Does "those drugs" refer back to "only three drugs"?

Context:

A new class of antibiotics to fight bacteria such as methicillin-resistant Staphylococcus aureus and other drug-resistant bacteria that threaten public health has been discovered by a team of chemists. The new class, called oxadiazoles, was discovered in silico (by computer) screening and has shown promise in the treatment of MRSA in mouse models of infection. MRSA has become a global public-health problem since the 1960s because of its resistance to antibiotics. In the United States alone, 278,000 people are hospitalized and 19,000 die each year from infections caused by MRSA. Only three drugs currently are effective treatments, and resistance to each of those drugs already exists.