New Drug of Abuse: Gabapentin

Gabapentin is increasingly being used by patients in methadone maintenance programs to get a high.

Increasing availability, infrequent drug testing, and potentiation of euphoria when combined with opioids have likely all contributed to gabapentin misuse.

• Drug Abuse Warning Network (DAWN) data show that ED visits involving thenonmedical use of gabapentin have increased by 90% in the United States since 2008. 
• DAWN data also suggest that 20% of patients in treatment may misuse or abuse gabapentin.

Meanwhile, there has been a rise in gabapentin prescribing.

Current advice on prescribing Gabapentin: use caution. Don't necessarily avoid prescribing it, but be careful and prescribe it from visit to visit. Don't just give somebody six refills and say you will see them in 6 months. 

source: http://www.medscape.com/viewarticle/855819?nlid=93367_2982, (Medscape Medical News from the American Academy of Addiction Psychiatry (AAAP) 26th Annual Meeting)

Pre-emptive analgesia

Ñ Pre-emptive analgesia is an antinociceptive treatment that prevents establishment of altered processing of afferent input, which amplifies postoperative pain.

Ñ Concept of preemptive analgesia was formulated by Crile

Ñ DEFINITION: Treatment  that:

ü  Starts before surgery

ü  Prevents the establishment of central sensitization by incisional injury ( covers period of surgery)

ü  Prevents establishment of central sensitization caused by incisional and inflammatory injury (covers the period of surgery and the initial postoperative period).

Ñ Strategies:

ü  Local skin infiltration-pre and post operative

ü  PCM and NSAIDS: reduces inflammation, pain , fever:

Ø  Diclofenac - used in orally, per-rectally,intramuscularly and continuous infusion.Single dose: 1.0 - 2.0 mg/kg; maximum dose; 3mg /kg /day. Interval: 6- 8 hours.

Ø  Paracetamol - can be administered in orally, infusion and per-rectally. Single dose: 10 - 15 mg/kg; maximum dose: 60mg/kg/day. Interval: 4- 6 hours.

ü  Intravenous  Opioids:

Sites of action:

Ø  Periaqueductal Grey (PAG), Limbic system

Ø  Caudal brain stem (nucleus raphe magus, magnocellular reticular formation)

Ø  Spinal cord

Mechanism of action:

Ø  inhibition of neuronal activity

Ø  inhibit the release of neurotransmitters

Ø  activate descending inhibitory systems

ü  Epidural anaesthesia, Nerve blocks: Commonly practiced agents are Bupivacaine and Lidocaine with or without Epinephrine (1:200,000 or 5 ug/ml).

ü  Both agents can be given local infiltration, intrathecal, caudal or epidural and peripheral nerve block (llioinguinal and iliohypogastric nerve block, penile nerve block, intercostal nerve block, brachial plexus block etc.).

ü  Alpha 2 agonists:

Ø  play a key part in the descending modulation of pain.

Ø  Descending supraspinal pathways include the periaqueductal gray area of the midbrain, stimulation of which results in widespread analgesia.

Ø  In particular, stimulation of alpha-2 receptors located in the locus ceruleus and parabrachial nucleus of the medulla affords analgesia through G-protein mediated potassium channel conductance

ü  NMDA  receptor antagonists:

Ø  Magnesium, Ketamine : Combinations of ketamine and magnesium potentiate each other.Combinations are more effective analgesics than either alone; Superadditive (>90%) effect of coadministration allows for reduced doses of each; thus, less side effects. 

ü  Others:

Ø   Dextromethorphan, Methadone

Ø   Tricyclic antidepressants, Nicotine agonists

ü  repeated episodes of constant noxious input primes NMDA receptors for chronic pain state (central sensitization)