthetic agents have been in short supply for years, the current shortages of amoxicillin and antiviral drugs are unusual, Dr. Ganio said. He attributed the spike in demand to the early surge in respiratory illnesses this year.

“These are not your typical drug shortages, which are associated with manufacturing or supply chain disruptions,” he said. While most drug manufacturers prepare for seasonal variations, he said, “We don’t use a lot of Tamiflu in the northern hemisphere in the summertime, and the manufacturers plan accordingly. This has hit earlier than expected.”

The F.D.A., which tracks drug shortages on its website, said that there was no national shortage of Tamiflu, but that some regions of the country were experiencing temporary shortages. There are a number of alternatives to Tamiflu, which can prevent the flu and reduce the severity and duration of the illness, but many doctors are unfamiliar with those options, experts say.

The shortages highlight the fragility of the nation’s drug supply chain, especially for inexpensive generics like amoxicillin that are manufactured by just a handful of companies. Experts say the low prices for such drugs discourage investment in sophisticated quality management systems, which can improve manufacturers’ agility in shortages and enable them to scale up production more quickly.

One manufacturer, Sandoz, said it was ramping up production to meet the increased demand and hoped to double its output in the coming months. “We are facing challenges to meet this sudden spike in demand now that the flu season is in full swing,” the company said in a statement.