Lithium 300 mg 2–3 times per 24 hours. Effective concentration 0.8-1.2 mmol / l and toxic symptoms at concentrations above 1.5 mmol / l. For prevention and maintenance treatment, lithium levels are considered to be somewhat lower than 0.6 to 1.0 mmol / l during the treatment period. Lithium, anti-manic efficacy apparent to the requisite dose of a gradually within 7-21 hours a day. If mania (or depression or irritability) has not been relieved by adequate plasma levels at all within four weeks, lithium, at least without the additive, will not be therapeutically effective. In severe or psychotic mania, either second generation antipsychotics (aripiprazole, quetiapine, olanzapine, risperidone, ziprasidone, lurasidone, asenapine), valproic acid or sometimes benzodiazepine 4 loracepam 4-8 mg / day).

https://www.terveyskirjasto.fi/terveyskirjasto/tk.koti?p_artikkeli=lam00049

Matti Huttunen 2017

Low lithium is better than no lithium.

I am not aware of a dose response curve re suicidality though

I prefer to use the slow release once a day lithium

Am not 100 percent sure

Li 0.4 to 0.6 mmL seems to work well and is safer in many cases.

Low levels of lithium do appear to confer some protection against suicidality. Please see here for a recent supporting review - Article Lithium Suicide Prevention: A Brief Review and Reminder