Switching patterns of immediate-release forms of generic mixed amphetamine salts products among privately and publicly insured individuals aged 15-64 years in the United States, 2013-2019

PURPOSE

Immediate-release forms of generic mixed amphetamine salts (MAS) have been the subject of passive surveillance reports signaling lack of effectiveness. We examined switching patterns that might suggest whether long-term users of specific MAS are more likely to switch away or switch back after use of the MAS of interest in the FDA's Sentinel Distributed Database.

METHODS

We required at least 60-day continuous supply of selected MAS grouped by Abbreviated New Drug Application (ANDA) to describe patterns of switching away from and to generics approved under the ANDAs of interest among individuals ages 15-64 years with attention deficit hyperactivity disorder or narcolepsy during 2013-2019.

RESULTS

We observed the greatest number of treatment episodes for ANDA 040422 (n = 525 771), followed by ANDA 202424 (n = 181 693), ANDA 040439 (n = 62 363), ANDA 040440 (n = 21 143), and ANDA 040480 (n = 8792). Of those with switches away from their original ANDA, episodes initiated on generic products under ANDA 040422 (48.6%) and ANDA 202424 (43.0%) were most likely to switch back, while those initiated on generic product under ANDA 040480 were least likely (24.1%). Of those episodes with switches to a generic under an ANDA of interest, about one-third (range 27.1% to 37.0%) switched back to the same product. These switches back had a median time to switch of about 30 days.

CONCLUSIONS

These descriptive analyses, although subject to limitations, did not suggest increased switching away or switching back after use of the generics of interest. Continued post-marketing surveillance is warranted.

Folding kinetics of villin 14T, a protein domain with a central beta-sheet and two hydrophobic cores

The thermodynamics and kinetics of folding are characterized for villin 14T, a 126-residue protein domain. Equilibrium fluorescence measurements reveal that villin 14T unfolds and refolds reversibly. The folding kinetics was monitored using stopped-flow with fluorescence and quenched-flow with NMR and mass spectrometry. Unfolding occurs in a single-exponential phase in the stopped-flow experiments, and about 75% of the total amplitude is recovered in the fast phase of refolding. The remaining 25% of the amplitude probably represents trapping in cis-trans proline isomerization pathways. At 25 degreesC, the stability estimate obtained by extrapolation from the transition region of the stopped-flow chevron matches the stability value from equilibrium urea titrations (DeltaG = 9.7 kcal/mol, m value = 2.2 kcal mol-1 M-1). At low final urea concentrations, however, the refolding kinetics deviates from the two-state model, indicating the formation of an intermediate. Under these conditions, quenched-flow followed by NMR and mass spectrometry show no detectable hydrogen-bonded intermediate in the fast refolding phase. In contrast, agreement is observed between the equilibrium and kinetic estimates of stability at 37 degreesC (DeltaG = 6.0 kcal/mol, m value = 1.6 kcal mol-1 M-1), at all observed urea concentrations, demonstrating apparent two-state folding at this temperature. This result shows that the two-state folding model, previously applied to small domains with single, central hydrophobic cores, can also describe the folding of a larger domain with multiple core structures.

Identification of a structural element in phospholipase C beta2 that interacts with G protein betagamma subunits

To delineate the specific regions of phospholipase C beta2 (PLC beta2) involved in binding and activation by G protein betagamma subunits, we synthesized peptides corresponding to segments of PLC beta2. Two overlapping peptides corresponding to Asn-564-Lys-583 (N20K) and Glu-574-Lys-593 (E20K) inhibited the activation of PLC beta2 by betagamma subunits (IC50 50 and 150 microM, respectively), whereas two control peptides did not. N20K and E20K, but not the control peptides, inhibited betagamma-dependent ADP-ribosylation of Galphai1 by pertussis toxin and betagamma-dependent activation of phosphoinositide 3-kinase. To demonstrate direct binding of the peptides to betagamma subunits, the peptides were chemically cross-linked to purified beta1gamma2. N20K and E20K cross-linked to both beta1 and gamma2 subunits, whereas the control peptides did not. Cross-linking to beta and gamma was inhibited by incubation with excess PLC beta2 or PLC beta3, whereas cross-linking to gamma but not beta was inhibited by r-myr-alphai1. These data together demonstrate specificity of N20K and E20K for G betagamma binding and inhibition of effector activation by betagamma subunits. The results suggest that an overlapping region of the two active peptides, Glu-574-Lys-583, mimics a region of PLC beta2 that is involved in binding to betagamma subunits. Changing a tyrosine to a glutamine in this overlapping region of the peptides inhibited binding of the peptide to betagamma subunits. Alignment of these peptides with the three-dimensional structure from PLC delta1 identifies a putative alpha helical region on the surface of the catalytic domain of PLC beta2 that could interact with betagamma subunits.