To better understand the pharmacokinetics and potential advantages of a 
levothyroxine oral solution vs. tablets and soft gel capsules.4 randomized, 
2-treatment, single-dose (600 mcg levothyroxine), 2-way crossover bioequivalence 
studies in 84 healthy subjects were analyzed. Samples were collected before 
dosing and until 48-72 h post-dose to calculate noncompartmental 
baseline-adjusted pharmacokinetic parameters: maximum concentration, time to 
maximum concentration, and area-under-the-concentration-time-curve from 0 to 
48 h and from 0 to 2 h.Mean pharmacokinetic parameters (±standard deviation) for 
tablets, capsules and solution, respectively, were: 
area-under-the-concentration-time-curve from 0 to 2 h (ng*h/mL)=68.4±32.8, 
64.4±24.4, 99.1±22.7; area-under-the-concentration-time-curve from 0 to 48 h 
(ng*h/mL)=1 632±424, 1 752±445, 1 862±439; maximum concentration 
(ng/mL)=67.6±20.9, 68.0±15.9, 71.4±16.0; time of maximum concentration 
(hours)=2.25±0.99, 2.38±1.58, 1.96±1.07. Overall rate and extent of exposure 
were not statistically different between formulations, but a faster onset of 
absorption for the solution was suggested (greater 
area-under-the-concentration-time-curve from 0 to 2 h and faster time to maximum 
concentration by an average of 30 min).Levothyroxine rate and extent of exposure 
are similar between tested formulations. The solution appears however to reach 
systemic circulation quicker as dissolution is not needed before absorption 
starts. The solution's greater early exposure and a faster time to maximal 
concentration of around 30 min may be of benefit to minimize drug-food 
interactions and deserves further investigations.