Future Treatment?

The neurotransmitter gamma-aminobutyric acid (GABA) is a major inhibitory agent in the human brain. Medications such as the benzodiazepines are agonists at this site, and so would be expected to reduce the symptoms of HPPD if the disinhibition hypothesis were correct. Indeed, this seems to be the case, but unfortunately only partially so. One possible explanation for an incomplete treatment response may be pharmacokinetic, that is, too little drug reaching its destination in the brain. Indeed, when treating six patients with a short-acting benzodiazepine, the volunteer (a psychologist) excitedly said, ‘I can see normally for the first time in years.’ Similar strong responses were observed in the other volunteers. But the excitement was misplaced, since midazolam must be administered intravenously, and has a half-life of two hours. Clinical studies by my colleague Dr Lerner and his group in Israel have shown that clonazepam appears to be the benzodiazepine drug of choice for HPPD (Lerner et al., 2003)

There is an axiom in clinical medicine that the more mysterious the ailment, the more multitudinous the treatments. That is certainly the case with HPPD. In addition to the benzodiazepines, a long list of other agents have been tried, including antipsychotics, antidepressants, antiepileptics, alpha-two adrenergic agonists, and antiparkinsonian drugs. Levetiracetam was reported helpful in one study (Casa & Bosio, 2005). Some patients report that the use of psychostimulants improved the symptoms, leading me to try a study of tolcapone supplemented with carbidopa and l-DOPA in HPPD. The combination of medications reduced symptoms significantly in about a third of the sample (Abraham, 2012). While this may be a biological effect, it is equally consistent with a placebo response, since the study was an open-label one.



..Persistent flashbacks of the HPPD variety may represent permanent neural disruptions due to “disinhibition of visual processing related to a loss of serotonin receptors on inhibitory interneurons,” says Henry Abraham, a lecturer in psychiatry at Tufts University School of Medicine in Boston who has published several papers on HPPD...

..But there are two different benzodiazepines used as anticonvulsants, Clonazepam and Midazolam, that have shown promise for mitigating HPPD symptoms...

..Levetiracetam, a medication used for epilepsy, also performed well. However, anti-psychotic drugs like risperidone can dramatically worsen symptoms...




Source: http://dana.org/News/Details.aspx?id=43275