Pharmacokinetics of acetazolimide after intravenous and oral administration in horses

Acetazolamide and human carbonic anhydrases: retrospect, review and discussion of an intimate relationship

Acetazolamide (AZM) is a strong pharmacological sulphonamide-type (R-SO2-NH2, pKa 7.2) inhibitor of the activity of several carbonic anhydrase (CA) isoforms, notably of renal CA II (Ki, 12 nM) and CA IV (Ki, 74 nM). AZM is clinically used for about eighty years in various diseases including epilepsy and glaucoma. Pharmacological AZM increases temporarily the urinary excretion of bicarbonate (HCO3-) and sodium ions (Na+) and sustainably the urinary pH. AZM is excreted almost unchanged over several hours at high rates in the urine. Closely parallel concentrations of circulating and excretory AZM are observed upon administration of therapeutical doses of AZM. In a proof-of-principle study, we investigated the effects of the ingestion of a 250-mg AZM-containing tablet by a healthy volunteer on the urinary excretion of organic and inorganic substances over 5 h (range, 0, 0.5, 1, 1.5, 2, 3, 4, 5 h). Measured analytes included: AZM, amino acids and their metabolites such as guanidinoacetate, i.e. the precursor of creatine, of asymmetrically (ADMA) and symmetrically (SDMA) dimethylated arginine, nitrite (O = N-O-, pKa 3.4) and nitrate (O2N-O-, pKa -1.37), the major metabolites of nitric oxide (NO), the C-H acidic malondialdehyde (MDA; (CHO)2CH2, pKa 4.5), and creatinine for correction of analytes excretion. All analytes were measured by validated isotopologues using gas chromatography-mass spectrometry (GC-MS) methods. AZM excretion in the urine reached its maximum value after 2 h and was fairly stable for the next 3 h. Time series analysis by the ARIMA method was performed. AZM ingestion increased temporarily the urinary excretion of the amino acids Leu + Ile, nitrite and nitrate, decreased temporarily the urinary excretion of other amino acids. AZM decreased sustainably the urinary excretion of MDA, a biomarker of oxidative stress (i.e. lipid peroxidation). Whether this decrease is due to inhibition of the excretion of MDA or attenuation of oxidative stress by AZM is unknown. The acute and chronic effects of AZM on the urinary excretion of electrolytes and physiological substances reported in the literature are discussed in depth in the light of its extraordinary pharmacokinetics and pharmacodynamics. Tolerance development/drug resistance to AZM in chronic use and potential mechanisms are also addressed.

The effect of systemic acetazolamide administration on intraocular pressure in healthy horses-A preliminary study

OBJECTIVES

In equine glaucoma, topical treatment with carbonic anhydrase inhibitors (CAIs) is recommended. Oral acetazolamide, a systemic CAI, is used in horses with hyperkalemic periodic paralysis. Information regarding its effect on equine intraocular pressure (IOP) is scarce. The aim of the study was to determine the effect of oral acetazolamide treatment on IOP in horses, in a case-control study.

ANIMALS

Ten healthy horses.

PROCEDURES

Horses were treated with oral acetazolamide (4.4 mg/kg) BID for 1 week. Serum acetazolamide concentrations were determined by liquid chromatography/tandem mass spectrometry, and IOP were measured before treatment, daily during treatment, and at 48 and 72 h after treatment.

RESULTS

Acetazolamide serum levels reached steady state at 72 h after the first oral dose. In a mixed effect model logistic regression, there was a significant decrease in IOP on the third treatment day, of 2.4 mmHg (p = .012) and 2.7 mmHg (p = .006) in the left (OS) and right eye (OD), respectively. On the seventh day, there was a decrease in 2.5 mmHg (p = .008) and 2.7 mmHg (p = .007) OS and OD, respectively. A significant increase occurred 48 h following treatment discontinuation (3.6 mmHg, p < .001 and 3.5 mmHg, p < .001 OS and OD, respectively). The area under the concentration versus time curve (AUC(0-10h)) was 1.1 ± 0.5 μg/mL*h, mean residence time 6.7 ± 4.3 h, peak plasma concentration (Cmax) 0.4 ± 0.4 μg/mL and time to reach Cmax 1.8 h. There was a significant increase in serum concentrations 1, 2, 48, 72, and 156 h following the first drug administration (p < .05).

CONCLUSIONS

Further studies are required to determine whether acetazolamide is a potential treatment for equine glaucoma.

Premedication with acetazolamide: Is its use for postoperative pain and stress control after laparoscopic ovariectomy in dogs ruled out?

BACKGROUND

Studies in human medicine have concluded that acetazolamide reduces pain associated with carbon dioxide insufflation during laparoscopic surgery. However, there are no published reports regarding the use of acetazolamide for this purpose in companion animals, despite the increasing popularity of laparoscopic techniques in veterinary medicine due to their advantages over open surgeries.

OBJECTIVES

Thirty mixed-breed female dogs were included in the study and randomly assigned to one of three groups: OVE (median celiotomy ovariectomy; n = 10), OVEL (laparoscopic ovariectomy, n = 10) and OVELA (laparoscopic ovariectomy with acetazolamide preoperative administration; n = 10). Experienced surgeons performed all procedures, and the anaesthetic and analgesic protocols were identical for all animals. Acetazolamide was administered orally (at a dose of 25 mg/kg) 2 h prior to induction in the OVELA group. Postoperative pain was evaluated using serum cortisol, salivary cortisol, and the University of Melbourne Pain Scale (UMPS) Score.

RESULTS

Any statistical differences were observed in the UMPS scores when the OVELA group was compared to the OVEL group at 1 h after surgery (p = 0.515), 12 h (p = 0.375) and 24 h (p = 0.242). Animals undergoing open surgery (OVE group) had significantly higher pain scores at all times after surgery when compared with OVEL and OVELA groups. A high positive correlation (r = 0.792; p = 0.01) was found between serum and saliva cortisol concentrations. Mean saliva cortisol concentration was not significantly lower for the OVELA group compared to the other groups.

CONCLUSIONS

This study found evidence that preoperative administration of acetazolamide may be beneficial in managing postoperative pain in dogs after laparoscopic surgeries. However, further research with a larger sample size is needed to confirm this and to determine if acetazolamide should be included in a multimodal postoperative analgesia protocol for laparoscopic ovariectomy in dogs.

Nano-hydroxyapatite improves intestinal absorption of acetazolamide (BCS Class IV drug)–but how?

We earlier reported that coating poorly water-soluble drugs with nano-hydroxyapatite (nano-HAP) improves bioavailability after oral administration. In the present study, we coated BCS Class IV drug acetazolamide (AZ) with nano-HAP (AZ/HAP formulation), and investigated its bioavailability and nano-HAP’s role in promoting it. We tested AZ bioavailability after a single oral dose of the AZ/HAP formulation in rats, followed by a series of in vitro, ex vivo and in vivo testing. The binding state of AZ and nano-HAP was analyzed by gel filtration chromatography. AZ permeability was studied using a Caco-2 cell monolayer assay kit, to test for tight junction penetration, then using an Ussing chamber mounted with intestinal epithelium, both with and without Peyer’s patch tissue, to examine the role of intracellular transport. Fluorescence-labeled nano-HAP particles were administered orally in rats to investigate their localization in the intestinal tract. The area under the blood concentration time-curve in rats was about 4 times higher in the AZ/HAP formulation group than in the untreated AZ group. Gel filtration analysis showed AZ and nano-HAP were not bound. The Caco-2 study showed equivalent AZ permeability for both groups, but without significant change in transepithelial electrical resistance (TEER), indicating that tight junctions were not penetrated. In the Ussing chamber study, no significant difference in AZ permeability between the two groups was observed for epithelium containing Peyer’s patch tissue, but for epithelium without Peyer’s patch tissue, at high concentration, significantly higher permeability in the AZ/HAP formulation group was observed. Fluorescent labeling showed nano-HAP particles were present in both intestinal villi and Peyer’s patch tissue 30 min after oral administration. Our results suggest that nano-HAP’s enhancement of drug permeability from the small intestine occurs not via tight junctions, but intracellularly, via the intestinal villi. Further study to elucidate the mechanism of this permeability enhancement is required.

A Structural Analysis of the FDA Green Book-Approved Veterinary Drugs and Roles in Human Medicine

The FDA Green Book is a list of all drug products that have been approved by the FDA for use in veterinary medicine. The Green Book, as published, lacks structural information corresponding to approved drugs. To address this gap, we have compiled the structural data for all FDA Green Book drugs approved through the end of 2019. Herein we discuss the relevance of this data set to human drugs in the context of structural classes and physicochemical properties. Analysis reveals that physicochemical properties are highly optimized and consistent with a high probability of favorable drug metabolism and pharmacokinetic properties, including good oral bioavailability for most compounds. We provide a detailed analysis of this data set organized on the basis of structure and function. Slightly over half (51%) of vet drugs are also approved in human medicine. Combination drugs are biologics are also discussed.

Acetazolamide attenuates transvascular fluid flux in equine lungs during intense exercise

  During intense exercise in horses the transvascular fluid flux in the pulmonary circulation (Jv-a) represents 4% of cardiac output (Q). This fluid flux has been attributed to an increase in pulmonary transmural hydrostatic forces, increases in perfused microvascular surface area, and reversible alterations in capillary permeability under conditions of high flow and pressure. Erythrocyte fluid efflux, however, accounts for a significant fraction of Jv-a. In the lung the Jacobs-Stewart cycle occurs with diffusion of CO2 into alveolar space with possible accompanying chloride (Cl-) and water movement from the erythrocyte directly into the pulmonary interstitium. We hypothesised that inhibition of carbonic anhydrase in erythrocytes inhibits the Jacobs-Stewart cycle and attenuates Jv-a. Five horses were exercised on a treadmill until fatigue without (control) and with acetazolamide treatment (30 mg kg(-1) 30 min before exercise). Erythrocyte fluid efflux, plasma fluid flux across the lung and Jv-a were calculated using haemoglobin, haematocrit, plasma protein and Q. Fluid fluxes were used to calculate erythrocyte, plasma and whole blood Cl- fluxes across the lung. Cardiac output was not different between control and acetazolamide treatment. During exercise erythrocyte fluid efflux and Jv-a increased in control (9.3±3.3 and 11.0±4.4 l min(-1), respectively) and was higher than after acetazolamide treatment (3.8±1.6 and 1.2±1.2 l min(-1), respectively) (P<0.05). Plasma fluid flux did not change from rest in control and decreased after acetazolamide treatment (-4.5±1.5 l min(-1)) (P<0.05). Erythrocyte Cl- flux increased during exercise in control and after acetazolamide treatment (P<0.05). During exercise plasma Cl- flux across the lung did not change in control; however, it increased with acetazolamide treatment (P=0.0001). During exercise whole blood Cl- flux increased across the lung in control (P<0.05) but not after acetazolamide treatment. The results indicate that Jv-a in the lung is dependent on the Jacobs-Stewart cycle and mostly independent of transmural hydrostatic forces. It also appears that Jv-a is mediated by Cl- and water egress from erythrocytes directly into the interstitium without transit through plasma.

Effects of chronic acetazolamide administration on gas exchange and acid-base control in pulmonary circulation in exercising horses

REASONS FOR PERFORMING STUDY

Carbonic anhydrase (CA) catalyses the hydration/dehydration reaction of CO(2) and increases the rate of Cl(-) and HCO(3)(-) exchange between the erythrocytes and plasma. Therefore, chronic inhibition of CA has a potential to attenuate CO(2) output and induce greater metabolic and respiratory acidosis in exercising horses.

OBJECTIVES

To determine the effects of Carbonic anhydrase inhibition on CO(2) output and ionic exchange between erythrocytes and plasma and their influence on acid-base balance in the pulmonary circulation (across the lung) in exercising horses with and without CA inhibition.

METHODS

Six horses were exercised to exhaustion on a treadmill without (Con) and with CA inhibition (AczTr). CA inhibition was achieved with administration of acetazolamide (10 mg/kg bwt t.i.d. for 3 days and 30 mg/kg bwt before exercise). Arterial, mixed venous blood and CO(2) output were sampled at rest and during exercise. An integrated physicochemical systems approach was used to describe acid base changes.

RESULTS

AczTr decreased the duration of exercise by 45% (P < 0.0001). During the transition from rest to exercise CO(2) output was lower in AczTr (P < 0.0001). Arterial PCO(2) (P < 0.0001; mean ± s.e. 71 ± 2 mmHg AczTr, 46 ± 2 mmHg Con) was higher, whereas hydrogen ion (P = 0.01; 12.8 ± 0.6 nEq/l AczTr, 15.5 ± 0.6 nEq/l Con) and bicarbonate (P = 0.007; 5.5 ± 0.7 mEq/l AczTr, 10.1 ± 1.3 mEq/l Con) differences across the lung were lower in AczTr compared to Con. No difference was observed in weak electrolytes across the lung. Strong ion difference across the lung was lower in AczTr (P = 0.0003; 4.9 ± 0.8 mEq AczTr, 7.5 ± 1.2 mEq Con), which was affected by strong ion changes across the lung with exception of lactate.

CONCLUSIONS

CO(2) and chloride changes in erythrocytes across the lung seem to be the major contributors to acid-base and ions balance in pulmonary circulation in exercising horses.

Effects of chronic acetazolamide administration on fluid flux from the pulmonary vasculature at rest and during exercise in horses

REASONS FOR PERFORMING STUDY

Horses develop high pulmonary pressures during exercise, which force fluid out of pulmonary capillaries. Specific airway diseases in horses, especially those associated with hypoxaemia, hypercapnoea and acidosis may influence pulmonary haemodynamics and pulmonary interstitial fluid equilibrium.

OBJECTIVES

This study was designed to determine fluid flux (J(V-A) l/min) across the lung in exercising horses treated chronically with acetazolamide.

METHODS

Six horses were exercised on a treadmill until fatigue without (Con) and with chronic carbonic anhydrase (CA) inhibition (AczTr) and associated hypercapnoea and acidosis. Carbonic anhydrase inhibition was achieved with administration of acetazolamide (Acz). Arterial and mixed venous blood were sampled, and VCO2 and VO2 measured. Blood volume changes across the lung (deltaBV%) were calculated from changes in plasma protein, haemoglobin and packed cell volume (PCV). Cardiac output (Q) was calculated using Fick principle. J(V-A) across the alveolar-capillary barrier was then quantified based on Q and deltaBV. Variables were analysed using 2-way repeated-measures ANOVA (P<0.05). A significant F ratio was further analysed using Tukey post hoc analysis.

RESULTS

Treatment had a significant effect on J(V-A) (P = 0.002). At rest there was no J(V-A) in Con (0.63 +/- 0.6 l/min) and AczTr (0.84 +/- 0.3 l/min). During exercise Con fluid moved from the pulmonary circulation into the pulmonary interstitium (mean +/- s.e. J(V-A) 9.4 +/- 2.4 l/min). This was different from AczTr (mean +/- s.e. J(V-A) 1.8 +/- 1.9 l/min), where no transvascular fluxes from pulmonary circulation were present during exercise (P = 0.008).

CONCLUSIONS

Chronic Acz treatment with associated hypercapnoea and acidosis affects J(V-A) in lungs of exercising horses. Lung fluid dynamics adapted to hypercapnoea and acidosis with reduction of fluid flow from the pulmonary circulation.

POTENTIAL RELEVANCE

The current data provide comprehensive evidence of in vivo fluid homeostasis in lungs of exercising horses without and with CA inhibition.

Classification of orally administered drugs on the World Health Organization Model list of Essential Medicines according to the biopharmaceutics classification system

Since its inception in 1995, the biopharmaceutical classification system (BCS) has become an increasingly important tool for regulation of drug products world-wide. Until now, application of the BCS has been partially hindered by the lack of a freely available and accurate database summarising solubility and permeability characteristics of drug substances. In this report, orally administered drugs on the Model list of Essential Medicines of the World Health Organization (WHO) are assigned BCS classifications on the basis of data available in the public domain. Of the 130 orally administered drugs on the WHO list, 61 could be classified with certainty. Twenty-one (84%) of these belong to class I (highly soluble, highly permeable), 10 (17%) to class II (poorly soluble, highly permeable), 24 (39%) to class III (highly soluble, poorly permeable) and 6 (10%) to class IV (poorly soluble, poorly permeable). A further 28 drugs could be provisionally assigned, while for 41 drugs insufficient or conflicting data precluded assignment to a specific BCS class. A total of 32 class I drugs (either certain or provisional classification) were identified. These drugs can be further considered for biowaiver status (drug product approval based on dissolution tests rather than bioequivalence studies in humans).

Carbonic anhydrase activity and sweat gland morphology in trained and untrained Standardbred trotters

Sweat gland morphology and carbonic anhydrase (CA) distribution was studied after exercise in trained and untrained horses using a histochemical technique and light microscopic image analysis. Three trained and 3 untrained Standardbred trotters performed an exercise test (20 min trot at 6 m/s with 5 min walk at 1.8 m/s in the beginning and end) on a high-speed treadmill at 35 degrees C. Skin biopsies were taken before exercise and after trot. The fluid loss after exercise was 10, 12 and 12 g/kg bwt in the untrained horses and 4, 6 and 11 g/kg in the trained. Trained horses had a larger cell area than untrained after exercise, which might be related to an increase in secretory capacity. The area of the cell occupied by CA was independent of training status, but increased with exercise in both groups. The CA activity was higher in untrained animals and increased after exercise in both groups. The change in CA during exercise might be a response to an increasing demand for HCO3- secretion during sweat formation. Therefore, the sweat gland undergoes morphological changes due to stimuli such as heat, exercise and training, but species differences are evident. To our knowledge, no one has previously studied the influence of training on the morphology of the equine sweat gland.