Drug Cross Sensitivity

Cross-reactivity with drugs is an important clinical problem in drug hypersensitivity. Once a patient is labeled 'drug-allergic' all drugs of the same class are withheld and future therapeutic interventions are limited.

Antiepileptics
Development of drug hyper­sensitivity is one of the major complication of their usage. Antiepileptics are blamed for 20% of all drug rashes and are commonly incriminated drugs in severe cutaneous adverse reactions like Stevens-Johnson syndrome(SJS) or toxic epider­mal necrolysis (TEN). The overall prevalence of rash is 2-3% due to antiepileptic drugs in epilepsy patients.

Cross-reactivity between phenytoin, phenobarbital and carbamazepine is thought to exceed 50%.

In patients suspected of having Anticonvulsant Hypersensitivity Syndrome (AHS), anticonvulsant therapy should be discontinued immediately; seizure control may be attempted with a benzodiazepine.

Another alternative for patients with partial or secondarily generalized seizures is gabapentin, which is thought to be safe for administration during the acute phase of AHS.

Valproic acid reportedly has been successful as well but should not be administered during the acute phase of AHS as it is metabolized hepatically.

Refenrence
Cross-Sensitivity between Phenytoin and Carbamazepine. Pharmacotherapy. 2001;21(4) © 2001 Pharmacotherapy Publications. http://www.medscape.com/viewarticle/409706_4.


Penicillin
The risk of cross-reactivity to carbapenems among patients with documented or self-reported penicillin allergy is more than five times higher in patients with a history of penicillin allergy than in those without such a history.

Physicians to be cautious when administering a carbapenem to patients with a history of penicillin allergy, particularly if the allergy has been documented by a health care professional. Cephalosporins should be used cautiously as well.

Penicillins, carbapenems, and cephalosporins are alike in that they have a characteristic bicyclic core structure, which is believed to play a large role in β-lactam hypersensitivity.

Physician should consider a different type of antibiotic, such as a fluoroquinolone, for patients with a history of penicillin sensitivity.

References
1. Apter AJ, Kinman JL, Bilker WB, et al. Represcription of penicillin after allergic-like events. J Allergy Clin Immunol. 2004;113:764-770.
2. Prescott WA, DePestel DD, Ellis JJ, Regal RE. Incidence of carbapenem-associated allergic-type reactions among patients with versus patients without a reported penicillin allergy. Clin Infect Dis. 2004;38:1102-1107.