Treatment pattern and frequency of serum TSH measurement in users of different levothyroxine formulations: a population-based study during the years 2009-2015.
BACKGROUND
Several conditions can modify the intestinal absorption of levothyroxine tablets, with potential consequences on their therapeutic effect. Pre-dosed ampoules and oral drops have been recently made available to overcome this limitation.


OBJECTIVE
To describe the pattern of use of different formulations of levothyroxine in a general population of Southern Italy and to perform an exploratory analysis investigating the effect of switching from levothyroxine tablets to oral liquid formulations.


METHODS
Data were extracted from the Caserta Local Health Unit database. All patients receiving at least one levothyroxine prescription during the years 2009-2015 were identified. 1-year incidence of use of formulation-specific levothyroxine was calculated. Switchers between levothyroxine tablets and oral liquid formulations were identified and the frequency of thyroid-stimulating hormone measurement within 2 years prior and after the switch date was explored.


RESULTS
Overall, 56,354 levothyroxine users were included in the study. Of these, 55,147 patients received at least one prescription for tablets (97.9%), 1867 pre-dosed ampoules (3.3%) and 1550 oral drops (2.8%). The proportion of levothyroxine users receiving oral liquid formulations slightly increased over time. Patients switching from tablets to oral liquid formulations showed a statistically significant reduction in the number of thyroid-stimulating hormone measurements after switching from tablets, especially in presence of drugs interacting with levothyroxine potentially altering its absorption.


CONCLUSIONS
Use of levothyroxine oral liquid formulations is increasing over time even though their use is still limited in a general population of Southern Italy. Our exploratory analysis showed that the frequency of thyroid-stimulating hormone measurement was reduced in patients switching from levothyroxine tablet to new formulations.
Unit of Clinical Pharmacology, Academic Hospital G. Martino, Messina, Italy.
Rosarita
R
Ferrara
Unit of Clinical Pharmacology, Academic Hospital G. Martino, Messina, Italy.
Valentina
V
Ientile
Unit of Clinical Pharmacology, Academic Hospital G. Martino, Messina, Italy.|Department of Clinical and Experimental Medicine, University of Messina, Messina, Italy.
Vincenzo
V
Arcoraci
Department of Experimental Medicine, Second University of Naples, Naples, Italy.
Carmen
C
Ferrajolo
Unit of Clinical Pharmacology, Academic Hospital G. Martino, Messina, Italy.|Department of Medical and Surgical Sciences, University of Bologna, Bologna, Italy.
Carlo
C
Piccinni
Unit of Biostatistics, IRCCS "Casa Sollievo della Sofferenza", San Giovanni Rotondo (FG), Italy.
Andrea
A
Fontana
Department of Clinical and Experimental Medicine, University of Messina, Messina, Italy.
Salvatore
S
Benvenga
Unit of Clinical Pharmacology, Academic Hospital G. Martino, Messina, Italy. trifirog@unime.it.|Department of Biomedical and Dental Sciences and Morpho-functional Imaging, University of Messina, Messina, Italy. trifirog@unime.it.
Gianluca
G
Trifirò
D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D004339:Drug Compounding; D005260:Female; D020249:Hormone Replacement Therapy; D006801:Humans; D007037:Hypothyroidism / Q000188:drug therapy / Q000453:epidemiology; D015994:Incidence; D007558:Italy; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D019999:Pharmaceutical Solutions; D015995:Prevalence; D013607:Tablets; D013972:Thyrotropin / Q000097:blood*; D013974:Thyroxine / Q000008:administration & dosage* / Q000737:chemistry / Q000627:therapeutic use*; D055815:Young Adult
D019999:Pharmaceutical Solutions; D013607:Tablets; D013972:Thyrotropin; D013974:Thyroxine
Absorption; Formulations; Levothyroxine; Switching; TSH