Moujahed Labidi , MD PGY-II Neurosurgery Jérome Villeneuve, PhD Sylvine Cottin , PhD

1. Drug consumption and medication cost analysis after spinal cord stimulation in chronic pain patients MoujahedLabidi, MD PGY-II Neurosurgery Jérome Villeneuve, PhD SylvineCottin, PhD Sarah-Maude Caron-Cantin Véronique Briand-Carle Michel Prud’homme, MD PhD LéoCantin, MD FRCSC

2. Introduction • Chronic neuropathic pain is a frequent clinical entity with reported prevalence of 27 % of patients in pain clinics and up to 8% in the general population (Torrance et al., 2006). It is a debilitating and costly disease (Berger et al., 2004) • In a retrospective review of our cases of spinal cord stimulation for these patients, we demonstrated that 40% mean reduction in pain levels, a significant improvement in quality of life and an 80% satisfaction rate(unpublished data).

3. Introduction • Does SCS reduce medication consumption and drug cost? • The cost-effectiveness of the procedure is established in some indications • CRPS (Kemler et al., 2002) • FBSS (Kumar et al., 2002) (North et al., 2007) • Relatively few data on medication following SCS implantation • North et al. 2005 • Kumar et al. 2008

4. Methods • Retrospective observationalstudy of all consecutive patients who underwent implantation of a SCS between January 1st, 2000 and June 31st, 2009. • Consent was obtained from all the participants • Baseline characteristics and indication for surgery were obtained from charts. • Medication was assessed with the profiles as effective in the immediate preoperative period and as of July 2009. They were obtained from charts and community pharmacies, respectively. • Morphine equivalents were calculated according to a published equianalgesic tables. Total medication cost was calculated on a price per pill basis, according to our institution’s formulary in July 1st.

5. Patients 131 SCS implantations • 77 Exclusions • 23 Data unavailable • 20 SCS removed • 12 Refusal to participate • 8 Invalid data • 4 Deceased • 3 Non-functioning SCS • 2 IT morphine pump 54 included patients

6. Results • There was 21 women (39%) and 33 men (61%) and the mean age at implantation was 50 ± 2 years and 48 ± 2 years for women and men, respectively • The mean duration since surgery was 33 ± 25 months • The most frequent indication was FBSS followed by CRPS

7. Results

8. Results *Reduction not associated with preop level of opiates or duration since surgery • Opiate consumption • Preop : 87 ± 118 mg/d • Postop : 99 ± 172 mg/d • P = 0.29 Increase (33%) Decrease (34%) Number of patients

9. Results *

10. Results *Reduction associated with lowerpreop total drug costs (p < 0.05) • Total drug costs • Preop : 181 ± 25 CAD$/m • Postop : 217 ± 25 CAD$/m • P = 0.23 * Drug cost difference (CAD$)

11. Results Correlation between drug cost difference and age among male patients Drug cost difference (CAD$) Age

12. Discussion • No statistically significant reduction in opiate intake or drug consumption habits following SCS implantation • No statistically significant reduction in total drug cost either • However, 67% of patients achieved stabilisation or even reduction of their opiate intake while noting improvement in their pain levels and quality of life

13. Discussion • There may be a different response and evolution between genders • Different threshold and reaction to pain • Higher prevalence of chronic pain among females • Different expectations from surgery • Medication reduction may be harder among patients taking more medication initially • Limitations of the study • Retrospective design • Significant number of exclusion (59%) • Important variation in duration since implantation of SCS • No standardization of confounding parameters and medical management

14. Conclusion • Opiate consumption reduction is hard to achieve following SCS • This may be especially true for female patients • Actively reducing the medication may be possible without increasing pain levels; this should be studied in a prospective fashion in a pain clinic context