Belladonna alkaloids excretion

All the belladonna alkaloids are well absorbed from the GIT, from the site of injection and the mucous membrane. They are distributed throughout the body and cross the blood-brain barrier. About 50% of the atropine is metabolized in liver and remaining portion is excreted unchanged in urine. Atropine cross the placental barrier and is secreted in milk and saliva. 

The belladonna alkaloids are absorbed rapidly from the gastrointestinal tract. They also enter the circulation when applied locally to mucosal surfaces. Only limited absorption occurs from the intact skin. Atropine disappears rapidly from the blood and is distributed throughout the entire body. Most is excreted in the urine within the first 12 h, in part unchanged. Only about 1% of an oral dose of scopolamine is eliminated as such in the urine. Traces of atropine are found in various secretions, including milk. The total absorption of quaternary ammonium derivatives of the alkaloids after an oral dose is only about 10-25 percent (10,11) nevertheless, some of these compounds can cause mydriasis and cycloplegla if applied to the eye. 

The belladonna alkaloids are absorbed rapidly after oral administration (75). They enter the circulation when applied locally to the mucosal surfaces of the body. Atropine absorbed from inhaled smoke of medicated cigarettes can abolish the effects of intravenous infusion of methacholine in humans. The transconjunctival absorption of atropine is considerable. About 95% of radioactive atropine is absorbed and excreted followingsubconjunctival injection in the rabbit. The total absorption of quaternary ammonium derivatives (Section 3.5) of the alkaloids after an oral dose is only about 25%. The liver, kidney, lung, and pancreas are the most important organs that take up the labeled atropine. The liver probably excretes metabolic products of atropine by way of bile into the intestine (in mice and rats). 

Pharmacokinetics of atropine Atropine is the prototypical nonselective muscarinic blocker. This alkaloid is found in Atropa belladonna and many other plants. Because it is a tertiary amine, atropine is relatively lipid-soluble and readily crosses membrane barriers. The drug is well distributed into the CNS and other organs and is eliminated partially by metabolism in the liver and partially by renal excretion. The elimination half-life is approximately 2 hours, and the duration of action of normal doses is 4-8 hours except in the eye, where effects last for 72 hours or longer. 

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