I personally don't have any experience with serrapeptase. However, a quick search on PubMed
revealed a couple of interesting articles.
The first two suggest that there could be some serious negative side effects associated with its use.
Serrapeptase-induced lung injury manifesting as acute eosiniphilic pneumonia Nihon Kokyuki Gakkai Zasshi. 2000 Jul;38(7):540-4.
Department of Internal Medicine, National Himeji Hospital, Hyogo, Japan.
An 84-year-old man was referred to our hospital because of fever, cough, and hemoptysis. The patient had acute respiratory failure (PaO2 < 40 mmHg) on admission, with diffuse interstitial infiltration and bilateral pleural effusion. The bronchoalveolar lavage fluid was bloody, and contained a high percentage of eosinophils (32%). A diagnosis of acute eosinophilic pneumonia was established, and the patient made a rapid recovery after corticosteroids were administered. When the DLST (drug lymphocyte stimulation test) was performed after the corticosteroid therapy was stopped, it was positive for serrapeptase, which had been prescribed for chronic cystitis for 3 months before the onset of the pneumonia. This was a case of drug (serrapeptase)-induced pneumonitis manifesting as acute eosinophilic pneumonia.
A case of pneumonitis due to serrapeptase
Nihon Kyobu Shikkan Gakkai Zasshi. 1989 Oct;27(10):1231-6.
A case of pneumonitis due to Serrapeptase was described. A 69-year-old man was treated with Serrapeptase for 16 days because of common cold, then fever, nonproductive cough and dyspnea developed and chest X-ray revealed diffuse fine granular shadows in bilateral lung fields. Once the administration of Serrapeptase was halted, symptoms, chest X-ray abnormalities and laboratory data improved markedly. The fraction of lymphocytes increased in bronchoalveolar lavage fluid and OKT4/T8 decreased. Microscopic examination of transbronchial lung biopsy showed interstitial pneumonia. Both leukocyte migration inhibition test and sensitized hemagglutination test were positive for Serrapeptase. Based on these findings, we diagnosed this case as Serrapeptase-induced pneumonitis.
A third article found that serrapeptase was NOT significantly better than placebo when tested for treating chronic ear, nose, and throat inflammation. Although the abstract clearly states this point, it seems as though the authors might be trying to read too much from the data. However, not having the full paper available makes it difficult to know for certain.
Evaluation of Serratia peptidase in acute or chronic inflammation of otorhinolaryngology pathology: a multicentre, double-blind, randomized trial versus placebo. J Int Med Res. 1990 Sep-Oct;18(5):379-88.
The efficacy and tolerability of Serratia peptidase were evaluated in a multicentre, double-blind, placebo-controlled study of 193 subjects suffering from acute or chronic ear, nose or throat disorders. Treatment lasted 7-8 days, with the drug or placebo being administered at a rate of two tablets three times a day. After 3-4 days' treatment, significant symptom regression was observed in peptidase-treated patients. There was also a significant reduction in symptoms after 7-8 days for patients in both treatment groups but the response was more marked in those patients receiving the active drug. Statistical comparison between the two groups confirmed the greater efficacy and rapid action of the peptidase against all the symptoms examined at both stages. Tolerance was found to be very good and similar for both groups. It is concluded that Serratia peptidase has anti-inflammatory, anti-oedemic and fibrinolytic activity and acts rapidly on localized inflammation.
In spite of those papers, I did find a couple which reported positive results. Below is one such paper looking at carpal tunnel syndrome.
A preliminary trial of serratiopeptidase in patients with carpal tunnel syndrome. J Assoc Physicians India. 1999 Dec;47(12):1170-2.
OBJECTIVES: This study was planned to assess the response of serratiopeptidase in patients with carpal tunnel syndrome (CTS). METHODS: Twenty patients with CTS were evaluated clinically. After baseline electrophysiological studies, these patients were given serratiopeptidase 10 mg twice daily with initial short course of nimesulide. Clinical and electrophysiological reassessment was done after 6 weeks. RESULTS: Mean age was 43.9 years with male to female ratio of 1:2.33. Sixty five percent cases showed significant clinical improvement which was supported by significant improvement in electrophysiological parameters. Recurrence was reported in four cases. No significant side effect was observed. CONCLUSIONS: Serratiopeptidase therapy may proved to be a useful alternative mode of conservative treatment. Larger study may be further helpful to establish the role of serratiopeptidase in CTS.
Another more recent paper found a beneficial effect on alleviating the symptoms of chronic airway disease. However, this was an open label study so it's possible that investigator bias may have tainted the results.
Effect of the proteolytic enzyme serrapeptase in patients with chronic airway disease. Respirology. 2003 Sep;8(3):316-20.
OBJECTIVES: The proteolytic enzyme serrapeptase (SER) is widely used in clinical practice in Japan. We investigated the effect of SER on sputum properties and symptoms in patients with chronic airway diseases. METHODS: This study was an open-labelled trial with a non-treatment control group. Patients were randomly assigned to oral treatment with (n = 15) and without (n = 14) SER 30 mg/day for 4 weeks. Patients collected sputum samples for about 4 h in the morning on the day the trial began and 4 weeks later. We measured the amount of sputum by weighing. Part of each sputum sample was weighed and then completely dried and reweighed. The percentage solid component, viscosity and elasticity of the sputum were measured. Mucociliary transportability index was measured using ciliated bovine trachea ex vivo. Sputum smears were also prepared to count sputum neutrophils. Patients' symptoms were assessed by a questionnaire that used a visual analogue scale. RESULTS: After 4 weeks of SER treatment, sputum weight in the morning, percentage solid component, viscosity and elasticity of sputum, sputum neutrophil count, frequency of coughing and frequency of expectoration significantly decreased. The mean mucociliary transportability index increased from 13.3 +/- 1.8 to 24.4 +/- 2.5 (P = 0.0103). CONCLUSIONS: SER may exert a beneficial effect on mucus clearance by reducing neutrophil numbers and altering the viscoelasticity of sputum in patients with chronic airway diseases.
Overall, my PubMed search pulled up just 40 papers over the last 26 years with just a few appearing to be relevant to inflammation and with two indicating that there could be significant risks associated with serrapeptase use. If you're looking for a natural anti-inflammatory agent, then you might want to consider looking into curcumin which is an antioxidant present in the spice turmeric. A general search on PubMed for curcumin pulled up 1773 papers (with relevant papers going back some 36 years) many of which discuss its anti-inflammatory effects suggesting that curcumin has been much more thoroughly studied.