Mycophenolic Acid Dailymed

12.1 Mechanism of Action

Mycophenolic acid (MPA), an immunosuppressant, is an uncompetitive and reversible inhibitor of inosine monophosphate dehydrogenase (IMPDH), and therefore inhibits the de novopathway of guanosine nucleotide synthesis without incorporation to DNA. T- and B-lymphocytes are critically dependent for their proliferation on de novosynthesis of purines, whereas other cell types can utilize salvage pathways. MPA has cytostatic effects on lymphocytes. 

Mycophenolate sodium has been shown to prevent the occurrence of acute rejection in rat models of kidney and heart allotransplantation. Mycophenolate sodium also decreases antibody production in mice.

12.3 Pharmacokinetics

Mycophenolic acid delayed-release tablets exhibits linear and dose-proportional pharmacokinetics over the dose-range (360 mg to 2,160 mg) evaluated. The absolute bioavailability of mycophenolic acid delayed-release tablets in stable renal transplant patients on cyclosporine was 72%. MPA is highly protein bound (> 98% bound to albumin). The predominant metabolite of MPA is the phenolic glucuronide (MPAG) which is pharmacologically inactive. A minor metabolite AcMPAG which is an acyl glucuronide of MPAG is also formed and has pharmacological activity comparable to MPA. MPAG undergoes renal elimination. A fraction of MPAG also undergoes biliary excretion, followed by deconjugation by gut flora and subsequent reabsorption as MPA. The mean elimination half-lives of MPA and MPAG ranged between 8 and 16 hours, and 13 and 17 hours, respectively.

Absorption 

In vitrostudies demonstrated that the enteric-coated mycophenolic acid delayed-release tablet does not release MPA under acidic conditions (pH < 5) as in the stomach but is highly soluble in neutral pH conditions as in the intestine. Following mycophenolic acid delayed-release tablets oral administration without food in several pharmacokinetic studies conducted in renal transplant patients, consistent with its enteric-coated formulation, the median delay (T _lag) in the rise of MPA concentration ranged between 0.25 and 1.25 hours and the median time to maximum concentration (T _max) of MPA ranged between 1.5 and 2.75 hours. In comparison, following the administration of MMF, the median T _maxranged between 0.5 and 1 hours. In stable renal transplant patients on cyclosporine, USP MODIFIED based immunosuppression, gastrointestinal absorption and absolute bioavailability of MPA following the administration of mycophenolic acid delayed-release tablet was 93% and 72%, respectively. Mycophenolic acid delayed-release tablets pharmacokinetics is dose proportional over the dose range of 360 mg to 2,160 mg. 

Distribution 

The mean (± SD) volume of distribution at steady state and elimination phase for MPA is 54 (± 25) L and 112 (± 48) L, respectively. MPA is highly protein bound to albumin, > 98%. The protein binding of MPAG is 82%. The free MPA concentration may increase under conditions of decreased protein binding (uremia, hepatic failure, and hypoalbuminemia). 

Metabolism

 MPA is metabolized principally by glucuronyl transferase to glucuronidated metabolites. The phenolic glucuronide of MPA, MPAG, is the predominant metabolite of MPA and does not manifest pharmacological activity. The acyl glucuronide is a minor metabolite and has comparable pharmacological activity to MPA. In stable renal transplant patients on cyclosporine, USP MODIFIED based immunosuppression, approximately 28% of the oral mycophenolic acid delayed-release tablets dose was converted to MPAG by presystemic metabolism. The AUC ratio of MPA:MPAG:acyl glucuronide is approximately 1:24:0.28 at steady state. The mean clearance of MPA was 140 (± 30) mL/min. 

Elimination 

The majority of MPA dose administered is eliminated in the urine primarily as MPAG (> 60%) and approximately 3% as unchanged MPA following mycophenolic acid administration to stable renal transplant patients. The mean renal clearance of MPAG was 15.5 (± 5.9) mL/min. MPAG is also secreted in the bile and available for deconjugation by gut flora. MPA resulting from the deconjugation may then be reabsorbed and produce a second peak of MPA approximately 6 to 8 hours after mycophenolic acid dosing. The mean elimination half-life of MPA and MPAG ranged between 8 and 16 hours, and 13 and 17 hours, respectively. 

Food Effect 

Compared to the fasting state, administration of mycophenolic acid delayed-release tablets 720 mg with a high-fat meal (55 g fat, 1,000 calories) had no effect on the systemic exposure (AUC) of MPA. However, there was a 33% decrease in the maximal concentration (C _max), a 3.5-hour delay in the T _lag(range, -6 to 18 hours), and 5-hour delay in the T _max(range, -9 to 20 hours) of MPA. To avoid the variability in MPA absorption between doses, mycophenolic acid delayed-release tablets should be taken on an empty stomach [see Dosage and Administration ( 2.3) ]. 

Pharmacokinetics in Renal Transplant Patients 

The mean pharmacokinetic parameters for MPA following the administration of mycophenolic acid in renal transplant patients on cyclosporine, USP MODIFIED based immunosuppression are shown in Table 6. Single-dose mycophenolic acid pharmacokinetics predicts multiple-dose pharmacokinetics. However, in the early post-transplant period, mean MPA AUC and C _maxwere approximately one-half of those measured 6 months post-transplant. 

After near equimolar dosing of mycophenolic acid 720 mg twice daily and MMF 1,000 mg twice daily (739 mg as MPA) in both the single- and multiple-dose crossover trials, mean systemic MPA exposure (AUC) was similar.

Table 6: Mean ± SD Pharmacokinetic Parameters for MPA Following the Oral Administration of Mycophenolic Acid Delayed-Release Tablets to Renal Transplant Patients on Cyclosporine, USP MODIFIED Based Immunosuppressio n

Patient	Mycophenolic Acid Delayed-Release Tablets   Dosing		N		Dose (mg)	T max * (hr)		C max  (mcg/mL)			AUC 0 -12hr   (mcg*hr/mL)
Adult	Single		24		720	2 (0.8 – 8)		26.1 ± 12			66.5 ± 22.6**
Pediatric***	Single		10		450/m 2	2.5 (1.5 – 24)		36.3 ± 20.9			74.3 ± 22.5**
Adult	Multiple x 6 days, twice daily		10		720	2 (1.5 – 3)		37 ± 13.3			67.9 ± 20.3
Adult	Multiple x 28 days, twice daily		36		720	2.5 (1.5 – 8)		31.2 ± 18.1			71.2 ± 26.3
Adult	Chronic, multiple-dose, twice daily
	2 weeks post-transplant		12		720	1.8 (1 – 5.3)		15 ± 10.7			28.6 ± 11.5
	3 months post-transplant		12		720	2 (0.5 – 2.5)		26.2 ± 12.7			52.3 ± 17.4
	6 months post-transplant		12		720	2 (0 – 3)		24.1 ± 9.6			57.2 ± 15.3
Adult	Chronic, multiple-dose, twice daily		18		720	1.5 (0 – 6)		18.9 ± 7.9			57.4 ± 15

*median (range).

**AUC _inf

***age range of 5 to 16 years.

Specific Populations

Patients with Renal Insufficiency: No specific pharmacokinetic studies in individuals with renal impairment were conducted with mycophenolic acid delayed-release tablets. However, based on studies of renal impairment with MMF, MPA exposure is not expected to be appreciably increased over the range of normal to severely impaired renal function following mycophenolic acid delayed-release tablets administration. 

In contrast, MPAG exposure would be increased markedly with decreased renal function; MPAG exposure being approximately 8-fold higher in the setting of anuria. Although dialysis may be used to remove the inactive metabolite MPAG, it would not be expected to remove clinically significant amounts of the active moiety MPA. This is in large part due to the high plasma protein binding of MPA.

Patients withHepatic Insufficiency : No specific pharmacokinetic studies in individuals with hepatic impairment were conducted with mycophenolic acid delayed-release tablets. In a single dose (MMF 1,000 mg) trial of 18 volunteers with alcoholic cirrhosis and 6 healthy volunteers, hepatic MPA glucuronidation processes appeared to be relatively unaffected by hepatic parenchymal disease when the pharmacokinetic parameters of healthy volunteers and alcoholic cirrhosis patients within this trial were compared. However, it should be noted that for unexplained reasons, the healthy volunteers in this trial had about a 50% lower AUC compared to healthy volunteers in other studies, thus making comparison between volunteers with alcoholic cirrhosis and healthy volunteers difficult. Effects of hepatic disease on this process probably depend on the particular disease. Hepatic disease, such as primary biliary cirrhosis, with other etiologies may show a different effect.

Pediatric Patients: Limited data are available on the use of mycophenolic acid delayed-release tablets at a dose of 450 mg/m ²body surface area in children. The mean MPA pharmacokinetic parameters for stable pediatric renal transplant patients, 5 to 16 years, on cyclosporine, USP MODIFIED are shown in Table 6. At the same dose administered based on body surface area, the respective mean C _maxand AUC of MPA determined in children were higher by 33% and 18% than those determined for adults. The clinical impact of the increase in MPA exposure is not known [see Dosage and Administration ( 2.2, 2.3 )].

Male and Female Patients: There are no significant gender differences in mycophenolic acid delayed-release tablets pharmacokinetics. 

Geriatric Patients: Pharmacokinetics in the elderly have not been formally studied. 

Racial or Ethnic Groups: Following a single dose administration of 720 mg of mycophenolic acid delayed-release tablets to 18 Japanese and 18 Caucasian healthy subjects, the exposure (AUC _inf) for MPA and MPAG were 15% and 22% lower in Japanese subjects compared to Caucasians. The peak concentrations (C _max) for MPAG were similar between the two populations, however, Japanese subjects had 9.6% higher C _maxfor MPA. These results do not suggest any clinically relevant differences.

Drug Interactions:

Antacids With Magnesium and Aluminum Hydroxides:

Absorption of a single dose of mycophenolic acid delayed-release tablets was decreased when administered to 12 stable kidney transplant patients also taking magnesium-aluminum-containing antacids (30 mL): the mean C _maxand AUC _{(0 to t)}values for MPA were 25% and 37% lower, respectively, than when mycophenolic acid delayed-release tablets were administered alone under fasting conditions [see Drug Interactions ( 7.1) ]. 

Pantoprazole:

In a trial conducted in 12 healthy volunteers, the pharmacokinetics of MPA were observed to be similar when a single dose of 720 mg of mycophenolic acid delayed-release tablets was administered alone and following concomitant administration of mycophenolic acid delayed-release tablets and pantoprazole, which was administered at a dose of 40 mg twice daily for 4 days [see Drug Interactions ( 7.11 ) ].

The following drug interaction studies were conducted following the administration of MMF

Cholestyramine:  

Following single-dose oral administration of 1.5 grams MMF to 12 healthy volunteers pretreated with 4 grams three times daily of cholestyramine for 4 days, MPA AUC decreased approximately 40%. This decrease is consistent with interruption of enterohepatic recirculation which may be due to binding of recirculating MPAG with cholestyramine in the intestine [see Drug Interactions ( 7.3) ]. 

Sevelamer:

Concomitant administration of sevelamer and MMF in stable adult and pediatric kidney transplant patients decreased the mean MPA C _maxand AUC _(0-12h)by 36% and 26%, respectively [see Drug Interactions ( 7.4)] . 

Cyclosporine:

Cyclosporine (Sandimmune ^®) pharmacokinetics (at doses of 275 to 415 mg/day) were unaffected by single and multiple doses of 1.5 grams twice daily of MMF in 10 stable kidney transplant patients. The mean (± SD) AUC _(0-12h)and C _maxof cyclosporine after 14 days of multiple doses of MMF were 3,290 (± 822) ng•h/mL and 753 (± 161) ng/mL, respectively, compared to 3,245 (± 1,088) ng•h/mL and 700 (± 246) ng/mL, respectively, 1 week before administration of MMF.

A total of 73 de novokidney allograft recipients on MMF therapy received either low dose cyclosporine withdrawal by 6 months post-transplant (50 to 100 ng/mL for up to 3 months post-transplant followed by complete withdrawal at month 6 post-transplant) or standard dose cyclosporine (150 to 300 ng/mL from baseline through month 4 post-transplant and 100 to 200 ng/mL thereafter). At month 12 post-transplant, the mean MPA (AUC _(0-12h)) in the cyclosporine withdrawal group was approximately 40% higher, than that of the standard dose cyclosporine group. 

Cyclosporine inhibits multidrug-resistance-associated protein 2 (MRP-2) transporter in the biliary tract, thereby preventing the excretion of MPAG into the bile that would lead to enterohepatic recirculation of MPA [see Drug Interactions ( 7.5) ]. 

Norfloxacin and Metronidazole: 

Following single-dose administration of MMF (1 g) to 11 healthy volunteers on Day 4 of a 5-day course of a combination of norfloxacin and metronidazole, the mean MPA AUC _(0-48h)was reduced by 33% compared to the administration of MMF alone (p < 0.05). There was no significant effect on mean MPA AUC _(0-48h)when MMF was concomitantly administered with norfloxacin or metronidazole separately. The mean (± SD) MPA AUC _(0-48h)after coadministration of MMF with norfloxacin or metronidazole separately was 48.3 (± 24) mcg•h/mL and 42.7 (± 23) mcg•h/mL, respectively, compared with 56.2 (± 24) mcg•h/mL after administration of MMF alone [see Drug Interactions ( 7.6) ]. 

Rifampin:  

In a single heart-lung transplant patient on MMF therapy (1 gram twice daily), a 67% decrease in MPA exposure (AUC _(0-12h)) was observed with concomitant administration of MMF and 600 mg rifampin daily. 

In 8 kidney transplant patients on stable MMF therapy (1 gram twice daily), administration of 300 mg rifampin twice daily resulted in a 17.5% decrease in MPA AUC _(0-12h)due to inhibition of enterohepatic recirculation of MPAG by rifampin. Rifampin coadministration also resulted in a 22.4% increase in MPAG AUC _(0-12h) [see Drug Interactions ( 7.7) ]. 

Oral Contraceptives:  

In a drug-drug interaction trial, mean AUCs were similar for ethinyl estradiol and norethindrone, when coadministered with MMF as compared to administration of the oral contraceptives alone [see Drug Interactions ( 7.8) ]. 

Acyclovir:

Coadministration of MMF (1 gram) and acyclovir (800 mg) to 12 healthy volunteers resulted in no significant change in MPA AUC and C _max. However, MPAG and acyclovir plasma mean AUC _(0-24h)were increased 10% and 18%, respectively. Because MPAG plasma concentrations are increased in the presence of kidney impairment, as are acyclovir concentrations, the potential exists for mycophenolate and acyclovir or its prodrug (e.g., valacyclovir) to compete for tubular secretion, further increasing the concentrations of both drugs [see Drug Interactions ( 7.9) ].

Ganciclovir:

 Following single-dose administration to 12 stable kidney transplant patients, no pharmacokinetic interaction was observed between MMF (1.5 grams) and intravenous ganciclovir (5 mg per kg). Mean (± SD) ganciclovir AUC and C _max(n = 10) were 54.3 (± 19) mcg•h/mL and 11.5 (± 1.8) mcg/mL, respectively, after coadministration of the two drugs, compared to 51 (± 17) mcg•h/mL and 10.6 (± 2) mcg/mL, respectively, after administration of intravenous ganciclovir alone. The mean (± SD) AUC and C _maxof MPA (n = 12) after coadministration were 80.9 (± 21.6) mcg•h/mL and 27.8 (± 13.9) mcg/mL, respectively, compared to values of 80.3 (± 16.4) mcg•h/mL and 30.9 (± 11.2) mcg/mL, respectively, after administration of MMF alone. 

Because MPAG plasma concentrations are increased in the presence of renal impairment, as are ganciclovir concentrations, the two drugs will compete for tubular secretion and thus further increases in concentrations of both drugs may occur. In patients with renal impairment in which MMF and ganciclovir or its prodrug (e.g., valganciclovir) are coadministered, patients should be monitored carefully [see Drug Interactions ( 7.9) ].

Ciprofloxacin and Amoxicillin Plus Clavulanic Acid:  

A total of 64 MMF-treated kidney transplant recipients received either oral ciprofloxacin 500 mg twice daily or amoxicillin plus clavulanic acid 375 mg three times daily for 7 or at least 14 days. Approximately 50% reductions in median trough MPA concentrations (predose) from baseline (MMF alone) were observed in 3 days following commencement of oral ciprofloxacin or amoxicillin plus clavulanic acid. These reductions in trough MPA concentrations tended to diminish within 14 days of antibiotic therapy and ceased within 3 days after discontinuation of antibiotics. The postulated mechanism for this interaction is an antibiotic-induced reduction in glucuronidase-possessing enteric organisms leading to a decrease in enterohepatic recirculation of MPA. The change in trough level may not accurately represent changes in overall MPA exposure; therefore, clinical relevance of these observations is unclear [see Drug Interactions ( 7.10) ].