No abstract

1This study on 21 neurosurgical patients was set up to investigate the extent to which four chronically administered ,3-adrenoceptor blockers, propranolol, oxprenolol, metoprolol and atenolol, cross the blood-brain barrier and enter the cerebrospinal fluid (CSF) and brain tissue. The concentration in the CSF of the three lipophilic,/3-adrenoceptor blockers, propranolol, oxprenolol and metoprolol, approximated to the free drug concentration in the plasma, and was a poor predictor of brain concentration. These three lipophilic ,3-adrenoceptor blockers appeared in brain tissue at concentrations 10-20 times greater than that of hydrophilic atenolol. The approximate brain/plasma ratio for propranolol was 26, for oxprenolol 50, for metoprolol 12 and for atenolol 0.2. 2 The low concentration of atenolol in brain tissue is possibly responsible for the low incidence of central nervous system-related side effects in patients on this agent compared to lipophilic 3-adrenoceptor blockers.

I The whole blood concentrations of propranolol have been compared, over a 48 h period, in twelve healthy male volunteers dosed with a 160 mg long-acting capsule formulation (LA, United Kingdom patent application No. 23114/77) and three standard tablet regimens; 160 mg once a day (CP 160), 80 mg twice a day (CP80) and 40 mg four times a day (CP40). 2 The mean peak blood level for the long-acting formulation was significantly lower than that obtained with the 160 mg standard tablet. However, from 12 h on the mean levels for the long-acting formulation were higher. 3 The mean peak blood level for the long-acting formulation was significantly lower than that obtained with the 80 mg twice a day regimen and this difference was maintained up to 24 h. Thereafter, however, the situation was reversed. 4 The mean blood levels between 12 and 15 h were lower for the long-acting formulation when compared with the 40 mg four times a day regimen. At all other times, however, the observed levels were very similar. SThe profiles achieved with the long-acting formulation in two separate studies were almost identical over a 48 h period. 6 The percentage reductions in exercise heart rate over the 3-24 h post dosing period were similar for the long-acting formulation and the two standard regimens studied (i.e. CP40 and CP80) when compared with placebo. 7 In the 2 h post dosing period the 80 mg twice a day regimen produced a significant reduction in the post-exercise systolic blood pressure when compared with the long-acting formulation.

The non-stimulant cardioselective beta adrenocepter antagonist atenolol has been studied in volunteers in order to define its pharmacokinetic characteristics. Atenolol (100 and 200 mg orally) is rapidly absorbed, reductions in heart rate and systolic pressure being observed in 30 min. The effect persists for up to 8 h. Over 85% of an intravenous dose is excreted in urine within 24 h but only 50% of an oral dose. The bioavailability of approximately 50% is due to reduced absorption. Peak blood levels are observed at 2-4 h and the half life of atenolol given orally is 5-6 h. Atenolol reduces the cardiac response to standing and head-up tilt. It does not reduce circulating levels of renin but slightly impairs the renin response to tilt. Atenolol both orally and intravenously reduces supine diastolic pressure about four hours after administration, the effect persisting for up to 24 h.

1. The disposition and metabolism of 1-(4-carbamoyl[14C]methylphenoxy)-3-isopropylaminopan-2-ol (atenolol, Tenormin) has been studied in man following oral and intravenous doses. 2. Approx. 50% of an oral dose was eliminated in urine; the major radiolabelled component was atenolol (approx. 90%). Faecal extracts also contained largely unchanged atenolol, with small amounts of more polar metabolites. Biliary excretion of atenolol and its metabolites is not a major route of elimination in man. Metabolism of the compound is not extensive and route-dependent modes of metabolism do not appear to complicate the position. 3. Atenolol appeared to be the only major radiolabelled component in blood. 4. Oral doses of atenolol are incompletely absorbed (range 46-62%), even when formulated as a solution. 5. 1-[4-(C-Carbamoylhydroxymethyl)phenoxy]-3-isopropylaminopropan-2-ol was a minor urinary metabolite, which has only one tenth the activity of the parent compound as a beta-adrenergic blocking agent in the rat. 6. Pharmacological activity in man appears to be due to atenolol alone.