Cutaneous adverse reactions to antibiotics

Author: Dr Aarthy Uthayakumar, Core Medical Trainee, University College Hospital London, UK. DermNet NZ Editor-in-Chief: A/Prof Amanda Oakley, Dermatologist, Hamilton, New Zealand. 4 March 2018.

What are antibiotics?      

Antibiotics are drugs used to treat bacterial infections.

  • They are mainly derived from soil bacteria and fungi, but there are also semi-synthetic and synthetic varieties that are made purely in a laboratory.
  • They have several different mechanisms of action, allowing them to inhibit bacterial growth (bacteriostatic) or kill bacteria (bactericidal).

What is an adverse drug reaction?

An adverse drug reaction (ADR) is an unintended response to a drug at doses normally used for disease therapy. Cutaneous ADRs are ADRs affecting the skin.

Cutaneous adverse reactions to antibiotics

Who gets adverse drug reactions?

ADRs are common, particularly in hospital inpatients, with estimates of 2–3% of hospitalised patients experiencing an ADR, and 1 in 20 of them being potentially fatal. [1,2].  

Cutaneous ADRs account for 10–30% of ADRs, and are most commonly due to antibiotics [1]. The reactions can vary in severity; most are mild-moderate, but severe reactions are estimated to occur in 0.1–2% of cases [2]. 

How are adverse drug reactions classified?

ADRs can be classified as either non-immunological or immunological.

  • The majority of adverse drug reactions are non-immunologically mediated.
  • The reactions are often predictable pharmacological side effects.
  • Dose-related ADRs may be due to underlying renal or hepatic disease.
  • The ADRs can also be unpredictable and idiosyncratic.

Non-immunological adverse drug reactions

Non-immunological ADRs caused by antibiotics include:

Antibiotic-induced cutaneous infections

Immunological adverse drug reactions

There are 4 main types of immunologically mediated hypersensitivity or allergic responses to drugs. These make up approximately 20% of ADRs [3]:

  • Type 1 reaction is an immediate hypersensitivity reaction to a drug and occurs within minutes to hours, due to pre-formed antigen specific IgE antibodies and mast cell degranulation. It results in anaphylaxis, angioedema, and urticaria due to rapid vasodilation and increased vascular permeability.
  • Type 2 reaction is less common and is due to the development of specific antibodies to the drug, resulting in stimulation or inhibition of pathways.  
  • Type 3 reaction is due to immune complexes of drug and antibody deposited in tissues. An example is cutaneous vasculitis, in which deposition and subsequent complement activation in the blood vessels in the skin leads to palpable purpura. Type 3 reactions can be delayed from 1–3 weeks after exposure.
  • Type 4 or cell-mediated delayed responses to drugs develop over several hours. They are caused by immune T-cell responses and release of cytokines (immune mediators).  Most severe cutaneous adverse reactions are Type 4 reactions.

Severe ADRs to some antibiotics, such as Stevens Johnson syndrome due to sulphonamides, are caused by complex immunological mechanisms [3].

How are cutaneous drug reactions classified?

Rashes due to antibiotics are most often morbilliform (exanthematous) or urticarial [1].

It usually takes 7–10 days to become allergic to a drug, so if a reaction is rapid, it is either non-immunological or it is due to previous encounter of the same drug or a chemically similar substance [4].

Morbilliform eruption

  • Morbilliform eruption is the most common type of antibiotic rash. It is also called an exanthem.
  • The exact pathogeneisis is unclear. Some morbilliform eruptions do not recur when the patient is re-exposed to the drug.
  • Many antibiotics cause morbilliform eruptions.
  • A morbilliform rash usually starts within 7–14 days of starting a new antibiotic, and lasts for 5–10 days [4,5]. It may occur more quickly on re-exposure to the same drug.
  • It can look similar to a viral exanthem, but is usually pruritic, whereas similar viral rashes are not particularly itchy.
  • The morphology consists of fine pink macules or papules, hence it is sometimes called a maculopapular eruption.
  • The rash starts as a relatively symmetrical but often widespread eruption on the trunk and progresses to involve the proximal then distal limbs.
  • There is no mucosal involvement.
  • The rash may be more prominent on pressure-bearing points.
  • Systemic features may include fever and leucocytosis or lymphopenia on blood testing [5].

Acute urticaria

  • Acute urticaria is the second most common form of cutaneous drug reaction.
  • Many antibiotics can cause urticaria.
  • It presents as pruritic, pale or erythematous wheals.
  • Individual wheals last less than 24 hours.
  • The most common antibiotics causing urticaria are beta-lactams, sulphonamides and tetracyclines [1].

Several other adverse drug reactions affecting the skin can be due to antibiotics and are listed below alphabetically.

Acneiform rash

Acute generalised exanthematous pustulosis (AGEP)

  • AGEP is a rare reaction where sterile, superficial, small pustules, 1–2 mm diameter, develop in areas of extensive erythema.
  • AGEP is most often caused by beta lactams, sulfonamides and tetracyclines.
  • It usually develops within 1–2 days of starting a new drug. 
  • Pustules are followed by desquamation, with healing after approximately 2 weeks.
  • Internal organ involvement is rare [7].

Angioedema and anaphylaxis 

  • Angioedema, anaphylaxis and urticaria are immediate type 1 hypersensitivity reactions.
  • Antibiotics are the most frequent drug cause.
  • This is characterised by widespread vasodilation and increased vascular permeability, and subsequent deep soft tissue swelling, hypotension, and airway obstruction.
  • Anaphylaxis is a life-threatening medical emergency. Angioedema can also be life threatening due to airway involvement, and can be persistent [1,4,7].

Drug hypersensitivity syndrome (DHS)

  • DHS is also known as drug reaction with eosinophilia and systemic symptoms (DRESS).
  • Antibiotic causes include sulfonamides and less often, fluoroquinolones and minocycline.
  • DHS is a rare, life-threatening syndrome typically defined by the triad of fever, skin eruption and internal organ involvement [12].
  • It usually begins 2–6 weeks after drug exposure.
  • There is usually a widespread morbilliform rash, high fever, lymphadenopathy, haematological abnormalities, and internal organ involvement such as hepatitis [7].

Drug-induced pemphigus

  • Pemphigus is caused due to auto-antibodies reacting with desmogleins.
  • Antibiotic causes of pemphigus include penicillin, cephalosporin and vancomycin.
  • Blistering may resolve after drug withdrawal, but more often persists with the same natural history as non-drug associated pemphigus [4].

Erythema multiforme (EM)

  • EM is characterised by target lesions: these are darker in the centre, paler peripherally, with concentric rings of erythema [4].
  • It is classified into EM minor and EM major (in which there is mucosal involvement).
  • EM is most commonly caused by infection, especially herpes simplex virus (HSV).
  • Some cases due to antibiotics have been reported. These include sulphonamides and penicillins.
  • Note that EM is a different reaction to SJS/TEN (see below), but these diseases were originally thought to be due to the same process.

Fixed drug eruption

  • Fixed drug eruption presents as one or more localised skin lesions that recur with repeated drug exposure in the same location.
  • It may be caused by tetracycline antibiotics, cotrimoxasole, amoxicillin, ciprofloxacin, clarithromycin and others. Antibiotics in meat have also been incriminated.
  • Lesions usually appear 1–2 weeks after the first exposure, and within hours or a few days on subsequent exposure [1].
  • Lesions have predilection for the face, lips, genitalia and buttocks, although they can appear anywhere.
  • The fixed drug eruption starts an erythematous macule and progresses over a few days to form a blistered plaque.
  • The rash may itch or cause a burning sensation.

Hypersensitivity vasculitis

  • The hallmark of hypersensitivity vasculitis is palpable purpura (papules, plaques, bullae and erosions/ulcers).
  • Beta-lactam and sulfonamide antibiotics are the most common group of drugs to cause vasculitis.
  • Palpable purpura most commonly affects the lower legs but may become widespread.
  • The interval from exposure to onset of rash ranges from days to weeks.
  • Serum sickness-like reaction is a form of hypersensitivity vasculitis with specific skin features: erythema on the sides of fingers, hands and toes, followed by a more widespread morbilliform or urticarial eruption [1]. The rash usually occurs 2 weeks after exposure to the causative drug, accompanied by a low grade fever and arthralgia.
  • Complement levels are low in drug-induced hypersensitivity vasculitis [7].

Photosensitive reactions 

Stevens-Johnson syndrome / toxic epidermal necrolysis (SJS/TEN)

  • SJS/TEN is a serious, potentially fatal, systemic mucocutaneous reaction that is nearly always caused by a drug.
  • The most common antibiotics causing SJS/TEN are sulfonamides and penicillins, but many others have been rarely reported.
  • SJS/TEN occurs 4–28 days after the start of drug treatment [6].
  • Management is supportive, and the SCORTEN score can be used to predict morbidity and mortality [7].

Symmetrical drug related intertriginous and flexural exanthem (SDRIFE) 

  • SDRIFE is a delayed hypersensitivity reaction.
  • Amoxicillin and other penicillins account for about 50% of cases [6].
  • It characteristically causes erythema in the intergluteal and inguinal folds.
  • The rash presents and extends more widely over hours to days.

What is the differential diagnosis for antibiotic reactions?

It is sometimes difficult to elucidate whether an antibiotic has caused a rash. Drugs are rarely deliberately given to the affected patient again, as re-challenge has the potential to cause a life-threatening response in some cases. This means the true incidence of drug-inducted adverse drug reaction is difficult to calculate.

There are important differentials to consider when examining a suspected cutaneous drug reaction [8].

Classification of antibiotics causing cutaneous adverse drug reactions

A large number of antibiotics have the potential to cause cutaneous drug reactions. 

Beta lactams

The 4 classes of beta-lactam antibiotics are penicillins, cephalosporins, carbapenems, and monolactams. Allergic reactions to beta-lactam antibiotics are the most common cause of immunological ADR.

  • This is thought to be due to the structure of beta lactams.
  • IgG antibodies to penicillin can be detected in allergic patients and in non-allergic patients taking penicillin [9.10].

There is some cross reactivity between penicillins and cephalosporins.

  • If a patient has an anaphylactic response to penicillins, cephalosporins should be avoided.  

Cutaneous adverse reactions caused by beta lactams include

Though structurally similar, carbapenems can usually be safely used in patients with anaphylactoid reactions to penicillin. The major non-cutaneous side effects of beta-lactam use are diarrhoea, increased Clostridium difficile, and drug-induced liver injury, particularly due to co-amoxiclav.


In comparison to most other antibiotics, macrolides are considered relatively safe drugs.

  • Their side effects tend to be due to interactions with other drugs, due to their inhibition of the cytochrome p450 system.
  • Reports of morbilliform and urticarial rashes, and rarely SJS/TEN, have been reported [7,14].
  • Other non-cutaneous reactions include QT prolongation and liver injury.


Tetracycline antibiotics are frequently used in dermatology. Possible cutaneous reactions are:


Several older generation fluoroquinolones have been withdrawn from the market due to severe adverse reactions including photosensitivity [17].

Side effects of current generation quinolones include tendinopathy and QT prolongation. Common cutaneous reactions are:


Co-trimoxazole is a sulfonamide antibiotic commonly used in immunocompromised individuals, who are already more at risk of adverse drug reactions. The most frequent are morbilliform or urticarial rash; however serious ADRs can result, most commonly SJS [16]. Observed cutaneous drug reactions include:

Non-cutaneous reactions include thrombocytopenia, anaemia, and electrolyte abnormalities [4].


  • Red man syndrome is a histamine-mediated reaction to the rapid infusion of vancomycin, and is not an allergic reaction. This reaction can be minimised by administering the drug slowly when given intravenously [11].
  • DHS [5,13]
  • Non-cutaneous adverse reactions include thrombocytopenia [5]

Other antibiotics

How are antibiotic reactions diagnosed?

It is essential to take a careful history in the diagnosis of cutaneous drug reactions. Many affected patients have been taking several drugs. Form a timeline, including the initiation of any new drugs and the rash onset.

Sometimes, a skin biopsy will be taken to clarify the inflammatory pattern. The presence of eosinophils can be a helpful clue to drug cause, but is non-specific.

What is the treatment for antibiotic reactions?

The first principle of management is withdrawal of the causative drug.

Other measures include:


Antibiotics are one of the greatest discoveries in medicine, but they are not without complications.

Cutaneous side effects are commonly experienced, and have the potential to be life threatening, especially in at risk groups. Among the classes, penicillins, cephalosporins, sulfonamides and fluoroquinolones are the most common causes of cutaneous reactions, particularly severe ones.


Related Information


  1. P. Iannini, L. Mandell, J. Felmingham, G. Patou & G.S. Tillotson (2006) Adverse Cutaneous Reactions and Drugs: A Focus on Antimicrobials. Journal of Chemotherapy, 18:2, 127-139. PubMed.
  2. Marzano AV, Borghi A, Cugno M. Adverse drug reactions and organ damage: The skin. European Journal of Internal Medicine. 2016 Mar 31;28:17-24. PubMed.
  3. Riedl MA, Casillas AM. Adverse drug reactions: types and treatment options. American Family Physician. 2003 Nov 1;68(9):1781-94. Journal.
  4. Ardern‐Jones MR, Friedmann PS. Skin manifestations of drug allergy. British Journal of Clinical Pharmacology. 2011 May 1;71(5):672-83. PubMed Central.
  5. Wright J, Paauw DS. Complications of antibiotic therapy. Medical Clinics. 2013 Jul 1;97(4):667-79. PubMed.
  6. Harr T, French LE. Severe cutaneous adverse reactions: acute generalized exanthematous pustulosis, toxic epidermal necrolysis and Stevens-Johnson syndrome. Medical Clinics of North America. 2010 Jul 31;94(4):727-42. PubMed.
  7. Duong TA, Valeyrie-Allanore L, Chosidow O. Severe cutaneous adverse reactions to drugs. Lancet May 2017;390: 1996-2011. PubMed.
  8. Bachot N, Roujeau JC. Differential diagnosis of severe cutaneous drug eruptions. American Journal of Clinical Dermatology. 2003 Aug 1;4(8):561-72. PubMed.
  9. Blanca M, Vega JM, Garcia J et al. New aspects of allergic reactions to betalactams: cross reactions and unique specificities. Clinical and Experimental Allergy 1994; 24: 407- 415. PubMed.
  10. Edwards RG, Dewdney JM, Dobrzanski DL. Immunogenicity and allergenicity studies on two beta lactam structures, a clavam, clavulanic acid, and a carbapenem: structure-activity relationships. Int Archs Allergy Appl Immun 1988; 85: 184-189. PubMed.
  11. Cunha BA. Antibiotic side effects. Medical Clinics of North America. 2001 Jan 1;85(1):149-85. PubMed.
  12. Wolf R, Orion E, Marcos B, Matz H. Life-threatening acute adverse cutaneous drug reactions. Clinics in Dermatology. 2005 Apr 30;23(2):171-81. PubMed.
  13. Lin YF, Yang CH, Sindy H, Lin JY, Rosaline Hui CY, Tsai YC, Wu TS, Huang CT, Kao KC, Hu HC, Chiu CH. Severe cutaneous adverse reactions related to systemic antibiotics. Clinical Infectious Diseases. 2014 Mar 5;58(10):1377-85. PubMed.
  14. Igea JM, Quirce S, De la Hoz B, Fraj J, Pola J, Diez GM. Adverse cutaneous reactions due to macrolides. Annals of Allergy. 1991 Mar;66(3):216-8. PubMed.
  15. Halkin H. Adverse effects of the fluoroquinolones. Reviews of infectious diseases. 1988 Jan 1;10(Supplement_1):S258-61. PubMed.
  16. Leone R, Venegoni M, Motola D, Moretti U, Piazzetta V, Cocci A, Resi D, Mozzo F, Velo G, Burzilleri L, Montanaro N, Conforti A. Adverse drug reactions related to the use of fluoroquinolone antimicrobials: an analysis of spontaneous reports and fluoroquinolone consumption data from three italian regions. Drug Saf. 2003;26(2):109-20. PubMed PMID: 12534327. PubMed.
  17. Chantachaeng W, Chularojanamontri L, Kulthanan K, Jongarearnprasert K, Dhana N. Cutaneous adverse reactions to sulfonamide antibiotics. Asian Pacific journal of allergy and immunology. 2011 Sep 1;29(3):284. PubMed.

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