The FDA published final guidance on its priority review voucher program for tropical diseases, saying that a voucher does not offer a complete guarantee of an approval within six months.

The agency also loosened its restrictions on the eligibility of drug-drug combinations, in a change from the 2008 draft version of the guidance.

The guidance reiterated the FDA’s commitment to responding to 90 percent of priority-designated applications within six months, but stated that its answer could also come in the form of a complete response letter, with a description of specific deficiencies, instead of an approval.