Does Nalfon (fenoprofen) cause side effects?

Nalfon (fenoprofen) is a nonsteroidal anti-inflammatory drug (NSAID) used for management of mild to moderate pain, fever, and inflammation. 

Nonsteroidal anti-inflammatory drugs work by reducing the levels of prostaglandins, chemicals that are responsible for the pain, fever, and swelling of inflammation. Nalfon blocks the enzymes that make prostaglandins (cyclooxygenases), resulting in lower concentrations of prostaglandins. As a consequence, inflammation, swelling, pain and fever are reduced. 

Common side effects of Nalfon include

Serious side effects of Nalfon include reduced ability of blood to clot and increased bleeding after an injury, stomach and intestinal bleeding and ulcers, impaired kidney function, heart attacks, high blood pressure (hypertension), and heart failure.

Drug interactions of Nalfon include lithium because Nalfon may increase the blood levels of lithium by reducing the excretion of lithium by the kidneys.

  • Increased levels of lithium may lead to lithium toxicity.
  • Nalfon may reduce the blood pressure lowering effects of blood pressure medications. This may occur because prostaglandins play a role in the regulation of blood pressure.
  • When NSAIDs are used in combination with or aminoglycosides the blood levels of the methotrexate or aminoglycoside may increase, presumably because their elimination from the body is reduced. This may lead to more methotrexate or aminoglycoside-related side effects.
  • Individuals taking oral blood thinners or anticoagulants, for example, warfarin, should avoid Nalfon because Nalfon also thins the blood, and excessive blood thinning may lead to bleeding.
  • Persons who have more than three alcoholic beverages per day are at increased risk of developing stomach ulcers when taking Nalfon or other NSAIDs. 

In late pregnancy, the third trimester, as with other NSAIDs, Nalfon should be avoided because it may cause premature closure of the ductus arteriosus. 

It is unknown if Nalfon is excreted in breast milk. Consult your doctor before breastfeeding.

What are the important side effects of Nalfon (fenoprofen)?

Common side effects include: 

NSAIDs reduce the ability of blood to clot and therefore increase bleeding after an injury. Fenoprofen also may cause stomach and intestinal bleeding and ulcers. Sometimes, stomach ulceration and intestinal bleeding may occur without any abdominal pain. Black tarry stools, weakness, and dizziness upon standing (orthostatic hypotension) may be the only signs of the bleeding.

People who are allergic to other NSAIDs should not use fenoprofen. NSAIDs reduce the flow of blood to the kidneys and impair function of the kidneys. The impairment is most likely to occur in patients with preexisting impairment of kidney function or congestive heart failure, and use of NSAIDs in these patients should be done cautiously.

Individuals with asthma are more likely to experience allergic reactions to fenoprofen and other NSAIDs. Fluid retention, blood clots, heart attacks, high blood pressure (hypertension), and heart failure also have been associated with the use of NSAIDs.

Nalfon (fenoprofen) side effects list for healthcare professionals

The following adverse reactions are discussed in greater detail in other sections of the labeling:

Clinical Trials Experience

Because clinical trials are conducted under widely varying conditions, adverse reaction rates observed in the clinical trials of a drug cannot be directly compared to rates in the clinical trials of another drug and may not reflect the rates observed in practice.

  • During clinical studies for rheumatoid arthritis, osteoarthritis, or mild to moderate pain and studies of pharmacokinetics, complaints were compiled from a checklist of potential adverse reactions, and the following data emerged.
  • These encompass observations in 6,786 patients, including 188 observed for at least 52 weeks.
  • For comparison, data are also presented from complaints received from the 266 patients who received placebo in these same trials.
  • During short-term studies for analgesia, the incidence of adverse reactions was markedly lower than that seen in longer-term studies.
Adverse Drug Reactions Reported In > 1% Of Patients During Clinical Trials
  • Digestive System During clinical trials with Nalfon, the most common adverse reactions were gastrointestinal in nature and occurred in 20.8% of patients receiving Nalfon as compared to 16.9% of patients receiving placebo. In descending order of frequency, these reactions included dyspepsia (10.3% Nalfon vs. 2.3% placebo), nausea (7.7% vs. 7.1%), constipation (7% vs. 1.5%), vomiting (2.6% vs. 1.9%), abdominal pain (2% vs. 1.1%), and diarrhea (1.8% vs. 4.1%). The drug was discontinued because of adverse gastrointestinal reactions in less than 2% of patients during premarketing studies.
  • Nervous System — The most frequent adverse neurologic reactions were headache (8.7% vs. 7.5%) and somnolence (8.5% vs. 6.4%). Dizziness (6.5% vs. 5.6%), tremor (2.2% vs. 0.4%), and confusion (1.4% vs. none) were noted less frequently. Nalfon was discontinued in less than 0.5% of patients because of these side effects during premarketing studies.
  • Skin and Appendages— Increased sweating (4.6% vs. 0.4%), pruritus (4.2% vs. 0.8%), and rash (3.7% vs. 0.4%) were reported. Nalfon was discontinued in about 1% of patients because of an adverse effect related to the skin during premarketing studies.
  • Special Senses — Tinnitus (4.5% vs. 0.4%), blurred vision (2.2% vs. none), and decreased hearing (1.6% vs. none) were reported. Nalfon was discontinued in less than 0.5% of patients because of adverse effects related to the special senses during premarketing studies.
  • Cardiovascular — Palpitations (2.5% vs. 0.4%). Nalfon was discontinued in about 0.5% of patients because of adverse cardiovascular reactions during premarketing studies.
  • Miscellaneous — Nervousness (5.7% vs. 1.5%), asthenia (5.4% vs. 0.4%), peripheral edema (5.0% vs. 0.4%), dyspnea (2.8% vs. none), fatigue (1.7% vs. 1.5%), upper respiratory infection (1.5% vs. 5.6%), and nasopharyngitis (1.2% vs. none).
Adverse Drug Reactions Reported In < 1% Of Patients During Clinical Trials

What drugs interact with Nalfon (fenoprofen)?

See Table 1 for clinically significant drug interactions with fenoprophen.

Table 1: Clinically Significant Drug Interactions with Fenoprofen

Drugs That Interfere with Hemostasis
Clinical Impact:
  • Fenoprofen and anticoagulants such as warfarin have a synergistic effect on bleeding. The concomitant use of fenoprofen and anticoagulants have an increased risk of serious bleeding compared to the use of either drug alone.
  • Serotonin release by platelets plays an important role in hemostasis. Case-control and cohort epidemiological studies showed that concomitant use of drugs that interfere with serotonin reuptake and an NSAID may potentiate the risk of bleeding more than an NSAID alone.
Intervention: Monitor patients with concomitant use of Nalfon with anticoagulants (e.g., warfarin), antiplatelet agents (e.g., aspirin), selective serotonin reuptake inhibitors (SSRIs), and serotonin norepinephrine reuptake inhibitors (SNRIs) for signs of bleeding.
Aspirin
Clinical Impact: Controlled clinical studies showed that the concomitant use of NSAIDs and analgesic doses of aspirin does not produce any greater therapeutic effect than the use of NSAIDs alone. In a clinical study, the concomitant use of an NSAID and aspirin was associated with a significantly increased incidence of GI adverse reactions as compared to use of the NSAID alone.
Intervention: Concomitant use of Nalfon and analgesic doses of aspirin is not generally recommended because of the increased risk of bleeding. Nalfon is not a substitute for low dose aspirin for cardiovascular protection.
ACE Inhibitors, Angiotensin Receptor Blockers, and Beta-Blockers
Clinical Impact:
  • NSAIDs may diminish the antihypertensive effect of angiotensin converting enzyme (ACE) inhibitors, angiotensin receptor blockers (ARBs), or beta-blockers (including propranolol).
  • In patients who are elderly, volume-depleted (including those on diuretic therapy), or have renal impairment, co-administration of an NSAID with ACE inhibitors or ARBs may result in deterioration of renal function, including possible acute renal failure. These effects are usually reversible.
Intervention:
  • During concomitant use of Nalfon and ACE-inhibitors, ARBs, or betablockers, monitor blood pressure to ensure that the desired blood pressure is obtained.
  • During concomitant use of Nalfon ACE-inhibitors or ARBs in patients who are elderly, volume-depleted, or have impaired renal function, monitor for signs of worsening renal function.
  • When these drugs are administered concomitantly, patients should be adequately hydrated. Assess renal function at the beginning of the concomitant treatment and periodically thereafter.
Diuretics
Clinical Impact: Clinical studies, as well as post-marketing observations, showed that NSAIDs reduced the natriuretic effect of loop diuretics (e.g., furosemide) and thiazide diuretics in some patients. This effect has been attributed to the NSAID inhibition of renal prostaglandin synthesis.
Intervention: During concomitant use of Nalfon with diuretics, observe patients for signs of worsening renal function, in addition to assuring diuretic efficacy including antihypertensive effects.
Digoxin
Clinical Impact: The concomitant use of fenoprofen with digoxin has been reported to increase the serum concentration and prolong the half-life of digoxin.
Intervention: During concomitant use of Nalfon and digoxin, monitor serum digoxin levels.
Lithium
Clinical Impact: NSAIDs have produced elevations in plasma lithium levels and reductions in renal lithium clearance. The mean minimum lithium concentration increased 15%, and the renal clearance decreased by approximately 20%. This effect has been attributed to NSAID inhibition of renal prostaglandin synthesis.
Intervention: During concomitant use of Nalfon and lithium, monitor patients for signs of lithium toxicity.
Methotrexate
Clinical Impact: Concomitant use of NSAIDs and methotrexate may increase the risk for methotrexate toxicity (e.g., neutropenia, thrombocytopenia, renal dysfunction).
Intervention: During concomitant use of Nalfon and methotrexate, monitor patients for methotrexate toxicity.
Cyclosporine
Clinical Impact: Concomitant use of Nalfon and cyclosporine may increase cyclosporine’s nephrotoxicity.
Intervention: During concomitant use of Nalfon and cyclosporine, monitor patients for signs of worsening renal function.
NSAIDs and Salicylates
Clinical Impact: Concomitant use of fenoprofen with other NSAIDs or salicylates (e.g., diflunisal, salsalate) increases the risk of GI toxicity, with little or no increase in efficacy.
Intervention: The concomitant use of fenoprofen with other NSAIDs or salicylates is not recommended.
Pemetrexed
Clinical Impact: Concomitant use of Nalfon and pemetrexed may increase the risk of pemetrexed-associated myelosuppression, renal, and GI toxicity (see the pemetrexed prescribing information).
Intervention: During concomitant use of Nalfon and pemetrexed, in patients with renal impairment whose creatinine clearance ranges from 45 to 79 mL/min, monitor for myelosuppression, renal and GI toxicity. NSAIDs with short elimination half-lives (e.g., diclofenac, indomethacin) should be avoided for a period of two days before, the day of, and two days following administration of pemetrexed. In the absence of data regarding potential interaction between pemetrexed and NSAIDs with longer half-lives (e.g., meloxicam, nabumetone), patients taking these NSAIDs should interrupt dosing for at least five days before, the day of, and two days following pemetrexed administration.
Phenobarbital
Clinical Impact: Chronic administration of phenobarbital, a known enzyme inducer, may be associated with a decrease in the plasma half-life of fenoprofen.
Intervention: When phenobarbital is added to or withdrawn from treatment, dosage adjustment of Nalfon may be required.
Hydantoins, sulfonamides, or sulfonylureas
Clinical Impact: In vitro studies have shown that fenoprofen, because of its affinity for albumin, may displace from their binding sites other drugs that are also albumin bound, and this may lead to drug interactions. Theoretically, fenoprofen could likewise be displaced.
Intervention: Patients receiving hydantoins, sulfonamides, or sulfonylureas should be observed for increased activity of these drugs and, therefore, signs of toxicity from these drugs.

Drug/Laboratory Test Interactions

  • Amerlex-M kit assay values of total and free triiodothyronine in patients receiving Nalfon have been reported as falsely elevated on the basis of a chemical cross-reaction that directly interferes with the assay.
  • Thyroid-stimulating hormone, total thyroxine, and thyrotropin-releasing hormone response are not affected.
  • Thus, results of the Amerlex-M kit assay should be interpreted with caution in these patients.

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Medically Reviewed on 11/18/2020
References
FDA Prescribing Information

Professional side effects and drug interactions sections courtesy of the U.S. Food and Drug Administration.