- type 2 allergy
- Take an accurate history of any previous reactions to drugs, medicinal and related products and non-drug allergies.
- Examine a drug chart, and decide which drugs might pose a risk to the patient in light of known allergies.
- Recognise the signs and symptoms of allergic reactions to drugs.
- Distinguish allergic reactions from other adverse drug reactions.
- Manage acute allergic reactions to drugs.
- Arrange appropriate follow up in cases of suspected drug reactions.
Allergic Reactions
- mediated by histamine release from mast cells
- activation of mast cells
- directly like aspirin and contrast media
- Immunoglobulin E via penicillins
Any angioedema, urticaria, decrease in PEFR or blood pressure is evidence of an allergic response.
- Allergy to a medicine generally requires prior exposure to the drug in question, a drug of the same class or a cross reacting class.
- Some co-existing conditions can predispose your patients to allergic drug reactions.
- Take a thorough history to avoid withholding medication unnecessarily. You will need to decide whether your patient's description fits with a true allergy, or a non-allergic adverse drug reaction.
- The classic signs of a Type I allergic drug reaction are urticaria, itching, angioedema, bronchospasm, and hypotension. Symptoms typically occur within 30 minutes of drug administration but not necessarily with the first dose.
- Reactions to parenterally administered drugs are generally more severe than to oral medication, with a median time to cardiac arrest of 5 minutes from the first symptoms in extreme reactions.
- Intramuscular adrenaline should always be at hand when parenteral medication is being administered. For severe reactions (laryngeal oedema, bronchospasm, and hypotension), this should be administered as soon as possible.
- The intramuscular dose of adrenaline can kill a patient if given intravenously. Intravenous adrenaline must only be prescribed and administered by an experienced physician and with close cardiac monitoring (e.g. in critical care).
- IgE testing to drugs is unreliable. Where the cause of an allergic drug reaction is not clear, skin testing and possible challenge will be required to confirm or exclude the diagnosis.
- All serious allergic reactions to drugs should be reported to the Yellow Card Scheme.
You should confirm and document:
- All current and any recent drugs, including any over-the-counter medicines, herbal preparations and injections (including vaccines or contrast media).
- The generic (non-proprietary or approved) name for the drug(s) suspected of causing a reaction(s).
- The exact signs, symptoms and severity of the allergic reaction(s).
- When the reaction(s) occurred.
- How long the drug was taken before the reaction occurred.
- Whether the allergy is a first-hand recollection.
| Issue | Type 1 | Type 2 |
|---|---|---|
| Onset | Minutes to 2 hours | |
| First dose | Not always | |
| Syptoms | Itching Uticaria Hypotension Angioedema Wheeze |
Mobiliform rash – lesions enlarge Erythema Multiforme – secondary to penicllins, statins, phenytoin and infection Fixed drug eruptions – occur in same place Photosensitivity
- related to struncture of beta=lactam and thiazolidine rings
- variable side chains on 3rd-generation and later cephalosporins is lower as variable chains are bulky
Carbapenems contain a bicyclic nucleus with a beta-lactam ring. Patients who have experienced a true allergic reaction to a penicillin show a high degree of sensitivity to carbapenems by skin testing. In practice, however, only about 1% of penicillin allergic patients show clinical evidence of allergy to carbapenems on exposure.
You need to assess the risk carefully when deciding to prescribe a carbapenem to a penicillin allergic patient.
Aztreonam is a monobactam (or monocylic beta-lactam) antimicrobial that contains a beta-lactam ring.
However, unlike the other beta-lactam antimicrobials, aztreonam does not contain a bicyclic ring structure and can be safely prescribed for penicillin allergic patients.
The safety of prescribing and administering other beta-lactam antimicrobials to penicillin allergic patients is uncertain and based mainly on anecdotal information regarding the incidence of cross-reactivity.
When prescribing cross-reacting drugs to patients with penicillin allergy:
- Further investigate the penicillin allergy to determine the presence and nature of the allergic reaction.
- Hypersensitivity testing and specialist advice should be sought for patients where the use of a penicillin and cephalosporin are clinically required.
- Prescribe cephalosporins and carbapenems cautiously in patients who have experienced pronounced allergic reactions with penicillins (i.e. anaphylaxis, angioedema or so called mucosal symptoms, bronchospasm, itchy rash).
- You can safely prescribe and administer aztreonam to patients with a history of penicillin allergy.
- For all cases of known (or suspected drug allergy), prescribe a non-cross reacting drug if the effectiveness and cost are similar to the drug avoided.
Bronchospasm isn’t observed with AR2Bs
[Risk Factors](link to table)
If considerable history of allergy then review appropriateness of the commonly implicated drugs and possibly mitigate with steroid/antihistamine cover
Chlorhexidine Antimicrobials Opioids NSAIDs – COX-2 alright Plasma Expanders Muscle relaxants Radiocontrast
- Reactions to parenteral medicinal products generally occur rapidly and are more severe than reactions to oral or topical products.
- Administer the drug slowly (i.e. slow initial injection/infusion).
- Sometimes a test dose (small proportion of dose) is given slowly before the remaining dose is administered*.
- Observe response.
- Observe the injection site.
- Ensure adequate facilities to treat anaphylaxis are at hand; this includes adrenaline, parenteral corticosteroids and parenteral antihistamines.
Resuscitation Council Guidelines
| Severity | Treatment |
| Mild
Moderate | No evidence of systemic reaction |
| Severe | Hypotension
laryngeal oedema
wheeze
SpO2 <92%
impaired consciousness |
After all moderate to severe anaphylactic reactions to a medicine:
Prescribe prednisolone for up to 3 days. Prescribe a non-sedating antihistamine for up to 3 days (adhere to your Trust formulary). Issue or recommend a medical alert band if re-exposure is possible. Ensure the allergy is documented in the medical notes and on the drug chart (electronic or paper-based system). Communicate information to the general practitioner. Warn the patient if the drug or related drugs are found in medicines available over-the-counter (e.g. salicylates/acetylsalicylates in patients who have reacted to an NSAID). Advise they check with a pharmacist prior to self-medicating with over-the-counter medicines. Provide structured written information to the patient. Prescribe two adrenaline auto-injectors for self-administration only when there is a significant risk of re-exposure. Report the adverse drug reaction to the yellow card scheme.
Adrenaline auto-injectors are primarily prescribed for patients:
- At increased risk of an idiopathic anaphylactic reaction, or
- At high risk of exposure to anaphylactic triggers (e.g. venom stings, food)
For patients with a suspected drug allergy:
- Determine the reaction type (e.g. immediate rapidly evolving, non-immediate reaction without systemic involvement or non-immediate reaction with systemic involvement).
- Document the features of the new reaction (e.g. generic and proprietary name of the suspected drug including strength and formulation, description of the reaction, indication for the suspected drug, date and time of reaction, number of doses/days taken before onset of reaction, route of administration and drugs/drug classes to avoid in the future). Ensure information is clearly communicated to the GP.
- In patients 16 years or older, take timed blood samples for mast cell tryptase as soon as possible after emergency treatment has started and 1-2 hours (but no later than 4 hours) after the onset of symptoms.
- For patients under the age of 16 if the reaction is thought to be related to venom, drugs or is idiopathic, follow bullet point 3.
- Document drug allergy status separately from adverse drug reactions.
- Refer to a specialist allergy service if appropriate (e.g. anaphylactic reaction, severe non-immediate cutaneous reaction, suspected reaction to anaesthetic agent, future management will be complicated by drug avoidance).
- Observed for 6-12 hours from the onset of symptoms if they have received emergency treatment and are an adult or child aged 16 years or older.
- Admitted under the care of the paediatric medical team if a child younger than 16 years.
- Offered an appropriate adrenaline auto-injector as an interim measure if re-exposure to the drug is likely.
When discharging your patient from hospital, as well as informing the GP, ensure they understand:
- To avoid any known triggers for allergic reactions.
- To avoid any cross-reacting drug classes where necessary.
- How to use the adrenaline auto-injector if issued.
- To purchase an alert bracelet or similar if necessary.
Adverse drug reactions (ADRs) that include anaphylactic shock or which have resulted in hospilisation should be reported to the Medicines and Healthcare Products Regulatory Agency (MHRA) Yellow Card scheme.
Remember, you don't have to have proof that an adverse event was caused by the medicine, only a suspicion. If you think a new drug might have been responsible for a serious effect, then it is best to report.