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. 2010 Dec 8;67(5):493–506. doi: 10.1007/s00228-010-0948-5

Table 4.

Multiple linear regression models with factors predicting the serum concentrations of oxycodone and the ratios oxymorphone/oxycodone and noroxycodone/oxycodone

Factorsa associated with Unstandardised coefficientsb Standardised coefficients 95% confidence interval for B
B Standard error Beta Significance Lower bound Upper bound
Oxycodone (n = 433; R2 = 0.35)b
  Oxycodone total daily dose 0.002 0.0002 0.491 0.000 0.002 0.002
  CYP3A4 inducerc −0.786 0.233 −0.131 0.001 −1.242 −0.327
  CYP3A4 inhibitorc 0.204 0.101 0.078 0.044 0.005 0.403
  Sexd 0.113 0.045 0.098 0.012 0.025 0.201
  Time from last oxycodone dose to blood sample −0.027 0.006 −0.189 0.000 −0.038 −0.016
Ratio oxymorphone/oxycodone (n = 438; R2= 0.05)b
  Oxycodone total daily dose −0.0004 0.0001 −0.136 0.004 −0.0007 −0.0001
  CYP3A4 inducerc 0.607 0.234 0.122 0.010 0.147 1.067
  Number of medications (excluding opioids) taken in the last 24 h −0.024 0.008 −0.140 0.003 −0.039 −0.008
Ratio noroxycodone/oxycodone (n = 396; R2 = 0.19)b
  Oxycodone total daily dose 0.001 0.0001 0.231 0.000 0.0003 0.001
  Time from last oxycodone dose to blood sample 0.012 0.004 0.147 0.002 0.004 0.020
  Albumin 0.006 0.002 0.132 0.005 0.002 0.010
  Sexd −0.110 0.033 −0.160 0.001 −0.175 −0.045
  CYP3A4 inducerc 0.602 0.183 0.153 0.001 0.242 0.962
  CYP3A4 inhibitorc −0.294 0.068 −0.197 0.000 −0.427 −0.160
  Systemic steroidsc,e −0.070 0.032 −0.102 0.028 −0.132 −0.008
  BMI −0.009 0.004 −0.109 0.019 −0.017 −0.001
  Glomerular filtration rate −0.001 0.0004 −0.161 0.001 −0.002 −0.0005

aIndependent variables in all analyses were age (years), sex, BMI (kg m−2), Karnofsky performance status (%), time from last oxycodone dose to sample (h), oxycodone total daily dose (mg/24 h), time since starting opioids (months), number of concomitant medications in the last 24 h, use of CYP3A4 inhibitor (yes/no), use of CYP3A4 inducer (yes/no), glomerular filtration rate (ml min−1 1.73 m−2) and albumin (g l−1) serum concentrations

bCoefficients are in log 10 form (e.g. 100.002 × oxycodone daily dose)

cYes = 1, no = 0 (user of systemic steroids yes: 10−0.070 × 1, NO: 10−0.070 × 0)

dMen = 1, women = 0 (male oxycodone serum concentration: 100.113 × 1, women: 100.113 × 0, noroxycodone/oxycodone ratio men: 10−0.110 × 1, women: 10−0.110 × 0)

eThe patients in the CYP3A4 inducer (n = 4) group also used systemic steroids