Pharmacokinetics of mycophenolate mofetil following single-dose intravenous and single- and multiple-dose oral administration and clinicopathologic effects of mycophenolate mofetil following long-term oral administration in healthy horses

Autoimmune Dermatopathies of Horses

Autoimmune dermatopathies are not common in horses. These autoimmune diseases can be idiopathic or triggered by an antigen such as drugs, vaccines, or neoplasia. The most common one is pemphigus foliaceus, which manifests as a pustular, crusting eruption. Other more common pustular diseases should be ruled out before considering pemphigus. Vasculitis is relatively common in horses and can be triggered by a variety of antigenic stimulations. Systemic lupus and true idiopathic autoimmune vasculitis are very rare in horses. Every effort should be made to reach a final diagnosis, as the prognosis for true idiopathic autoimmune skin diseases is poor.

The effects of food on the pharmacokinetics of mycophenolate mofetil in healthy horses

Additional immunomodulatory treatment is needed for the management of immune-mediated disease in horses. Mycophenolate mofetil (MMF) is an immunomodulatory agent used in human and veterinary medicine for the prevention of graft rejection and the management of autoimmune diseases. Few studies exist investigating the pharmacokinetics of MMF in horses. The aim of this study was to evaluate the pharmacokinetics of a single dose of MMF in healthy horses in the fed vs. fasted state. Six healthy Standardbred mares were administered MMF 10 mg/kg by a nasogastric (NG) tube in a fed and fasted state. A six-day washout period was performed between the two doses. No statistically significant differences in mycophenolic acid (MPA) concentrations were seen at any time point apart from 8 h, when plasma metabolite concentrations were significantly higher in the fasted state compared to the fed state (p = .038). Evidence of enterohepatic recirculation was seen only in the fasted state; this did not yield clinical differences in horses administered a single-dose administration but may be significant in horses receiving long-term MMF treatment.

Pharmacokinetics and tolerability of multiple-day oral dosing of mycophenolate mofetil in healthy horses

BACKGROUND

Additional efficacious immunomodulatory treatment is needed for the management of immune-mediated disease in horses. Mycophenolate mofetil (MMF) is an immunosuppressive drug that warrants assessment as a viable therapeutic agent for horses.

HYPOTHESIS/OBJECTIVES

To evaluate the pharmacokinetics (PK) of multiple-day oral dosing of MMF in healthy horses and to determine the tolerability of this dosing regimen.

ANIMALS

Six healthy Standardbred mares.

METHODS

Horses received MMF 10 mg/kg PO q12h for 7 days in the fed state. Serial sampling was performed over 12 hours on Days 1 and 7 with trough samples collected every 24 hours, immediately before morning drug administration. Noncompartmental PK analyses were performed to determine primary PK parameters, followed by calculation of geometric means and coefficients of variation. A CBC, serum biochemical profile, physical examination, and fecal scoring were used to assess dose tolerability.

RESULTS

Seven days of treatment resulted in a mycophenolic acid (MPA) area under the curve (AUC0-12 ) of 12 594 h × ng/mL (8567-19 488 h × ng/mL) and terminal half-life (T1/2 ) of 11.3 hours (7.5-15.9 hours), yielding minor metabolite accumulation in all horses treated. Salmonellosis was detected in the feces of 2 horses by Day 7, and all horses developed myelosuppression, hyperbilirubinemia, hyporexia, decreased gastrointestinal motility, and decreased fecal output by the seventh day of treatment.

CONCLUSION AND CLINICAL IMPORTANCE

Administration of MMF at 10 mg/kg PO q12h resulted in hematologic and clinical toxicity within 1 week of treatment. A decreased MMF dose, frequency, or both is needed to avoid colic. Drug monitoring should include frequent hemograms, serum biochemical profiles, and strict biosecurity protocols.

Morphology of the male rat gonad after in Utero exposure to immunosuppressants

The protocol for immunosuppression of pregnant women is based on immunosuppressant panels. The aim of the study was to determine the influence of commonly applied combinations of immunosuppressants to pregnant rats on the morphology of the offspring' testes. Pregnant rats were treated with cyclosporin A (CsA), mycophenolate mofetil (MMF) and prednisone (Pred) (CMG); tacrolimus (Tc), MMF and Pred (TMG); CsA, everolimus (Ev) and Pred (CEG). Testes of mature offspring underwent morphological analysis. Mainly in the testes of CMG and TMG rats the morphological and functional changes were observed: immature germ cells (GCs) in the seminiferous tubule (ST) lumen, invaginations of the basement membrane, infolding to the seminiferous epithelium (SE), the ST wall thickening, increased acidophilia of Sertoli cells' (SCs) cytoplasm, large residual bodies near the lumen, dystrophic ST and tubules look like the Sertoli cell-only syndrome, Leydig cells with abnormal cell nucleus, hypertrophy of the interstitium, blurring of the boundary between ST wall and interstitium, a reduced number of GCs in the SE, vacuolation of the SE. In the CEG there were only a reduced number of GCs in some tubules and vacuolization of SCs. The safest combination of drugs was CEG, while the TMG and CMG were gonadotoxic.

Noncompartmental pharmacokinetics of three intravenous mycophenolate mofetil concentrations in healthy Standardbred mares

BACKGROUND

Mycophenolate mofetil (MMF) is the prodrug of mycophenolic acid (MPA) which acts as an immunosuppressive agent. During the biotransformation of MMF to MPA, additional metabolites including MPA phenol glucuronide (MPAG), MPA acyl glucuronide (AcMPAG) and MPA phenol glucoside (MPG) are formed.

OBJECTIVE

To define the noncompartmental pharmacokinetic (PK) parameters of three single doses of intravenous (i.v.) MMF and its downstream metabolites in healthy horses.

ANIMALS

Six healthy Standardbred mares.

MATERIALS AND METHODS

Generic MMF (Par Pharmaceuticals; Chestnut Ridge, NY, USA) was reconstituted and administered as a single i.v. bolus at 1.0 mg/kg, 5.0 mg/kg and 10.0 mg/kg with an eight day washout between treatments. Blood samples were collected immediately before MMF administration and over 24 h. A liquid chromatography-tandem mass spectrometry assay was developed following FDA guidance to determine plasma MMF, MPA, MPAG, AcMPAG and MPG concentrations. Plasma concentrations were analysed independently, followed by calculation of geometric mean and coefficient of variation.

RESULTS

Noncompartmental PK parameters were determined for MMF and all metabolites at all doses. MMF was rapidly converted to MPA in all horses. Each incremental dose of MMF resulted in increases in C_max and AUC_inf _obs for MPA and the three additional metabolites. Within the 10-fold dose range, the increase in C_max and AUC_inf _obs for MMF and its metabolites was nonlinear.

CONCLUSIONS AND CLINICAL RELEVANCE

Horses biotransform MMF into MPA, MPAG, AcMPAG and MPG via the glucuronidation and glucosidation clearance pathways. Equine reference PK profiles for MPA and the metabolites, MPAG, AcMPAG and MPG were established.