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.

Are topical anti-fungals all the same?

1. Whitfield's ointment (benzoic acid) - useful for web intertrigo
2. Polyenes (ineffective for dermatophyte infection)
Nystatin (Nilstat®; Mycostatin®)
3. Imidazoles
Clotrimazole (Canesten®; Clocreme®; Clomazol®, Fungizid®)
Econazole (Ecreme®; Pevaryl®)
Ketoconazole (Daktagold®; Ketopine®, Nizoral®; Sebizole®)
Miconazole (Daktarin®; Micreme®; Resolve®; Tinasolve®)
Tioconazole
4. Allylamine (higher cure rates & more rapid responses)
Terbinafine (Lamisil®)

Topical Anti-fungal

Topical antifungal creams can be used
1. As monotherapy to treat Dermatophyte, Yeast infections & mould skin infections.
2. As an adjunct to oral therapy for tinea capitis and tinea barbae.

The creams are applied to the affected area 2x / day for 2-4 weeks, including a margin of several centimetres of normal skin.

Continue for 1-2 weeks after the last visible rash has cleared. Repeated treatment is often necessary

Principle of Prescribing Topical Dermatological Therapy

1. Correct diagnosis is the key to correct treatment
2. Be familiar with the treatment & their preparation
3. Know the do’s & don’ts of each topical medications
4. Give clear instructions to patient &alert them the possible events / side effect
5. Cure Sometimes; Relief Often; Comfort Always; Harm Never

HIV & SKIN

HIV infection leads to progressive failure of cell-mediated immunity due to HIV- mediated loss of CD4 helper T cells. Virtually all HIV infected persons will develop some skin disorder during the course of their illness.

Dermatological manifestations can be the first sign of asymptomatic HIV disease. They can be important markers for the diagnosis of HIV infection. Certain skin diseases typically appear at certain stages of HIV infection, sometimes allowing the physician to predict the stage of HIV infection.

The skin changes in HIV / AIDS can be classified into 4 categories:
I. Infections
II. Inflammatory diseases
III. Neoplasms
IV. Cutaneous Adverse Drug Reactions (CADR)

Penang Dermatology Symposium 2010

Department of Dermatology, Penang General Hospital will organise Penang Dermatology Symposium at Auditorium, Ambulatory Care Center (ACC) Penang General Hospital on 8th – 9th May 2010 (Saturday-Sunday).

This workshop is organised in collaboration with PGMES Hospital Pulau Pinang, Dermatological Society of Malaysia (PDM) and Faculty of Dermatology, Academy of Medicine, Malaysia.

Penang Dermatology Symposium is specially dedicated to doctors with special interest in Dermatology. This symposium is opened to all doctors (both government & private).

The aims for this event are to provide a regular continuous medical education (CME) programme in dermatology for practicing practitioners and to provide an update of various topics in dermatology.

For those interested, pls email me (tanwooichiang@yahoo.com). I will send you the detail and registration form.

The 3 "P"s of small vessel vasculitis

1 P = Painful
2 P = Palpable
3 P = Purpura