Low dose subcutaneous adrenaline to prevent acute adverse reactions to antivenom serum in people bitten by snakes: randomised,placebo controlled trial

EDITOR: Premawardhena et al have listed medical contraindications to
adrenaline premed administration to prevent acute adverse reactions to
polyspecific antivenom serum in snake bite victims (1).

I suggest that potential drug interactions should also be considered.

Patients taking nonselective beta adrenergic receptor blockers could
be at risk of an increased hypertensive response to parenteral adrenaline.
Most patients on beta blockers would be excluded because of the underlying
condition such as hypertension or ischaemic heart disease. Patients on
beta blockers for migraine prophylaxis could be included.

Patients taking drugs with alpha adrenergic receptor blocking
activity could theoretically, via the reverse adrenaline effect, have a
hypotensive response to parenteral adrenaline (2,3).Patients taking
prazosin for hypertension would be excluded. Patients taking prazosin for
bladder neck obstruction would not be excluded.

There are very few published reports of clinical misadventure as a
result of the reverse adrenaline effect (3). I suspect however that the
many unexplained deaths in children (4,5) and adults on tricyclic
antidepressants and/or phenothiazines are related to the fact that both of
these groups of drugs have major alpha adrenergic receptor blocking
activity.

It is conceivable from accepted pharmacological principles that
patients taking alpha adrenergic blockers who have a hypotensive collapse
(from whatever cause- anaphylaxis, septicaemia, snake bite, vasovagal)
would further drop their blood pressure as a result of a physiological
endogenous adrenaline surge. Physician administered parenteral adrenaline
in such patients could also exacerbate the hypotension possibly with fatal
consequences (4,5).

In summary snake bite victims taking adrenergic blockers may merit
exclusion from adrenaline premed because of possible adverse drug
interactions.

References:

1. Premawardhena AP, de Silva CE, Fonseka MMD, Gunatilake SB, de
Silva HJ. Low dose subcutaneous adrenaline to prevent acute adverse
reactions to antivenom serum in people bitten by snakes: randomised,
placebo controlled trial. BMJ 1999;318:1041-1043 (17 April).

2. Watson A. Don't get stung with the adrenergic blockers (beta or
alpha). Australian Family Physician Vol. 24, No.10, October 1995 1879

3. Watson A. Alpha adrenergic blockers and adrenaline- a mysterious
collapse. Australian Family Physician Vol. 27 No. 8, August 1998 714-715.

4. Popper CW, Zimnitzky B. Sudden death putatively related to
desipramine treatment in youth: a fifth case and a review of speculative
mechanisms. Journal Of Child And Adolescent Psychopharmacology Vol. 5, No.
4,1995 283-300.

5. Varley CK, McLennan J. Case study: two additional sudden deaths
with tricyclic antidepressants. J.Am.Acad.Child Adolesc. Psychiatry 36:3,
March 1997 390-394.