Table 3.

Best‐fit parameters for the oxypurinol concentration– and allopurinol dose–response relationships with serum urate in gout patients (47 patients, 98 plasma samples)

	ID 50 [Allopurinol mg dose‐resp, mg] or IC 50 [Oxypurinol mg l –1 conc–response] (95% CI)	U R , mmol l –1 (95% CI)	k or d a (95% CI)	r 2 , OFV	P‐value
Concentration–response
No U R (Eqn (2) , U R = 0)	21.0 (19.2–23.0)	0	‐	0.60, 0.29	‐
With U R (Eqn (2) )	11.3 (8.0–16.2)	0.17 (0.09–0.23)	‐	0.64, 0.26	7.71 × 10–4 b
With U R , k*CL CR (Eqn (4) )	11.7 (8.1–17.1)	0.18 (0.09–0.25)	–1.0 × 10–4 (–4.0 × 10–4 – 2.5 × 10–4)	0.66, 0.25	0.51c
With U R , d*DIU ( Eqn (6) )	10.6 (7.4–15.3)	0.18 (0.10–0.24)	0.01 (–0.01–0.04)	0.64, 0.25	0.26c
Dose–response
No U R (Eqn (3) , U R = 0)	417 (371–472)	0	‐	0.36, 0.47	‐
With U R (Eqn (3) )	117 (82–163)	0.26 (0.22–0.30)	‐	0.60, 0.29	7.27 × 10–12 d
With U R , k*CL CR (Eqn (5) )	112 (81–153)	0.22 (0.17–0.27)	4.5 × 10–4 (4.8 × 10–5 – 8.6 × 10–4)	0.62, 0.28	0.03e
With U R , d * DIU ( Eqn (7) )	121 (83–176)	0.26 (0.22–0.30)	‐0.01 (–0.03–0.02)	0.59, 0.29	0.67e

CL_CR, creatinine clearance; d, covariate constant for diuretic use; DIU, concomitant diuretic use; Eqn, equation; IC₅₀, the concentration of oxypurinol that has reduced the inhibitable urate concentration (U_P – U_R) by 50%; ID₅₀, the dose of allopurinol that has reduced the inhibitable urate concentration (U_P – U_R) by 50%; k, covariate constant for CL_CR; OFV, objective function value; r, correlation coefficient; r ², coefficient of determination; U_P, pretreatment serum urate concentration; U_R, ‘resistant’ serum urate concentration.

^acovariate constants depending on whether CL_CR (k) or DIU (d) were entered as covariates.

^b P‐value compared to fit to Equation (2) where U_R = 0.

^c P‐value compared to fit to Equation (2).

^d P‐value compared the fit to Equation (3) where U_R = 0.

^e p‐value compared the fit to Equation (3).