Phensuximide is an anticonvulsant in the succinimide class. It suppresses the paroxysmal three cycle per second spike and wave EEG pattern associated with lapses of consciousness in petit mal seizures. The frequency of attacks is reduced by depression of nerve transmission in the motor cortex.

Perphenazine is a phenothiazine derivative and a dopamine antagonist with antiemetic and antipsychotic properties. Perphenazine blocks postsynaptic dopamine 2(D2) receptors in the mesolimbic and medullary chemoreceptor trigger zone (CTZ), thereby preventing the excess of dopamine in the brain. This leads to reduction in psychotic symptoms, such as hallucinations and delusions.

Permethrin is a widely-used pesticide of the pyrethroid family. Permethrin interacts with voltage-gated Na+ channels and inhibits their natural deactivation, causing the channels to remain open for a long time and destroying equilibrium of the neuronal system. Pyrethroids are also thought to interact with GABA receptors and associated pathways.

Pentamidine isethionate inhibits constitutive NOS1 in the brain and acts as a NMDA Glu antagonist. Pentamidine isethionate is an antimicrobial and neuroprotective agent.

Pentagastrin is a synthetic polypeptide that has effects like gastrin when given parenterally. It stimulates the secretion of gastric acid, pepsin, and intrinsic factor, and has been used as a diagnostic aid as the pentagastrin-stimulated calcitonin test. Pentagastrin binds to the cholecystokinin-B receptor, which is expressed widely in the brain. Activation of these receptors activates the phospholipase C second messenger system.

Penbutolol Sulfate is a medication in the class of beta blockers, used in the treatment of high blood pressure. Penbutolol is able to bind to both beta-1 adrenergic receptors and beta-2 adrenergic receptors, thus making it a non-selective β blocker. Penbutolol is a sympathomimetic drug with properties allowing it to act as a partial agonist at β adrenergic receptors. Penbutolol has also been found to be one of very few compounds that are 5-HT1A antagonists. 5-HT1A receptors are activated by serotonin, which have many different actions in different species. This makes it difficult to create generalizations about serotonin and its effects.

Pefloxacin mesylate dihydrate is a synthetic broad-spectrum fluoroquinolone antibacterial agent active against most gram-negative and gram-positive bacteria.

Paroxetine hydrochloride is a serotonin uptake inhibitor that is effective in the treatment of depression. It is a highly potent and selective ST (serotonin transporter/5-HT) uptake inhibitor. It acts by binding to ST (serotonin transporter/SERT) with high affinity. Paroxetine binds to the pre-synaptic serotonin transporter complex resulting in negative allosteric modulation of the complex thereby blocking reuptake of serotonin by the pre-synaptic transporter. Paroxetine HCl has also displayed a high affinity for muscarinic acetylcholine receptors.

Paramethadione is an anticonvulsant agent in the oxazolidinedione class.

Paramethasone Acetate is a fluorinated glucocorticoid with anti-inflammatory and immunosuppressant properties.

Oxytetracycline Hydrochloride is the hydrochloride salt form of oxytetracycline, a tetracycline derivative produced by Streptomyces rimosus exhibiting antimicrobial activity. Oxytetracycline Hydrochloride is an antibacterial compound isolated from the elaboration products of the actinomycete, Streptomyces rimosus, when grown on a suitable medium. Oxytetracycline hydrochloride interferes with binding of aminoacyl-tRNA to the mRNA-ribosome complex, thereby preventing peptide elongation and inhibiting protein synthesis. It is often used to treat skin conditions.

Oxybutynin is an anticholinergic medication used to relieve urinary and bladder difficulties, including frequent urination and inability to control urination (urge incontinence), by decreasing muscle spasms of the bladder. It is also given to help with symptoms associated with kidney stones.

Oxtriphylline is a cough medicine derived from xanthine that acts as a bronchodilator to open up airways in the lung. Chemically, it is a salt of choline and theophylline. It classifies as an expectorant.

Oxaprozin is a non-steroidal anti-inflammatory drug (NSAID), used to relieve the inflammation, swelling, stiffness, and joint pain associated with osteoarthritis and rheumatoid arthritis. Chemically, it is a propionic acid derivative.

Oxacillin is a narrow-spectrum beta-lactam antibiotic of the penicillin class. It is similar to methicillin, and has replaced methicillin in clinical use. Other related compounds are nafcillin, cloxacillin, dicloxacillin, and flucloxacillin. Since it is resistant to penicillinase enzymes, such as that produced by Staphylococcus aureus, it is widely used clinically in the US to treat penicillin-resistant Staphylococcus aureus.

Olsalazine is an anti-inflammatory drug used in the treatment of inflammatory bowel disease such as ulcerative colitis. Like balsalazide, olsalazine is believed to deliver mesalazine, or 5-aminosalicylic acid (5-ASA), past the small intestine, directly to the large intestine, which is the active site of disease in ulcerative colitis.

Olopatadine is an antihistamine, as well as anticholinergic and mast cell stabilizer. It is used to treat itching associated with allergic conjunctivitis (eye allergies). There is also a potential for Olopatadine as a treatment modality for steroid rebound (red skin syndrome).

Ofloxacin is a synthetic antibiotic of the fluoroquinolone drug class considered to be a second-generation fluoroquinolone.

Nortriptyline is a second-generation tricyclic antidepressant (TCA). It is used in the treatment of major depression and childhood nocturnal enuresis (bedwetting). Its off-label uses include treatment of chronic fatigue syndrome, chronic pain and migraine, and labile affect in some neurological disorders.

Norgestimate is an acetylated progestinused in combination with ethinyl estradiol as an oral contraceptive. It acts as a prodrug to norelgestromin (17-deacetylnorgestimate or levonorgestrel 3-oxime), the primary active metabolite, and levonorgestrel (deacetylation of norgestimate occurs in the intestines and the liver). Unlike levonorgestrel, norgestimate shows high selectivity for the progesterone receptor and low androgenic action due to a large drug-induced elevation in the level of sex hormone-binding globulin (SHBG) (which preferentially binds androgens and thus inhibits their action). In accordance, clinical trials have observed minimal androgenic side effects. Norgestimate and its metabolites themselves, unlike many other progestins, do not bind to SHBG.

Norfloxacin is a synthetic chemotherapeutic antibacterial agent occasionally used to treat common as well as complicated urinary tract infections. It is a first generation synthetic fluoroquinolone (quinolone) and is approved for the treatment of urinary tract infections, prostatitis, and sexually transmitted diseases, although it is no longer used for the latter due to bacterial resistance.

Norepinephrine is an organic chemical in the catecholamine family that functions in the human brain and body as a hormone and neurotransmitter. Norepinephrine directly stimulates adrenergic receptors. Stimulation of alpha-adrenergic receptors causes vasoconstriction of the radial smooth muscle of the iris, arteries, arterioles, veins, urinary bladder, and the sphincter of the gastrointestinal tract. Stimulation of beta-1 adrenergic receptors causes an increase in myocardial contractility, heart rate, automaticity, and atrioventricular (AV) conduction while stimulation of beta-2 adrenergic receptors causes bronchiolar and vascular smooth muscle dilatation.

Norelgestromin is a steroidal progestin used in contraceptive patches, where it is combined with the estrogen ethinyl estradiol. It is one of the active metabolites of norgestimate.

Nizatidine is a histamine H2 receptor antagonist that inhibits stomach acid production. It is commonly used in the treatment of peptic ulcer disease and gastroesophageal reflux disease.

Nitroxoline is an antibiotic that has been in use in Europe for about fifty years, and has proven to be very effective at combating biofilm infections. Nitroxoline was shown to cause a decrease in the biofilm density of P. aeruginosa infections, which would allow access to the infection by the immune system in vivo. It was shown that nitroxoline functions by chelating Fe2+ and Zn2+ ions from the biofilm matrix; when Fe2+ and Zn2+ were reintroduced into the system, biofilm formation was reconstituted. The activity of biofilm degradation is comparable to EDTA, but has a history of human use in clinical settings and therefore has a precedent with which to allow its use against “slimy” biofilm infections.

Nitrofurazone is a topical anti-infective agent that is effective against gram-negative and gram-positive bacteria. It is used for superficial wounds and injuries and skin infections. Nitrofurazone has also been administered orally in the treatment of trypanosomiasis.

Nitrofurantoin is an antibiotic used to treat bladder infections. Although sulfonamides and antibiotics are usually the agents of choice for urinary tract infections, nitrofurantoin is widely used for prophylaxis and long-term suppression. It is not effective for kidney infections.

Niflumic acid is a drug used for joint and muscular pain. It is categorized as an inhibitor of cyclooxygenase-2. In experimental biology, it has been employed to inhibit chloride channels. Niflumic acid has also been reported to act on GABA-A and NMDA channels and to block T-type calcium channels.

Nicergoline is an ergot derivative used to treat senile dementia and other disorders with vascular origins. It has been found to increase mental agility and enhance clarity and perception. It decreases vascular resistance and increases arterial blood flow in the brain, improving the utilization of oxygen and glucose by brain cells. It has similar vasoactive properties in other areas of the body, particularly the lungs. Nicergoline is used for vascular disorders such as cerebral thrombosis and atherosclerosis, arterial blockages in the limbs, Raynaud's disease, vascular migraines, and retinopathy.

Naratriptan is a triptan drug marketed by GlaxoSmithKline and is used for the treatment of migraine headaches. Naratriptan is available in 2.5 mg tablets. It is a selective 5-HT1 receptor subtype agonist.