Johnson & Johnson (NYSE:JNJ) is a massive cruise ship in the pharmaceutical industry, but there are plenty of fast-moving sharks skimming around its waters. Which of them do we need to be worried about? Let's take three of J&J's key money-making drugs and see which threats might cause this ship to sink.

Potential patent scares
In the first quarter of this year, the top-selling drug for J&J was anti-inflammatory treatment Remicade, comprising $1.6 billion of J&J's total $17.4 billion in reported sales. Remicade had 2.8% operational sales growth (excluding currency impacts), which the company attributed to strong growth in Canada. The big news on the Remicade front is that the U.S. Patent and Trademark Office rejected J&J's patent for exclusivity, which was on the books until 2018. Although J&J has plans to appeal, this process could take a while, leaving the door open to new sharks. Hospira and Celltrion have a biosimilar for Remicade already approved in Europe, and currently on the books for US FDA review. Since J&J has been trading lawsuits with these companies already, it's safe to say that Hospira, being acquired by Pfizer, is chomping at the bit to get its drug, Inflectra, into the U.S. market. Another company, Epirus, is also in phase 3 European trials at present, and has already started infiltrating J&J's India market. This is a key space to watch over the next few years, as a further patent rejection for Remicade could have significant implications for J&J.

Sharks ahoy
Second on the list of J&J sales performers is Zytiga, at $556 million in Q1. Zytiga is approved for treating prostate cancer by stopping hormone production, but there are numerous other competitors coming into this field. The frontrunner is Medivation and Astellas' Xtandi, which had $357 million in sales in Q1, twice the sales of Q1 in 2014. This is compared to Zytiga operational sales growth of 19.2% year over year. Xtandi is projected to have U.S. sales in 2015 between $1.05 billion and $1.125 billion, which will certainly eat into J&J's market share. Currently, some insurance companies only cover Xtandi after the patient has tried Zytiga, but as Xtandi becomes more accepted as a primary treatment mechanism, particularly now that it has a chemotherapy-naive indication , this will be critical to keep an eye on. Provenge, an immunotherapy drug for the same type of cancer, is also competition in this field, and has recently been acquired by Valeant. Although currently Provenge's high price tag has prevented it from encroaching on Zytiga, it's one to watch closely over the next years.

Dangerous waters ahead but long term clear sailing
Stelara, making up $549 million in sales, is the third highest seller for J&J and one of its faster-growing drugs, with 27.4% operational growth in Q1, with the majority of the inflammatory psoriatic arthritis treatment market share. Earlier this year, a drug by Amgen, Brodalumab, also for the treatment of psoriasis, was pulled back due to a risk of suicidal ideations. Although Celgene's Otezla, approved in 2014, had sales of $60mn in Q1, its continued momentum is a watch item for investors concerned about Stelara competition. With J&J seeking further indications for Stelara for use in pediatric patients, the market size will grow even further, bringing out more sharks eager to take a bite. 

Overall, J&J is very widely diversified with pharmaceuticals, consumer health, and medical devices mitigating any shark bites. Although blockbuster drugs like these three are ripe for nibbles from competitors given their large markets, I would consider any stock price drops for J&J as a buying opportunity for the long term. 

Shruti Basavaraj Ahluwalia owns shares of Johnson & Johnson. The Motley Fool recommends Celgene, Johnson & Johnson, and Valeant Pharmaceuticals. The Motley Fool owns shares of Valeant Pharmaceuticals. Try any of our Foolish newsletter services free for 30 days. We Fools may not all hold the same opinions, but we all believe that considering a diverse range of insights makes us better investors. The Motley Fool has a disclosure policy.