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Table 1 Baseline characteristics of knee OA patients according to the use of opioids as the first analgesic treatment

From: Factors related to the use of opioids as early treatment in patients with knee osteoarthritis

Variable Opioid users§ Opioid non-users
Total (n = 348,516) Tramadol (n = 346,544) Stronger opioids (n = 1972) (n = 2,509,483)
  N (%) N (%) N (%) N (%)
Age, years (mean ± SD) 64.2 ± 9.9 64.1 ± 9.8 68.3 ± 11.0 64.0 ± 9.8
 50–59 137,190 (39.4) 136,658 (39.4) 532 (27.0) 997,164 (39.7)
 60–69 107,022 (30.7) 106,485 (30.7) 537 (27.2) 781,375 (31.1)
 ≥ 70 104,304 (29.9) 103,401 (9.8) 903 (45.8) 730,944 (29.1)
Sex (female) 195,021 (56.0) 193,960 (56.0) 1061 (53.8) 1,562,071 (62.2)
Health insurance
 National insurance 323,934 (92.9) 322,308 (93.0) 1626 (82.5) 2,352,280 (93.7)
 Medical aid 22,104 (6.3) 21,809 (6.3) 295 (15.0) 136,862 (5.5)
 Veterans 2478 (0.7) 2427 (0.7) 51 (2.6) 20,341 (0.8)
Type of institution
 Tertiary hospital 5597 (1.6) 5119 (1.5) 478 (24.2) 33,123 (1.3)
 General hospital 29,424 (8.4) 28,395 (8.2) 1029 (52.2) 182,805 (7.3)
 Hospital 54,905 (15.8) 54,519 (15.7) 386 (19.6) 336,196 (13.4)
 Clinic 253,698 (72.8) 253,624 (73.2) 74 (3.8) 1,684,123 (67.1)
 Oriental medical hospital 74 (0.0) 74 (0.0) 222,631 (8.9)
 Others 4818 (1.4) 4813 (1.4) 5 (0.3) 50,605 (2.0)
Type of department
 Internal medicine 33,778 (9.7) 33,420 (9.6) 358 (18.2) 219,877 (8.8)
 Orthopedics 244,305 (70.1) 243,184 (70.2) 1121 (56.8) 1,588,219 (63.3)
 Rehabilitation 5480 (1.6) 5424 (1.6) 56 (2.8) 46,811 (1.9)
 Oriental medicine 226,250 (9.0)
 Others 64,953 (18.6) 64,516 (18.6) 437 (22.2) 428,326 (17.1)
Elixhauser score 4.5 ± 6.4 4.5 ± 6.3 10.3 ± 10.6 4.4 ± 6.2
Comorbidity††
 Congestive heart failure 16,502 (4.7) 16,294 (4.7) 208 (10.5) 112,668 (4.5)
 Cardiac arrhythmias 12,515 (3.6) 12,364 (3.6) 151 (7.7) 92,539 (3.7)
 Peripheral vascular disorders 54,070 (15.5) 53,668 (15.5) 402 (20.4) 356,803 (14.2)
 Hypertension, uncomplicated 158,773 (45.6) 157,611 (45.5) 1162 (58.9) 1,125,517 (44.9)
 Hypertension, complicated 17,426 (5.0) 17,263 (5.0) 163 (8.3) 123,765 (4.9)
 Paralysis 3317 (1.0) 3232 (0.9) 85 (4.3) 22,838 (0.9)
 Other neurological disorders 14,069 (4.0) 13,860 (4.0) 209 (10.6) 97,410 (3.9)
 Chronic pulmonary disease 104,644 (30.0) 103,822 (30.0) 822 (41.7) 734,749 (29.3)
 Diabetes, uncomplicated 67,736 (19.4) 67,064 (19.4) 672 (34.1) 478,114 (19.1)
 Diabetes, complicated 37,415 (10.7) 37,046 (10.7) 369 (18.7) 259,686 (10.3)
 Hypothyroidism 14,665 (4.2) 14,546 (4.2) 119 (6.0) 120,335 (4.8)
 Renal failure 5111 (1.5) 5023 (1.4) 88 (4.5) 36,877 (1.5)
 Liver disease 73,216 (21.0) 72,548 (20.9) 668 (33.9) 522,157 (20.8)
 Peptic ulcer disease excluding bleeding 80,772 (23.2) 80,162 (23.1) 610 (30.9) 542,506 (21.6)
 Metastatic cancer 1614 (0.5) 1386 (0.4) 228 (11.6) 10,203 (0.4)
 Solid tumor without metastasis 17,432 (5.0) 17,016 (4.9) 416 (21.1) 136,534 (5.4)
 Weight loss 3000 (0.9) 2847 (0.8) 153 (7.8) 19,827 (0.8)
 Fluid and electrolyte disorders 13,631 (3.9) 13,341 (3.8) 290 (14.7) 88,210 (3.5)
 Deficiency anemia 15,807 (4.5) 15,513 (4.5) 294 (14.9) 115,735 (4.6)
 Alcohol abuse 7674 (2.2) 7593 (2.2) 81 (4.1) 48,089 (1.9)
 Depression 41,634 (11.9) 41,113 (11.9) 521 (26.4) 277,119 (11.0)
Musculoskeletal disorders
 Low back pain 187,194 (53.7) 185,990 (53.7) 1204 (61.1) 1,257,774 (50.1)
 Intervertebral disc disorder 69,342 (19.9) 68,789 (19.9) 553 (28.0) 413,702 (16.5)
 Spinal stenosis 74,070 (21.3) 73,357 (21.2) 713 (36.2) 405,241 (16.1)
 Fibromyalgia 6576 (1.9) 6532 (1.9) 44 (2.2) 39,799 (1.6)
Medication
NSAIDs 246,933 (70.9) 245,578 (70.9) 1355 (68.7) 1,492,548 (59.5)
 Nonselective 233,275 (66.9) 232,418 (67.1) 857 (43.5) 1,372,520 (54.7)
 Cox-2 inhibitor use 14,793 (4.2) 14,175 (4.1) 618 (31.3) 123,006 (4.9)
Acetaminophen 7909 (2.3) 7589 (2.2) 320 (16.2) 143,820 (5.7)
SYSADOA* 78,876 (22.6) 78,593 (22.7) 283 (14.4) 554,849 (22.1)
Steroid 15,561 (4.5) 15,443 (4.5) 118 (6.0) 59,245 (2.4)
GI-protective agents 217,241 (62.3) 215,953 (62.3) 1288 (65.3) 976,102 (38.9)
  1. OA osteoarthritis, NSAIDs nonsteroidal anti-inflammatory drugs, SYSADOA symptomatic slow-acting drugs for OA, GI gastrointestinal
  2. Type of institution, department, and medication were determined at the index date
  3. ††Comorbidities with more than 3% prevalence
  4. *SYSADOA includes diacerein, avocado, glucosamine, sadenin, chondroitin sulfate, and herbal SYSADOA such as Layla, Joins, and Shinbaro
  5. GI protective agents include proton pump inhibitors, H2 blockers, rebamipide, teprenone, and Artemisia asiatica
  6. §Opioid user includes combination products of acetaminophen