Drug-induced tremor, clinical features, diagnostic approach and management.

Tremor is the most common movement disorder and there are numerous causes of tremor. In many individuals, tremor can be due to drugs. The most common drugs associated with tremor include amiodarone, selective serotonin (and norepinephrine) reuptake inhibitors (SSRIs/SNRIs), amitriptyline, lithium, valproate, ß-adrenoceptor agonists, dopamine receptor antagonists, VMAT2 inhibitors, or drugs of abuse: ethanol, cocaine, etc. Drug-induced tremor usually resembles essential or parkinsonian tremor, depending on the offending drug; however, features such as unilateral, task-specific, position-dependent tremor or sudden onset, distractibility, entrainment and arrest with contralateral movements suggest etiologies such as dystonic or functional (psychogenic) tremor. Risk factors for drug-induced tremor include polypharmacy, male gender, older age, high doses and immediate-release preparations or reaching toxic levels of the offending drugs. Drug-induced tremor usually resolves once the offending medication is discontinued, however, persistent tremor may be observed in some cases (tardive tremor). In this manuscript, we discuss the most common causes of drug-induced tremor. This article is part of the Special Issue "Tremor" edited by Daniel D. Truong, Mark Hallett, and Aasef Shaikh.

Development of natural products as drugs acting on central nervous system

We have recenty studied several natural product constituents which have effects on the CNS. (1) Tetrahydropalmatine (THP) and its analogues were isolated from Corydalis ambigua and various species of Stephania. (+)-THP and (-)-THP posses not only analgesic activity, but also exert sedative-tranquillizing and hypnotic actions. Results of receptor binding assay and their pre-and post-synaptic effects on dopaminergic system indicate that (-)-THP and (-)-stepholidine are dopamine receptor antagonists while (+)-THP is a selective dopamine depletor. (2) 3-Acetylaconitine (AAC) is an alkaloid isolated from Aconitum flavum. The relative potency of analgesic action of AAC was 5.1-35.6 and 1250-3912 times that of morphine and aspirin, respectively. The analgesic effect of AAC was antagonized by naloxone, but was eliminated by reserpine. In monkeys, after AAC was injected for 92 days, no abstinence syndrome was seen after sudden AAC withdrawal or when challenged with nalorphine. (3) Huperzine A (Hup-A) is an alkaloid isolated from Huperzia serrata which was found to be a selective ChE inhibitor and could improve learning and retrieval process. Preliminary clinical studies showed that Hup-A improve short-and long-term memory in patients of cerebral arteriosclerosis with memory impairment. (4) Ranamargarin is a new tetradecapeptide isolated from the skin of the Chines frog Rana margaratae. This peptide may mainly act on NK-1 receptor.