A nurse is administering a medication with a half-life of 6 hours. If the initial dose is 800 mg, how much of the medication will remain in the patient's system after 18 hours?

A. Second-generation antihistamines have shorter half-lives and require more frequent dosing compared to first-generation antihistamines: Second-generation antihistamines typically have longer half-lives, allowing once-daily dosing. They are designed for sustained action with improved compliance and fewer side effects.
B. First-generation antihistamines block both histamine and muscarinic receptors, while second-generation antihistamines primarily block histamine receptors: First-generation agents, such as diphenhydramine, cross the blood-brain barrier and exert anticholinergic effects by blocking muscarinic receptors. Second-generation antihistamines are more selective for peripheral H1 receptors, resulting in fewer CNS and anticholinergic side effects.
C. First-generation antihistamines are less likely to cause sedation compared to second-generation antihistamines: First-generation antihistamines are more likely to cause sedation because they easily penetrate the blood-brain barrier and affect central H1 receptors, unlike second-generation agents.
D. Second-generation antihistamines cross the blood-brain barrier, causing significant central nervous system effects: These medications are designed not to cross the blood-brain barrier significantly, which is why they are much less sedating and have minimal CNS effects compared to first-generation antihistamines.

A. Intramuscular Phenobarbital: While effective as an anticonvulsant, phenobarbital has a slower onset of action and is not the preferred first-line treatment for acute seizures. It is more commonly used in refractory cases or for long-term seizure control.
B. Intravenous Lorazepam: Lorazepam is a benzodiazepine and the first-line treatment for active seizures, especially status epilepticus. Given IV, it acts quickly by enhancing GABA activity, which calms neuronal excitability and stops seizure activity efficiently.
C. Oral Phenytoin: Phenytoin is used for long-term seizure prevention but is not effective for terminating ongoing seizures due to its slow onset when taken orally. It may be used after benzodiazepines to prevent seizure recurrence but not as the initial agent.
D. Subcutaneous Sumatriptan: Sumatriptan is used for treating acute migraines and has no role in managing seizures. It acts on serotonin receptors to relieve migraine symptoms, not to control abnormal neuronal discharges.