ANALEPTICS

Analeptics stimulate the central nervous system and, in large  doses, they cause generalized convulsions. Thus, these drugs Th have a wide range of effects of which, stimulation of breathing is only one. Many forms of illness, both mental and physical, involve a depression of mental activity. Analeptics often stimulate respiratory centre and other centres. The vasomotor centre,  which maintains the constriction of the blood vessel walls, is frequently affected. Some analeptic agents increase vasoconstrictions. " These result in an increased peripheral by resistance to the flow of blood, thereby causing an elevation of blood supply.

Picrotoxin, pentylenetetrazol, nikethamide, doxapram, ethamivan, lobeline and purine bases (caffeine) are the drugs used as analeptics to counteract respiratory depression and coma arose from overdosage of central depressant agents.

Purines, Pyrimidines and Related Heterocyclic Compounds

Purine is a close-chain compound containing the fused carbonnitrogen skeletons of pyrimidine and imidazole. Purine and pyrimidine bases are constituents of the nucleic acids. The purine bases occur in nature primarily as oxidized derivatives. The basic analogues of purines, known as alkaloids, occur in plants. The three most common naturally occurring xanthines include caffeine, theobromine and theophivline which have diuretic properties.