An example of covalent drug-receptor interaction is:

ref ;KD Tripathi Pharmacology 7th edition (page no;60) A Nonequilibrium type of enzyme inhibition can also occur with drugs which react with the same catalytic site of the enzyme but either form strong covalent bonds or have such high affinity for the enzyme that the normal substrate is not able to displace the inhibitor, e.g. Organophosphates react covalently with the esteretic site of the enzyme cholinesterase. Methotrexate has 50,000 times higher affinity for dihydrofolate reductase than the normal substrate DHFA. Phenoxybenzamine is a nonequilibrium antagonist of adrenaline at the alpha adrenergic receptor- irreversible inhibitor of alpha receptors