Pharmacologic modulation of hypermetabolism

Overview

Severe burn injury triggers a hypermetabolic response that can persist for two or more years after injury, characterized by up to 50-fold elevations in plasma catecholamines, cortisol, and glucagon ^[1][2]. This response drives whole-body catabolism, elevated resting energy expenditure, insulin resistance, skeletal muscle wasting, and multiorgan dysfunction ^[1][3]. While the hypermetabolic response cannot be completely reversed, it can be modulated through both pharmacologic and nonpharmacologic strategies ^[4][5]. This page provides an overview of pharmacologic approaches; individual agents with extensive evidence bases (propranolol, oxandrolone) have dedicated topic pages.

Nonpharmacologic foundations

Before pharmacologic intervention, nonpharmacologic strategies form the essential foundation of hypermetabolism management ^[4][5]. These include early burn wound excision and complete wound closure, aggressive treatment of sepsis, maintenance of environmental thermoneutrality (31.5 +/- 0.7 degrees C), high-carbohydrate high-protein continuous enteral feeding, and early institution of resistive exercise programs ^[4]. Williams et al. emphasized that modulation of the response by early excision, thermoregulation, early and continuous enteral feeding, and pharmacologic treatments have markedly decreased morbidity ^[1][5].

Beta-adrenergic blockade

Propranolol, a nonselective beta-1/beta-2 adrenergic antagonist, is the most widely used anticatabolic therapy in burn care ^[6]. It reduces resting energy expenditure, peripheral lipolysis, cardiac work, and supraphysiological thermogenesis while improving the efficiency of muscle protein synthesis ^[4]. Propranolol is dosed to achieve a 15-20% reduction in resting heart rate and is continued throughout hospitalization and often into the outpatient rehabilitation period. See propranolol-in-burn-patients for detailed evidence.

Insulin therapy

Continuous low-dose insulin infusion addresses the insulin resistance that characterizes postburn hypermetabolism. Badoiu et al. reviewed the biological substances that induce hyperglycemic responses after burns and the pharmacologic agents available for glucose metabolism modulation ^[7]. Insulin infusion improves muscle protein synthesis and promotes anabolic processes, though the risk of hypoglycemia requires careful glucose monitoring ^[4][6]. Moderate glucose control has been shown to be safe in adult burn patients; data in children are less certain due to higher hypoglycemia risk VERIFY. In a large retrospective analysis using the TriNetX database, Hallman et al. found that burn patients treated with insulin alone had significantly higher risks of hypoglycemia, sepsis, and death compared to those treated with metformin, raising questions about insulin monotherapy as the default first-line agent for postburn hyperglycemia ^[10]. See glycemic-control-in-burn-patients for a detailed comparison of glycemic agents.

Anabolic steroids

Oxandrolone, a synthetic testosterone analog, was historically the most cost-effective and least toxic anabolic agent available for burn patients ^[4]. It enhanced protein synthesis efficiency, preserved lean body mass, and improved bone mineral content ^[8]. Oxandrolone has been removed from the US market by the FDA and is no longer available domestically. See oxandrolone-in-burn-patients for detailed evidence and historical context.

Testosterone itself has been studied and shown to improve muscle protein net balance, though its use in burn patients is less well characterized than oxandrolone ^[8].

Recombinant human growth hormone

Recombinant human growth hormone (rhGH) increases protein synthesis, promotes wound healing, and attenuates muscle catabolism ^[4]. However, rhGH increases hepatic glucose output and may worsen hyperglycemia and insulin resistance. Takala et al. demonstrated in a multicenter randomized trial of 532 critically ill adults that rhGH significantly increased mortality (relative risk of death 1.9-2.4) compared to placebo, primarily through increased infectious complications and multiorgan failure ^[11]. This finding has severely limited rhGH use in burn and critical care populations, despite the drug's documented anabolic benefits. In pediatric burn patients at specialized centers, rhGH continues to be studied, often in combination with insulin-like growth factor-1 (IGF-1) and IGF binding protein-3 (IGFBP-3) to mitigate side effects VERIFY.

Metformin

Metformin improves insulin sensitivity and reduces hepatic glucose production without the hypoglycemia risk associated with exogenous insulin. It has been studied in burn patients as an alternative or adjunct to insulin therapy ^[6]. Stanojcic et al. identified metformin, along with glucagon-like peptide-1 and peroxisome proliferator-activated receptor agonists, as promising investigational agents ^[6]. Hallman et al. reported that metformin monotherapy was associated with reduced risk of mortality and morbidity compared to insulin alone in burn patients, and that the combination of insulin and metformin was no more effective in reducing hyperglycemia and hypoglycemia than insulin alone ^[10]. These findings support a growing role for metformin in postburn metabolic management, though the retrospective study design warrants confirmation in prospective trials.

Combination approaches

The concept of a "metabolic bundle" combining multiple pharmacologic and nonpharmacologic interventions has gained traction. Early surgical excision, thermoregulation, high-protein enteral nutrition, propranolol, trace element supplementation, and anabolic agents can be delivered as a standardized package ^[4][5]. Diaz et al. reviewed stable isotope tracer studies and confirmed that the mechanisms by which different agents improve muscle protein net balance differ: propranolol acts primarily through improved protein synthesis efficiency, while insulin and growth hormone directly stimulate protein synthesis ^[8].

Controversies and Evidence Gaps

Most pharmacologic modulation studies have been conducted at a small number of specialized centers (primarily Shriners Hospitals for Children/UTMB Galveston and Sunnybrook), limiting generalizability. The majority of evidence comes from pediatric populations, and data in adult burn patients are comparatively sparse ^[4]. Optimal duration of pharmacologic therapy is not established; some evidence suggests benefit extending 2 to 3 years postburn, but long-term safety data are limited. The removal of oxandrolone from the US market has eliminated one of the three most cost-effective agents identified in the literature. Growth hormone remains contraindicated in the critically ill phase based on the Takala et al. mortality data ^[11]. Emerging agents (GLP-1 agonists, PPAR agonists) lack burn-specific clinical trial data.

References

[1] Williams FN et al. "The hypermetabolic response to burn injury and interventions to modify this response." Clin Plast Surg 2009;36:583-596. PMID: 19793553 [2] Auger C et al. "The biochemical alterations underlying post-burn hypermetabolism." Biochim Biophys Acta Mol Basis Dis 2017;1863:2633-2644. PMID: 28219767 [3] Knuth CM et al. "Burn-induced hypermetabolism and skeletal muscle dysfunction." Am J Physiol Cell Physiol 2021;321:C58-C71. PMID: 33909503 [4] Pereira CT et al. "The pharmacologic modulation of the hypermetabolic response to burns." Adv Surg 2005;39:245-261. PMID: 16250555 [5] Pereira CT et al. "Altering metabolism." J Burn Care Rehabil 2005;26:194-199. PMID: 15879740 [6] Stanojcic M et al. "Anabolic and anticatabolic agents in critical care." Curr Opin Crit Care 2016;22:325-331. PMID: 27272101 [7] Badoiu SC et al. "Glucose Metabolism in Burns-What Happens?" Int J Mol Sci 2021;22:5159. PMID: 34068151 [8] Diaz EC et al. "Effects of pharmacological interventions on muscle protein synthesis and breakdown in recovery from burns." Burns 2015;41:649-657. PMID: 25468473 [9] Williams FN et al. "Metabolic and Endocrine Considerations After Burn Injury." Clin Plast Surg 2017;44:541-553. PMID: 28576243 [10] Hallman TG et al. "Metformin is associated with reduced risk of mortality and morbidity in burn patients compared to insulin." Burns 2024;50(7):1779-1789. PMID: 38981799 [11] Takala J et al. "Increased mortality associated with growth hormone treatment in critically ill adults." N Engl J Med 1999;341:785-792. PMID: 10477776