SCORPION STING – ROLE OF PRAZOSIN AS A

PHYSIOLOGICAL ANTIDOTE

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ABSTRACT 

            Scorpion stings are a common problem in many parts of the world often reported from rural areas in developing countries like India. Here we report 2 cases from a particular locality of Western Orissa, received in different clinical states and studied the effect of Prazosin , which is its first trial report from this Medical College. 

INTRODUCTION

          Clinical , experimental and laboratory investigations have confirmed the inter-relationship between  stimulatory effects of the scorpion venom on Autonomic Nervous System (A.N.S) and adrenals and subsequent effect of released transmitters on C.V.S. The envenomation due to Mesobuthus tamulus , an Indian Red Scoripion sting can result in an acute life threatening medical emergency.  It has been reported that the severity of Scorpion sting depends upon the time between the sting and administation of Prazosin. Prazosin , an alpha adrenergic blocker acts as a physiological antidote to venom of Scorpion.

KEY WORDS

Scorpion sting, Prazosin, Autonomic storm, Pulmonary edema.

CASE REPORT

Case No. 1 

A 32 year male admitted to Medicine – III unit on 24/09/2005 being bitten by an Indian Red Scorpion over right occipital area, 5 cm from mastoid process while  sleeping over a Log of wood at around 9 P.M.  After ½ hour of the bite he had blurring of  vision, dryness of mouth, burning sensation over lips, with 2-4 bouts of vomiting. He was confused at that time and unable to identify his relatives, with urinary urgency and retention of urine. Then he was transferred to a local hospital and treated with injection Hydrocortisone Deriphylline, Nikethamide, IV fluids and Oxygen. As the condition deteriorated he was referred to V.S.S. Medical College Hospital , Burla.

          There was no history of fever, convulsion and patient was not a known case of Diabetes Mellitus, HTN, PTB, Sickle Cell Disease. He was a farmer by profession with no addiction to smoking or alcohol.

          At the time of admission patient was conscious, afebrile. On examination Pulse – 148/min., regular BP 90 mmHg, systolic (diastolic  not recordable), respiratory rate 40/min regular, abdominothoracic type. There was pallor, central cyanosis. There was no edema, lymphadenopathy, JVP was not raised, skin was cold and clammy with features of dehydration. Chest examination revealed B/L, normal vesicular breath sounds with basal crepitations . Heart sounds were normal without any murmur, P/A revealed abdomen soft, non tender and no organomegaly, CNS examination was within normal limit. Local examination at the site of bite revealed no abnormality.

INVESTIGATION

Hb%                      :         9.8gm%

DC                        :         N ⁸⁴%, L ¹⁶%, M⁰, B⁰, E⁰

ESR                      :         08mm 1^st hour

TLC                       :         29,500/mm³ of blood

RBS                      :         138mg%

Serum Urea           :         42mg%

Serum creatinine    :         1.9mg%

Serum Ca⁺⁺            :         7.7mg%

Serum Mg⁺             :         1.6mg%

Uric Acid               :         6.0mg%

LFT                                

Serum Bilirubin      :         T(1.6mg%), D (0.4mg%)

S.G.O.T                 :         42 I.U./L

S.G.P.T.                :         52 I.U./L

S. Alkaline Phosphatase: 120 I.U./L

Chest X-Ray:

          Showed shaggy heart borders with features of pulmonary edema. Echo study showed normal LV function with global hypokinesia, decreased LV systolic function, mild M.R., mild TR without PAH.

ECG:

          Within normal limit in all 12 leads.

TREATMENT

          Patient was treated with injection Dopamine , Dobutamin, Deriphyline, Ceftriaxone, Odansetron, Ranitin and O₂ inhalation. Patient did not show signs of improvement till 2^nd day of treatment. On 3^rd day Prazosin (2.5 mg/day orally) started in low dose. Patient started improving, BP increased gradually, chest became clear. Then on 5^th day Prazosin was increased to 5 mg/day orally and patient improved rapidly. On 7^th day patient became completely asymptomatic. Repeat chest X-ray and Echo were normal and finally discharged with advice to continue Prazosin for another 7 days.

          After 15 days patient attended OPD for follow up. He was totally asymptomatic , lungs were clear, blood pressure and CVS examination were normal. Finally Prazosin was stopped 

Case No. 2

A patient aged 40 years, a resident of village about 4 kilometers distant from 1^st case was admitted on 29/09/2005 being bitten by an Indian Red Scorpion on right 2^nd toe at around 9:30 P.M. He suddenly developed severe pain without local reaction at the site of bite. After half an hour he developed 2 episodes of vomiting and profuse sweating and severe breathlessness. He was taken to a local hospital and treated with injection Dopamine, Deriphylline, I/V fluids, Steroid. When he lost his consciousness he was referred to this Hospital.

          At the time of admission patient was confused with pallor, central cyanosis, dyspnoeic, with respiration rate – 48/min abdominothoracic regular, Pulse – 110/min regular , BP – 100/60 mmHg , cold and clammy extremities. Systemic examination revealed B/L Vesicular BS, coarse crepitations on lung bases associated with rhonchi.  Heart sounds were normal without any murmur, CNS examination revealed patient was confused without any cranial nerve and motor involvement. Plantar reflex was normal and  DTR normal without any meningeal signs.

INVESTIGATION

Hb%                      :         8gm%

DC                        :         N ⁸⁷%, L ¹³%, E⁰, M⁰, B⁰

ESR                      :         08mm 1^st hour

TLC                       :         25,400/mm³ of blood

RBS                      :         156mg%

Serum Urea           :         22mg%

Serum creatinine    :         1.6mg%

Serum Na⁺             :         123meq/lit

Serum K⁺               :         3.8meq/lit

Ca⁺⁺                                     :         7.8mg%

Mg⁺                       :         1.9mg%

Uric Acid               :         6.2mg%

LFT                               

Serum Bilirubin      :         T(1.4mg%), D (0.3mg%)

S.G.O.T                 :         44 I.U/L

S.G.P.T.                :         58 I.U/L

S. Alkaline Phosphatase: 130I.U./L

Chest X-Ray: Within normal limit

ECG:  Within normal limit in all 12 leads

TREATMENT

Patient was treated with Tablet Prazosin 5mg injection Dopamin,  Dobutamine, Deriphyline, Cefriaxone, Odansetron, Ranitin, O₂ inhalation. Patient responded dramatically. On 3^rd day he became asymptomatic with normal BP. Lungs became clear. Patient was stable on 5^th day with normal vital signs and finally discharged on 4/10/2005.        

          Patient was followed up after one week. He was completely normal and Prazosin was stopped.

DISCUSSION

          Indian Red Scorpion sting can present as an acute life threatening medical emergency often reported from rural areas. The sting frequently occurs at night because of Scorpion’s nocturnal habit.

          Scorpion sting activates sodium neuronal channels causing excessive neuronal discharge.

          The severity of Scorpion stings depends on patients age, season, the time between the sting and treatment with Prazosin. The signs and symptoms are due to potent autonomic storm in victims characterized by transient cholinergic effects¹ – profuse sweating – hypersalivation, priapism in males, hypotension, bradycardia, ventricular ectopics and prolonged adrenergic effects – hypertension, tachycardia, cool extremities and pulmonary oedema. Vomiting , sweating, priapism and cool extremities are early diagnostic features of M. tamulus envenomation.

          Pulmonary  edema in Scorpion stings is of haemodynamic origin and related to a severe and prominent impairment of left ventricular systolic function.

          Alpha receptor stimulation plays an important role in pathogenesis of  Scorpion stings. Prazosin, an adrenergic alpha –1 blocker (invented in 1983-84) possesses pharmacologic properties that render it most suitable in antagonizing the toxic effect of Scorpion venom.

          Prazosin reduces the pre-load and left ventricular impedance without rise in heart rate and rennin secretion³. It decreases pre-load and therefore causes no increase in cardiac output and heart rate contrast to hydralazine. It counters the action of local tissue liberated angiotensin – 2 in myocardium and also counters the vasoconstriction induced by liberated endothelin due to catecholamine excess by enhancing Nitric Oxide as a result of accumulation of C-GMP in vascular tissues by inhibiting phosphodiesterase. Scorpion venom inhibits insulin secretion which is counter acted by Prazosin.

          Usual dosages² is 250 mcg in children and 500 mcg in adults given to those having signs and symptoms of sever Scorpion sting irrespective of blood pressure provided there is no signs of hypovolemia.

CONCLUSION :

          From  the above case report studies it was concluded that Prazosin reverses blood pressure, pulmonary edema irrespective of blood pressure and acts as a physiological antidote to scorpion venom.

REFERENCES

1.     Symptoms , Signs and Management of Indian Red Scorpion Envenomation – H.S. Bawasar , P.H Bawasar, Medicine Update , Vol No. 8, 1998, P 752 – 753.

2.     Harrison’s Principle of Internal Medicine, Vol II, 16^th Edition, P. 2604.

3.     Bawasar H.S, Bawasar P.H., Prazosin in the management of Cardiovascular manifestation of scorpion sting – Lancet, 1986, P 510- 511.