Bioavailability of bromhexine in the horse.

This study examines the bioavailability (absorption and utilization by the body) of Bromhexine – a medication often used as a mucus thinning agent, when administered to horses both orally and intravenously. The researchers found that the rate of uptake was quite low and fast removal of the drug from the system leads to reservations about the drug’s clinical efficacy in equines.

Methodology

• This research was conducted using three horses as subjects. The horses were given bromhexine in two different methods: orally (2 mg./kg.) and intravenously (1 mg./kg.).
• By testing plasma levels at regular intervals post-administration, the scientists were able to determine how quickly and to what extent the drug is absorbed and utilized by the horse’s body (bioavailability).

Findings

• Following intravenous administration, the bromhexine was eliminated from the horse’s system within a range of 3.1 to 4.4 hours (half-life).
• The volume of distribution of the drug, a parameter that indicates how well it disperses throughout the body, was calculated to be around 16.2 l./kg. for the total body and 3.3 l./kg. specifically for the central compartment (essentially the blood volume and large organs).
• The study also revealed a high plasma clearance rate (how quickly the drug is removed from the body) with range between 49.8 to 59 ml./kg./min.
• Around an hour after oral administration, peak plasma levels reached approximately 14 ng./ml., indicating the rate of absorption of the drug into the bloodstream orally.
• Unfortunately, the systemic bioavailability of the drug (how much reaches the circulatory system and hence can have an effect) was quite poor, only 5.7%. This low rate could be attributed to what’s known as first-pass metabolism – the initial processing of the drug by the liver, which leaves a reduced amount available for circulation.

Interpretation

• Given these findings, particularly the low bioavailability and relatively short half-life, the researchers expressed doubt about the therapeutic efficiency of orally administered bromhexine in horses.