Uncommon drug abuse: An anesthetist dilemma.

Although mephentermine (Termin) and ephedrine are commonly used drugs for the treatment of hypotension during anesthesia but their abuse have markedly increased, especially in the young population due to its stimulant properties. Here, we report a case of 23-year-old man with a history of chronic mephentermine abuse, posted for Achilles tendon repair under spinal anesthesia. During intraoperative period, spinal induced hypotension showed unusual resistance to ephedrine boluses and was managed by using directly acting vasoconstrictor, that is, phenylephrine.

INTRODUCTION

Misuse of drugs especially of stimulants and anabolic steroids by young population to enhance performance has gained much attention in the past years. Mephentermine is methamphetamine, derivative of stimulant drug an amphetamine. Like amphetamines, it has shown to increase athletic performance in strength exercises and endurance in a dose of 14 mg/70 kg body weight. Anesthetic management is significantly affected by the physiologic changes and clinical manifestation of drug abuse itself. Anesthesia literature regarding the clinical intraoperative experience of patients with chronic I.V./I.M. abuse of mephentermine is very much limited. Here we share our experience.

CASE REPORT

A 23-year-old male kabbadi player by profession, presented in the hospital for tendon of Achilles repair. During preanesthetic check-up, history of chronic abuse of injection mephentermine in the doses of 30–60 mg I.M. almost daily for over last 3 years was obtained. After days of intense activity, he felt fatigue and soreness. A physical examination revealed scars on both upper limbs from the injections. His baseline vitals heart rate (HR), noninvasive blood pressure (NIBP), SpO2 were within normal limits. His weight was 78 kg. His routine preoperative blood investigations along with chest X-ray were normal. Electrocardiogram (ECG) showed normal sinus rhythm. After proper examination, surgery was planned under spinal anesthesia. On the day of surgery after confirming fasting status, good I.V. access was obtained with 18-gauge I.V. cannula and patient preloaded with 20 ml/kg of ringer lactate. After attaching essential monitors, note was made of patient's baseline vitals. Under all aseptic condition, subarachnoid block was performed in lateral position with affected limb downside with 25-gauge spinal needle in L3-L4 subarachnoid space with 15 mg of injection bupivacaine 0.5% heavy after confirming free flow of cerebrospinal fluid.

Electrocardiogram, NIBP, HR, SpO2 and temp were continuously monitored during the perioperative period. Patient was made supine and spinal level achieved up to T10 dermatome. After 5 min of spinal anesthesia, mean arterial blood pressure (BP) started showing a continuous downward trend, going down to 54 mm of Hg (>20% of baseline) rapidly. HR however remained stable within limit of 60–70/min during this period. Injection ephedrine 5 mg I.V. bolus was given along with rapid normal saline infusion. After 2 min of bolus, mean BP was still <60 mm of Hg. Another bolus of injection ephedrine 10 mg was given but patient's BP did not respond. After this injection phenylephrine 50 μg I.V. bolus was given, and mean arterial BP started returning toward baseline within 2 min. After stabilizing vitals, patient moved into prone position for tendon Achilles repair and surgery started. At 35 min, there was again fall in BP which was managed by phenylephrine bolus successfully. All other parameters like HR, SpO2, temperature and ECG remained within normal range during this period. Rest of the intraoperative period was uneventful. Postoperatively patient was monitored for any hemodynamic changes and discharged from hospital after 4 days without any complication.

DISCUSSION

Mephentermine is commonly used drug by all anesthesiologist, but its abuse potential has increased, especially in young sports person for last few years due to its stimulant properties.[1] Its misuse to achieve better physical performance by humans has been described. However limited data is available on the dependence and misuse of mephentermine.[12] Mephentermine is an amphetamine-derived phenethylamine, which shares a strong chemical similarity with methamphetamine. It has been proposed that phentermine, which is the main metabolite of mephentermine, acts by inhibiting monoaminoxidases A and B.[3] Amphetamines are most often abused orally, but in the case of mephentermine, abuse is via the I.V./I.M. or intranasal route.[4] Mephentermine is mainly used as a vasopressor agent with a sympathomimetic action, primarily causing release of noradrenaline and increasing cardiac output due to positive inotropic effect on the myocardium. There will be an increase in venous return because of dilatation in arteries and arterioles in the skeletal muscle and mesenteric vascular beds. It is available in India as 10 mg oral tablets and also as intramuscular or intravenous injection of 15 mg/ml or 30 mg/ml. The injectable preparation is commonly used for the short-term treatment of various hypotensive states, e.g., shock or hypotension accompanying myocardial infarction or spinal anesthesia or surgical procedures like cesarean section.[5]

Chronic abuse of this class of drugs can significantly affect patient outcome during anesthesia. Chronic amphetamine abuse may be associated with markedly decreased anesthetic requirements, presumably as a result of catecholamine depletion in the central nervous system (CNS). Refractory hypotension and blunted sympathetic response can reflect depletion of catecholamine stores in CNS and peripheral neurons.[6] Direct-acting vasopressors, including phenylephrine and epinephrine, should be used to treat hypotension because the response to indirect-acting vasopressors such as ephedrine may be attenuated by the amphetamine-induced catecholamine depletion.[7] Postoperatively, there is the potential for orthostatic hypotension once patient begins to ambulate. Intraoperative monitoring of BP using an intra-arterial catheter is a consideration. Samuels et al. reported a case of cardiac arrest and death during a cesarean delivery in a chronic amphetamine abuser. He speculated that chronic catecholamine depletion led to an inability to respond to the stress of anesthetic induction, specifically, the increase in venous capacitance and the resulting decrease in preload that resulted from the induction dose of thiopental.[8] Catecholamine store depletion may also manifest as somnolence and anxiety or a psychotic state during the recovery period. Other physiologic abnormalities reported with long-term amphetamine abuse include hypertension, cardiac dysrhythmias, and malnutrition. During general anesthesia, drugs are causing major hemodynamic changes should be used carefully due to decreased anesthetic requirement in this patients.[7]

CONCLUSION

We conclude that proper anesthetic plan along with invasive monitoring should be used and directly acting vasopressor like phenylephrine or epinephrine should be preferred over indirect-acting sympathomimetic for treating hypotension in these patients. However to formulate safe anesthesia plan, still a lot of reporting of clinical experiences of anesthesia in these patients is required.