CASE REPORT

Best Practices for Drug Substance Stress and Stability StudiesDuring Early-Stage Development Part II—ConductingAbbreviated Long-Term and Accelerated Stability Testingon the First Clinical Drug Substance Batch to Confirmand Adjust the Drug Substance Retest Period/Powder for OralSolution Shelf Life

Q. Chan Li & K. Cohen & T. Tougas & F. Qiu & J. Li &J. McCaffrey & T. Purdue & Jinhua J. Song & F. Swanek &

S. Abelaira

Published online: 24 January 2013# Springer Science+Business Media New York 2013

Abstract In pursuit of continuous process improvement,the authors streamlined the drug substance (DS) stress andstability testing process from preclinical to the first clinicalbatch. High temperature/high humidity stress and ICH Q1Bconfirmatory photostability testing on an early DS batchprovide stability data that help quickly assess the new DSstability behavior, extrapolate the initial DS retest periodand the initial powder for oral solution (PFOS) shelf life,and evaluate packaging requirements. Then, concurrent sta-bility testing on the first clinical batch (or alternatively arepresentative nonclinical batch) is conducted under long-term (LT) and accelerated (AC) storage conditions. TheLT/AC stability testing is used to verify the solid stresstesting results and to adjust the DS retest period and theshelf life of (PFOS), if necessary. This paper describes howto perform abbreviated LT/AC stability testing, comparesLT/AC stability results with the solid stress results, showshow to adjust the DS retest period and PFOS shelf life if

necessary, and shares our regulatory experiences with thisnew approach. Our science- and risk-based DS stress andstability process has offered a quick turnaround in obtainingadequate stability information for new DS development,eliminated redundancies, improved efficiency and consisten-cy, achieved an optimal balance between risk and cost forearly drug development, and received regulatory acceptances.

Keywords Drug substance . Powder for oral solution(PFOS) . Early-stage development . Solid stress . Hightemperature/high humidity . Photostability . Retest period .

Shelf life

AbbreviationsAC Accelerated storage condition (e.g., 40 °C/75 %

RH)HT/HH High temperature and high humidity (e.g., 70 °C/

75 % RH)ICH International Conference on Harmonisation1× ICHQ1B

Light exposure for confirmatory studies, notless than 1.2 million lux hours of overall illu-mination of visible light and an integrated nearultraviolet energy of not less than 200 Wh/m2

LT Long-term storage condition, e.g., 25 °C/60 %RH

LT/AC Long-term storage condition and acceleratedstorage condition (25 °C/60 % RH and 40 °C/75 % RH)

J Pharm Innov (2013) 8:56–65DOI 10.1007/s12247-013-9147-0

Q. C. Li (*) :K. Cohen : T. Tougas : F. Qiu : J. Li :J. McCaffrey : T. Purdue : J. J. Song : F. SwanekBoehringer Ingelheim Pharmaceuticals, Inc., Ridgefield, CT06877, USAe-mail: chan.li@boehringer-ingelheim.com

S. AbelairaBoehringer Ingelheim, Argentina, Juana Azurduy 1534,1429, Buenos Aires, Argentina

PFOS Powder for oral solution (DS in bottle, withoutexcipients)

RH Relative humidity

Introduction

As stated in our part I paper [1], establishing the stability ofdrug substance (DS) and drug product is a very importantdrug development task, and is a regulatory expectation toensure product quality, which may affect product safety andefficacy. For the stability testing of drug substance and drugproduct to support registration, regulatory guidances [2–6]harmonize and delineate expectations (e.g., protocol design,the amount of data). For drug stability to support phase I andphase II clinical trials (early development), regulatory gui-dances [7, 8] are usually worded generally. For phase I drugsubstance stability, the US FDA guidance [7] states that “Abrief description of the stability study and the test methodsused to monitor the stability of the drug substance should besubmitted. Preliminary tabular data based on representativematerial may be submitted. Neither detailed stability datanor the stability protocol should be submitted.” The EMAguidance [8] has similar requirements.

The generality of the regulatory guidances for theearly development stage is intended to allow flexibilitywhen changes and improvements are constantly made.This flexibility leads pharmaceutical companies and reg-ulatory agencies to make their own interpretations of theguidances. Consequently, companies either conduct morestability studies than necessary just to avoid regulatoryquestions but at the expense of valuable resources, orperform insufficient stability work, resulting in regulato-ry questions that must be answered and/or that maydemand more stability work and thus cause delays indrug development. Also, regulatory interpretations andexpectations are not entirely consistent from agency toagency and even from reviewer to reviewer. Hence, thereexist a pressing need and a great opportunity for phar-maceutical companies to share drug stability testingpractices, rationales, and regulatory experiences for theearly stages of development. Li [1], Waterman [9–11],Colgan [12, 13], and Mazzo [14] have published scien-tific, practical, and efficient stability testing proposalsand practices.

As described in the part I paper [1], several years ago, weimproved our DS stability testing process to support phase Iclinical trials. The improved (recommended) process pro-ceeds in two steps:

A suitably selected early lab scale batch of a new drugsubstance in both open and closed containers is stressedat high temperature/high humidity (HT/HH), preferably70 °C/75 % relative humidity (RH) for 3 weeks, and atconfirmatory photostability testing condition per Interna-tional Conference on Harmonisation (ICH) Q1B [3]. Thisdesign is called solid stress testing or simply solid stress.The open container subjects the DS to a continuousexposure to moisture (a worst case for bulk packaging)and thus helps quickly determine whether moistureaffects DS stability. The closed container, which repre-sents the packaging of powder for oral solution (PFOS),protects the DS from exposure to moisture. This solidstress is designed to get a quick readout of the new DSstability behavior. Testing results for the open containerare used to extrapolate a retest period for the DS, where-as testing results for the closed containers are used toextrapolate a shelf life for PFOS. All the solid stressresults are used to define packaging requirements.

The extrapolation principles and criteria have been de-scribed in part I [1]. Briefly, the extrapolation is based on the

classic Arrhenius relationship between temperature and thereaction (degradation) rate, by assuming that the degrada-tion reaction proceeds in a pseudo-zero order and that thedegradation rate constant doubles for every 10 °C increasein temperature, i.e., the 2 for 10 rule (k(T)=2ΔT/10), whichroughly corresponds to an activation energy (Ea) of 12–14 Kcal/mol (50–59 kJ/mol). This assumed Ea is veryconservative when compared with the Ea value of83.144 kJ/mol (20 Kcal/mol) used for the calculation ofmean kinetic temperature for various climatic zones in theUS Pharmacopoeia [15]. The extrapolation criteria andArrhenius extrapolations from 70 and 60 to 25 °C arepresented in Table 1 and Table 2, respectively.

The part I paper [1] has also described the solid stressdesigns, DS batch selection, the stress testing results of11 new drug substances, the extrapolations of initial DSretest periods, and the PFOS shelf lives. As stated in [1],the stress-extrapolated retest periods and shelf livesshould be verified with stability studies of the first clin-ical batch (or alternatively a representative nonclinicalbatch) under long-term (LT) and accelerated (AC)

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storage conditions. Part II (this paper) describes how toperform abbreviated LT/AC stability testing, comparesLT/AC stability results with the solid stress results,shows how to adjust the DS retest periods and PFOSshelf lives if necessary, and shares our regulatory expe-riences with the improved process.

Abbreviated LT/AC Stability Testing of the FirstClinical Batch

DS Batch Selection

Ideally, the first clinical batch of the DS is selected for theLT/AC stability studies, which are usually conducted con-currently with the Phase 1a clinical trial. Alternatively, anonclinical batch can be selected for the LT/AC stabilitystudy, provided that the quality and particularly stability-related quality attributes of the batch, packaging configura-tions, and analytical methods are all representative. In thealternate case, the stability testing is not required for the firstclinical batch. However, it is recommended that sufficientsamples from the clinical batch be stored at the LT/ACstorage conditions in the event testing is requested.

Bulk DS Stability Design

Drug substance material is packaged in polyethylenebags closed with twist ties and placed in fiber shippingcontainers. This packaging simulates the worst case pro-tection among various packaging configurations that canbe used for bulk drug substance. Because this packagingis less protective, the stability results can be used to set

and/or extend a shelf life for the clinical PFOS whoseprimary packaging is more protective (typically glass andtight screw cap). A DS stability design example is givenin Table 3, which uses the ICH Q1A construct [2] butwith fewer time points at LT conditions, i.e., the 9- and18-month time points are not included (thus called ab-breviated LT/AC stability testing). The Table 3 design isefficient and justified because stability data from 3-, 6-,12-, and 24-month time points can adequately verify theDS stability behavior from the solid stress, and 9- and18-month time points do not add much new informationbased on our many years of experience and that statisti-cal analyses requiring a sufficient number of data pointsare hardly ever done or needed in early development. Onthe other hand, the 9- and 18-month time points can betested if retest periods/shelf lives of 21 and 30 months,respectively, are desired. Typical tests (A) are: descrip-tion, assay and impurities by HPLC, water content, andX-ray powder diffraction. Chiral impurity by HPLC isgenerally not performed unless the solid stress testingshows chiral conversion. Although literature [16] dis-courages the assay test for routine stability testing, ourHPLC methods typically combine assay and impuritydetermination in the same procedure, which does notdemand much extra time, but can yield useful informa-tion when the DS is not stable.

PFOS Stability Design

One representative fill weight should be placed on stability.This fill weight typically contains the least amount of drugsubstance to allow full testing. Samples from clinical suppliesare preferred for this study. A PFOS LT/AC stability design

Table 1 Solid stress extrapola-tion criteria

NMT not more thanaInitial (time zero) assay result isdetermined by area percent (in theabsence of a reference standard)b2× ICH 3A qualification thresh-old = two times the qualificationthreshold by ICH Q3A [17]

Tests Stress extrapolation criteria

Description Report result and compare with initial result

Assay (compared with time 0a) Within 97.0–102.0 % of the time 0 assay value

Individual degradation products Each NMT 2× ICH 3A qualification thresholdb

Total degradation products NMT 2.0 %

Peak homogeneity The DS peak is spectrally homogeneous

Chiral impurity (if applicable) NMT 2× ICH 3A qualification threshold

Table 2 Arrhenius extrapola-tions of retest period and shelflife in month at 25 °C

Temperature (°C) Storage duration (weeks) Extrapolated retest period/shelf life in month at 25 °C

70 1 5

2 11

3 15.6 → reduced to 15

60 4 10

5 13

6 15.6 → reduced to 15

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example is shown in Table 4. Typical tests (B) are descriptionand assessment of packaging material. The assay and impuri-ties by HPLC test is performed only if needed, for example, ifthere is a stability question relating to the clinical PFOS. ThePFOS stability design has fewer tests and is shorter in durationthan the bulk DS stability design in Table 3. This is because, asmentioned above, the bulk DS stability results are used to setand extend the clinical PFOS shelf life.

Data Evaluation and Retest Period/Shelf Life Assignment

The results from the LT/AC stability study are evaluated toconfirm and/or adjust the DS retest period and PFOS shelflife. While formal statistical evaluations are typically notperformed at this stage of development, data trending shouldbe examined to evaluate changes that may occur during astability study and to assess whether stability results areapproaching or have exceeded the acceptance criteria forspecified impurities/degradation products. Two times (2×)the ICH Q3A [17] qualification threshold is used as thecriterion for evaluating each unspecified impurity/degrada-tion product in this early stage of drug development. It isunderstood that other pharmaceutical companies, dependingon their risk tolerance, may choose more lenient criteria.

Table 5 shows our recommendations for setting DS retestperiod and PFOS shelf life on the basis of both the solidstress testing results and the LT/AC stability testing results,when both data sets show no degradation trends towards anunacceptable level of degradant. It should be pointed outthat longer or shorter shelf lives may be proposed,

depending on the rigor of scientific justifications, the risktolerance of the pharmaceutical company, and the regulatoryexpectations of authorities that approve the clinical trials[14]. It is also noted that Beaman [18] proposed the durationof primary stability testing and a decision tree to assignproduct shelf lives for registration. Also, if a significantdegradation trend is observed in samples stored at acceler-ated conditions, but the long-term data show no degradationtrend, the DS retest period/PFOS shelf life are set shorterthan those proposed in Table 5, and this has to be handled ona case-by-case basis. In such a case, testing DS stored at theintermediate condition 30 °C/75 % RH would provide use-ful data.

Comparisons Between Solid Stress Testing Resultsand LT/AC Stability Results

The improved approach has been implemented on 11 newdrug substances, all of which underwent solid stress testingand 10 of which underwent the abbreviated LT/AC stabilitytesting. The chemical stability results are summarized inTable 6 for DS 1–6, Table 7 for DS 7–9, and Table 8 forDS 11. DS 10 was not subjected to LT/AC stability testingbecause the first clinical batch was not manufactured. For allthe drug substances, the physical stress/stability data (typi-cally for XRPD and DSC and water content), which wereused for understanding DS physical behavior and for for-mulation development purposes, were gathered and ana-lyzed but are not presented in this paper, as all 10compounds exhibited no physical stability-related changes.

As shown in Table 6, DS 1 showed a single, minordegradation product (Imp 3) when stressed at 70 °C/75 %RH, but no degradation under the ICH Q1B confirmatoryphotostability testing. Since the maximum daily dose forphase I was below 25 mg, the solid stress extrapolationcriterion for degradation was set to not more than (NMT)0.30 %, which is two times the ICH Q3A qualificationthreshold (2×0.15 %=0.30 %). Because the degradationproduct (Imp 3) was NMT 0.14 % in both open and closedcontainers at 3 weeks at 70 °C/75 % RH, both the initial DSretest period and the initial PFOS shelf life were

Table 3 Bulk drug substance LT/AC stability design example

Storage conditions Time 0 3 months 6 months 12 months 24 months

25 °C/60 % RHa Typically release testing results A A A A

30 °C/75 % RHb – – – –

40 °C/75 % RHa A A – –

a If the stress data suggest that the bulk DS should be refrigerated, then the long-term storage condition 25 °C/60 % RH is changed to 5±3 °C, andthe accelerated storage condition 40 °C/75 % RH is changed to 25±2 °C/60±5 % RHb Samples may be stored but tested only if significant degradation is observed at 40 °C/75 % RH

Table 4 PFOS stability design example

Storage conditions Time 0 3 months 6 months Endof study

25 °C/60 % RHa B – B Bb

40 °C/75 % RHa B B –

a If the stress data suggest that the PFOS should be refrigerated, thenthe long-term storage condition 25 °C/60 % RH is changed to 5 °C±3 °C, and the accelerated storage condition 40 °C/75 % RH is changed to25±2 °C/60±5 % RHb Performed at the end of study to cover the duration of clinical trials

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extrapolated to 15 months per Table 2. The stress findingsand the conservatively extrapolated 15 months shelf lifewere confirmed by the LT/AC stability results. After12 months at 25 °C/60 % RH and 5 months at 40 °C/75 %RH, the degradant Imp 3 did not exceed 0.08 and 0.14 %,respectively (Table 6). According to Table 5, the DS retestperiod was extended to 24 months. The 15-month PFOSshelf life could have been extended to 24 months. However,15 months was sufficient to cover packaging, labeling,shipping, storage, and the clinical trial duration. In ourexperience, a 15-month shelf life for a PFOS can coverphase Ia clinical trials in most cases.

As shown in Tables 6 and 7, drug substances 2, 3, and9 showed little or no degradation in open or closedcontainers after 3 weeks stress at 70 °C/75 % RH butshowed degradation under the Q1B confirmatory photo-stability testing. Thus, according to Table 2, both theinitial DS retest period and the PFOS shelf life wereset to 15 months with the storage requirement that eachDS be protected from light. The results of the 3-weekstress at 70 °C/75 % RH and the 15-month shelf lifewere confirmed by the LT/AC stability results. DS 2 andDS 3 in Table 6 did not show degradation after storageof 12 months at 25 °C/60 % RH and 6 months at 40 °C/75 % RH. According to Table 5, the retest period forDS 2 and DS 3 was extended to 24 months. Since DS 9showed no degradation after 6 months at 25 °C/60 % RHand 6 months at 40 °C/75 % RH (Table 7), the retestperiod for DS 9 was extended to 18 months (Table 5).For these three drug substances, there was no businessneed to extend the initial PFOS shelf life beyond15 months, although longer shelf lives were justified(Table 5) based on the LT/AC stability results.

As shown in Tables 6 and 7, drug substances 4–8 showedno degradation after 3 weeks stress at 70 °C/75 % RH inopen or closed containers and by the confirmatory photo-stability testing. In our experience, this stable behavior istypical of most of the drug substances. For each of thesedrug substances, the initial DS retest period and the initialPFOS shelf life were set to 15 months according to Table 2.The results of the 3-week stress at 70 °C/75 % RH and the15-month shelf life were confirmed by the LT/AC stability

results, since no degradation was observed at 25 °C/60 %RH after 6 or 12 months and at 40 °C/75 % RH after6 months (Tables 6 and 7). For DS 4–6, the DS retest periodwas extended to 24 months (Table 5) on the basis of theLT/AC stability results obtained after 6 months at 40 °C/75 % RH and after 12 months at 25 °C/60 % RH (Table 6).For DS 7–8, the DS retest period was extended to 18 monthsbased on the LT/AC stability results obtained after 6 monthsat 40 °C/75 % RH and at 25 °C/60 % RH (Table 7).

DS 11 is an interest example as shown in Table 8 anddescribed in detail in part I [1]. The first lab batch wassubjected to 70 °C/75 % RH and the Q1B confirmatoryphotostability testing, and one significant, predominantdegradation product Imp 2 was observed. Imp 2 was0.12 % at time 0. Imp 2 increased to 0.43, 0.66, and0.80 % in the open container, and to 0.23, 0.29, and0.37 % in the closed container, at 70 °C/75 % RH after1 week (8 days), 2 weeks, and 3 weeks, respectively. Itshould be noted that the open container showed greaterdegradation than the closed container, pointing to wateras a stability-related quality attribute. Imp 2 increased to1.8 % under the confirmatory photostability testing. Theextrapolated DS retest period was only 6 months basedon Table 2. Efforts were immediately made to identifyImp 2 and the degradation pathway. LC-MS work iden-tified Imp 2 as a rotamer (a conformational isomer pro-duced by restricted rotation). It was then hypothesizedthat high contents of volatiles (residual solvent and wa-ter) could promote the formation of the rotamer (Imp 2),particularly when the volatiles possess high kinetic ener-gy at high temperature (e.g., 70 °C). Note that the firstlab batch contained the relatively high levels of isopro-panol (1.6 %) and water (0.26 %). Thus, a second labbatch was produced intentionally with low levels ofwater (0.08 %) and residual solvent ethanol (0.10 %),which replaced isopropanol for recrystallization. Whenthis second lab batch was subjected to 70 °C/75 % RHstress for 2 and 3 weeks, Imp 2 virtually did not change,i.e., from 0.09 % at time 0 to 0.11 % at 3 weeks, in bothopen and closed containers (Table 8). From the secondlab batch stress data, the initial DS retest period and theinitial PFOS shelf life were extrapolated to 15 months,

Table 5 DS retest period andPFOS shelf life extrapolatedfrom long-term and acceleratedstability data, along with solidstress testing data

aBoth data sets show no degra-dation trends towards an unac-ceptable level of degradantbIn case these time points areanalyzed

Available stability dataa Proposed retest period and shelf life

Time 0 15 months

3-month accelerated and long-term data 15 months (support stress extrapolation)

6-month accelerated and long-term data 18 months

9-month long-term datab 21 months

12-month long-term data 24 months

18-month long-term datab 30 months

24-month long-term data 36 months

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with protection from light, according to Table 2. Thestress results of the second lab batch were confirmedby the LT/AC stability results of the first clinical batch:

no degradation was observed after 12 months at 25 °C/60 % RH and after 6 months at 40 °C/75 % RH(Table 8). The DS retest period was then extended to

Table 6 Comparisons between solid stress and LT/AC stability results for DS 1–6

Test Lab batch solid stress 1st clinical batch (or representative non-GMP batch) (DS in polyethylenebag placed in fiber tube)

Time 0 70 °C/75 % RH Photo Time 0 25 °C/60 % RH (LT) 40 °C/75 % RH (AC)

3 weeks, open 3 weeks,closed

1× ICHclosed

6 months 12 months 3 months 6 months

DS 1

Description White White White White White Whitea White White Whiteb

Assay (%) 100.0 100.0 100.0 99.0 100.0 100.3a 99.0 99.8 100.2b

Imp 1 (%) 0.07 0.08 0.07 0.08 0.07 0.08a 0.08 0.08 0.08b

Imp 2 (%) 0.07 0.08 0.07 0.07 0.07 0.08a 0.07 0.07 0.07b

Imp 3 (%) <0.05 0.14 0.14 <0.05 <0.05 0.07a 0.08 <0.05 0.14b

DS 2

Description Off-white Off-white Off-white Off-white Off-white Off-white Off-white Off-white Off-white

Assay (%) 100.0 99.2 99.9 99.3 100.1 99.2 99.3 100.3 99.9

Imp 1 (%) <0.05 0.10 <0.05 <0.05 <0.05 0.10 <0.05 <0.05 <0.05

Imp 2 (%) <0.05 0.11 0.10 <0.05 0.08 0.08 0.08 0.08 0.08

Imp 3 (%) <0.05 <0.05 <0.05 0.66 <0.05 0.10 <0.05 <0.05 <0.05

Imp 4 (%) 0.55 0.59 0.56 0.56 0.52 0.51 0.51 0.52 0.51

DS 3

Description Off-white Off-white Off-white Off-whitec White White White White White

Assay (%) 99.9 99.2 99.2 98.9c 101.3 99.4 98.9 99.2 100.4

Imp 1 (%) 0.09 0.09 0.12 0.09c <0.05 <0.05 <0.05 <0.05 <0.05

Imp 2 (%) <0.05 <0.05 <0.05 1.7c <0.05 <0.05 <0.05 <0.05 <0.05

DS 4

Description White White White White White White White White White

Assay (%) 99.8 98.9 100.0 100.6 99.4 99.8 100.3 99.6 99.6

Imp 1 (%) <0.05 <0.05 <0.05 <0.05 0.06 0.06 0.05 0.05 0.06

Imp 2 (%) <0.05 <0.05 <0.05 <0.05 0.10 0.09 0.09 0.09 0.09

Imp 3 (%) <0.05 <0.05 <0.05 <0.05 0.08 0.08 0.09 0.08 0.09

Chiral Imp (%) 0.21 0.22 0.21 0.21 0.17 0.18 0.18 0.18 0.16

DS 5

Description Off-white Off-white Off-white Off-white White White White White White

Assay (%) 99.9 99.8 99.8 99.7 99.9 100.4 99.9 100.1 100.4

Imp 1 (%) 0.05 0.06 0.06 0.05 0.07 0.08 0.11 0.06 0.08

Imp 2 (%) <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05

DS 6

Description Off-white Off-white Off-white Off-white Off-white Off-white Off-white Off-white Off-white

Assay (%) 100.0 101.0 100.9 NA 99.3 99.3 99.9 98.8 99.4

Imp 1 (%) 0.09 0.09 0.09 0.09 0.12 0.16 0.12 0.16 0.17

General designations Imp 1 and Imp 2 are specific to each DS. All impurity levels <0.05 % including not detected are simply reported as <0.05 %.Photo 1× ICH closed is the confirmatory photostability of ICH Q1B

Imp impurity, White white powder, Off-white off-white powdera Five months at 25 °C/60 % RH; Normal practice is 6 monthsb Five months at 40 °C/75 % RH; Normal practice is 6 monthsc 2× ICH photo stress in this case, although normal practice is 1× ICH photo stress

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24 months per Table 5. Note that the clinical batchcontained low levels of ethanol (0.18 %) and water(0.08 %) (Table 8), consistent with the stability-relatedquality attributes identified by the stress stability datafrom lab batch 1 and lab batch 2. Thus, it is obviousthat the HT/HH and photo stress can quickly reveal theinstability behavior and stability-related quality attributesof the new DS. After the identification of degradationproducts and degradation mechanisms, stability-relatedquality attributes were confirmed and controlled, thechemical manufacturing process improved, and the pack-aging properly selected.

An approach alternative to our simple HT/HH stress is theAccelerated Stability Assessment Program (ASAP) [9–11].ASAP uses several combinations of temperature and

humidity conditions, requires multiple stress chambers andthe amounts of degradation be kept consistent (isoconversion,tied to specification limits) at different conditions, involvesstatistical analysis, and uses a humidity-corrected Arrheniusequation to extrapolate a DS retest period. If isoconversion isnot achieved, more iterations of the experiments are con-ducted. However, in early development, specification limitsare either not set or changeable, therefore isoconversion ishard to achieve. For the requirements and amount of work,ASAP is best used for drug substances that have shownchemical stability challenges. Since most drug substances inour experience are stable or moderately stable, our oneHT/HH stress condition that requires only one stability cham-ber (or two conditions on occasion) is reliable, efficient, andeffective for assessing all new DS stability behaviors.

Table 7 Comparisons between solid stress and LT/AC stability results for DS 7–9

Test Lab batch solid stress 1st clinical batch (DS in polyethylene bag placed in fiber tube)

Time 0 70 °C/75 % RH Light Time 0 25 °C/60 % RH (LT) 40 °C/75 % RH (AC)

3 weeks,open

3 weeks,closed

1× ICHclosed

3 months 6 months 3 months 6 months

DS 7

Description White White White White White White White White White

Assay (%) 100.1 99.0 99.7 101.1 100.4 100.2 99.8 99.9 99.8

Imp 1 (%) 0.06 0.07 0.06 0.06 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 2 (%) 0.10 0.10 0.10 0.10 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 3 (%) 0.20 0.17 0.17 0.20 <0.05 <0.05 <0.05 <0.05 <0.05

DS 8

Description Light yellow Light yellow Light yellow Light yellow Light yellow Light yellow Light yellow Light yellow Light yellow

Assay (%) 100.0 98.1 98.9 99.5 99.7 100.3 99.4 100.2 99.3

Imp 1 (%) <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 2 (%) <0.05 <0.05 <0.05 0.08 <0.05 <0.05 <0.05 <0.05 <0.05

DS 9

Description Off-white Off-white Off-white Off-white White White White White White

Assay (%) 100.0 100.4 102.2 97.0 100.2 100.0 100.1 99.7 100.2

Imp 1 (%) 0.06 0.21 0.12 <0.05 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 2 (%) 0.08 0.10 0.10 0.10 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 3 (%) <0.05 <0.05 <0.05 0.45 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 4 (%) 0.07 0.06 0.07 0.06 0.06 0.06 <0.05 0.06 <0.05

Imp 5 (%) <0.05 0.06 0.07 0.54 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 6 (%) <0.05 0.08 <0.05 0.54 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 7 (%) 0.17 0.19 0.19 0.20 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 8 (%) 0.11 0.10 0.11 0.11 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 9 (%) 0.13 0.13 0.13 0.10 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 10 (%) 0.52 0.50 0.50 0.46 <0.05 <0.05 <0.05 <0.05 <0.05

Imp 11 (%) 0.13 0.12 0.12 0.12 <0.05 <0.05 <0.05 <0.05 <0.05

General designations Imp 1 and Imp 2 are specific to each DS. All impurity levels <0.05 % including not detected are simply reported as <0.05 %.Photo 1× ICH closed is the confirmatory photostability of ICH Q1B

Imp impurity, White white powder, Off-white off-white powder, Light yellow light yellow powder

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From the studies of these 10 drug substances, it is evidentthat the solid stress testing and extrapolations are reliable,useful to quickly evaluate DS stability behaviors, whetherthe substances are stable or not (DS 1 and DS 11, in partic-ular, being not stable), and the abbreviated LT/AC stabilitystudy is confirmatory and concurrent with the clinical trial,satisfying both scientific rigor and regulatory expectations.

Regulatory Experiences

Of the 10 drug substances cited in Tables 6, 7, and 8, sixhave been filed with a regulatory agency for phase Ia clin-ical trials conducted in Europe. Table 9 summarizes relevantstability data and shelf lives presented in these six IMPDs(Investigational Medicinal Product Dossier).

Table 8 Comparisons between solid stress and LT/AC stability results for DS 11

1st lab batch solid stress

Conditions Open container Closed container

Description % Assay % Imp 1 % Imp 2 % IPA % Water Description % Assay % Imp 1 % Imp 2

Time 0 Brown 100.0 <0.05 0.12 1.6 0.26 Brown 100.0 <0.05 0.12

70 °C/75 % RH 8 daysa Brown 100.2 <0.05 0.43 NP NP Brown 100.5 <0.05 0.23

2 weeks Brown 100.4 0.06 0.66 NP NP Brown 99.8 0.06 0.29

3 weeks Brown 99.0 0.08 0.80 NP NP Brown 99.8 0.08 0.37

1× ICH photo Dark brown 98.6 0.08 1.8 NP NP Dark brown 98.6 0.08 2.1

2nd lab batch solid stress

Conditions Open container Closed container

Description % Assay % Imp 1 % Imp 2 % Ethanol % Water Description % Assay % Imp 1 % Imp 2

Time 0 Brown 100.5 <0.05 0.09 0.10 0.08 Brown 100.5 <0.05 0.09

70 °C/75 % RH 1 week NP NP NP NP NP NP NP NP NP NP

2 weeks Brown 99.6 <0.05 0.10 NP NP Brown 100.4 <0.05 0.10

3 weeks Brown 100.1 <0.05 0.11 NP NP Brown 99.9 <0.05 0.11

1st clinical batch LT/AC (DS in polyethylene bag placed in fiber tube)

Conditions Description % Assay % Imp 1 % Imp 2 % Ethanol % Water

Time 0 Brown 99.1 <0.05 0.14 0.18 0.08

25 °C/60 % RH(LT)

6 months Brown 100.8 <0.05 0.14 NP 0.15

12 months Brown 99.3 <0.05 0.13 NP 0.12

40 °C/75 % RH(AC)

3 months Brown 100.5 <0.05 0.14 NP 0.17

6 months Brown 101.8 <0.05 0.14 NP 0.16

General designations Imp 1 and Imp 2 are specific to each DS. All impurity levels <0.05 % including not detected are simply reported as <0.05 %.Photo 1× ICH closed is the confirmatory photostability of ICH Q1B

Imp Impurity, Brown brown powder, IPA isopropanol, NP not performeda Eight days in this case, although 1 week (7 days) is the normal practice

Table 9 DS stability information and PFOS shelf lives presented in six IMPDs

DS # 6 3 5, 7, 8, 9

Solid stress results for 3 weeksat 70 °C/75 % RH (open andclosed glass vials) and at ICHQ1B photo

No degradation No degradation except at ICHQ1B photo

Little or no degradation exceptthat DS 9 showed degradationat ICH Q1B photo

LT/AC stability test results Data not available at filing. Committed toperform concurrent LT/AC stability testing

No degradation after 6 monthsat LT/AC

No degradation after 3 monthsat LT/AC

PFOS shelf life proposed 12 months 18 months (DS and its PFOSmust be protected from light)

15 months (DS 9 and its PFOSmust be protected from light)

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In the DS 6 IMPD, we elected to be conservative byproposing a PFOS shelf life of 12months instead of 15monthsbecause it was the first time we used the solid stress testingresults to derive a PFOS shelf life. Initially, the regulatoryagency questioned the basis for this proposal. After weresponded by presenting the Arrhenius equation, explainingthoroughly our extrapolations and rationales for the solidstress testing, and reaffirming our commitment to the LT/ACstability testing concurrent with the phase 1a clinical trial, theregulatory agency accepted our proposed shelf life of12 months.

In the DS 3 IMPD, we submitted solid stress data, pre-sented the Arrhenius equation, explained our extrapolationsand rationales for the solid stress testing, presented up to6 months of LT/AC stability results for the clinical batch,and committed to continue the abbreviated LT/AC stabilitytesting on the clinical batch. We proposed a PFOS shelf lifeof 18 months and received regulatory acceptance of thisproposal without question.

In the DS 8 IMPD, we submitted solid stress data, pre-sented the Arrhenius equation, provided a summary of ourextrapolations and rationales for the solid state stress testing,and committed to perform the LT/AC stability testing on theclinical batch. There were no LT/AC stability results of theclinical batch available at the time of initial filing. Weproposed a PFOS shelf life of 15 months. Initially, theregulatory agency questioned the basis for proposing a shelflife of 15 months. We responded by (1) explaining morethoroughly the Arrhenius equation, extrapolations, andrationales, (2) providing references for the solid state stresstesting, (3) providing 3 months of LT/AC stability results forthe clinical batch, and (4) reaffirming our commitment tocontinue to perform the LT/AC stability testing concurrentwith the phase 1a clinical trial. The regulatory agency ac-cepted our proposed shelf life of 15 months.

In the DS 5, DS 7, and DS 9 IMPDs, we submitted solidstress data, presented the Arrhenius equation, explained ourextrapolations and rationales for the solid stress testing,presented 3 months LT/AC stability results for the clinicalbatches, and committed to continue the LT/AC stabilitytesting on the clinical batch. We proposed a PFOS shelf lifeof 15 months and the regulatory agency accepted our pro-posals without question.

For future initial IMPD filings, we recommend follow-ing the paradigm of the DS 5, 7, 9, or 3. Our experiencesindicate that the solid stress results and 3-month (or 6-month) LT/AC stability results have received regulatoryacceptance of a 15-month (or 18-month) shelf life withoutquestion. Again, longer or shorter shelf lives may beproposed, depending on the rigor of scientific justifica-tions, the risk tolerance of the pharmaceutical company,and the expectations of authorities that approve the clinicaltrials [14].

Conclusions

In pursuit of continuous process improvement, we improvedthe drug substance stress and stability testing process frompreclinical to the first clinical batch. A high temperature/-high humidity stress (typically 3 weeks in open and closedcontainers at 70 °C/75 % RH) and ICH Q1B confirmatoryphotostability testing on an early DS batch provide stabilitydata that help quickly assess the new DS stability behavior,extrapolate the initial DS retest period and the initial PFOSshelf life, and evaluate packaging requirements. Then, con-current with the phase 1a clinical trial, an abbreviated long-term and accelerated stability testing on the first clinicalbatch (or representative nonclinical batch) provides stabilitydata that are used to verify the solid stress testing conclu-sions and to adjust the DS retest period and the PFOS shelflife, if necessary. This improved process was based onestablished scientific principles, experimentally tested, andimplemented on 10 new drug substances. Since implemen-tation, the improved DS stability process has offered a quickturnaround in obtaining adequate stability information fornew DS development, eliminated redundancies, improvedefficiency and consistency, achieved an optimal balancebetween risk and cost for early drug development whenattrition rate is very high, and received regulatory accept-ances. Parts III (currently in preparation) of this series willdiscuss how to make risk-based and data-driven evaluationof the need for further stability studies on DS batchessubsequent to the first clinical batch.

Acknowledgments Special thanks go to Mr. Gordon Hansen, Drs.Chris Senanayake and Keith Horspool, and Ms. Patricia Watson formanagement support and to Ms. Cornelia Field, Drs. Christian Kulinnaand Reggie Saraceno, and many BI colleagues for constructive dis-cussions and contributions.

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