Coadministration with food appears to enhance bioavailability. Despite complete absorption, propranolol has a  variable bioavailability due to extensive first-pass metabolism. Hepatic impairment therefore increases its bioavailability. The main metabolite 4-hydroxypropranolol, with a longer half-life (5.2–7.5 hours) than the parent compound (3–4 hours), is also pharmacologically active. Most of the metabolites are excreted in the urine.Propranolol is a highly lipophilic drug achieving high concentrations in the brain. The duration of action of a single oral dose is longer than the half-life and may be up to 12 hours, if the single dose is high enough (e.g., 80 mg). Effective plasma concentrations are between 10 and 100 mg/L. Toxic levels are associated with plasma concentrations above 2000 mg/L. History
Scottish scientist James W. Black developed propranolol in the 1960s. It was the first beta-blocker effectively used in the treatment of coronary artery disease and hypertension. In 1988, Black was awarded the Nobel Prize in Medicine for this discovery. Propranolol was inspired by the early β-adrenergic antagonists dichloroisoprenaline and pronethalol. The key difference, which was carried through to essentially all subsequent beta blockers, was the inclusion of an oxymethylene group (-O-CH2-) between the aryl and ethanolamine moieties of pronethalol, greatly increasing the potency of the compound. This also apparently eliminated the carcinogenicity found with pronethalol in animal models. Newer, more cardio-selective beta blockers (such as bisoprolol, nebivolol, carvedilol, or metoprolol) are now used preferentially in the treatment of hypertension.
Interactions
Since beta blockers are known to relax the cardiac muscle and to constrict the smooth muscle, beta-adrenergic antagonists, including propranolol, have an additive effect with other drugs which decrease blood pressure, or which decrease cardiac contractility or conductivity. Clinically significant interactions particularly occur with:
Verapamil
Epinephrine (adrenaline)
β2-adrenergic receptor agonists
Salbutamol, levosalbutamol, formoterol, salmeterol, clenbuterol  etc. Clonidine
Ergot alkaloids
Isoprenaline (isoproterenol)
Nonsteroidal anti-inflammatory drugs (NSAIDs)
Quinidine
Cimetidine
Lidocaine
Phenobarbital
Rifampicin
Fluvoxamine (slows down the metabolism of propranolol significantly, leading to increased blood levels of propranolol)

Pharmacology
Pharmacodynamics
Propranolol is classified as a competitive non-cardioselective sympatholytic beta blocker that crosses the blood–brain barrier. It is lipid soluble and also has sodium channel blocking effects. Propranolol is a non-selective β-adrenergic receptor antagonist, or beta blocker; that is, it blocks the action of epinephrine (adrenaline) and norepinephrine (noradrenaline) at both β1- and β2-adrenergic receptors. It has little intrinsic sympathomimetic activity, but has strong membrane stabilizing activity (only at high blood concentrations, e.g. overdose). Propranolol is able to cross the blood–brain barrier and exert effects in the central nervous system in addition to its peripheral activity.In addition to blockade of adrenergic receptors, propranolol has very weak inhibitory effects on the norepinephrine transporter and/or weakly stimulates norepinephrine release (i.e., the concentration of norepinephrine is increased in the synapse). Since propranolol blocks β-adrenoceptors, the increase in synaptic norepinephrine only results in α-adrenoceptor activation, with the α1-adrenoceptor being particularly important for effects observed in animal models. Therefore, it can be looked upon as a weak indirect α1-adrenoceptor agonist in addition to potent β-adrenoceptor antagonist.