Clomiphene binds the estrogen receptor. It typically acts as a partial antagonist; however, it can exhibit full antagonism or no effect at all. It stimulates ovulation in disorders of ovulation and in amenorrheic patients. In patients who fail to ovulate, it is suggested that clomiphene interferes with the negative feedback of endogenous estrogens, thereby increasing the release of LH and FSH by the pituatary.
Mifepristone is structurally related to norethindrone. This compound is classified as a progesterone antagonist with weak agonistic properties. A single dose can function as an emergency postcoital contraceptive. It also can induce an abortion by causing contraction of the myometrium, which leads to detachment of the embryo. The drug is used in single or multiple doses followed by the administration of a prostaglandin to cause the abortion. Estrogens used alone or in combination with progestins have also proven effective in postcoital contraception.
The organophosphorus insecticides inactivate cholinesterases, which results in accumulation of endogenous acetylcholine (ACh) in nerve tissue and effector organs. Very severe cases of acute poisoning should be treated first with atropine followed immediately by intravenous 2-PAM. Atropine inhibits the actions of ACh at muscarinic cholinergic receptors, whereas 2-PAM reactivates the inactivated cholinesterases. The effectiveness of 2-PAM in reversing cholinesterase inhibition depends on early treatment inasmuch as the "aged" inhibited enzyme cannot be reactivated. Diethyldithiocarbamic acid is the active biotransformation product of disulfiram, which is an irreversible inhibitor of aldehyde dehydrogenase. N-acetyl-L-cysteine is an antidote used in the treatment of acetaminophen overdosage to prevent hepatotoxicities. Carbachol is a cholinomimetic drug, and EDTA is a chelating agent. These compounds have no therapeutic value in the treatment of organophosphate poisoning.