B&O Pharmacology, Pharmacokinetics, Studies, Metabolism - Belladonna and Opium

B&O Pharmacology, Pharmacokinetics, Studies, Metabolism - Belladonna and Opium

CLINICAL PHARMACOLOGY

Through its parasympatholytic action, atropine relaxes smooth muscle resulting from parasympathetic stimulation. It is the dl isomer of 1-hyoscyamine and therefore exhibits the same clinical effects. It is, however, approximately one-half as active peripherally as 1-hyoscyamine, the latter being the major active plant alkaloid. The dl isomer, atropine, is formed during the process of isolation of the belladonna extract.¹

Morphine, the major active principle of powdered opium, is responsible for the action of powdered opium although the other alkaloids present also contribute to it. The sedative and analgesic action of morphine, the effect desired by inclusion in belladonna and opium suppositories of powdered opium, are thought to be due to the depressant effect on the cerebral cortex, hypothalamus and medullary centers. In large doses, the opiates and their analogs also exhibit synaptic conduction in the spinothalamic tracts, depress the function of the reticular formation, the lemniscus and the thalamic relays, and inhibit spinal synaptic reflexes: but these inhibitor actions should not be elicited with therapeutic doses of the drug. Moderate doses of powdered opium should not alter the electroencephalogram.

The action of morphine consists mainly of a descending depression of the central nervous system. It exerts its analgesic action by increasing the pain threshold or the magnitude of stimulus required to evoke pain and by dulling the sensibility or reaction to pain. In addition to its action in abolishing pain, morphine induces a sense of well-being (euphoria) facilitating certain mental processes while retarding others. Upon absorption of morphine, oxidative dealkylation to produce nor-compounds appears to be the first step in the reaction sequence which imparts analgesia. Morphine is conjugated in the liver to form the 3-glucuronide which passes into the bile and is reabsorbed and excreted in the urine. The atropine effect of the belladonna extract serves to eliminate morphine induced smooth muscle spasm without affecting the sedative analgesic action of powdered opium².