New Zealand Practice Guidelines for Opioid Substitution ...

At a pH of 5.5 or less, 23% is excreted unchanged. At a pH of 8, only 2% is excreted in the urine. The effect of urinary pH on total clearance is entirely due to changes in renal clearance. Blood cotinine levels, and possibly, saliva cotinine levels, are good measures of passive smoking. ................
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