Drug-related side effects and adverse reactions

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Drug toxicity, also called adverse drug reaction (ADR) or adverse drug event (ADE), is defined as "manifestations of the adverse effects of drugs administered therapeutically or in the course of diagnostic techniques. It does not include accidental or intentional poisoning..."[1] The meaning of this expression differs from the meaning of "side effect", as this last expression might also imply that the effects can be beneficial.[2]

Classification

Cause

The World Health Organization (WHO) classifies ADRs by cause:[3]

  • Type A: pharmacologically predictable. In a study of older adults, this type was the most common with the most common offending drugs being warfarin, insulin, and digoxin.[4]
  • Type B: bizarre and unpredictable (idiosyncratic)
  • Type C: arising from chronic use
  • Type D: delayed reaction
  • Type E: end of dose reaction
  • Type F: failure of therapy

Types A and B were proposed in the 1970s,[5] and the other types were proposed subsequently when the first two proved insufficient to classify ADRs.[6]

Describing ADRs

ADRs may be described by their frequency and severity

Frequency

The World Health Organization recommends standardization of descriptions of frequency.[7] Although the WHO document is not currenlty available online, their recommendations have been summarized by others.[8]

  • very common (>1/10 patients)
  • common (>1/100)
  • uncommon (>1/1000)
  • rare (>1/10,000)
  • very rare (<1/100,000)

Severity

The American Food and Drug Administration defines severe effects as:[9]:

  • Death
  • Life-Threatening
  • Hospitalization (initial or prolonged)
  • Disability - significant, persistent, or permanent change, impairment, damage or disruption in the patient's body function/structure, physical activities or quality of life.
  • Congenital Anomaly
  • - or -
  • Requires Intervention to Prevent Permanent Impairment or Damage

Mechanisms

As research better explains the biochemistry of drug use, less ADRs are Type B ('idiosyncratic') and more are Type A (pharmacologically predictable). Common mechanisms are:

  • Abnormal pharmacokinetics due to
    • genetic factors
    • comorbid disease states
  • Synergistic effects between either
    • a drug and a disease
    • two drugs

Abnormal pharmacokinetics

Comorbid disease states

Various diseases, especially those that cause renal or hepatic insufficiency, may alter drug metabolism. Resources are available that report changes in a drug's metabolism due to disease states.[10]

Genetic factors

Abnormal drug metabolism may be due to inherited factors of either Phase I oxidation or Phase II conjugation.[11][12] Pharmacogenomics is the study on the inherited basis of drug reactions.

Phase I reactions

Inheriting abnormal alleles of cytochrome P450can alter drug metabolism. Tables are available to check for drug interactions due to P450 interactions.[13].[14]

Inheriting abnormal butyrylcholinesterase (pseudocholinesterase) may affect metabolism of drugs such as succinylcholine[15]

Phase II reactions

Inheriting abnormal N-acetyltransferase which conjugated some drugs to facilitate excretion may affect the metabolism of drugs such as isoniazid, hydralazine, and procainamide.[15][14]

Inheriting abnormal thiopurine S-methyltransferase may affect the metabolism of the thiopurine drugs mercaptopurine and azathioprine.[14]

Interactions with other drugs

Protein binding

These interactions are usually transient and mild until a new steady state is achieved.[16][17] These are mainly for drugs without much first-pass liver metabolism. The principle plasma proteins for drug binding are:[18]

  1. albumin
  2. α1-acid glycoprotein
  3. lipoproteins

Some drug interactions with warfarin are due to changes in protein binding.[18]

Cytochrome P450

Patients have abnormal metabolism by cytochrome P450 due to either inheriting abnormal alleles or due to drug interactions. Tables are available to check for drug interactions due to P450 interactions.[19].

Synergistic effects

An example of synergism is two drugs that both prolong the cardiac QT interval.

Other factors that my increase ADRs

Polypharmacy

For more information, see: polypharmacy.

The risk of drug interactions may be increased with polypharmacy.

Fragmented health care

When controlled for other factors such as the number of prescribing physicians, the number of medicatations may not be a risk factor for adverse drug reactions.[20]

Assessing causality

A scale proposed by the World Health Organization (WHO) is below:[21][3][2]

Certain

  • "A clinical event, including a laboratory test abnormality, that occurs in a plausible time relation to drug administration, and which cannot be explained by concurrent disease or other drugs or chemicals"
  • "The response to withdrawal of the drug (dechallenge) should be clinically plausible"
  • "The event must be definitive pharmacologically or phenomenologically, using a satisfactory rechallenge procedure if necessary"

Probable/likely

  • "A clinical event, including a laboratory test abnormality, with a reasonable time relation to administration of the drug, unlikely to be attributed to concurrent disease or other drugs or chemicals, and which follows a clinically reasonable response on withdrawal (dechallenge)"
  • "Rechallenge information is not required to fulfil this definition"

Possible

  • "A clinical event, including a laboratory test abnormality, with a reasonable time relation to administration of the drug, but which could also be explained by concurrent disease or other drugs or chemicals"
  • "Information on drug withdrawal may be lacking or unclear"

Unlikely

  • "A clinical event, including a laboratory test abnormality, with a temporal relation to administration of the drug, which makes a causal relation improbable, and in which other drugs, chemicals, or underlying disease provide plausible explanations"

Conditional/unclassified

  • "A clinical event, including a laboratory test abnormality, reported as an adverse reaction, about which more data are essential for a proper assessment or the additional data are being examined"

Unassessable/unclassifiable

  • "A report suggesting an adverse reaction that cannot be judged, because information is insufficient or contradictory and cannot be supplemented or verified"

An alternative scale is the Naranjo algorithm.

Intolerance to multiple drugs

Amplification may contribute to multiple-drug intolerance (if the adverse effects that are reported are non-specific).[22] This is distinct from multiple drug hypersensitivity.[23]

Monitoring bodies

Many countries have official bodies that monitor drug safety and reactions. On an international level, the World Health Organization (WHO) runs the Uppsala Monitoring Centre, and the European Union runs the European Medicines Agency (EMEA). In the United States, the Food and Drug Administration (FDA) is responsible for monitoring post-marketing studies. However, the book, Physicians' Desk Reference, which is a collection of FDA approved drug labels, may contribute to adverse drug effects by systematically underreporting the lowest effect dose of drugs.[24]

References

  1. ↑ National Library of Medicine. Drug toxicity. Retrieved on 2007-11-23.
  2. ↑ 2.0 2.1 Nebeker JR, Barach P, Samore MH (2004). "Clarifying adverse drug events: a clinician's guide to terminology, documentation, and reporting". Ann. Intern. Med. 140 (10): 795-801. PMID 15148066. [e] Cite error: Invalid <ref> tag; name "pmid15148066" defined multiple times with different content
  3. ↑ 3.0 3.1 Edwards IR, Aronson JK (2000). "Adverse drug reactions: definitions, diagnosis, and management". Lancet 356 (9237): 1255–9. DOI:10.1016/S0140-6736(00)02799-9. PMID 11072960. Research Blogging.
  4. ↑ Daniel S. Budnitz et al., “Medication Use Leading to Emergency Department Visits for Adverse Drug Events in Older Adults,” Ann Intern Med 147, no. 11 (December 4, 2007), http://www.annals.org/cgi/content/abstract/147/11/755 (accessed December 5, 2007).
  5. ↑ Rawlins MD, Thompson JW. Pathogenesis of adverse drug reactions. In: Davies DM, ed. Textbook of adverse drug reactions. Oxford: Oxford University Press, 1977:10.
  6. ↑ Aronson JK. Drug therapy. In: Haslett C, Chilvers ER, Boon NA, Colledge NR, Hunter JAA, eds. Davidson's principles and practice of medicine 19th ed. Edinburgh: Elsevier Science, 2002:147-63. ISBN 0-44307-035-0.
  7. ↑ Council for International Organizations of Medical Sciences. Guidelines for preparing core clinical safety information on drugs. Geneva: CIOMS, 1995.
  8. ↑ Hoes JN, Jacobs JW, Boers M, et al (2007). "EULAR evidence-based recommendations on the management of systemic glucocorticoid therapy in rheumatic diseases". Ann. Rheum. Dis. 66 (12): 1560–7. DOI:10.1136/ard.2007.072157. PMID 17660219. Research Blogging.
  9. ↑ MedWatch - What Is A Serious Adverse Event?. Retrieved on 2007-09-18.
  10. ↑ Clinical Drug Use. Retrieved on 2007-09-18.
  11. ↑ Phillips KA, Veenstra DL, Oren E, Lee JK, Sadee W (2001). "Potential role of pharmacogenomics in reducing adverse drug reactions: a systematic review". JAMA 286 (18): 2270–9. PMID 11710893. [e]
  12. ↑ Goldstein DB (2003). "Pharmacogenetics in the laboratory and the clinic". N. Engl. J. Med. 348 (6): 553–6. DOI:10.1056/NEJMe020173. PMID 12571264. Research Blogging.
  13. ↑ Drug-Interactions.com. Retrieved on 2007-09-18.
  14. ↑ 14.0 14.1 14.2 Weinshilboum R (2003). "Inheritance and drug response". N. Engl. J. Med. 348 (6): 529–37. DOI:10.1056/NEJMra020021. PMID 12571261. Research Blogging.
  15. ↑ 15.0 15.1 Evans WE, McLeod HL (2003). "Pharmacogenomics--drug disposition, drug targets, and side effects". N. Engl. J. Med. 348 (6): 538–49. DOI:10.1056/NEJMra020526. PMID 12571262. Research Blogging.
  16. ↑ DeVane CL (2002). "Clinical significance of drug binding, protein binding, and binding displacement drug interactions". Psychopharmacology bulletin. 36 (3): 5–21. PMID 12473961. [e]
  17. ↑ Benet LZ, Hoener BA (2002). "Changes in plasma protein binding have little clinical relevance". Clin. Pharmacol. Ther. 71 (3): 115–21. DOI:10.1067/mcp.2002.121829. PMID 11907485. Research Blogging. OVID full text summary table at OVID
  18. ↑ 18.0 18.1 Sands CD, Chan ES, Welty TE (2002). "Revisiting the significance of warfarin protein-binding displacement interactions". The Annals of pharmacotherapy 36 (10): 1642–4. PMID 12369572. [e]
  19. ↑ Drug-Interactions.com. Retrieved on 2007-09-18.
  20. ↑ Green JL, Hawley JN, Rask KJ (2007). "Is the number of prescribing physicians an independent risk factor for adverse drug events in an elderly outpatient population?". Am J Geriatr Pharmacother 5 (1): 31–9. DOI:10.1016/j.amjopharm.2007.03.004. PMID 17608245. Research Blogging.
  21. ↑ UMC Causality Assessment of Suspected Adverse Reactions. World Health Organization. Retrieved on 2008-01-14.
  22. ↑ Davies SJ, Jackson PR, Ramsay LE, Ghahramani P (2003). "Drug intolerance due to nonspecific adverse effects related to psychiatric morbidity in hypertensive patients". Arch. Intern. Med. 163 (5): 592-600. PMID 12622606. [e]
  23. ↑ Gex-Collet C, Helbling A, Pichler WJ (2005). "Multiple drug hypersensitivity--proof of multiple drug hypersensitivity by patch and lymphocyte transformation tests". J Investig Allergol Clin Immunol 15 (4): 293–6. PMID 16433211. [e]
  24. ↑ Cohen JS (2001). "Dose discrepancies between the Physicians' Desk Reference and the medical literature, and their possible role in the high incidence of dose-related adverse drug events". Arch. Intern. Med. 161 (7): 957–64. PMID 11295958. [e]

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