The document discusses severity assessment of adverse drug reactions (ADRs). It describes several scales used to assess the causality and severity of ADRs, including: - The WHO-UMC Causality Assessment Scale which categorizes ADR causality as certain, probable, possible, unlikely, conditional/unclassified, or unassessable. - Scales that categorize ADR severity as mild, moderate, severe or lethal based on factors like treatment required and effects on hospitalization. - The Naranjo Algorithm/ADR Probability Scale which assigns a probability score to determine if an ADR is definite, probable, possible, or doubtful based on responses to 10 questions.

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1) WHO–UMC CAUSALITY ASSESSMENTSCALE
Causality term Assessment criteria(all points shouldbe
reasonably complied)
Certain
 Event or laboratory test abnormality, with
plausible time relationship to drug intake
 Cannot be explained by diseaseor other
drugs
 Responseto withdrawalplausible
(pharmacologically, pathologically)
 Event definitive pharmacologically or
phenomenologically (ie. an objective and
specific medical disorder or a recognized
pharmacologic phenomenon)
 Rechallenge satisfactory, if necessary
Probable/likely  Event or laboratory test abnormality, with
reasonabletime relationship to drug intake
 Unlikely to be attributed to diseaseor other
drugs
 Responseto withdrawalclinically reasonable
 Rechallenge not required
Possible  Event or laboratory test abnormality, with
reasonabletime relationship to drug intake
 Could also be explained by disease or other
drugs

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Causality term Assessment criteria(all points shouldbe
reasonably complied)
 Information on drug withdrawalmay be
lacking or unclear
Unlikely  Event or laboratory test abnormality, with a
time to drug intake that makes a
relationship improbable(but not impossible)
 Diseaseor other drugs provideplausible
explanation
Conditional/unclassified  Event or laboratory test abnormality
 More data for proper assessmentneeded,
or
 Additional data under examination
Unassessable/unclassifiable  Report suggesting an adversereaction
 Cannot be judged because information is
insufficient or contradictory
 Data cannot be supplemented or verified

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2) The term severity is often used to describe the intensity of a medical
event, as in grading ‘mild’, ‘moderate’ and ‘severe’. Severity assessment
categorizes the ADRs as mild, moderate, or severebased on the based on
the steps taken for the management of the ADRs.
Karch and Lasagna classified severity into minor, moderate, severeand
lethal as defined below:
i. Minor: no antidote, therapy or prolongation of hospitalization required.
ii. Moderate: requires a changein drug therapy, specific treatment or an
increase in hospitalization by at least 1 day.
iii. Severe: potentially life threatening, causing permanent damage or
requiring intensive medical care.
iv. Lethal: directly or indirectly contributes to the death of the patient.
The USFDA classifies an ADR as serious when it resultsin death, life-
threatening causes, or prolongshospitalization, causesa significant
persistent disability, resultsin a congenital anomaly, or requires
intervention to prevent permanent damage.

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3) Hartwig et al categorized ADRs into seven levels as per their severity.
Level 1 & 2 fall under mild category, level 3 & 4 under moderate and level
5, 6 & 7 fall under category severe.
ADR severity assessmentscale
(ModifiedHartwig andSiegel)
Mild
Level 1: The ADR requires no change in treatment with the suspected drug.
OR
Level 2: The ADRrequires that the suspected drug be withheld,
discontinued or otherwisechanged. No antidote or other treatment is
required, and there is no increase in lenght of stay.
Moderate
Level 3: The ADR requires that the suspected drug be withheld,
discontinued or otherwisechanged, and/ or an antidote or other treatment
is required. There is no increase in lenght of stay.
OR
Level 4 (a): Any level 3 ADRthat increases lenght of stay by at least one day.
OR
Level 4 (b): The ADR is the reason for admission.
Severe
Level 5: Any level 4 ADR that requires intensive medical care.
OR
Level 6: The ADR causes parmanentharm to the patient.
OR
Level 7: The ADR either directly or indirectly leads to the death of the
patient.

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4) Adverse Drug ReactionProbability Scale (Naranjo)
The AdverseDrug Reaction (ADR) Probability Scale was developed in 1991 by
Naranjo and coworkers fromtheUniversity of Toronto and is often referred to as
the Naranjo Scale. The scale was also designed for use in controlled trials and
registration studies of new medications, rather than in routine clinical
practice. Nevertheless, it is simple to apply and widely used. Many publications
on drug induced liver injury mention results of applying the ADRProbability Scale.
The ADR Probability Scale consists of 10 questions that are answered as either
Yes, No, or “Do not know”. Differentpoint values (-1, 0, +1 or +2) are assigned to
each answer. A simplified version of the 10 questions is provided below:
 Are there previous conclusivereports of this reaction?
 Did the adverseevent appear after the drug was given?
 Did the adversereaction improve when the drug was discontinued or a
specific antagonistwas given?
 Did the adversereaction reappear upon readministering the drug?
 Were there other possiblecauses for the reaction?
 Did the adversereaction reappear upon administration of placebo?
 Was the drug detected in the blood or other fluids in toxic concentrations?
 Was the reaction worsened upon increasing the dose? Or, was the reaction
lessened upon decreasing the dose?
 Did the patient have a similar reaction to the drug or a related agent in the
past?
 Was the adverseevent confirmed by any other objective evidence?
The actual ADRProbability Scale formand instructions on how it is completed are
provided below. Total scores rangefrom -4 to +13; the reaction is considered
definite if the scoreis 9 or higher, probable if 5 to 8, possible if 1 to 4, and
doubtful if 0 or less.

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While this scale includes all of the usual features that are important in assessing
causality, the scale is not weighted for the mostcritical elements in judging the
likelihood of drug induced liver injury, such as specific time to onset, criteria for
time of recovery, and list of critical diagnoses to exclude, making the scale of
limited use in assessing hepatotoxicity. The Naranjo scale also relies upon testing
for drug levels, which is rarely helpful in idiosyncratic drug induced liver
disease. Finally, the scalewas designed for use in clinical trials, and points are
subtracted if the reaction reappears with administration of placebo, which does
not apply to the usualcase of drug induced liver disease. Direct comparisons to
the RUCAM system haveshown that the ADRProbability Scale is easier to apply,
but has less sensitivity and specificity in assigning causality to cases of drug
induced liver injury.
Naranjo Algorithm - ADR Probability Scale
The Naranjo Algorithm, or AdverseDrug Reaction Probability Scale, is a method
by which to assess whether there is a causalrelationship between an identified
untoward clinical event and a drug using a simple questionnaire to assign
probability scores.

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Adverse Drug Reaction Probability Scale
Question YesNo
Do Not
Know
Score
1. Are there previousconclusivereportsonthisreaction? +1 0 0
2. Did the adverse eventappearafterthe suspecteddrugwasadministered? +2 -1 0
3. Did the adverse eventimprovewhenthe drugwasdiscontinued oraspecific
antagonistwasadministered?
+1 0 0
4. Did the adverse eventreappearwhenthe drugwasreadministered? +2 -1 0
5. Are there alternativecausesthatcouldontheirownhave causedthe
reaction?
-1 +2 0
6. Did the reactionreappearwhen aplacebowasgiven? -1 +1 0
7. Was the drug detectedinbloodorotherfluidsinconcentrationsknownto
be toxic?
+1 0 0
8. Was the reactionmore severe whenthe dose wasincreasedorlesssevere
whenthe dose wasdecreased?
+1 0 0
9. Did the patienthave a similarreactiontothe same or similardrugsinany
previousexposure?
+1 0 0
10. Was the adverse eventconfirmedbyanyobjective evidence? +1 0 0
Total Score:

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Naranjo Algorithm - ADR Probability Scale
Score Interpretationof Scores
Total
Score
>9
Definite. Thereaction (1) followed a reasonabletemporal sequence
after a drug or in which a toxic drug level had been established in body
fluids or tissues, (2) followed a recognized responseto the suspected
drug, and (3) was confirmed by improvement on withdrawing the drug
and reappeared on reexposure.
Total
Score
5 to 8
Probable. The reaction (1) followed a reasonabletemporal sequence
after a drug, (2) followed a recognized responseto the suspected drug,
(3) was confirmed by withdrawalbut not by exposure to the drug, and
(4) could not be reasonably explained by the known characteristics of the
patient’s clinical state.
Total
Score
1 to 4
Possible. Thereaction (1) followed a temporal sequence after a drug, (2)
possibly followed a recognized pattern to the suspected drug, and (3)
could be explained by characteristics of the patient’s disease.
Total
Score
≤0
Doubtful. The reaction was likely related to factors other than a drug.

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Instructions for Using the ADR Probability Scale
The response“Do not know” should be used sparingly and only when the quality
of the data does not permit a “Yes” or “No” answer. “Do notknow” can be
applicable if the information is not available and also if the question is
inapplicable to the case. When more than one drug is involved or suspected, the
ADR Probability Scale is usually applied separately to each of the possibleetiologic
agents, and the drug with the highest scoreshould be considered the causative
agent. In addition, the potential of interaction should be evaluated.
Question1. Arethere previous conclusive reports on this reaction? The answer
“Yes” (+1) applies if there have been two or more published reports in which the
adversereaction has been described in detail or if the adversereaction is listed in
a reliable source, such as a medical textbook, review article on the medication or
on adversedrug reactions, or the productpackage insert. The response“No”
applies when the adverseevent has not been described previously or if only one
reporthas been published, or if published reports wereconsidered inconclusive
or unconvincing. The answer “Do not know” is applicable only when there is no
information, because the agent has not been available for an adequate period of
time or has not been previously evaluated for this adversereaction. The scores
given for “No” and “Do not know” are the same (0), so it is not critical to decide
between these two answers.
Question2. Did the adverseevent appear after the suspected drug was
administered? This question evaluates the temporal relationship between the
reaction and administration of the medication. The answer “Yes” (+2) applies if
there is definitive evidence that the adverseevent occurred after the medication
was started. “No” (-1) applies when the adverseevent developed before the first
doseof the drug. “Do not know” (0) applies if the information is not available or
is unclear.
Question3. Did the adverseevent improvewhen the drug was discontinued or a
specific antagonistwas administered? This question evaluates the responseto

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dechallenge or stopping the medication. The answer “Yes” (+1) applies if the
adverseevent diminishes or disappears at any time after stopping the medication,
or if the reaction disappears upon administration of a specific pharmacologic
antagonist(for example, an anticholinergic given for a cholinergic reaction to
physostigmine). Theanswer “No” (0) applies if the adverseevent does not
improveor improves in responseto a nonspecific therapy or an antidote to
another medication or treatment of the underlying disease. The answer “Do not
know” (0) applies if the medication was not stopped or the subsequentcourse
was unknown, inconclusiveor unclear.
Question4. Did the adverseevent reappear when the drug was
readministered? This question evaluates the responseto rechallenge or
reexposure. An answer of “Yes” (+2) indicates that the medication was stopped,
the adverseevent resolved or improved, and there was an unequivocal
reappearanceor worsening of the reaction when the medicine was restarted in a
similar doseand by the same route. The Naranjo scale also allows for a “Yes” if
the causalassociation is well known and rechallenge cannot be done for clinical or
ethical reasons. An answer of “No” (-1) only applies if rechallenge was done, but
the adverseevent did not reappear or worsen. The answer “Do not know” (0)
applies if rechallenge was not done or information on rechallenge is not available
or the reaction was ambiguous.
Question5. Arethere alternative causes that could on their own have caused the
reaction? This question assesses alternativeexplanations for the adverse
event. Because adverseevents are often nonspecific and can be manifestations
of the disease being treated or an unrelated, concurrentdiseaseor condition,
other diagnoses need to be considered and excluded. The answer “No” (+2)
applies if alternative causes havebeen excluded, based upon a systematic and
complete evaluation, thus implicating the drug morestrongly. A risk or
susceptibility factor is not an alternative cause. The answer “Yes” (-1) applies
when there is an alternative cause or explanation. “Do not know” (0) applies if
the investigation of other causes is incomplete, inconclusiveor was not done.

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Question6. Did the reaction reappear when a placebo was given? This question
applies to clinical research studies in which a placebo was administered. The
answer “Yes” (-1) applies if the medication was stopped and the adversereaction
resolved or improved conclusively, and there was an unequivocal reappearanceof
the adverseevent after administration of placebo (single or double blind). The
answer “No” (+1) applies if the reaction did not reappear or worsen after
administration of placebo. “Do not know” (0) applies if placebo challenge was not
done or the results were inconclusive.
Question7. Was the drug detected in blood or other fluids in concentrations
known to be toxic? This question applies specifically to dosedependent adverse
reactions when blood, urine, tissueor other specimen concentrations of the
medicine are available. The answer “Yes” (+1) applies if the concentration is in
the accepted toxic or supratherapeutic range. “No” (0) applies if the
concentration is below the toxic range. The answer “Do not know” (0) applies if
drug levels are not available or are inconclusive.
Question8. Was the reaction more severe when the dosewas increased or less
severewhen the dose was decreased? This question evaluates the doseresponse
relationship of medication and the adversereaction. “Yes” (+1) applies if the
adverseevent was more severeor worsened when the dose of the medication
was increased, or was less severeand improved when the dose was
decreased. “No” (0) applies if there was no appreciable change in the severity of
the adverseevent with dosemodification. “Do not know” (0) applies if the dose
or regimen was not altered or the information was not available or inconclusive.
Question9. Did the patient have a similar reaction to the sameor similar drugs in
any previous exposure? This question is directed at past medical history of
adversereactions to the same or a structurally related drug. “Yes” (+1) applies
when there is documentation of a previous similar reaction to the specific drug or
a related medication. “No” (0) applies when the patient does not havea previous
exposureto the same medicine or when the patient did not develop the adverse
reaction in a previous exposureto the same or related drugs. “Do not know” (0)

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applies when there is no information on previous reactions or the information is
inconclusive.
Question10. Was the adverseevent confirmed by any objective evidence? The
final question assesses thequality of the data on which the adverseevent is
assessed. “Yes” (+1) indicates that there is laboratory test documentation of the
adverseevent or that the event was directly observed by a qualified person (for
example, a skin rash described in nursing or physician notes). The answer “No”
(0) applies when neither laboratory tests nor direct clinical documentation can
verify the reaction. “Do not know” (0) applies if there is no specific information
available (no laboratory testing and no clinical description) or the information is
inconclusive. The scores given for “No” and “Do not know” are the same (0), so it
is not critical to decide between these two answers.