It's hard to believe, but 2013 is already more than halfway over. This year has been a good one for many pharmaceutical stocks -- at least so far. No one knows what the remainder of the year holds in store, but some pharma stocks are sure to move one way or the other based on big upcoming events. Here are three pharma stocks you need to watch for the rest of 2013.

1. Antares Pharma (ATRS)
Antares has experienced a roller-coaster ride so far this year. The stock was up more than 10% early in January, then proceeded to fall by more than 20% by late February. Since then, Antares has clawed its way back and now stands up a little over 10% for the year. 

The big event on the calendar for Antares is the Food and Drug Administration decision on Otrexup scheduled for Oct. 14. Otrexup allows patients to self-administer methotrexate for treating rheumatoid arthritis and psoriasis. Methotrexate is widely used in the treatment of rheumatoid arthritis and other autoimmune diseases. Otrexup uses Antares' Medi-Jet technology, which has a shielded needle that makes it easier for patients to self-administer the drug.

Otrexup is more convenient than taking methotrexate via regular injection methods. Methotrexate can be taken orally, but patients can experience gastrointestinal side effects, and absorption of the drug tends to decrease as dosage levels increase. Otrexup should prove appealing to patients, assuming it gets cleared for commercialization. I expect the FDA approval to come through and that Antares shares will get a nice bump later this year.

2. Isis Pharmaceuticals (IONS -0.02%)
Isis shareholders are likely thrilled with 2013 thus far. The stock has soared over 170% year-to-date. These huge gains were driven primarily by FDA approval of Kynamro in January for treating rare disease homozygous familial hypercholesterolemia, or HoFH. More recently, Isis shares jumped on positive mid-stage data for its ISIS-APOCIII Rx drug, which targets treatment of patients with high triglycerides and type 2 diabetes.

There are plenty of catalysts remaining for Isis throughout the remainder of 2013. The company is expected to announce mid-stage clinical results for several experimental drugs, including ISIS-CRPRx for rheumatoid arthritis, ISIS-FXIRx for clotting disorders in patients undergoing knee replacement surgery, ISIS-EIF4ERx for lung cancer and prostate cancer, OGX-427 for metastatic castration-resistant prostate cancer, and iCo-007 for diabetic macular edema. Yep, the folks at Isis are quite busy these days.

And there's more. Teva (TEVA 4.34%) and Oncogenex plan to announce phase 3 results for custirsen in treating patients with first-line advanced metastatic castration-resistant prostate cancer in the fourth quarter. Isis and Oncogenex first developed the drug using Isis' antisense technology. Teva formed an alliance with Oncogenex to completed development and commercialization of custirsen.

3. Ligand Pharmaceuticals (LGND 1.09%)
Ligand hasn't had quite the banner year that Isis has had in 2013, but its year-to-date gains of almost 90% are still impressive. This strong performance stems largely from plenty of royalties and milestone payments for drugs initially developed by Ligand, particularly Kyprolis.

One of the significant events for Ligand during the second half of the year will be the FDA's decision on bazedoxifene/conjugated estrogens, or BZA/CE, scheduled for Oct. 3. The drug, which is being developed with Pfizer (PFE 1.03%), targets treatment of moderate-to-severe vasomotor symptoms and vulvar and vaginal atrophy associated with menopause, as well as the prevention of postmenopausal osteoporosis. Pfizer and Ligand have also submitted BZA/CE for approval in Europe.

There has been considerable skepticism for the drug, though, due in part from repeated delays by Pfizer in submitting for approval. The FDA decided against approval for bazedoxifene as a stand-alone drug several years ago because of concerns about the incidence of strokes and blood clotting, although the drug is approved in Europe and Japan. An FDA approval for BZA/CE probably wouldn't move Pfizer shares much, but a positive decision could help Ligand keep up its winning ways.

Watch and wait
I like all three stocks, especially Isis with its antisense technology. Favorable clinical results and FDA decisions later this year could boost the fortunes of all three of these pharma stocks. However, there's always a chance that things won't go the way the companies would prefer. For now, we'll have to watch and wait.