A 55-year-old patient with late-onset schizophrenia develops dystonia on administration of antipsychotics. He is prescribed anticholinergic medications for this side-effect.
Which one of the following anticholinergic drugs is most stimulating in its properties?
A. The most commonly used anticholinergic drugs for extrapyramidal symptoms in patients taking antipsychotics are trihexyphenidyl (benzhexol), benztropine, biperiden, and procyclidine. Orphenadrine is an antihistaminergic agent with prominent anticholinergic action. Benztropine also has some antihistaminergic effects. All these agents are antimuscarinic. Trihexyphenidyl (benzhexol) is the most stimulating of all anticholinergics.
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Which one of the following anticholinergic drugs has the least abuse potential due to a relative lack of stimulating properties?
C. Benztropine is the least stimulating anticholinergic agent and so it is least associated with drug-abuse potential. Benztropine reaches peak plasma concentrations in 2 to 3 hours after oral administration and acts for 1 to 12 hours. Benztropine is available as an intramuscular preparation and this is preferred when available in acute dystonia.
A 55-year-old patient with late-onset schizophrenia develops dystonia on administration of antipsychotics. He is prescribed trihexyphenidyl for this side-effect.
Which one of the following properties makes this drug most stimulating of all anticholinergics?
A. Trihexyphenidyl is suspected to have some dopaminergic activities which produce stimulating effects. It has a higher abuse potential than other anticholinergic drugs.
All of the following measures help to reduce postural tremors induced by lithium therapy except:
E. Lithium-induced tremor is frequently postural in nature and occurs at 8 to 12 Hz frequency. It is most notable in outstretched hands. If troublesome, the tremor can be reduced by giving lithium in divided doses or using a sustained release formulation wherein peaks and troughs in plasma level are better managed. A reduction in tremors can be noted if the patient’s anxiety is better managed and caffeine intake is reduced. β-blockers, such as propranolol, have been used to reduce lithium-induced tremor. If the tremors turn coarse, suspect lithium toxicity. Procyclidine can alleviate extrapyramidal symptoms but it has no effects on lithium-induced tremors.
The half-life of donepezil in an elderly patient with dementia is around:
A. Donepezil is an anticholinesterase drug widely used in patients with a moderate degree of Alzheimer’s dementia. It is administered orally once daily. The half-life of donepezil is 70 hours in the elderly and steady-state levels are achieved within about 2 weeks. The half-life of rivastigmine, another antidementia drug, is 1 hour, but it dissociates slowly from cholinesterase enzyme, thus a single dose is therapeutically active for 10 hours. Rivastigmine is taken twice daily. Galantamine is an alkaloid (extracted from daffodils (Narcissus pseudonarcissus) and snow drops (Galanthus nivalis)); it has an elimination half-life of nearly 6 hours, and so is administered twice daily. A sustained release preparation is now available.
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