Age may also be a significant factor. Some psychoactive drugs such as LSD, methaqualone, or phencyclidine can cause hyperacusis. An antibiotic, ciprofloxacin, has also been seen to be a cause, known as ciprofloxacin-related hyperacusis. Benzodiazepine withdrawal syndrome is also a possible cause. Neurophysiological mechanisms
As one important mechanism, adaptation processes in the auditory brain that influence the dynamic range of neural responses, are assumed to be distorted by irregular input from the inner ear. This is mainly caused by hearing loss related damage in the inner ear. The mechanism behind hyperacusis is not currently known, but it is suspected to be caused by damage to the inner ear and cochlea. It is theorized that type II afferent fibers become excited after damage to hair cells and synapses, triggering  a release of ATP in response. This release of ATP results in pain, sound sensitivity, and cochlear inflammation. Diagnosis
The basic diagnostic test is similar to a normal audiogram. The difference is that additionally to the hearing threshold at each test frequency also the lowest uncomfortable sound level is measured. This level is called loudness discomfort level (LDL), uncomfortable listening level (UCL), or uncomfortable loudness level (ULL). In patients with hyperacusis this level is considerably lower than in normal subjects, and usually across most parts of the auditory spectrum.
Stereochemistry
Midodrine contains a stereocenter and consists of two enantiomers, making it a racemate; i.e., a 1:1 mixture of (R)- and (S)-forms:

Synthesis
Acylation of 1,4-dimethoxybenzene with chloroacetyl chloride gives the chloroketone 2. The halogen is then converted to the amine 3 by any set of standard schemes, and the ketone reduced to an alcohol with borohydride (4). Acylation of the amino group in this last intermediate with chloroacetyl chloride affords the amide 5. The halogen is then displaced with azide and the resulting product 6 reduced catalytically to the glycinamide, midodrine (7). References
External links
 Media related to Midodrine at Wikimedia Commons

"Midodrine". Drug Information Portal. U.S. National Library of Medicine.