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Abstract
1. The fate of [14C]rimiterol given orally, by aerosol, and intravenously to asthmatic patients has been investigated.
2. Following oral dosage (10 mg) < 50% dose was excreted in the urine. Two peaks in plasma concn. were seen, at 1–2 h and 3–5 h after dosing. Plasma radioactivity due to free rimiterol varied but never exceeded 10%. Of the urine radioactivity 50.5% was excreted as rimiterol (free and sulphate ester), and 30.5% as 3-O-methyl rimiterol (free and sulphate ester); free rimiterol accounted for only 1.7% and free 3-O-methyl rimiterol 2.5% of dose.
3. Following aerosol administration (0.39–0.56 mg) the pattern of metabolism and excretion was similar to that seen after oral administration.
4. After intravenous infusion (0.038 and 0.216 mg over 10 min) 92% of dose was excreted in the urine, suggesting little biliary excretion. Peak plasma concn. were seen 2–4 min after the end of injection at which time most of the radioactivity was due to free rimiterol. Of the urine radioactivity, 28.45% was excreted as rimiterol (free and sulphate ester), and 44.9% as 3-O-methyl rimiterol (free and sulphate ester), with 26.5% as unchanged rimiterol. Thus after intravenous administration a greater amount of free drug was excreted and a higher percentage of the dose was 3-O-methylated.