452
Personalized Analgesics
Pharmacogenetics has been used in drug development and clinical pharmacology
of various diseases but not for pain because the genetic aspects of pain are just begin-
ning to be unraveled. Moreover, the effect of a drug on acute pain and any adverse
reaction are apparent immediately, enabling the switching over to another drug.
Pharmacogenetics may be applicable in the treatment of some chronic pain syn-
dromes, particularly those with neuropathic pain. Pharmacogenomics, by improving
the discovery of analgesic medications and defi nition of the type of patients for which
it would be suitable, will contribute to personalized medicines. Personalized medi-
cines tailored to a patient’s needs and selected on a genomic basis are defi nitely going
to be effective and safer, facilitating signifi cant long-term cost savings for the health-
care sector in a managed care environment. This system would enable the selection
of an appropriate analgesic for a patient taking into consideration his/her genetic
makeup, concomitant disease and comedications. In such a system, two patients
presenting with pain due to rheumatoid arthritis may receive different medications.
Signature of Pain on Brain Imaging
Brain imaging studies have been conducted to develop a fMRI-based measure for
predicting pain intensity at the level of the individual person (Wager et al. 2013 ).
Machine-learning analyses were to identify a pattern of fMRI activity across brain
regions – a neurologic signature – that was associated with heat-induced pain. Pattern
included the thalamus, the posterior and anterior insulae, the secondary somatosensory
cortex, the anterior cingulate cortex, the periaqueductal gray matter, and other regions.
Further studies tested the sensitivity as well as specifi city of the signature to pain ver-
sus warmth in a new sample and assessed specifi city relative to social pain, which
activates many of the same brain regions as physical pain. Finally, the responsiveness
of the measure to the analgesic agent remifentanil was assessed. The neurologic signa-
ture showed sensitivity and specifi city of ~94 % in discriminating painful heat from
nonpainful warmth, pain anticipation, and pain recall. The strength of the signature
response was substantially reduced when remifentanil was administered. The study
concluded that it is possible to use fMRI to assess pain elicited by noxious heat in
healthy persons. Future studies are needed to assess whether the signature predicts
clinical pain and to use it as a guide to development of personalized analgesics.
Concluding Remarks on Personalized Management of Pain
Pain is a complex problem in management. Treatment is guided by the type of pain
and response to initial measures. An algorithm is shown in Fig. 12.7 as a simple
guide to basics of sequence of various steps for management of infl ammatory and
neuropathic pain. Details are shown in a special report on pain therapeutics and vary
according to type of pain (Jain 2015d ). Mechanism-based personalized manage-
ment of neuropathic pain is shown in Table 12.9.
12 Personalized Management of Neurological Disorders