title: A thyroxine absorption test followed by weekly thyroxine administration: a method to assess non-adherence to treatment.
abstract: OBJECTIVE
  For patients who remain hypothyroid despite the administration of what would seem adequate doses of levothyroxine (L-T4), the underlying cause can be difficult to determine. The possibility of a biological cause should first be explored; however, in the majority of cases, poor adherence to medication is likely to be the main cause of treatment failure. When non-adherence is suspected but not volunteered, options to confirm the suspicion are limited. In this study, we identified patients for whom known drugs and pathological causes of L-T4 malabsorption were excluded, and despite often high doses of L-T4, the patients remained hypothyroid.
  
  
  METHODS
  Using a weight-determined oral L-T4 bolus administration, absorption was initially assessed in 23 patients. In nearly all patients, this was shown to be maximal at 120 min post-ingestion. This was then followed by the continued administration of a weekly T4 bolus for a 4-week period after which TSH and free T4 (fT4) levels were recorded.
  
  
  RESULTS
  All patients showed a rise in fT4 at 120 min following the administration of the L-T4 bolus, with a mean increase of 54±3% from baseline. Following the treatment period, using an equivalent weekly L-T4 dose, which was significantly less than that of the daily dose taken by the patients before the test, TSH reduced from baseline in ~75% of cases.
  
  
  CONCLUSIONS
  Using this combination of tests allows significant malabsorptive problems to be identified first and then potential non-adherence to be demonstrated. A management plan can then be implemented to increase adherence, aiming to improve treatment outcomes.
authors.affiliation: Department of Endocrinology, Oxford University Hospitals NHS Trust, OCDEM, Oxford OX3 7LJ, UK. neilwalker1@nhs.net
authors.forename: J N
authors.initials: JN
authors.lastname: Walker
authors.forename: P
authors.initials: P
authors.lastname: Shillo
authors.forename: V
authors.initials: V
authors.lastname: Ibbotson
authors.forename: A
authors.initials: A
authors.lastname: Vincent
authors.forename: N
authors.initials: N
authors.lastname: Karavitaki
authors.forename: A P
authors.initials: AP
authors.lastname: Weetman
authors.forename: J A H
authors.initials: JA
authors.lastname: Wass
authors.forename: A
authors.initials: A
authors.lastname: Allahabadia
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D004334:Drug Administration Schedule; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D013972:Thyrotropin / Q000097:blood; D013974:Thyroxine / Q000008:administration & dosage / Q000009:adverse effects / Q000627:therapeutic use*; D055815:Young Adult
chemical_list: D013972:Thyrotropin; D013974:Thyroxine