Extensively drug-resistant TB is also resistant to three or more of the six classes of second-line drugs.

It requires expensive, "second-line" drugs, which must be taken for years instead of months, and which have many side effects.

"We are terribly afraid of liberal use of second-line drugs," Dr. Farmer said.

The editorial suggested metformin should be used as a second-line drug if clomifene treatment fails.

Procyclidine is also a second-line drug for the treatment of Parkinson's disease.

Experience with using the majority of the second-line drugs for TB during pregnancy is limited.

The following concerns should be considered when selecting second-line anti-TB drugs for use among pregnant women:

In addition, second-line drugs are extremely expensive compared with the cost of drugs for standard TB treatment.

Effective treatment requires that all six classes of second-line drugs be available to clinicians who have special expertise in treating such cases.

Amodiaquine was to be the second-line drug.