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Type of drugs used by subsystem and year of introduction. Note. Every drug was used beginning at the year marked in the figure during the period of study, with the following exceptions in the INS: DELAV was used between 1998 and 1999, HU was used between 1999 and 2000, and DDC was used between 1992 and 1998. The “x” indicates the year the FDA approved the drug, except for AZT which was approved in 1987 [15].
