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Thread: How to estimate the probability of ADRs

  1. #1
    PharmD Year 1 TomHsiung's Avatar
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    Thumbs up How to estimate the probability of ADRs

    How to assess the possibility for the causality between a drug and a drug-induced disease?

    1.Strength of association. Association does not imply causation. This means that while a reaction may appear to occur in tandem with a particular drug, it dose not necessarily imply that the drug caused the reaction.

    Is there a strong association between a suspected drug-induced disease in people taking the drug versus those not taking the drug? If the association is strong (e.g., a relative risk >3), then one would be more confident that a causal effect exists.

    2.Consistency.

    Does the suspected drug-induced disease occur repeatedly in different persons, at different times, and in different places? Indeed, consistency is a hallmark feature that must occur before causality can even be suggested.

    3.Specificity.

    Is the suspected drug-induced disease specific to that drug? For example, individuals who take excessive doses of digitalis for heart failure often see "halos." When they stop taking the drug and the plasma digitalis concentrations decrease, the halo effect disappears. Could there be other causes for these patients seeing halos or is it likely only due to digitalis overdose?

    4.Temporality.

    Does the suspected drug-induced disease manifest before or after drug exposure? To even consider causality, the person must be exposed to the drug before the occurrence of the adverse outcome. If the person is not exposed to the drug before the drug-induced disease occurs, then causality cannot be considered.

    5.Biologic gradient.

    Dose the incidence of the suspected drug-induced disease increase when higher doses of the drug are taken? For example, can we detect increased toxicity with increased doses of a particular drug (e.g., acetaminophen and liver toxicity)?

    6.Plausibility.

    Is the suspected causation plausible? That is, if a particular adverse event occurs after administration of a particular drug, is it biologically (pharmacologically and physiologically) plausible that the drug caused the event or was it merely coincidental?

    7.Coherence.

    Does the suspected causation conflict or support that which is generally known about the disease and it progressive pathology?

    8.Experiment.

    Is it possible to manipulate the degree of exposure to prevent or enhance the outcome? For example, if a particular drug is suspected of causing a rash in a patient, does the rash disappear after discontinuing the medication, and does subsequent rechallenge cause the rash to reappear? (Note that rechallenge is rarely desirable or ethically appropriate in a clinical setting.)

    9.Analogy.

    Can the previous experience with a particular drug causing a particular drug-induced disease be used to enhance our ability to detect or accept a similar outcome with a different drug under similar circumstances? For example, because of the thalidomide debacle of the 1960s, we now know that it is within the realm of possibility that a drug taken during pregnancy can cause birth defects.
    B.S. Pharm, West China School of Pharmacy, Class of 2007, Health System Pharmacist, RPh. Hematology, Infectious Disease.

  2. #2
    PharmD Year 1 TomHsiung's Avatar
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    Default

    Also there is another method called "Naranjo algorithm".



    Questionnaire


    1. Are there previous conclusive reports on this reaction?

    Yes (+1) No (0) Do not know or not done (0)

    2. Did the adverse events appear after the suspected drug was given?

    Yes (+2) No (-1) Do not know or not done (0)

    3. Did the adverse reaction improve when the drug was discontinued or a specific antagonist was given?

    Yes (+1) No (0) Do not know or not done (0)

    4. Did the adverse reaction appear when the drug was readministered?

    Yes (+2) No (-1) Do not know or not done (0)

    5. Are there alternative causes that could have caused the reaction?

    Yes (-1) No (+2) Do not know or not done (0)

    6. Did the reaction reappear when a placebo was given?

    Yes (-1) No (+1) Do not know or not done (0)

    7. Was the drug detected in any body fluid in toxic concentrations?

    Yes (+1) No (0) Do not know or not done (0)

    8. Was the reaction more severe when the dose was increased, or less severe when the dose was decreased?

    Yes (+1) No (0) Do not know or not done (0)

    9. Did the patient have a similar reaction to the same or similar drugs in any previous exposure?

    Yes (+1) No (0) Do not know or not done (0)

    10. Was the adverse event confirmed by any objective evidence?

    Yes (+1) No (0) Do not know or not done (0)

    Scoring

    ≥ 9 = definite ADR
    5-8 = probable ADR
    1-4 = possible ADR
    0 = doubtful ADR

    References

    Naranjo CA, Busto U, Sellers EM et al. (1981). "A method for estimating the probability of adverse drug reactions". Clin. Pharmacol. Ther. 30 (2): 239–45. doi:10.1038/clpt.1981.154. PMID 7249508.
    Last edited by admin; Fri 13th March '15 at 11:37pm.
    B.S. Pharm, West China School of Pharmacy, Class of 2007, Health System Pharmacist, RPh. Hematology, Infectious Disease.

  3. #3
    PharmD Year 1 TomHsiung's Avatar
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    Exclamation Categorisation of Drug-Induced Adverse Events

    Once association between a drug and an adverse event is determined, it is useful to classify the adverse event.

    Four categories have been suggested to aid in the proper management of any iatrogenic illness, including conscious risk, unexpected complications, inept care, and overzealous care.

    Conscious risk and unexpected complications represent adverse events due to "balanced, informed consideration of benefits and risks." In essence, these two types of drug-induced adverse events are part of the normal risk-benefit consideration inherent when prescribing any drug for any condition to any person. That is, there is always the potential for unintended or unpredictable drug effects on the body.

    Inept care and overzealous care represent "errors of omission" and "errors of commission," respectively, and represent inappropriate medication use due to a lack of understanding or education about the drug and its impact in the patient for whom it is prescribed.
    B.S. Pharm, West China School of Pharmacy, Class of 2007, Health System Pharmacist, RPh. Hematology, Infectious Disease.

  4. #4
    PharmD Year 1 TomHsiung's Avatar
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    Default Re: How to estimate the probability of ADRs

    Terms describing the frequencies of adverse drug reactions
    How to estimate the probability of ADRs-screen-shot-2016-07-01-at-4-21-40-pm-png
    B.S. Pharm, West China School of Pharmacy, Class of 2007, Health System Pharmacist, RPh. Hematology, Infectious Disease.

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