Oral antihistamines for insect bites

Oral antihistamines for insect bites

Report by Bernard A Foëx, Consultant in Emergency Medicine and Critical Care

Checked by Caroline Lee, SpR Midlands rotation Manchester Royal Infirmary

A short cut review was carried out to establish whether oral antihistamines are effective in the management of insect bites. In total, 994 citations were reviewed of which seven answered the three part question. The clinical bottom line is that antihistamines, used before and after, appear to be effective in reducing the immediate/early symptoms of mosquito bites in both adults and children. It is not clear whether the same antihistamine will be effective for both adults and children.

Three part question

In [patients with previous symptomatic reactions to insect bites] are [oral antihistamines] effective in [reducing symptoms]?

Clinical scenario

You are going on a family holiday to Scandinavia during the summer. You wonder what evidence there is that oral antihistamines will reduce the symptoms of the inevitable insect bites.

Search strategy

Medline 1966–30.09.2005, CINAHL (R)‐1982 to date 4th Oct 2005, Cochrane Library.

Medline: [(exp Insect Bites/and Stings.mp.) or insect bite$.mp. AND exp insects/or insect$.mp. AND (exp Bites/and Stings.mp.) or bite$.mp. or sting$.mp.] AND

[exp Histamine H1 Antagonists OR antihistamine$.mp OR exp chlorpheniramine OR chlorpheniramine.mp OR exp pyrilamine OR mepyramine.mp]

CINAHL: “(INSECT‐BITES‐AND‐STINGS#.DE. OR MOSQUITOES#.W..DE. OR BEES‐AND‐WASPS#.DE. OR BITES‐AND‐STINGS#.DE. OR INSECTS#.W..DE. OR TICKS#.W..DE. OR ARTHROPODS#.W..DE. OR TICK‐BORNE‐DISEASES#.DE. OR SPIDERS#.W..DE.) AND ABSTRACT = YES NOT (EXECUTIVE ADJ SUMMARY).AB. AND LG = EN”.

Search outcome

Medline search returned 214 citations, only seven of which were clinical trials addressing the question. CINAHL search returned 780 citations. None was a trial addressing the question. Search of the Cochrane database did not find any relevant reviews.

Table.

Author, date and country		Patient group		Study type (level of evidence)		Outcomes		Key results		Study weaknesses
Coulie et al,1 1989 Belgium		10 healthy adult volunteers exposed to Anopheles stephensi mosquitoes in a laboratory.		Double blind randomized crossover trial of cetirizine 10 mg BD v placebo.		Effect on pruritus and cutaneous reaction		Reduced pruritus but not intensity or duration of cutaneous reaction		1 volunteer dropped out after a severe skin reaction to cetirizine.
Reunala et al,2 1991 Finland CA		27 adult volunteers exposed to Aedes ommunis mosquitoes in a forest in Southern Finland.		Double blind, placebo‐controlled trial of cetirizine 10 mg od.		Effect on pruritus and cutaneous reaction		Cetirizine reduced immediate but not delayed pruritus and cutaneous skin reaction		4 subjects excluded because baseline reactions to bites were too mild.
Reunala et al,3 1993 Finland		28 adults with previous significant reaction tomosquito bites. Exposed to Aedes communis in forests in Finland		Double blind, crossover trial of cetirizine 10 mg od v placebo.		Effect on pruritus and cutaneous skin reaction		Cetirizine reduced immediate pruritus and cutaneous reaction		Subjects were patients and hospital employees. Field studies in 2 different forests. No washout period. All subjects allowed to use 1% hydrocortisone cream. Only 18 subjects completed the study.
Reunala 1997 Finland CA		30 volunteers, all sensitive to mosquito bites. Exposure to Aedes egypti in the laboratory.		Double blind, crossover of ebastine (10 mg or 20 mg) v placebo.		Effect on prutitus and cutaneous reaction		Ebastine reduced immediate pruritus and cutaneous reaction		Only 25 subjects evaluable because of trial violations (2) and possible adverse events (2)… numbers don't add up, I know.
Karppinen et al,4 2000 Finland		28 children (2–11 years), sensitive to mosquito bites. Exposure to Aedes egypti mosquitoes in the laboratory.		Double blind, crossover of 0.3 mg/kg loratadine v placebo		Effect on immediate and delayed cutaneous reaction, and immediate pruritus		Loratadine reduced cutaneous reaction and pruritus		25 completed the study. Only 12 evaluated pruritus on a visual analogue scale.
Karppinen et al,5 2000 Finland		28 mosquito allergic adults exposed to Aedes communis in forests in Finland.		Double blind, crossover study of ebastine 20 mg od v placebo.		Effect on pruritus and cutaneous reaction		Reduced immediate cutaneous reaction and both immediate and delayed pruritus.		Different forest sites.
Karppinen et al,6 2002 Finland		29 adults, sensitive to mosquito bites, exposed to Aedes egypti in the laboratory.		Double blind, crossover study comparing cetirizine 10 mg, ebastine 10 mg, loratadine 10 mg and placebo.		Effect on pruritus and cutaneous reaction		Cetirizine and ebastine reduced immediate cutaneous reaction and pruritus compared with placebo. Loratadine seemed ineffective		27 subjects completed the study. Dose of loratadine probably too low, given dose used in paediatric study (above).

od, once daily.

Comment(s)

Six of the seven trials were performed by a small group of researchers, addressing the problem of mosquito bites in Finland. Three mosquito species were studied. Inclusion criteria were not uniform; in some studies, subjects were known to have a significant reactions, in others they did not. Most studies used a crossover design; however, neither the treatment nor the washout periods were not uniform.

Clinical bottom line

Antihistamines, used before and after, appear to be effective in reducing the immediate/early symptoms of mosquito bites in both adults and children. It is not clear whether the same antihistamine will be effective for both adults and children.