Lithium plasma half-life

The clinical value of monitoring drug therapy by measuring plasma levels is probably best exemplified by reference to lithium (F6). It is a useful drug, which has a narrow therapeutic index, and treatment without reference to plasma levels is probably not ethically justified. Toxic side effects are predictable and severe. It has an acceptably long plasma half-life, and its measurement both in blood and urine is comparatively simple. Moreover, there is no problem of interference from either active or inactive metabolites. 

Lithium excretion is exclusively via the urine, but it is complicated and does not obey first-order kinetics. Nevertheless, for practical purposes, lithium can be considered to have a plasma half-life of between 24 and 48 hours, which is decreased by salt feeding and increased by salt deprivation or kidney damage (T5). 

Excretion Virtually entirely in urine. Lithium clearance about 20% of creatinine. Plasma half-life about 20 hours. 

In rats, lithium pretreatment reduced the plasma half-life of valproate by 25% and increased urinary excretion of valproate glucuronide (609). 

Half-life. Plasma half-life, about 20 hours after a single dose but appears to be dependent on the duration of treatment. In patients on their first course of treatment a plasma half-life averaging 31 hours has been reported this increased to 40 hours in subjects receiving lithium for less than one year and 58 hours in those taking the drug for longer than one year. 

Lithium carbonate is completely absorbed by the gastrointestinal tract and reaches peak plasma levels in 1-2 hours. The elimination half-life is approximately 24 hours. Steady-state lithium levels are achieved in approximately 5 days. Therapeutic plasma levels range from 0.5 to 1.2 mEq/L. Lower plasma levels are associated with less troubling side effects, but levels of at least 0.8 mEq/L are often required in the treatment of acute manic episodes. Therefore, when intolerable side effects have not intervened, treatment of acute mania with lithium should not be considered a failure until plasma levels of 1.0-1.2 mEq/L have been reached and have been maintained for 2 weeks. As discussed at the end of this chapter (see Treatment of Mania or Mixed Episodes ), more severely ill patients may require combination treatment. 

Lithium carbonate 0.9-1.2gq.24hr Renal 100% 50-75% 25-50% Nephrotoxic adverse effects include nephrogenic diabetes insipidus, nephrotic syndrome, renal tubular acidosis, and interstitial fibrosis acute toxicity when serum levels > 1.2 mEq/L serum levels should be measured periodically 12 hr after dosing half life does not reflect extensive tissue accumulation plasma levels rebound after dialysis toxicity enhanced by volume depletion, NSAIDs, and diuretics Dose after dialysis NC Dose for GFR 10-50 ml/min... 

A. Pharmacokinetics Lithium is absorbed rapidly and completely from the gut. The dmg is distributed throughout the body water and excreted by the kidneys with a half-life of about 20 hours. Plasma levels should be monitored, especially during the first weeks of therapy, to establish an effective and safe dosage regimen. The therapeutic plasma concentration is 0.6-1.4 meq/L. Plasma levels of the drag may be altered by changes in body water. Thus, dehydration or treatment with diuretics (thiazides), may result in an increase of lithium in the blood to toxic levels. Theophylline increases the renal clearance of lithium. 

The absorption of lithium is rapid and complete within 6 to 8 hours. The absorption rate of slow-release capsules is slower and the total amount of lithium absorbed lower than with other dosage forms. Lithium is not protein bound. The elimination half-life for elderly patients (39 hours) is longer than that for adult patients (24 hours), which in turn is longer than that for adolescent patients (18 hours). The time to peak serum concentration for lithium carbonate is dependent on the dosage form (tablets, 1-3 hours extended tab, 4 hours slow release, 3 hours). Steady-state serum concentrations are reached in 4 days, with the desirable dose targeted to give a maintenance lithium ion plasma concentration range of 0.6 to 1.2 mEq/L, with a level... 

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