Case-population studies in pharmacoepidemiology

Postmarketing Safety Concerns of Teprotumumab: A Real-World Pharmacovigilance Assessment

CONTEXT

Teprotumumab, which targets the insulin-like growth factor-1 receptor, is the only drug approved by the US Food and Drug Administration (FDA) for the treatment of thyroid eye disease (TED).

OBJECTIVE

This study aimed to identify potential safety signals of teprotumumab by analyzing postmarketing safety data from the FDA Adverse Event Reporting System (FAERS) database in 2023.

METHODS

The case/noncase approach was used to estimate the reporting odds ratio (ROR) and information component (IC) with relevant 95% CI for adverse events (AEs) that numbered 3 or more.

RESULTS

A total of 2158 cases were included in the analysis. Main safety signals identified were ear and labyrinth disorders, reproductive system and breast disorders, metabolism and nutrition disorders, and gastrointestinal disorders. Specifically, autophony (ROR [95% CI] = 4188.34 [1403.29-12500.8]), eyelid retraction (ROR [95% CI] = 2094.17 [850.69-5155.29]), permanent deafness (ROR [95% CI] = 1552.35 [789.07-3053.98]), bilateral deafness (ROR [95% CI] = 73.12 [41.14-129.97]), inflammatory bowel disease (ROR [95% CI] = 23.26 [13.46-40.19]), hyperglycemic hyperosmolar nonketotic syndrome (ROR [95% CI] = 17.75 [5.70-55.28]), and amenorrhea (ROR [95% CI] = 47.98 [36.22-63.54]) showed significant safety signals with teprotumumab.

CONCLUSION

This study identified ear and labyrinth disorders, and reproductive system and breast disorders, as specific safety signals of teprotumumab. Clinicians and pharmacists should be vigilant regarding these AEs. However, available data are currently insufficient, and further pharmacovigilance and surveillance are needed to fully understand this issue.

Post-marketing safety concern of PI3K inhibitors in the cancer therapies: an 8-year disproportionality analysis from the FDA Adverse Event Reporting System

BACKGROUND

The Phosphoinositide 3-kinases (PI3Ks) family plays a crucial role in tumorigenesis. Alpelisib (inhibiting PI3Kα), copanlisib (inhibiting PI3Kα andPI3Kδ), duvelisib (inhibiting PI3Kδ and PI3Kγ), and idelalisib (inhibiting PI3Kδ) were developed to target the PI3K pathway. However, the toxicity limits their application to some extent. It's necessary to investigate the adverse effects (AEs) of these inhibitors.

RESEARCH DESIGN AND METHODS

We conducted a comparative analysis of the safety signals of AEs in PI3K inhibitors using disproportionality analysis in the FDA Adverse Event Reporting System database(FAERS).

RESULTS

Our study identified significant safety signals for metabolic disorders with all PI3K inhibitors. Notable safety signals for gastrointestinal disorders were observed with most PI3K inhibitors, with the exception of copanlisib. Common AEs shared among all PI3K inhibitors included colitis and dehydration. Alpelisib displayed unique AEs associated with metabolic disorders, whereas copanlisib exhibited idiosyncratic AEs linked to cardiac and vascular disorders. Stevens-Johnson syndrome emerged as a common severe adverse event (SAE) among alpelisib, copanlisib, and idelalisib, while febrile neutropenia was prevalent among copanlisib, duvelisib, and idelalisib. Intestinal perforation was solely associated with alpelisib.

CONCLUSIONS

The safety profiles of the five PI3K inhibitors vary concerning adverse events. These findings could guide drug selection and inform future prospective research.

Assessing safety concerns of interstitial lung disease associated with antibody-drug conjugates: a real-world pharmacovigilance evaluation of the FDA adverse event reporting system

BACKGROUND

Antibody-drug conjugates have revolutionized cancer therapy due to their selectivity and efficacy. However, concerns have been raised regarding the potential effects of trastuzumab deruxtecan in interstitial lung diseases.

AIM

This study aimed to investigate the safety signals and time to onset of antibody-drug conjugates induced interstitial lung disease.

METHOD

We utilized the FDA Adverse Event Reporting System database (2004-2022) to identify interstitial lung disease safety signals in 13 FDA-approved antibody-drug conjugates. Disproportionality analysis was conducted to estimate the reporting odds ratios for interstitial lung disease.

RESULTS

Seven antibody-drug conjugates exhibited safety signals of interstitial lung disease: trastuzumab deruxtecan [reporting odds ratio, ROR (95% confidence intervals, CI) = 64.15 (57.07-72.10)], enfortumab vedotin [ROR (95% CI) = 5.24 (3.25-8.43)], trastuzumab emtansine [ROR (95% CI) = 3.62 (2.90-4.53)], brentuximab vedotin [ROR (95% CI) = 3.22 (2.49-4.17)], polatuzumab vedotin [ROR (95% CI) = 2.56 (1.59-4.12)], gemtuzumab ozogamicin [ROR (95% CI) = 2.53 (1.70-3.78)], and inotuzumab ozogamicin [ROR (95% CI) = 2.33 (1.21-4.49)]. Five antibody-drug conjugates with limited reports were excluded from further analysis: belantamab mafodotin, loncastuximab tesirine, mirvetuximab sorafenib, tisotumab vedotin, and moxetumomab pasudotox. Japan and the United States were the primary reporting countries.

CONCLUSION

This real-world study highlights high safety signals of interstitial lung disease associated with antibody-drug conjugates. Clinicians should be aware of these safety concerns and risk factors and implement early identification measures for their patients. Future research should prioritize comprehensively exploring the relationship between antibody-drug conjugates and lung diseases.

Assessing real-world safety concerns of Sacituzumab govitecan: a disproportionality analysis using spontaneous reports in the FDA adverse event reporting system

Aim

The aim of this study was to identify potential safety concerns associated with Sacituzumab Govitecan (SG), an antibody-drug conjugate targeting trophoblastic cell-surface antigen-2, by analyzing real-world safety data from the largest publicly available worldwide pharmacovigilance database.

Methods

All data obtained from the FDA Adverse Event Reporting System (FAERS) database from the second quarter of 2020 to the fourth quarter of 2022 underwent disproportionality analysis and Bayesian analysis to detect and assess the adverse event signals of SG, considering statistical significance when the lower limit of the 95% CI >1, based on at least 3 reports.

Results

Total of 1072 cases were included. The main safety signals were blood and lymphatic system disorders [ROR(95CI)=7.23 (6.43-8.14)], gastrointestinal disorders [ROR(95CI)=2.01 (1.81-2.22)], and relative infection adverse events, such as neutropenic sepsis [ROR(95CI)=46.02 (27.15-77.99)] and neutropenic colitis [ROR(95CI)=188.02 (120.09-294.37)]. We also noted unexpected serious safety signals, including large intestine perforation [ROR(95CI)=10.77 (3.47-33.45)] and hepatic failure [ROR(95CI)=3.87 (1.45-10.31)], as well as a high signal for pneumonitis [ROR(95CI)=9.93 (5.75-17.12)]. Additionally, age sub-group analysis revealed that geriatric patients (>65 years old) were at an increased risk of neutropenic colitis [ROR(95CI)=282.05 (116.36-683.66)], neutropenic sepsis [ROR(95CI)=101.11 (41.83-244.43)], acute kidney injury [ROR(95CI)=3.29 (1.36-7.94)], and atrial fibrillation [ROR(95CI)=6.91 (2.86-16.69)].

Conclusion

This study provides crucial real-world safety data on SG, complementing existing clinical trial information. Practitioners should identify contributing factors, employ monitoring and intervention strategies, and focus on adverse events like neutropenic sepsis, large intestine perforation, and hepatic failure. Further prospective studies are needed to address these safety concerns for a comprehensive understanding and effective management of associated risks.

Post-Marketing Safety Concerns with Esketamine: A Disproportionality Analysis of Spontaneous Reports Submitted to the FDA Adverse Event Reporting System

INTRODUCTION

Esketamine nasal spray received approval for treatment-resistant depression in March 2019.

OBJECTIVE

Using the FDA Adverse Event Reporting System (FAERS) database (March 2019-March 2020), we analysed esketamine-related adverse events (AEs) to detect and characterize relevant safety signals.

METHODS

We used the consolidated case/non-case approach to estimate the reporting odds ratio (ROR) and information component (IC) with relevant confidence intervals (95% CI) for esketamine-related AEs with ≥4 counts. Comparisons between serious and non-serious AEs were performed using non-parametric tests.

RESULTS

The FAERS database contained 962 cases of esketamine-related AEs, with signals detected for several AEs, such as dissociation (ROR = 1,612.64, 95% CI = 1,354.63, 1,919.79; IC = 8.19, 95% CI = 7.96, 8.35), sedation (ROR = 238.46, 95% CI = 202.98, 280.15; IC = 7, 95% CI = 6.75, 7.18), feeling drunk (ROR = 96.17, 95% CI = 61.42, 150.57; IC = 4.84, 95% CI = 4.09, 5.36), suicidal ideation (ROR = 24.03, 95% CI = 18.72, 30.84; IC = 4.31, 95% CI = 3.9, 4.61), and completed suicide (ROR = 5.75, 95% CI = 3.18, 10.41; IC = 2.25, 95% CI = 1.23, 2.94). Signals for suicidal and self-injurious ideation, but not suicide attempt and completed suicide, remained when comparing esketamine to venlafaxine. Females and patients receiving antidepressant polypharmacy, co-medication with mood stabilizers, antipsychotics, benzodiazepines, or somatic medications were more likely to suffer from serious versus non-serious AEs (χ2 = 125.29, p < 0.001, χ2 = 9.08, p = 0.003, χ2 = 8.14, p = 0.004, χ2 = 19.48, p < 0.001, χ2 = 25.62, p < 0.001, and χ2 = 16.79, p < 0.001, respectively).

CONCLUSIONS

Esketamine may carry a clear potential for serious AEs, which deserves urgent clarification by means of further prospective studies.

Antipsychotics and cardiovascular risk: A case/non-case study

Severe mental disorders have been reported to be associated with an increased cardiovascular risk. To measure the potential risk excess as compared, not with the baseline cardiovascular risk for the general population, but with the cardiovascular risk associated with drug iatrogenia. 197 reported cases of cardiovascular adverse reaction to antipsychotic drugs as compared to the reported cases of this type of adverse reactions to drugs other than antipsychotics entered in the Spanish Pharmacovigilance System database (FEDRA) (1995-2018) in an observational case/non-case study. Risk estimates of association were reporting odds ratio (ROR), and, chi-square test (χ²). Overall disproportionality for the whole drug class was found [ROR 2.3 (95% CI 2.0-2.7)], χ² = 127.07]. When the two types of antipsychotics (typical and atypical) were analysed separately, we also found statistically significant disproportionality, and this disproportionality is similar between both groups, with disproportionality measures around 2.30, with the confidence intervals not including the 1. The disproportionality observed suggests a risk excess that might be greater than expected, which holds particularly true for torsade de pointes, sudden death and cardiac arrhythmias in patients treated with any of the two types of antipsychotics. There was no significant risk for ischaemic heart disease.

Risk of hospital admission for liver injury in users of NSAIDs and nonoverdose paracetamol: Preliminary results from the EPIHAM study

PURPOSE

The SALT study found similar per-user risks of acute liver failure (ALF) leading to transplantation (ALFT) between NSAIDs and a threefold higher risk in nonoverdose paracetamol (NOP) users. The objective of EPIHAM was to identify the risks of hospital admission for acute liver injury (ALI) associated with NSAIDs and NOP.

METHODS

Case-population study in the 1/97 sample of the French population claims database. Acute liver injury was identified from hospital discharge summaries, from 2009 to 2013. Exposure for cases was dispensing of NSAID or NOP resulting in exposure within 30 days before admission. Population exposure was the number of patients using the drugs over the study timeframe and total number of DDD dispensed.

RESULTS

Of 63 cases of ALI, 13 had been exposed to NSAIDs and 24 to NOP. Events per million DDD (95% CI) ranged from 0.46 (0.09-1.34) (ketoprofen) to 1.43 (0.04-7.97) (diclofenac combinations), 0.43 (0.23-0.73) all NSAIDs combined, 0.58 (0.37-0.86) for NOP. There was no association with average duration of treatment. Per patient risk ranged from 19.5 (5.31-49.9) (ibuprofen) per million users to 37.2 (19.8-63.6) all NSAIDs combined, 58.0 (37.2-86.3) for NOP. There was a linear relationship between average treatment duration and per-user risk (R²  = 0.51, P < .05 for NSAIDs, R²  = 0.97, P < .01 for NOP).

CONCLUSIONS

Risk of hospital admission for ALI with NSAIDs and NOP was similar and indicative of a dose and duration-related effect (pharmacological) effect. Acute liver injury rates were not predictive of ALFT risk.

Cardiovascular and gastrointestinal safety of selective cyclooxygenase-2 inhibitors: a case/non-case study

Background Coxibs cardiovascular (CV) safety continues being a current issue after rofecoxib worldwide withdrawal in 2004. Objective To evaluate the cardiovascular and gastrointestinal (GI) risk of coxibs through case/non-case study. Setting The Spanish Pharmacovigilance System for Human Use Drugs (FEDRA) and the Uppsala Monitoring Centre (VigiBase) databases. Method We identified adverse drug reactions (ADRs) cases reported under the MedDRA system organ classes of "cardiac disorders", "vascular disorders", "nervous system disorder" and "gastrointestinal disorders". Disproportionality was considered when the following criteria were met simultaneously: proportional reporting ratio (PRR) ≥ 2, 95% confidence interval lower limit of reporting odds ratio (ROR) > 1, Chi square test (χ²) ≥ 4; and number of ADR reports (n rep.) > 3. Main outcome measure Potential disproportionality between cardiovascular and GI ADRs as reported to FEDRA and VigiBase and the use of coxibs. Results We found association between coxibs and CV-ADRs in FEDRA [PRR 2.11 (95% CI 1.97-2.27); ROR 2.53 (95% CI 2.29-2.89); χ² 367.81; n rep., 561] and VigiBase [PRR 2.67 (95% CI 2.64-2.71); ROR 3.26 (95% CI 3.20-3.31); χ² 23,950.93; n rep., 21,047]; and between coxibs and GI-ADRs in VigiBase [PRR 2.91 (95% CI 2.84-2.97); ROR 3.08 (95% CI 3.01-3.16); χ² 8762.82; n rep. 6954]. No association was found between coxibs and GI-ADRs in FEDRA. Conclusion The association found support a potential coxibs class effect in terms of cardiovascular safety. Classical NSAIDs GI risk may be higher than that for coxibs.

Active surveillance of severe cutaneous adverse reactions: A case-population approach using a registry and a health care database

PURPOSE

The "case-population" design has been proposed for the surveillance of rare events like Stevens-Johnson syndrome/toxic epidermal necrolysis (SJS/TEN), wherein a registry of cases is combined with sales data from the source population in order to estimate crude odds ratios (ORs). A major drawback of this method is the inability to distinguish between new and non-new users of drugs, which for the study of hypersensitivity reactions is of utmost importance.

METHODS

We have explored an approach in which the exposure to the drugs of interest in the source population is inferred from a primary health care database (BIFAP), which helped us to identify drug initiators among all users and additionally adjust for potential confounders. A total of 44 SJS/TEN cases from the Registry and 44 000 controls randomly sampled from BIFAP and matched with cases for index date were included. We estimated the adjusted ORs (AORs) and 95% confidence intervals (CI) of SJS/TEN associated with the new use of 13 drugs (for which we had at least two exposed cases) through a conditional logistic regression model.

RESULTS

AORs (95% CI) were estimated for phenytoin, 4618 (434-49112); cotrimoxazole, 1142 (163-8015); allopurinol, 160 (36-709); dexamethasone, 38 (1.33-1077); ibuprofen, 33 (8.6-124); lorazepam, 27 (5.8-124); paracetamol, 13 (2.8-62); levofloxacine, 12 (1.24-120); amoxicillin, 6.9 (1.39-35); pantoprazole, 6.5 (0.10-420); metamizole, 6.3 (0.69-57); amoxicillin clavulanic acid, 4.2 (0.53-34); and omeprazole, 1.34 (0.06-31). The inclusion of non-new users dramatically decreased the AORs for all drugs.

CONCLUSIONS

The case-population approach using a registry of cases and a primary health care database proved feasible and efficient for the active surveillance of SJS/TEN.

Vaccine Case-Population: A New Method for Vaccine Safety Surveillance

INTRODUCTION

The case-population approach compares exposure among cases to that of their source population. By using aggregated data to estimate the denominator, this approach can provide a real-time estimate of an association that could be particularly valuable to explore urgent vaccine safety concerns and to generate signals during a vaccine campaign.

OBJECTIVE

Our objective was to present the vaccine case-population method, a method derived from the case-population approach and adapted for vaccine safety surveillance, and to test it using several published examples.

METHODS

For the vaccine case-population method, exposure in the population is estimated from the sum of at-risk periods using the number of vaccinated individuals, or data of vaccine sales, and the at-risk period considered for the vaccine-event pair. The vaccine case-population method was applied to data from published case-control studies retrieved from the MEDLINE database and having quantified risks associated with vaccines. Odds ratios derived from the vaccine case-population method were compared with those from published case-control studies.

RESULTS

A total of 20 vaccine-event pairs were retrieved in which the vaccine case-population method could be applied. For all identified vaccine-event pairs, when a significant association was found using the vaccine case-population method, a significant association was also found in the corresponding case-control study. Conversely, when no association was found by the vaccine case-population method, no association was found in the corresponding case-control study.

CONCLUSION

These results suggest that the vaccine case-population method can produce coherent conclusions and may be used in the future for prospective investigation of urgent vaccine safety concerns or for the prospective generation of vaccine safety signals. This method could also be used to identify selection bias from cases excluded from the case-control study.

Identifying associations between maternal medication use and birth defects using a case-population approach: an exploratory study on signal detection

BACKGROUND

The effects of many drugs on the unborn child are unknown. In a case-population design, drug exposure of cases is compared with that of a source population; this kind of study can be useful for generating signals.

OBJECTIVE

To see whether a comparison of drug use rates from the birth defect registry EUROCAT NNL (cases) with prescription rates from a population-based prescription database, the IADB (population), could be used to detect signals of teratogenic risk of drugs.

METHODS

We defined 3,212 cases from the EUROCAT NNL database, a population-based birth defect registry in the Northern Netherlands and 29,223 population controls from the IADB, a prescription database with data from community pharmacies in the same geographical area, born between 1998 and 2008. We classified the malformations of the 3,212 cases into several malformation groups according to organ system (based on the International Classification of Diseases codes and the EUROCAT guidelines). If a child had multiple malformations in several organ systems (n = 253, 7.9 %), he/she was counted in all the categories represented. For several groups of malformations we calculated rate ratios (RR) and 95 % confidence intervals for drugs acting on the central nervous system and for drugs considered to be safe for use in pregnancy. The RRs were based on first-trimester drug use rates from the cases in the EUROCAT NNL database and prescription rates from the population controls in the IADB.

RESULTS

For drugs acting on the central nervous system we found significantly increased RRs for the anti-epileptic drug valproic acid and for some selective serotonin reuptake inhibitors. For drugs considered to be safe only the anti-hypertensive methyldopa showed significantly increased RRs.

CONCLUSION

We show that a case-population study is a suitable method for detecting signals of possible teratogenicity, provided that the teratogenic effects and the drugs under study are as specific as possible and the drugs are widely used.

Sources of European drug consumption data at a country level

OBJECTIVES

This study aimed at outlining the characteristics of nationwide administrative databases monitoring drug consumption in Europe.

METHODS

Internet and bibliographic databases (April 2010) were searched and experts in drug utilization (DU) research interviewed to find nationwide administrative medicines consumption databases in Europe, with data for the out- and inpatient healthcare sector. A questionnaire was developed to gather additional information. We collected data providers, websites, accessibility, data sources, healthcare settings, population coverage, medicines-related data, patient and prescriber data, periods covered, and linkage to other databases.

RESULTS

Thirty-one administrative nationwide medicine consumption databases in 25 countries were identified. Questionnaires were responded for 20 databases. Eleven provided wholesalers' sales data, 11 on reimbursed, 5 on prescribed, and 4 on dispensing medicines. Fifteen databases provided inpatient drug consumption data, mainly wholesalers' sales.

CONCLUSIONS

Nationwide administrative databases are of value to all stakeholders involved in the conduct and interpretation of post-marketing safety studies, and in the conduct of DU research. The endorsement of the anatomical therapeutic chemical/defined daily dose methodology by these databases contributes to data harmonization. However, there is still a lack of information on inpatient medicines consumption at a patient-level.

The case-population study design: an analysis of its application in pharmacovigilance

BACKGROUND

The case-population approach or population-based case-cohort approach is derived from the case-control design and consists of comparing past exposure to a given risk factor in subjects presenting a given disease or symptom (cases) with the exposure rate to this factor in the whole cohort or in the source population of cases. In the same way as the case-control approach, the case-population approach measures the disproportionality of exposure between cases of a given disease and their source population expressed in the form of an odds ratio approximating the ratio of the risks in exposed and not-exposed populations (relative risk).

OBJECTIVE

The aim of this study was to (i) present the case-population principle design in a way understandable for non-statisticians; (ii) propose the easiest way of using it for pharmacovigilance purposes (mainly alerting and hypothesis testing); (iii) propose simple formulae for computing an odds ratio and its confidence interval; (iv) apply the approach to several practical and published examples; and (v) discuss its pros and cons in the context of real life.

METHODS

The approach used is derived from that comparing two rates expressed as person-time denominators. It allows easy computation of an odds ratio and its confidence interval under several hypotheses. Results obtained with the case-population approach were compared with those of case-control studies published in the literature.

RESULTS

Relevance and limits of the proposed approach are illustrated by examples taken from published pharmacoepidemiological studies. The odds ratio (OR) reported in a European case-control study on centrally acting appetite suppressants and primary pulmonary hypertension was 23.1 (95% CI 6.9, 77.7) versus 31 (95% CI 16.2, 59.2) using the case-population approach. In the European case-control studies SCAR (Severe Cutaneous Adverse Reactions) and EuroSCAR on the risk of toxic epidermal necrolysis associated with the use of medicines, the OR for cotrimoxazole was 160 and 102, respectively, versus 44.4 using the case-population approach. Similarly, these two case-control studies found ORs of 12 and 72 for carbamazepine versus 24.4 using the case-population approach, 8.7 and 16 for phenobarbital versus 21.9, 12 for piroxicam (analysed in the SCAR study only) versus 14.5, and 5.5 and 18 for allopurinol versus 3.4 using the case-population approach.

CONCLUSIONS

Being based on the estimate derived from sales statistics of the total exposure time in the source population of cases, the method can be used even when there is no information about the actual number of exposed subjects in this population. Although the case-population approach suffers from limitations stemming from its main advantage, i.e. impossibility to control possible confounders and to quantify the strength of associations due to the absence of an ad hoc control group, it is particularly useful to use in routine practice, mainly for purposes of signal generation and hypothesis testing in drug surveillance.

Risk of acute liver injury associated with the use of drugs: a multicentre population survey

BACKGROUND

Acute liver injury of uncertain aetiology is often drug related and quantitative information about the associated risk is scarce.

AIM

To estimate the risk of acute liver injury associated with the use of drugs.

METHODS

In a population survey study, 126 cases of acute liver injury were prospectively assembled from January 1993 to December 1999, in patients over 15 years of age, in 12 hospitals in Barcelona (Spain). We estimated the relative risk for each drug as the ratio between the incidence of acute liver injury among the exposed population to the drug and the incidence of acute liver injury among those not exposed to it. Drug consumption data were used to estimate the exposed population.

RESULTS

Isoniazid, pyrazinamide, rifampicin, amoxicillin with clavulanic acid, erythromicin, chlorpromazine, nimesulide, and ticlopidine presented the highest risk (point relative risk > 25). Amoxicillin, metoclopramide, captopril and enalapril, furosemide, hydrochlorothiazide, fluoxetine, paroxetine, diazepam, alprazolam, lorazepam, metamizole, low-dose acetylsalicylic acid and salbutamol showed the lowest risk (point relative risk < 5).

CONCLUSIONS

This study provides a risk estimation of serious liver disease for various drugs that will be useful in its diagnosis and management, and when comparing with the drug therapeutic benefit in each indication. Some observed associations would be worth specific studies.

Estimating post-marketing exposure to pharmaceutical products using ex-factory distribution data

The pharmaceutical industry has an obligation to identify adverse reactions to drug products during all phases of drug development, including the post-marketing period. Estimates of population exposure to pharmaceutical products are important to the post-marketing surveillance of drugs, and provide a context for assessing the various risks and benefits, including drug safety, associated with drug treatment. This paper describes a systematic approach to estimating post-marketing drug exposure using ex-factory shipment data to estimate the quantity of medication available, and dosage information (stratified by indication or other factors as appropriate) to convert the quantity of medication to person time of exposure. Unlike the non-standardized methods often used to estimate exposure, this approach provides estimates whose calculations are explicit, documented, and consistent across products and over time. The methods can readily be carried out by an individual or small group specializing in this function, and lend themselves to automation. The present estimation approach is practical and relatively uncomplicated to implement. We believe it is a useful innovation.