General
Hypotension: Because nifedipine decreases peripheral
vascular resistance, careful monitoring of blood pressure during the initial
administration and titration of Afeditab
® CR is
suggested. Close observation is especially recommended for patients already
taking medications that are known to lower blood pressure (See
WARNINGS).
Peripheral Edema
Mild to moderate peripheral edema occurs in a dose-dependent manner with
Afeditab
® CR. The placebo subtracted rate is
approximately 8% at 30 mg, 12% at 60 mg and 19% at 90 mg daily. This edema is a
localized phenomenon, thought to be associated with vasodilation of dependent
arterioles and small blood vessels and not due to left ventricular dysfunction
or generalized fluid retention. With patients whose hypertension is complicated
by congestive heart failure, care should be taken to differentiate this
peripheral edema from the effects of increasing left ventricular dysfunction.
Information for Patients
Afeditab® CR is an extended-release tablet
and should be swallowed whole and taken on an empty stomach. It should not be
administered with food. Do not chew, divide or crush tablets.
Patients should be advised that empty matrix “ghosts” (tablets) may pass via
colostomy or in the stool, and that this is of no concern since the active
medication has already been absorbed.
Laboratory Tests
Rare, usually transient, but occasionally significant elevations
of enzymes such as alkaline phosphatase, CPK, LDH, SGOT, and SGPT have been
noted. The relationship to nifedipine therapy is uncertain in most cases, but
probable in some. These laboratory abnormalities have rarely been associated
with clinical symptoms; however, cholestasis with or without jaundice has been
reported. A small increase in mean alkaline phosphatase was noted in
patients treated with nifedipine extended-release tablets. This was an isolated
finding and it rarely resulted in values which fell outside the normal range.
Rare instances f allergic hepatitis have been reported with nifedipine
treatment. In controlled studies, nifedipine extended-release tablets did not
adversely affect serum uric acid, glucose, cholesterol or potassium.
Nifedipine, like other calcium channel blockers, decreases platelet
aggregation in vitro. Limited clinical studies have
demonstrated a moderate but statistically significant decrease in platelet
aggregation and increase in bleeding time in some nifedipine patients. This is
thought to be a function of inhibition of calcium transport across the platelet
membrane. No clinical significance for these findings has been demonstrated.
Positive direct Coombs’ test with or without hemolytic anemia has been
reported but a causal relationship between nifedipine administration and
positivity of this laboratory test, including hemolysis, could not be
determined.
Although nifedipine has been used safely in patients with renal dysfunction
and has been reported to exert a beneficial effect in certain cases, rare
reversible elevations in BUN and serum creatinine have been reported in patients
with pre-existing chronic renal insufficiency. The relationship to nifedipine
therapy is uncertain in most cases but probable in some.
Drug Interactions
Beta-adrenergic blocking
agents (See WARNINGS.)
Nifedipine is mainly eliminated by metabolism and is a substrate of CYP3A.
Inhibitors and inducers of CYP3A4 can impact the exposure to nifedipine and
consequently its desirable and undesirable effects. In
vitro and in vivo data indicate that
nifedipine can inhibit the metabolism of drugs hat are substrates of CYP3A,
thereby increasing the exposure to other drugs. Nifedipine is a vasodilator, and
o-administration of other drugs affecting blood pressure may result in
pharmacodynamic interactions.
Cardiovascular Drugs
Antiarrhythmics
Quinidine: Quinidine is a substrate of CYP3A and
has been shown to inhibit CYP3A in vitro.
Co-administration of multiple doses of quinidine sulfate, 200 mg t.i.d., and
nifedipine, 20 mg t.i.d., increased Cmax and AUC of
nifedipine in healthy volunteers by factors of 2.30 and 1.37, respectively. The
heart rate in the initial interval after drug administration was increased by up
to 17.9 beats/minute. The exposure to quinidine was not importantly changed in
the presence of nifedipine. Monitoring of heart rate and adjustment of the
nifedipine dose, if necessary, are recommended when quinidine is added to a
treatment with nifedipine.
Flecainide: There has been too little experience
with the o-administration of TAMBOCOR with nifedipine to recommend concomitant
use.
Calcium Channel Blockers
Diltiazem: Pre-treatment of healthy volunteers
with 30 mg or 90 mg t.i.d. diltiazem p.o. increased the AUC of nifedipine after
a single dose of 20 mg nifedipine by factors of 2.2 and 3.1, respectively. The
corresponding Cmax values of nifedipine increased by
factors of 2.0 and 1.7, respectively. Caution should be exercised when
co-administering diltiazem and nifedipine and a reduction of the dose of
nifedipine should be considered.
Verapamil: Verapamil, a CYP3A inhibitor, can
inhibit the metabolism of nifedipine and increase the exposure to nifedipine
during concomitant therapy. Blood pressure should be monitored and reduction of
the dose of nifedipine considered.
ACE Inhibitors
Benazepril: In healthy volunteers receiving single
dose of 20 mg nifedipine ER and benazepril 20 mg, the plasma concentrations of
benazeprilat and nifedipine in the presence and absence of each other were not
statistically significantly different. A hypotensive effect was only seen after
co-administration of the two drugs. The tachycardic effect of nifedipine was
attenuated in the presence of benazepril.
Angiotensin-II Blockers
Irbesartan:In vitro
studies show significant inhibition of the formation of oxidized irbesartan
metabolites by nifedipine. However, in clinical studies, concomitant nifedipine
had no effect on irbesartan pharmacokinetics.
Candesartan: No significant drug interaction has
been reported in studies with candesartan cilexitil given together with
nifedipine. Because candesartan is not significantly metabolized by the
cytochrome P450 system and at therapeutic concentrations has no effect on
cytochrome 450 enzymes, interactions with drugs that inhibit or are metabolized
by those enzymes would not be expected.
Beta-blockers
Nifedipine extended-release tablets was well tolerated when administered in
combination with beta-blockers in 187 hypertensive patients in a
placebo-controlled clinical trial. However, there have been occasional
literature reports suggesting that the combination of nifedipine and
beta-adrenergic blocking drugs may increase the likelihood f congestive heart
failure, severe hypotension or exacerbation of angina in patients with
cardiovascular disease. Clinical monitoring is recommended and a dose adjustment
of nifedipine should be considered.
Timolol: Hypotension is more likely to occur if
dihydropryridine calcium antagonists such as nifedipine are co-administered with
timolol.
Central Alpha1-Blockers
Doxazosin: Healthy volunteers participating in a
multiple dose doxazosin-nifedipine interaction study received 2 mg doxazosin
q.d. alone or combined with 20 mg nifedipine ER b.i.d. Co-administration of
nifedipine resulted in a decrease in AUC and Cmax of
doxazosin to 83% and 86% of the values in the absence of nifedipine,
respectively. In the presence of doxazosin, AUC and Cmax
of nifedipine were increased by factors of 1.13 and 1.23, respectively. Compared
to nifedipine monotherapy, blood pressure was lower in the presence of
doxazosin. Blood pressure should be monitored when doxazosin is co-administered
with nifedipine, and dose reduction of nifedipine considered.
Digitalis
Digoxin: Since there have been isolated reports of
patients with elevated digoxin levels, and there is a possible interaction
between digoxin and nifedipine, it is recommended that digoxin levels be
monitored when initiating, adjusting and discontinuing nifedipine
extended-release tablets to avoid possible over- or under-digitalization.
Antithrombotics
Coumarins: There have been rare reports of
increased prothrombin time in patients taking coumarin anticoagulants to whom
nifedipine was administered. However, the relationship to nifedipine therapy is
uncertain.
Platelet Aggregation Inhibitors
Clopidogrel: No clinically significant
pharmacodynamic interactions were observed when clopidrogrel was co-administered
with nifedipine.
Tirofiban: Co-administration of nifedipine did not
alter the exposure to tirofiban importantly.
Non-Cardiovascular Drugs
Antifungal Drugs
Ketoconazole, itraconazole and fluconazole are CYP3A inhibitors and can
inhibit the metabolism of nifedipine and increase the exposure to nifedipine
during concomitant therapy. Blood pressure should be monitored and a dose
reduction of nifedipine considered.
Antisecretory Drugs
Omeprazole: In healthy volunteers receiving a
single dose of 10 mg nifedipine, AUC and Cmax of
nifedipine after pretreatment with omeprazole 20 mg q.d. for 8 days were 1.26
and 0.87 times those after pre-treatment with placebo. Pretreatment with or
co-administration of omeprazole did not impact the effect of nifedipine on blood
pressure or heart rate. The impact of omeprazole on nifedipine is not likely to
be of clinical relevance.
Pantoprazole: In healthy volunteers the exposure
to neither drug was changed significantly in the presence of the other drug.
Ranitidine: Five studies in healthy volunteers
investigated the impact of multiple ranitidine doses on the single or multiple
dose pharmacokinetics of nifedipine. Two studies investigated the impact of
coadministered ranitidine on blood pressure in hypertensive subjects on
nifedipine. Co-administration of ranitidine did not have relevant effects on the
exposure to nifedipine that affected the blood pressure or heart rate in
normotensive or hypertensive subjects.
Cimetidine: Five studies in healthy volunteers
investigated the impact of multiple cimetidine doses on the single or multiple
dose pharmacokinetics of nifedipine. Two studies investigated the impact of
coadministered cimetidine on blood pressure in hypertensive subjects on
nifedipine.
In normotensive subjects receiving single doses of 10 mg or multiple doses of
up to 20 mg nifedipine t.i.d. alone or together with cimetidine up to 1000
mg/day, the AUC values of nifedipine in the presence of cimetidine were between
1.52 and 2.01 times those in the absence of cimetidine. The Cmax values of nifedipine in the presence of cimetidine were
increased by factors ranging between 1.60 and 2.02. The increase in exposure to
nifedipine by cimetidine was accompanied by relevant changes in blood pressure
or heart rate in normotensive subjects. Hypertensive subjects receiving 10 mg
q.d. nifedipine alone or in combination with cimetidine 1000 mg q.d. also
experienced relevant changes in blood pressure when cimetidine was added to
nifedipine. The interaction between cimetidine and nifedipine is of clinical
relevance and blood pressure should be monitored and a reduction of the dose of
nifedipine considered.
Antibacterial Drugs
Quinupristin/Dalfopristin:In
vitro drug interaction studies have demonstrated that
quinupristin/dalfopristin significantly inhibits the CYP3A metabolism of
nifedipine. Concomitant administration of quinupristin/dalfopristin and
nifedipine (repeated oral dose) in healthy volunteers increased AUC and Cmax for nifedipine by factors of 1.44 and 1.18, respectively,
compared to nifedipine monotherapy. Upon co-administration of
quinupristin/dalfopristin with nifedipine, blood pressure should be monitored
and a reduction of the dose of nifedipine considered.
Erythromycin: Erythromycin, a CYP3A inhibitor, can
inhibit the metabolism of nifedipine and increase the exposure to nifedipine
during concomitant therapy. Blood pressure should be monitored and reduction of
the dose of nifedipine considered.
Antitubercular Drugs
Rifampin: Pretreatment of healthy volunteers with
600 mg/day rifampin p.o. decreased the exposure to oral nifedipine (20 μg/kg) to
13%. The exposure to intravenous nifedipine by the same rifampin treatment was
decreased to 70%. Dose adjustment of nifedipine may be necessary if nifedipine
is co-administered with rifampin.
Rifapentine: Rifapentine, as an inducer of CYP3A4,
can decrease the exposure to nifedipine. A dose adjustment of nifedipine when
co-administered with rifapentine should be considered.
Antiviral Drugs
Amprenavir, atanazavir, delavirine, fosamprinavir,
indinavir, nelfinavirandritonavir, as CYP3A
inhibitors, can inhibit the metabolism of nifedipine and increase the exposure
to nifedipine. Caution is warranted and clinical monitoring of patients
recommended.
CNS Drugs
Nefazodone, a CYP3A inhibitor, can inhibit the
metabolism of nifedipine and increase the exposure to nifedipine during
concomitant therapy. Blood pressure should be monitored and a reduction of the
dose of nifedipine considered.
Valproic acid may increase the exposure to
nifedipine during concomitant therapy. Blood pressure should be monitored and a
dose reduction of nifedipine considered.
Phenytoin: Nifedipine is metabolized by CYP3A4.
Co-administration of nifedipine 10 mg capsule and 60 mg nifedipine coat-core
tablet with phenytoin, an inducer of CYP3A4, lowered the AUC and Cmax of nifedipine by approximately 70%. When using nifedipine
with phenytoin, the clinical response to nifedipine should be monitored and its
dose adjusted if necessary.
Phenobarbitone and carbamazepine as inducers of
CYP3A can decrease the exposure to nifedipine. Dose adjustment of nifedipine may
be necessary if phenobarbitone, carbamazepine or phenytoin is
coadministered.
Antiemetic Drugs
Dolasetron: In patients taking dolasetron by the
oral or intravenous route and nifedipine, no effect was shown on the clearance
of hydrodolasetron.
Immunosuppressive Drugs
Tacrolimus: Nifedipine has been shown to inhibit
the metabolism of tacrolimus in vitro. Transplant
patients on tacrolimus and nifedipine required from 26% to 38% smaller doses
than patients not receiving nifedipine. Nifedipine can increase the exposure to
tacrolimus. When nifedipine is co-administered with tacrolimus the blood
concentrations of tacrolimus should be monitored and a reduction of the dose of
tacrolimus considered.
Sirolimus: A single 60 mg dose of nifedipine and a
single 10 mg dose of sirolimus oral solution were administered to 24 healthy
volunteers. Clinically significant pharmacokinetic drug interactions were not
observed.
Glucose Lowering Drugs
Pioglitazone: Co-administration of pioglitazone
for 7 days with 30 mg nifedipine ER administered orally q.d. for 4 days to male
and female volunteers resulted in least square mean (90% CI) values for
unchanged nifedipine of 0.83 (0.73-0.95) for Cmax and
0.88 (0.80-0.96) for AUC relative to nifedipine monotherapy. In view of the high
variability of nifedipine pharmacokinetics, the clinical significance of this
finding is unknown.
Rosiglitazone: Co-administration of rosiglitazone
(4 mg b.i.d.) was shown to have no clinically relevant effect on the
pharmacokinetics of nifedipine.
Metformin: A single dose metformin-nifedipine
interaction study in normal healthy volunteers demonstrated that
co-administration of nifedipine increased plasma metformin Cmax and AUC by 20% and 9%, respectively, and increased the
amount of metformin excreted in urine. Tmax and half-life
were unaffected. Nifedipine appears to enhance the absorption of metformin.
Miglitol: No effect of miglitol was observed on
the pharmacokinetics and pharmacodynamics of nifedipine.
Repaglinide: Co-administration of 10 mg nifedipine
with a single dose of 2 mg repaglinide (after 4 days nifedipine 10 mg t.i.d. and
repaglinide 2 mg t.i.d.) resulted in unchanged AUC and Cmax values for both drugs.
Acarbose: Nifedipine tends to produce
hyperglycemia and may lead to loss of glucose control. If nifedipine is
co-administered with acarbose, blood glucose levels should be monitored
carefully and a dose adjustment of nifedipine considered.
Drugs Interfering with Food Absorption
Orlistat: In 17 normal-weight subjects receiving
orlistat 120 mg t.i.d. for 6 days, orlistat did not alter the bioavailability of
60 mg nifedipine (extended-release tablets).
Dietary Supplements
Grapefruit Juice: In healthy volunteers, a single
dose co-administration of 250 mL double strength grapefruit juice with 10 mg
nifedipine increased AUC and Cmax by factors of 1.35 and
1.13, respectively. Ingestion of repeated doses of grapefruit juice (5 x 200 mL
in 12 hours) after administration of 20 mg nifedipine ER increased AUC and
Cmax of nifedipine by a factor of 2.0. Grapefruit juice
should be avoided by patients on nifedipine. The intake of grapefruit juice
should be stopped at least 3 days prior to initiating patients on
nifedipine.
Herbals
St. John’s Wort: Is an inducer of CYP3A4 and may
decrease the exposure to nifedipine. Dose adjustment of nifedipine may be
necessary if St. John’s Wort is co-administered.
CYP2D6 Probe Drug
Debrisoquine: In healthy volunteers, pretreatment
with nifedipine 20 mg t.i.d. for 5 days did not change the metabolic ratio of
hydroxydebrisoquine to debrisoquine measured in urine after a single dose of 10
mg debrisoquine. Thus, it is improbable that nifedipine inhibits in vivo the metabolism of other drugs that are substrates
of CYP2D6.
Carcinogenesis, Mutagenesis, Impairment of Fertility
Nifedipine was administered orally to rats for two years and was
not shown to be carcinogenic. When given to rats prior to mating, nifedipine
caused reduced fertility at a dose approximately 30 times the maximum
recommended human dose. There is a literature report of
reversible reduction in the ability of human sperm obtained from a limited
number of infertile men taking recommended doses of nifedipine to bind to and
fertilize an ovum in vitro.In vivo
mutagenicity studies were negative.
Pregnancy
Pregnancy Category C. In rodents, rabbits and monkeys, nifedipine
has been shown to have a variety of embryotoxic, placentotoxic and fetotoxic
effects, including stunted fetuses (rats, mice and rabbits), digital anomalies
(rats and rabbits), rib deformities (mice), cleft palate (mice), small placentas
and underdeveloped chorionic villi (monkeys), embryonic and fetal deaths (rats,
mice and rabbits), prolonged pregnancy (rats; not evaluated in other species),
and decreased neonatal survival (rats; not evaluated in other species). On a
mg/kg or mg/m2 basis, some of the doses associated with
these various effects are higher than the maximum recommended human dose and
some are lower, but all are within an order of magnitude of it.
The digital anomalies seen in nifedipine-exposed rabbit pups are strikingly
similar to those seen in pups exposed to phenytoin, and these are in turn
similar to the phalangeal deformities that are the most common malformation seen
in human children with in utero exposure to
phenytoin.
There are no adequate and well-controlled studies in pregnant women.
Nifedipine should generally be avoided during pregnancy and used only if the
potential benefit justifies the potential risk to the fetus.
Nursing Mothers
Nursing Mothers: Nifedipine is excreted in human milk. Therefore,
a decision should be made to discontinue nursing or to discontinue the drug,
taking into account the importance of the drug to the mother.
Geriatric Use
Geriatric Use: Although small pharmacokinetic studies have
identified an increased half-life and increased Cmax and
AUC (SeeCLINICAL PHARMACOLOGY:
Pharmacokinetics and Metabolism), clinical studies of nifedipine did
not include sufficient numbers of subjects aged 65 and over to determine whether
they respond differently from younger subjects. Other reported clinical
experience has not identified differences in responses between the elderly and
younger patients. In general, dose selection for an elderly patient should be
cautious, usually starting at the low end of the dosing range, reflecting the
greater frequency of decreased hepatic, renal, or cardiac function, and of
concomitant disease or other drug therapy.