Liquid levothyroxine and its potential use
AM Formenti, L Daffini, I Pirola, E Gandossi, A Cristiano, C Cappelli
Pharmacokinetics and potential advantages of a new oral solution of levothyroxine vs. other available dosage forms
CS Yue et al.
Nieuwe pillen, capsules, druppels en drankjes levothyroxine een aanwinst?
Nowadays, novel levothyroxine formulations are available, namely, soft gel capsules and liquid form. The soft gel capsule contains L-T4 dissolved in glycerine in an outer gelatine shell. This structure provides protection from the variations of gastric pH and could also prevent binding to other substances in the intestinal lumen, such as coffee or other medicaments (for example calcium or iron salts).
The liquid form is composed only of L-T4 of variable concentrations, glycerine and ethanol. The most important advantage of an oral solution, compared to the solid formulation, is the possibility of administration also in patients who are not able to swallow intact capsules or tablets.
Furthermore, as shown in a recent in vivo study, liquid L-T4 formulation also has a better absorption rate. In fact, Yue et al have shown that L-T4 in liquid formulation peaks in blood faster than the tablet or the soft gel capsule (faster at maximum concentration (ng/mL) by an average of 30 min). The levothyroxine rate and the extent of exposure are similar in the three types of formulations (tablets, soft gel capsule and liquid form), but the solution appears to reach the systemic circulation faster as dissolution is not needed before absorption starts.