The association of monoamine oxidase B functional polymorphism with postoperative pain intensity.

OBJECTIVES: The monoamine oxidase B (MAO-B) is an enzyme involved in metabolism of dopamine, benzylamine, phenylethylamine, tyramine and tryptamine. The A/G polymorphism in intron 13 of the MAO-B gene has been previously found to be associated with variability of the MAO-B enzyme activity. The aim of the present association study has been to examine the relationship between the A/G polymorphism in intron 13 and postoperative pain intensity. METHODS: 284 subjects (105 males and 179 females) undergoing planned tonsillectomy were examined. The intensity of pain was evaluated using 100-mm visual analogue scale (VAS). A PCR method with allele specific primers for detection of A/G polymorphism was used. RESULTS: We found a relationship between the A/G polymorphism in intron 13 of the MAO-B gene and average intensity of postoperative pain in male subjects. Higher average intensity of postoperative pain was detected in males with the G allele (3.96) in comparison with males with the A allele (3.45) and the difference was statistically significant (p<0,03). CONCLUSIONS: Results of this study indicate the relationship between the MAO-B polymorphism and postoperative pain intensity in the Czech male population. A potential role of MAO-B in the perception of pain intensity is discussed.

Pain research update from a genetic point of view.

Molecular biology investigates the genetic causes of many diseases. Currently, molecular biology in pain research lags behind the investigations of the molecular basis of mental disorders. A significant challenge in pain genetic research is the fact that pain involves emotional factors. Tools available for pain measurements and interindividual comparisons have been imperfect. Another problem relates to research ethics. Unlike animal studies, there is very limited ability to evoke experimental pain in a group of humans with precisely defined age, sex, medication, and pain experience. Nevertheless, pain investigations at the gene level have commenced. Recent progress in molecular biology has enabled gene expression modulation in animal models using "knockout," "oligo-antisense," and viral vector techniques. These methods enable investigation, at molecular level, as to which of the approximately 30,000 genes of the human genome might be involved in pain mediation, which of these are polymorphic, and which polymorphisms are responsible for interindividual differences in pain perception. Recently, the genetic bases of familial hemiplegic migraine and congenital insensitivity to pain with anhidrosis have been shown. In the last 6 years, genetic pain research has focused on potential gene therapy for patients with chronic pain. Results of these studies are encouraging and potentially applicable to clinical practice in the near future.

A high initial VAS score and sedation after iv morphine titration are associated with the need for rescue analgesia.

PURPOSE: Administration of sc morphine has been recommended two hours after the end of iv morphine titration in the postanesthesia care unit (PACU), but in some cases patients complain of pain earlier than this. We assessed pain after the end of iv morphine titration and studied the characteristics of patients who needed rescue sc morphine. METHODS: Postoperative pain was assessed using the visual analogue scale (VAS; 0 to 100) and the threshold required to administer morphine in the PACU was a score of 30. VAS was measured every 15 min up to two hours after the end of iv morphine titration. Patients were divided into two groups, those who required sc morphine before two hours and those who did not. Data are expressed as mean +/- SD or odds ratio (OR; 95% confidence interval). RESULTS: Four hundred and two patients were analyzed. Mean age was 51 +/- 19 yr, initial VAS 69 +/- 19, and the dose of iv morphine 11.7 +/- 6.6 mg. The number of patients requiring sc morphine within two hours was 84 (21%). These patients had more severe initial postoperative pain (73 +/- 20 vs 68 +/- 19, P < 0.05), and experienced sedation more frequently during morphine titration (45 vs 25%, P < 0.001). Using a multivariate analysis, occurrence of sedation during titration [OR 2.3 (1.4-3.8), P < 0.001] and an initial pain score > or = 60 [OR 1.9 (1.0-3.4), P < 0.05] were significantly associated with the need for rescue sc morphine. CONCLUSION: Sedation during titration and an initial VAS > or = 60 are characteristics of the patients who require rescue (less than two hours) sc morphine after iv morphine titration.