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Safety Information

Revised: 4 July 2013

Eltroxin Formulation Change

GlaxoSmithKline (GSK) began distributing a changed formulation of Eltroxin tablets in New Zealand, in June 2007. Subsequently, the Centre for Adverse Reactions Monitoring (CARM) received an increase in adverse reaction reports associated with the new formulation.

In the interests of transparency, Medsafe is providing a comprehensive description of the change in formulation, the evaluation process, and the actions taken in response to the increase in adverse reaction reports.

The information provided in this document includes:

Eltroxin Timeline

Date Action Link
March 2004 Medsafe receives an application from GSK in support of a new formulation of Eltroxin Medsafe Evaluation Report - Eltroxin
Medsafe evaluates the application as a new medicine due to the formulation change.
Follow the link to view Medsafe's evaluation report for the change in Eltroxin formulation
November 2006 New Eltroxin formulation consented for distribution in New Zealand Eltroxin Gazette Notice (64kb this is a pdf document and Acrobat Reader is required for viewing) Eltroxin Datasheet
June 2007
GlaxoSmithKline (GSK) notifies healthcare professionals of the change in formulation GSK Letter (40kb this is a pdf document and Acrobat Reader is  required for viewing)
GlaxoSmithKline (GSK) notifies healthcare professionals of the change in formulation for a second time GSK Letter (300kb this is a pdf document and Acrobat Reader is  required for viewing) Patient Resource (270kb this is a pdf document and Acrobat Reader is  required for viewing)
GSK begins distribution of the new Eltroxin formulation in New Zealand
September 2007 GSK notifies Pharmacists of a labelling error. The letter also describes the size, colour and shape of the newly formulated Eltroxin tablets GSK Notification (60kb this is a pdf document and Acrobat Reader is  required for viewing)
October 2007 CARM receives the first adverse reaction report associated with the new Eltroxin formulation  
June 2008 An increase in adverse reaction reports to Eltroxin is identified to Medsafe by CARM  
In response to the increase in adverse reaction reports, Medsafe:
  • Re-assesses the new formulation and confirms that it meets all international standards for quality, safety, and bioequivalence
  • Obtains batch information from GSK for all batches supplied in New Zealand
  • Seeks adverse reaction data from other countries where the new formulation has been introduced
  • Requires GSK to notify all New Zealand GPs and pharmacies of the change for a third time. The public are notified directly via national newspapers
  • Requests that GSK investigates the availability of alternative Eltroxin formulations
  • Initiates independent testing with ESR, to rule out contamination or a poor quality product
  • Consults with expert endocrinologists on adverse reactions and likely causes
  • Releases advice to all New Zealand GPs, specialists, and pharmacies.
Advice from GSK (232kb this is a pdf document and Acrobat Reader is  required for viewing) Advice from Medsafe (37kb this is a pdf document and Acrobat Reader is  required for viewing)
July 2008 CARM produces report on Eltroxin adverse reactions due to the new formulation CARM Report (84kb this is a pdf document and Acrobat Reader is  required for viewing)
GSK provides results from re-testing all batches supplied in New Zealand GSK Re-test Results (30kb this is a pdf document and Acrobat Reader is  required for viewing)
August 2008 ESR provides results from independent testing of all batches supplied in New Zealand ESR Re-test Results (336kb this is a pdf document and Acrobat Reader is  required for viewing)
Medsafe consults further with expert endocrinologists
Medsafe advises healthcare professionals again by publishing an article in Best Practice Journal (in conjunction with BPAC). Best Practice Journal Article (112kb this is a pdf document and Acrobat Reader is  required for viewing)
The Pharmacy Guild and PSNZ, in conjunction with Medsafe, further reinforce information to pharmacists regarding Section 29 access to alternatives Pharmacy Guild Advice (37kb this is a pdf document and Acrobat Reader is  required for viewing)
September 2008 Medsafe receives two applications for alternative brands of levothyroxine tablets  
Medsafe requests further test results from GSK and ESR
CARM provides an updated analysis on adverse reaction reports CARM Report (135kb this is a pdf document and Acrobat Reader is  required for viewing)
The Medicines Adverse Reaction Committee (MARC) reviews the Eltroxin adverse reaction data and actions taken by Medsafe. MARC supports Medsafe's actions and the advice issued to healthcare professionals. CARM Report (135kb this is a pdf document and Acrobat Reader is  required for viewing)
October 2008 The Minister of Health approves for two alternative brands of levothyroxine to be distribution in New Zealand. These brands are Goldshield Levothyroxine, and Synthroid (Abbott). Gazette Notice - Alternative Brands (75kb this is a pdf document and Acrobat Reader is  required for viewing)
April 2009 The Ministry of Health commissions an independent review of the circumstances surrounding the supply of a new formulation of Eltroxin in New Zealand.

The United Kingdom Medicines and Healthcare products Regulatory Agency (MHRA) agrees to undertake the independent review.
 
November 2009 Medsafe receives MHRA's final report
Follow the link to view the MHRA's final report
MHRA Report

Eltroxin Questions and Answers

When did GSK inform Medsafe of their intention to change the formulation of Eltroxin tablets?

The manufacturer of Eltroxin tablets, GlaxoSmithKline (GSK), notified Medsafe of the reformulation of Eltroxin tablets in a letter dated 17 March 2004. The letter accompanied an application requesting approval of the new formulation.

Assessment of the application involved evaluation, peer review and quality assurance processes. Additional information was required from the applicant and, as is common for this type of application, there were several cycles of additional information requested, provided and evaluated. When the assessment of the application was complete, a recommendation to consent the medicine was made to the Minister's delegate who formally approved the distribution of the product in New Zealand.

When was the new formulation approved?

The new formulation was approved for use in New Zealand on 16 November 2006.

When was the new formulation introduced to the New Zealand market?

The new formulation of Eltroxin was introduced to the New Zealand market in July 2007. Although the change occurred in July 2007, supplies of the old formulation were slowly used up by pharmacies meaning patients may not have been dispensed the new formulation until the end of 2007 or even early 2008.

Why did the formulation of Eltroxin change?

GSK made the decision to change the formulation. This was not due to a request from Medsafe or PHARMAC.

The reasons provided by GSK for the change in formulation were firstly that the new formulation will become the standard formulation marketed globally and secondly to improve stability of the product.

What information was assessed by Medsafe prior to approval of the new formulation of Eltroxin?

The application for the new formulation of Eltroxin consisted of administrative information, quality information and a bioequivalence study.

The new formulation of Eltroxin met the criteria for a new intermediate-risk medicine as the active ingredient and dose form had been previously approved by the Minister of Health.

The International Conference on Harmonisation of Technical Requirements for Registration of Pharmaceuticals for Human Use (ICH) stipulates that specific information is included in Modules 1, 2, 3 and 5 of a New Medicine Application as summarised in Table 1.

Table 1: Summary of Modules 1, 2, 3 and 5 of a New Medicine Application

Module 1 Administrative information Documents specific to each region; for example, application forms or the proposed label for use in the region.

The New Zealand Regulatory Guidelines For Medicines, Volume 1, Fifth Edition, October 2001 requires that the following information is included in Module 1.
  • A covering letter
  • A completed New Medicine Application Form
  • A comprehensive table of contents
  • Copies of proposed labeling
  • A draft datasheet and package insert (where applicable)
  • Evidence of Good Manufacturing Practice
  • Copies of European Certificates of Suitability (where applicable)
  • Letters of Access to required Drug Master Files (where applicable)
Module 2 Overviews and summaries Overviews and summaries of the Quality, Non-clinical and Clinical data
Module 3 Quality (Chemical and Pharmaceutical Data) 3.1 TABLE OF CONTENTS

3.2 BODY OF DATA

3.2.S DRUG SUBSTANCE
3.2.S.1   General Information
3.2.S.1.1 Nomenclature
3.2.S.1.2 Structure
3.2.S.1.3 General Properties

3.2.S.2 Manufacture
3.2.S.2.1 Manufacturer(s)
3.2.S.2.2 Description of manufacturing process & controls
3.2.S.2.3 Control of materials
3.2.S.2.4 Controls of critical steps and intermediates
3.2.S.2.5 Process validation and/or evaluation
3.2.S.2.6 Manufacturing process development
3.2.S.3 Characterisation
3.2.S.3.1 Elucidation of structure and other characteristics
3.2.S.3.2 Impurities
3.2.S.4 Control of drug substance
3.2.S.4.1 Specification
3.2.S.4.2 Analytical procedures
3.2.S.4.3 Validation of analytical procedures
3.2.S.4.4 Batch analyses
3.2.S.4.5 Justification of specification
3.2.S.5 Reference standards or materials
3.2.S.6 Container closure system
3.2.S.7 Stability

3.2.P DRUG PRODUCT
3.2.P.1 Description and composition of the drug product
3.2.P.2 Pharmaceutical development
3.2.P.3 Manufacture
3.2.P.3.1 Manufacturer(s)
3.2.P.3.2 Batch formula
3.2.P.3.3 Description of manufacturing process & controls
3.2.P.3.4 Controls of critical steps and intermediates
3.2.P.3.5 Process validation and / or evaluation
3.2.P.4 Control of excipients
3.2.P.4.1 Specifications
3.2.P.4.2 Analytical procedures
3.2.P.4.3 Validation of analytical procedures
3.2.P.4.4 Justification of specifications
3.2.P.4.5 Excipients of human or animal origin
3.2.P.4.6 Novel excipients
3.2.P.5 Control of drug product
3.2.P.5.1 Specification(s)
3.2.P.5.2 Analytical procedures
3.2.P.5.3 Validation of analytical procedures
3.2.P.5.4 Batch analyses
3.2.P.5.5 Characterisation of impurities
3.2.P.5.6 Justification of specification(s)
3.2.P.6 Reference standards or materials
3.2.P.7 Container closure system
3.2.P.8 Stability
3.2.P.8.1 Stability summary and conclusion
3.2.P.8.2 Post-approval stability protocol & committment
3.2.P.8.3 Stability data

3.2.A APPENDICES
3.2.A.1 Facilities and equipment
3.2.A.2 Adventitious agents safety evaluation
3.2.A.3 Novel excipients

3.2.R REGIONAL INFORMATION
3.3 LITERATURE REFERENCES
Module 5 Clinical Study Reports Human study reports (for new multi-source medicines this is generally a bioequivalence study report).


The application for the new formulation of Eltroxin was presented in the CTD format and consisted of Module 1, Module 2, Module 3 and Module 5. Module 4 was not required as the active ingredient and dose form had been previously approved by Medsafe and the excipients in the product are commonly used in tablet formulations.

All of the information in Module 1, Module 3 and Module 5 of the application for the new formulation of Eltroxin and the additional information requested during the evaluation process were considered during the assessment. Module 2 is merely a summarised version on Module 3.

Is there any difference in the active ingredient (levothyroxine) contained in the old formulation and the active ingredient contained in the newly formulated tablets?

No. The active ingredient (levothyroxine also known as thyroxine) contained in the new formulation is identical to the active ingredient contained in the old formulation, and is sourced from the same manufacturing site, namely Sandoz GmbH, Schaftenau Plant, Biochemiestrasse 10, Langkampfen, Tyrol, Austria.

How is the active ingredient (levothyroxine) manufactured?

The method of manufacture for the active ingredient has not changed and is the same for the active ingredient contained in the new formulation and the old formulation. Manufacture is by chemical synthesis and does not involve genetic engineering (recombinant technology).

What ingredients are contained in the new formulation of Eltroxin tablets?

A comparison of the ingredients contained in the old formulation and the new formulation is presented in Table 2.

Table 2: Ingredients contained in the old and new formulations

Component Old formulation New formulation
Active ingredient Levothyroxine sodium Levothyroxine sodium
Excipients Magnesium stearate Magnesium stearate
Lactose monohydrate Microcrystalline cellulose
Maize starch Pre-gelatinized maize starch
Acacia Purified talc
Silicon dioxide (Colloidal anhydrous silica)

All of the excipients in the new formulation comply with the requirements of the European Pharmacopoeia (an internationally recognised standard) and are commonly used in medicines.

The new formulation does not contain monosodium glutamate (MSG) or wheat-based products.

Who manufactures the new formulation of Eltroxin tablets?

Glaxo Wellcome GmbH & Co, Industriestrasse 32-36, Bad Oldesloe, Germany is responsible for manufacturing, packing and testing the new formulation of Eltroxin tablets.

How is the new formulation of Eltroxin manufactured?

The new formulation of Eltroxin is manufactured by blending of the ingredients (initially the levothyroxine and a portion of the microcrystalline cellulose and later the remaining ingredients), then direct compression of the blend to form tablets.

The old formulation of Eltroxin was manufactured by blending all the ingredients except for the magnesium stearate and a portion of the maize starch. The blend was wet granulated and the granules dried and blended with the magnesium stearate and remaining portion of the maize starch prior to compression into tablets.

The manufacturing processes for both the old formulation and new formulation utilise standard, internationally accepted processes.

The manufacture of the tablet does not involve any genetic engineering (recombinant technology) steps.

What quality systems are in place at the manufacturing site to ensure the quality of the product?

To ensure that products are consistently produced and controlled to appropriate quality standards, manufacturers of pharmaceutical products are required to comply with internationally accepted standards known as Good Manufacturing Practice (GMP) standards.

Good Manufacturing Practice is a set of quality requirements that must be met by a medicines manufacturer in order to ensure that medicines made meet the required quality standards and are consistently safe and effective. The requirements cover such areas as factory management, factory design and hygiene, processing operations, contamination and cross-contamination control, raw material quality, documentation and record keeping, testing and many other aspects of a manufacturer's operation. The aim is to ensure that everything is done during the manufacture of a product to ensure that a quality product is made and that it will meet the requirements before it is released for use.

Evidence of GMP compliance from a recognised authority is required for all finished product manufacturing, packing and testing sites prior to consent of a medicine by the Minister of Health. A GMP certificate, licence or report from an authority with GMP assessment systems that are compatible with internationally accepted standards is required.

Appropriate documentation from the Therapeutic Goods Administration in Australia was accepted as evidence that the site responsible for manufacturing, packing and testing the new Eltroxin formulation complies with internationally accepted GMP standards.

As part of the quality systems in place to ensure that a medicine is of an acceptable quality, the medicine must comply, for the duration of the product shelf-life, with specifications that were agreed between the company marketing the medicine and Medsafe. These specifications are known as shelf-life specifications.

Table 3: Approved finished product shelf-life specifications that the old and new Eltroxin formulations must comply with for the duration of the product shelf life

Test Acceptance criteria Comment
Old formulation New formulation
Description 50 mcg tablet:
A white, ¼", biconvex tablet,
with a bisecting breakline on one
face and "50" inscribed above the
breakline. The other face is plain.
50 mcg tablet:
White to off-white, round,
biconvex tablets imprinted
GS 11E on one face and
50 on the other.
Standard requirement for pharmaceutical products.
100 mcg tablet:
A yellow, ¼", biconvex tablet,
with a bisecting breakline on one
face and "100" inscribed above the
breakline. The other face is plain.
100 mcg tablet:
White to off-white, round,
biconvex tablets imprinted
GS 21C on one face and
100 on the other.
Identification of levothyroxine sodium      
By HPLC No specification The retention time of the principal peak in the sample chromatogram corresponds with that of the principal peak in the levothyroxine sodium reference material chromatogram. Standard requirement for pharmaceutical products.
By UV No specification The spectrum of the sample is concordant with that of the levothyroxine sodium reference material.  
Levothyroxine sodium content (% label claim) 90.0 - 110.0 90.0 - 105.0 Standard requirement for pharmaceutical products.
The upper limit for assay (levothyroxine) is tighter for the new formulation than the old formulation.
Drug-related impurities content (%)     The specification for impurities is significantly improved for the new formulation compared to that for the old formulation.

GSK developed an improved test method capable of detecting impurities that the old method was unable to detect. The new method is used to test the new formulation. The limit for liothyronine sodium is tighter for the new formulation and the content of tetrac, HDPhDB acid, unspecified impurities and total impurities is controlled. Testing of the old formulation using the new test method indicates that the old formulation also contained tetrac, HDPhDB acid and unspecified impurities.

Liothyronine sodium ≤ 2.0 ≤ 1.0
Tetrac* No specification ≤ 1.0
HDPhDB acid** No specification ≤ 2.5
Any unspecified impurity No specification ≤ 1.0
Total No specification ≤ 5.0
Loss on drying at 105°C (%w/w) No specification 3.0 - 6.5 Surrogate test for water content (permitted by ICH guideline Q6A).
Hardness 2.5 to 5.0 Kp No specification Hardness is not included in the specification for the new formulation as hardness testing is performed as an in-process control during manufacture. This is acceptable and is supported by ICH guideline Q6A.
Friability (performed only when hardness fails) ≤ 1.0 % No specification Tablet friability is not included in the specification for the new formulation as friability testing is performed as an in-process control during manufacture. This is acceptable and is supported by ICH guideline Q6A.
Dissolution (% levothyroxine sodium released) 55 % dissolution at 80 minutes 70 % dissolution in 45 minutes Standard pharmacopoeial requirement for tablets.
Microbial limits test:     Standard pharmacopoeial requirement for tablets.
The acceptance criteria applied for the new formulation are those specified in the European Pharmacopoeia.
Total viable aerobic count (cfu/mL)      
Bacteria No specification Not more than 103  
Fungi No specification Not more than 102  
E. coli No specification Absent from 1 g  
Packaging components To be inspected No specification It is not currently a standard requirement to include this type of specification in the shelf-life specifications as packaging materials are controlled during the manufacturing process.

* tetraiodothyroacetic acid

**4-[(4-hydroxy-3,5-diiodophenyl)oxy]-3,5-diiodobenzoic acid

How is the safety and efficacy of a New-Intermediate Risk Medicine established?

In relation to tablet formulations, the safety and efficacy of a New-Intermediate Risk Medicine is usually established by the demonstration of bioequivalence with a medicine that has already been approved as both safe and effective on the basis of clinical trial data. It is internationally accepted that demonstration of bioequivalence is an acceptable surrogate for performing full clinical trials. Conducting a bioequivalence trial is significantly cheaper and quicker than performing a full clinical assessment on the new product and is favoured amongst generic medicine manufacturers.

How is bioequivalence determined?

Bioequivalence is determined by comparing, as a ratio, the rate and extent of absorption, metabolism and excretion (plasma profile) of two medicines in the body. Medsafe evaluated the new formulation of Eltroxin against internationally accepted criteria for quality, safety, and bioequivalence.

Any brand or formulation change can affect the bioavailability of a medicine (how a medicine is absorbed, metabolised and excreted). As the assessment of bioequivalence is based on population statistics, even where bioequivalence is proven for two medicines, it is possible that a small proportion of patients may experience either an increased or decreased therapeutic effect when changed from one product to another. This occurs because of an individual's variability in how the medicine is absorbed, metabolised, and excreted.

For medicines that have a wide therapeutic index, i.e. the safety and efficacy of the product remains unchanged across a broad range of plasma levels of the medication, the effect of individual variability on bioavailability is likely to be unnoticeable and very few patients will report adverse effects.

For medicines that have a narrow therapeutic index (as with levothyroxine), small changes in its bioavailability may alter the plasma levels leading to either decreased or increased therapeutic effect. This means that it is expected that a small number of patients treated with levothyroxine will invariably notice an increased or decreased therapeutic effect.

The purpose of most bioequivalence trials is to compare a formulation of a medicine (i.e. a generic medicine) with an unknown efficacy profile, against a medicine which has already been approved as both safe and effective on the basis of clinical trial data.

Bioequivalence data are generated from small clinical trials using a statistically significant sample of participants. In these trials participants receive samples of each medicine in a random sequence. After receiving each medicine, blood samples are taken from participants for a sufficient period to allow a profile of the drug's absorption and elimination to be obtained. Statistical profiles of the two medicines are then compared for each trial participant.

Three metrics are compared: Cmax ratio (the maximum level of drug in the body); AUC ratio (Area Under Curve - this is a measure of the total dose absorbed and eliminated by the participant), and Tmax (the time to maximum drug concentration).

Bioequivalence is required to be determined and expressed statistically. This is due to the inherent variability of drug absorption between individuals. This variability is handled statistically by summing the blood results obtained for each of the two medicines from each individual and comparing the means and distribution of Cmax, AUC, and Tmax. When the data are assessed in this way they can be deemed to be representative of the entire population.

By international definition two medicines are considered bioequivalent if: the ratio of the geometric means of the Cmax and AUC lies within the range of 80% and 125% at a 90% confidence level, and the difference in Tmax is not of concern clinically. This is a statistical calculation.

A common misconception is that the bioequivalence acceptance range correlates to 20% - 25% variability between the two medicines. The design of bioequivalence studies, as conducted for Eltroxin, correlates with a potential Type 1 error of up to 5%. This means that there is a 5% chance of two medicines being incorrectly judged bioequivalent when the bioequivalence acceptance criteria is met.[1] To further reduce this risk additional parameters are evaluated, such as the comparability of dissolution profiles, and a full evaluation of the product as described above.

It is also important to note that even when a medicine meets the statistical requirements for bioequivalence there will still be a portion of the population whose individual variability falls outside the normal distribution. This is because bioequivalence studies are performed in a statistically significant sample of the population.

What information did GlaxoSmithKline provide to support the safety and efficacy of the new formulation of Eltroxin?

GlaxoSmithKline provided a bioequivalence study to support the clinical safety and effectiveness of the new formulation of Eltroxin. This study compared the new formulation of Eltroxin against a formulation of Eltroxin previously registered in New Zealand and currently marketed in Europe. This formulation was approved in New Zealand on 8 April 1981. This approach of building a bridge to a formulation that Medsafe has previously approved as safe and effective is permitted under New Zealand Medicine Guidelines.

An overview of the bioequivalence study provided for the new formulation of Eltroxin is presented in table 4.

Table 4: Overview of the bioequivalence study comparing the new formulation of Eltroxin against a formulation of Eltroxin previously registered in New Zealand and currently marketed in Europe.

Study name An open-label, single-centre, single dose, randomised, two-treatment, two-sequence crossover design study in healthy male and female volunteers to assess the bioequivalence of two ELTROXIN formulations.
Study number RES11116
Date of trial 17 December 2002 - 26 February 2003
Trial sites:  
Clinical site PAREXEL GmbH, Institute of Clinical Pharmacology, Klinikum Westend, Haus 18, Spandauer Damm 130, D-14050 Berlin, Germany
Analytical site W & T Laboratory, Turmstrasse 21, 10559 Berlin, Germany
Adverse events No serious adverse event was observed during the study and no subject was withdrawn from the study due to an adverse event. Adverse reactions were documented.

It is important to note the following in relation to adverse reactions in bioequivalence studies:
  • A bioequivalence study is not designed to compare adverse reactions in medicines
  • A bioequivalence study does not have enough participants to accurately assess and compare the frequency of adverse reactions in two medicines
  • A bioequivalence study only contains enough participants to assess the bioequivalence of two medicines
  • Due to the study design and the number of participants, it is inappropriate to extrapolate the proportion of adverse reactions reported in a bioequivalence study to the entire Eltroxin treatment population
  • Full clinical studies are required to enable an accurate assessment of the frequency of adverse reactions. Clinical studies have large numbers of participants (typically thousands) and are conducted over an extended period of time.
Reference product A formulation of Eltroxin tablets previously marketed in New Zealand and currently marketed in Europe.
Test product The new formulation of Eltroxin that was approved by the Ministry of Health on 16 November 2006.
Study design Open-label, single-centre, single dose, randomised, two-treatment, two-sequence crossover study in fasted healthy male and female volunteers.
Fasting period 10 hours pre-dose until 4 hours post-dose.


Subjects were allowed water up to 1 hour pre-dose and after 1 hour post-dose.

Dose administered A single 600 mcg dose (6 x 100 mcg tablets).


The dose was accompanied with 240 mL of water.

Time of day of dose administration 8:30 am to 10 am
Times and nature of meals and snacks consumed on study days Standardised low fibre meals at 4 and 10 hours following the dose, and a snack 14 hours following the dose.
Limitations applied to subjects' diet and medication during trial period No alcohol or xanthine-containing products were permitted for 24 hours prior to dosing until collection of the final blood sample during each period.

No smoking or use of nicotine-containing products (including nicotine patches) was permitted while subjects were in the Clinical Pharmacology Unit.

No grapefruit or grapefruit juice was permitted within seven days prior to the first dose of study medication until collection of the final blood sample during each period.

Medicines known to interfere with levothyroxine pharmacokinetics were not permitted for at least seven days prior to dosing and throughout the study unless approved by the Investigator and GSK. Subjects taking regular medicines (or a course of medication including herbal remedies or vitamin supplements), whether prescribed or not were excluded from the study. Over the counter preparations were not permitted for 48 hours before each study day until the end of the study period.

No subject was taking any regular medication prior to or during the study.

8 subjects received concomitant medications during the study. 3 subjects took 5 concomitant medications during the reference product treatment period and 5 subjects received 5 concomitant medications during the reformulated product treatment period. Drugs administered during treatment periods of the study were: paracetamol (po), lincomycin (po), ibuprofen (po), acetylsalicylic acid (po) and dexpanthenol ointment (topical). Acetylsalicylic acid (aspirin) and paracetamol were most commonly administered. Salicylates interfere with the protein binding of levothyroxine, therefore, the timing of salicylate use was examined to assess any effect on pharmacokinetic parameters. Only subject no. 7 had salicylate use within the 48-hour period of intensive pharmacokinetic sampling, which resulted in no apparent effect on this subject's pharmacokinetic parameters.
Limitations on subjects' posture and physical activity on study days Subjects remained upright or semi-recumbent for 4 hours after dosing and refrained from serious exercise for 24 hours prior to dosing and during the sample collection period.
Time between dosing of the reference and test products 37-39 days
Number of subjects who completed the study 36
Age range 20-40 years
Weight range BMI of 19.3-26.2 kg/m²; body weight 50-75 kg (females), 55-80 kg (males).
Ethnicity 35 Caucasian and one of 'other' origin (not further specified).
Subject withdrawals and reasons No subjects withdrew from the study.
Serum sampling times Pre-dose at 0.5, 0.25 and 0 hours and at 0.5, 1, 1.5, 2, 2.5, 3, 4, 6, 8, 10, 12, 18, 24 and 48 hours post-dose
Significant deviations from the study protocol There were no significant deviations from the study protocol.
Entities measured Levothyroxine (T4) and its physiologically active metabolite tri-iodothyronine (T3) were measured. In a blood sample, a proportion of T4 and T3 is bound to proteins and the remainder is free (not bound to proteins). Both total (bound + unbound) and free (unbound) T4 and T3 were measured.
Analytical test method Serum samples were tested using an Abbott AXSYM microparticle enzyme immunoassay.


The test method was validated at the site where the testing was performed.

Results Cmax (the maximum level of drug in the body); AUC (Area Under Curve - this is a measure of the total dose absorbed and eliminated by the participant), and Tmax (the time to maximum drug concentration) values for total T4, total T3 and corrected total T4 (results adjusted to account for levothyroxine produced by the body) were compared for the two products.

As per standard practice, Medsafe recalculated several of the provided datasets and the results of these recalculations are summarised below.

Bioequivalence trial data comparing the newly formulated Eltroxin tablets (100mcg) with a previously registered Eltroxin formulation.
Metric Previous Formulation New Formulation 90% Confidence Interval
Cmax value (nmolL-1)
TT4
TT3
Corrected TT4

181.4 ± 39
1.58 ± 0.24
0.089 ± 0.028*

170.5 ± 38
1.6 ± 0.22
0.079 ± 0.026*

85%-92%
91%-101%
77%- 89%
AUC Value (nmol.h.L-1)
TT4
TT3
Corrected TT4

6624 ± 1393
65.64 ± 10.26
131.6 ± 45.6

6487 ± 1292
64.81 ± 8.37
124.8 ± 41.3

90%-95%
89%-98%
82%-98%
Tmax Value (hours)
TT4
TT3
Corrected TT4

2.53 ± 1.88
16 ± 18.28
2.53 ± 1.88

3.02 ±1.72*
16.45 ± 19.08
3.02 ± 1.72*

0 - 1.0*
- 5.79 - 7.75
0 - 1.0*
TT4 = Total (bound + free) levothyroxine
TT3 = Total (bound + free) tri-iodothyronine
Corrected TT4 = Total levothyroxine adjusted to account for levothyroxine produced by the body

* Result differs slightly from the figures published on the Medsafe website previously, which were entered in error. The amended result does not affect the confidence interval calculation, or the outcome of the bioequivalence study.

In all but one instance the calculated bioequivalence values fell within the internationally accepted range of 0.8 to 1.25. The Cmax value for baseline corrected total levothyroxine (TT4) fell outside the accepted limits of 0.8 to 1.25. This result was considered acceptable given that: Cmax is not clinically important for this medicine because of its long half life (greater than 5 days), AUC is the better predictor of efficacy and safety; and the observed compliance of the remaining measurements. In addition, there is a lack of international consensus over the scientific validity of comparing baseline corrected values.
Did Medsafe require any further information from GlaxoSmithKline prior to the distribution of the new formulation in New Zealand?

Yes. Medsafe directed the manufacturer to:

See the attachments in the timeline above for copies of these documents.

References

  1. Patterson S, Jones B. 2006. Bioequivalence and Statistics in Clinical Pharmacology. Florida:Chapman and Hall CRC. Pg 30