Springer Online Journal Archives 1860-2000
Chemistry and Pharmacology
Summary 1. The metabolic fate of intravenous and oral propranolol has been studied after single doses in man using 14C labelled propranolol. — 2. After oral administration there is virtually complete absorption and peak blood levels of propranolol and 4-hydroxy propranolol (a beta blocking metabolite) are seen at about 1 1/4 h after administration. Studies in normal subjects confirm that the maximum degree of beta blockade occurs at this time. — 3. Following intravenous administration, no 4-hydroxy propranolol is seen and the possible reasons for this are discussed. — 4. Excretion of the administered radio-active dose is mainly in the urine, with only 1%–4% of the administered radio-activity appearing in the faeces after both intravenous and oral dosing. — 5. The major metabolite so far identified in the urine is naphthoxylactic acid, which accounts for approximately 20% and 40% of oral and i.v. doses respectively. — 6. The greater proportion of radio-activity excreted in the urine (30–60% of the administered dose) is as yet unidentified although it may be a conjugate of propranolol. The level of total blood radio-activity following both intravenous and oral propranolol is very much higher than that of either propranolol or 4-hydroxy propranolol. The major portion of this blood radio-activity appears to be the same as the unidentified urinary metabolite. — 7. Following intravenous doses the decline of pharmacological response roughly parallels that of propranolol concentration in the plasma, and does not correlate with the plasma concentration of the unidentified metabolite.
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