Comparison of availability and plasma clearance rates of β-hydroxy-β-methylbutyrate delivery in the free acid and calcium salt forms

Abstract

β-Hydroxy-β-methylbutyrate (HMB), a leucine metabolite, has long been supplemented as a Ca salt (Ca-HMB) to increase strength and performance gains with exercise and to reduce recovery time. Recently, the free acid form of HMB (HMB-FA) has become commercially available in capsule form (gelcap). The current study was conducted to compare the bioavailability of HMB using the two commercially available capsule forms of HMB-FA and Ca-HMB. We also compared the pharmacokinetics of each form when administered mixed in water. Ten human subjects (five male and five female) were studied in a randomised crossover design. There was no significant sex by treatment interaction for any of the pharmacokinetic parameters measured. HMB-FA administered in capsules was more efficient than Ca-HMB capsule at HMB delivery with a 37 % increase in plasma clearance rate (74.8 (sem 4.0) v. 54.5 (sem 3.2) ml/min, P<0.0001) and a 76 % increase in peak plasma HMB concentration (270.2 (sem 17.8) v. 153.9 (sem 17.9) μmol/l, P<0.006), which was reached in one-third the time (P<0.009). When HMB-FA and Ca-HMB were administered in water, the differences still favoured HMB-FA, albeit to a lesser degree. Plasma HMB with HMB-FA administered in water was greater during the early phase of absorption (up to 45 min postadministration, P<0.05); this resulted in increased AUC during the first 60 min after administration, when compared with Ca-HMB mixed in water (P<0.03). In conclusion, HMB-FA in capsule form improves clearance rate and availability of HMB compared with Ca-HMB in capsule form.