i.v. injection of approx. 5 ml/min,

i.v. infusion with isotonic saline solution over 30–60 min

children receive the same or a larger dose than adults;

repeated doses may be necessary

Repeated doses may be necessary, even if there is initial normalisation of crucial parameters; this can be explained by continued absorption of venom from a depot in the region of venom application;

Recurrent envenoming was common when rapidly cleared Fab antivenoms were introduced: EchiFab, Micropharm, London, UK for envenoming by Nigerian saw-scaled viper, ProlongaTab, Micropharm for envenoming by Sri Lankan Russell's viper (D. russelli), and CroFab, BTG, London, UK for envenoming by American rattlesnakes. Possible mechanisims: (a) continued absorption of antivenom from the bite site after antivenom has been cleared or has complexed with venom and (b) redistribution of venom after dissociation of the venom-antivenom complexes (Warrell 2010).

Repetition of the initial dose with snakebites if, for example, severe cardiovascular or neurological symptoms persist for longer than 30 min and if blood is incoagulable for more than 6 h (Warrell 1990b)

monitoring of the patient during and after antivenom administration; constant monitoring during the first 10–15 min after the start of antivenom administration (see below, Table 5.6 Antivenom reactions);

in the case of envenoming with impaired haemostasis ensuring that there is no persistent bleeding from the site of venipuncture, possibly compression bandage

The likelihood of the occurrence of early antivenom reactions is greatest during the first 15 min; however, so-called "early" reactions may also first appear after a period of hours; thus it is necessary to monitor the patient for several hours following antivenom administration

see below, Table 5.6 Antivenom reactions

the mechanisms have not yet been clearly elucidated;

complement activation by immune complexes (aggregates)?

rarely a type I hypersensitivity reaction to horse sera

adrenaline: 0.5–1.0 mg for adults (0.01 mg/kg BW for children), i.e. for adults 0.5–1.0 ml (for children 0.01 ml/kg BW) of adrenaline solution diluted 1:1,000 i.m.; repetition every 10 min, corresponding measurement of blood pressure and pulse until the patient's condition improves; in less severe cases the first dose can be given s.c. upon initial signs of an antivenom reaction;

and

antihistamines, e.g. chlorpheniramine: adults 10 mg, children 0.2 mg/kg BW, slowly i.v., beginning after adrenaline administration for 24–48 h;

if a patient continues to deteriorate despite this treatment, additional treatment with i.v. fluid replacement, aminophylline i.v., β₂-receptor stimulators, oxygen and assisted ventilation (Warrell 1990b, BNF 1995)

early anaphylactoid reactions, which make up the great majority of the early reactions, cannot be predicted with a sensitivity test (Malasit et al. 1986)

mild reactions: urticaria, nausea, vomiting, diarrhoea, headache, fever (Malasit et al. 1986)

severe (systemic) reactions: bronchospasm, arterial hypotension, angio-oedema (Malasit et al. 1986)

the more purified the antivenom used, the lower the incidence of such reactions (see "Essentials of the management of envenoming and poisoning": Table 2.1)

prevention of postural arterial hypotension;

reducing fever through cooling and antipyretics (paracetamol 15 mg/kg BW) (Warrell 1990b)

signs and symptoms: fever, chills, vasodilatation, arterial hypotension (febrile seizures can occur in children)

signs and symptoms: pruritus, urticaria, fever, arthralgia, lymphadenopathy, peri-articular swelling, albuminuria, neurological impairment (mononeuritis multiplex, rarely encephalopathy);

the incidence and speed with which the reaction develops are greater the higher the dose of antivenom administered (Warrell 1990b)