Chapter 43. Disorders of the Nervous System Caused by Drugs, Toxins, and Chemical Agents

Subsumed under this title is a diverse group of disorders of the nervous system that result from drugs and other injurious or poisonous substances. The neurologist must be concerned with the myriad of chemical agents that have no therapeutic utility but may adversely affect the nervous system; they abound in the environment as household products, insecticides, industrial solvents and other poisons, as well as substances that may have therapeutic value but are used for their "recreational" psychotropic effects, or are conventional medications with known toxic effects and may be accidentally ingested. These constitute the field of neurotoxicology. Also among the neurotoxins are those generated by bacteria and other infectious organisms, as well as toxins several found in nature, such as marine toxins.

It would hardly be possible within one chapter to discuss the innumerable drugs and toxins that affect the nervous system. The interested reader is referred to a number of comprehensive monographs and references listed at the end of this chapter. In addition, a current handbook of pharmacology and toxicology is a useful part of the library of every physician.

The scope of this chapter is also limited because the therapeutic and adverse effects of many drugs are considered elsewhere in this volume in relation to particular symptoms and diseases. Thus, the toxic effects of ethyl, methyl, amyl, and isopropyl alcohol, as well as ethylene and diethylene glycol, are discussed in Chap. 42. The adverse effects of antibiotics on cochlear and vestibular function and on neuromuscular transmission are discussed in Chaps. 15 and 49, respectively. Many of the undesirable side effects of the common drugs used in the treatment of extrapyramidal motor symptoms, pain, headache, seizure and sleep disorders, psychiatric illnesses, and so forth are also considered in the chapters dealing with each of these disorders and in the chapters that cover psychiatric diseases. Cyanide and carbon monoxide poisoning are discussed in relation to anoxic encephalopathy (see Chap. 40). A number of therapeutic agents that predictably damage the peripheral nerves (e.g., cisplatin, disulfiram, vincristine) are mentioned in this chapter but are discussed further in Chap. 46, and those that affect muscle are included in Chap. 48, "Diseases of Muscle."

The presentation of this subject is introduced by some general remarks on the action of drugs on the nervous system and is followed by discussion of the main classes of agents that affect nervous function. The references at the end of the chapter are listed in relation to each of these categories:

1. Opiates and synthetic analgesics

2. Sedative-hypnotic drugs

3. Antipsychosis drugs

4. Antidepressant drugs

5. Stimulants

6. Psychoactive drugs

7. Bacterial toxins

8. Plant poisons, venoms, bites, and stings

9. Heavy metals

10. Industrial toxins

11. Antineoplastic and immunosuppressive agents

12. Antibiotics

13. Cardioactive agents

The rational use of any drug requires knowledge of the best route of administration, the drug's absorption characteristics, its distribution in the nervous system and other organs, and its biotransformations and excretion (...